qemu-e2k/block/copy-before-write.c

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/*
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
* copy-before-write filter driver
*
* The driver performs Copy-Before-Write (CBW) operation: it is injected above
* some node, and before each write it copies _old_ data to the target node.
*
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
* Copyright (c) 2018-2021 Virtuozzo International GmbH.
*
* Author:
* Sementsov-Ogievskiy Vladimir <vsementsov@virtuozzo.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "qemu/osdep.h"
#include "sysemu/block-backend.h"
#include "qemu/cutils.h"
#include "qapi/error.h"
#include "block/block_int.h"
#include "block/qdict.h"
#include "block/block-copy.h"
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
#include "block/copy-before-write.h"
block: copy-before-write: realize snapshot-access API Current scheme of image fleecing looks like this: [guest] [NBD export] | | |root | root v v [copy-before-write] -----> [temp.qcow2] | target | |file |backing v | [active disk] <-------------+ - On guest writes copy-before-write filter copies old data from active disk to temp.qcow2. So fleecing client (NBD export) when reads changed regions from temp.qcow2 image and unchanged from active disk through backing link. This patch makes possible new image fleecing scheme: [guest] [NBD export] | | | root | root v file v [copy-before-write]<------[snapshot-access] | | | file | target v v [active-disk] [temp.img] - copy-before-write does CBW operations and also provides snapshot-access API. The API may be accessed through snapshot-access driver. Benefits of new scheme: 1. Access control: if remote client try to read data that not covered by original dirty bitmap used on copy-before-write open, client gets -EACCES. 2. Discard support: if remote client do DISCARD, this additionally to discarding data in temp.img informs block-copy process to not copy these clusters. Next read from discarded area will return -EACCES. This is significant thing: when fleecing user reads data that was not yet copied to temp.img, we can avoid copying it on further guest write. 3. Synchronisation between client reads and block-copy write is more efficient. In old scheme we just rely on BDRV_REQ_SERIALISING flag used for writes to temp.qcow2. New scheme is less blocking: - fleecing reads are never blocked: if data region is untouched or in-flight, we just read from active-disk, otherwise we read from temp.img - writes to temp.img are not blocked by fleecing reads - still, guest writes of-course are blocked by in-flight fleecing reads, that currently read from active-disk - it's the minimum necessary blocking 4. Temporary image may be of any format, as we don't rely on backing feature. 5. Permission relation are simplified. With old scheme we have to share write permission on target child of copy-before-write, otherwise backing link conflicts with copy-before-write file child write permissions. With new scheme we don't have backing link, and copy-before-write node may have unshared access to temporary node. (Not realized in this commit, will be in future). 6. Having control on fleecing reads we'll be able to implement alternative behavior on failed copy-before-write operations. Currently we just break guest request (that's a historical behavior of backup). But in some scenarios it's a bad behavior: better is to drop the backup as failed but don't break guest request. With new scheme we can simply unset some bits in a bitmap on CBW failure and further fleecing reads will -EACCES, or something like this. (Not implemented in this commit, will be in future) Additional application for this is implementing timeout for CBW operations. Iotest 257 output is updated, as two more bitmaps now live in copy-before-write filter. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20220303194349.2304213-13-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2022-03-03 20:43:45 +01:00
#include "block/reqlist.h"
#include "qapi/qapi-visit-block-core.h"
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
typedef struct BDRVCopyBeforeWriteState {
BlockCopyState *bcs;
BdrvChild *target;
block: copy-before-write: realize snapshot-access API Current scheme of image fleecing looks like this: [guest] [NBD export] | | |root | root v v [copy-before-write] -----> [temp.qcow2] | target | |file |backing v | [active disk] <-------------+ - On guest writes copy-before-write filter copies old data from active disk to temp.qcow2. So fleecing client (NBD export) when reads changed regions from temp.qcow2 image and unchanged from active disk through backing link. This patch makes possible new image fleecing scheme: [guest] [NBD export] | | | root | root v file v [copy-before-write]<------[snapshot-access] | | | file | target v v [active-disk] [temp.img] - copy-before-write does CBW operations and also provides snapshot-access API. The API may be accessed through snapshot-access driver. Benefits of new scheme: 1. Access control: if remote client try to read data that not covered by original dirty bitmap used on copy-before-write open, client gets -EACCES. 2. Discard support: if remote client do DISCARD, this additionally to discarding data in temp.img informs block-copy process to not copy these clusters. Next read from discarded area will return -EACCES. This is significant thing: when fleecing user reads data that was not yet copied to temp.img, we can avoid copying it on further guest write. 3. Synchronisation between client reads and block-copy write is more efficient. In old scheme we just rely on BDRV_REQ_SERIALISING flag used for writes to temp.qcow2. New scheme is less blocking: - fleecing reads are never blocked: if data region is untouched or in-flight, we just read from active-disk, otherwise we read from temp.img - writes to temp.img are not blocked by fleecing reads - still, guest writes of-course are blocked by in-flight fleecing reads, that currently read from active-disk - it's the minimum necessary blocking 4. Temporary image may be of any format, as we don't rely on backing feature. 5. Permission relation are simplified. With old scheme we have to share write permission on target child of copy-before-write, otherwise backing link conflicts with copy-before-write file child write permissions. With new scheme we don't have backing link, and copy-before-write node may have unshared access to temporary node. (Not realized in this commit, will be in future). 6. Having control on fleecing reads we'll be able to implement alternative behavior on failed copy-before-write operations. Currently we just break guest request (that's a historical behavior of backup). But in some scenarios it's a bad behavior: better is to drop the backup as failed but don't break guest request. With new scheme we can simply unset some bits in a bitmap on CBW failure and further fleecing reads will -EACCES, or something like this. (Not implemented in this commit, will be in future) Additional application for this is implementing timeout for CBW operations. Iotest 257 output is updated, as two more bitmaps now live in copy-before-write filter. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20220303194349.2304213-13-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2022-03-03 20:43:45 +01:00
/*
* @lock: protects access to @access_bitmap, @done_bitmap and
* @frozen_read_reqs
*/
CoMutex lock;
/*
* @access_bitmap: represents areas allowed for reading by fleecing user.
* Reading from non-dirty areas leads to -EACCES.
*/
BdrvDirtyBitmap *access_bitmap;
/*
* @done_bitmap: represents areas that was successfully copied to @target by
* copy-before-write operations.
*/
BdrvDirtyBitmap *done_bitmap;
/*
* @frozen_read_reqs: current read requests for fleecing user in bs->file
* node. These areas must not be rewritten by guest.
*/
BlockReqList frozen_read_reqs;
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
} BDRVCopyBeforeWriteState;
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
static coroutine_fn int cbw_co_preadv(
block: use int64_t instead of uint64_t in driver read handlers We are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). So, convert driver read handlers parameters which are already 64bit to signed type. While being here, convert also flags parameter to be BdrvRequestFlags. Now let's consider all callers. Simple git grep '\->bdrv_\(aio\|co\)_preadv\(_part\)\?' shows that's there three callers of driver function: bdrv_driver_preadv() in block/io.c, passes int64_t, checked by bdrv_check_qiov_request() to be non-negative. qcow2_load_vmstate() does bdrv_check_qiov_request(). do_perform_cow_read() has uint64_t argument. And a lot of things in qcow2 driver are uint64_t, so converting it is big job. But we must not work with requests that don't satisfy bdrv_check_qiov_request(), so let's just assert it here. Still, the functions may be called directly, not only by drv->... Let's check: git grep '\.bdrv_\(aio\|co\)_preadv\(_part\)\?\s*=' | \ awk '{print $4}' | sed 's/,//' | sed 's/&//' | sort | uniq | \ while read func; do git grep "$func(" | \ grep -v "$func(BlockDriverState"; done The only one such caller: QEMUIOVector qiov = QEMU_IOVEC_INIT_BUF(qiov, &data, 1); ... ret = bdrv_replace_test_co_preadv(bs, 0, 1, &qiov, 0); in tests/unit/test-bdrv-drain.c, and it's OK obviously. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20210903102807.27127-4-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> [eblake: fix typos] Signed-off-by: Eric Blake <eblake@redhat.com>
2021-09-03 12:27:59 +02:00
BlockDriverState *bs, int64_t offset, int64_t bytes,
QEMUIOVector *qiov, BdrvRequestFlags flags)
{
return bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
}
block: copy-before-write: realize snapshot-access API Current scheme of image fleecing looks like this: [guest] [NBD export] | | |root | root v v [copy-before-write] -----> [temp.qcow2] | target | |file |backing v | [active disk] <-------------+ - On guest writes copy-before-write filter copies old data from active disk to temp.qcow2. So fleecing client (NBD export) when reads changed regions from temp.qcow2 image and unchanged from active disk through backing link. This patch makes possible new image fleecing scheme: [guest] [NBD export] | | | root | root v file v [copy-before-write]<------[snapshot-access] | | | file | target v v [active-disk] [temp.img] - copy-before-write does CBW operations and also provides snapshot-access API. The API may be accessed through snapshot-access driver. Benefits of new scheme: 1. Access control: if remote client try to read data that not covered by original dirty bitmap used on copy-before-write open, client gets -EACCES. 2. Discard support: if remote client do DISCARD, this additionally to discarding data in temp.img informs block-copy process to not copy these clusters. Next read from discarded area will return -EACCES. This is significant thing: when fleecing user reads data that was not yet copied to temp.img, we can avoid copying it on further guest write. 3. Synchronisation between client reads and block-copy write is more efficient. In old scheme we just rely on BDRV_REQ_SERIALISING flag used for writes to temp.qcow2. New scheme is less blocking: - fleecing reads are never blocked: if data region is untouched or in-flight, we just read from active-disk, otherwise we read from temp.img - writes to temp.img are not blocked by fleecing reads - still, guest writes of-course are blocked by in-flight fleecing reads, that currently read from active-disk - it's the minimum necessary blocking 4. Temporary image may be of any format, as we don't rely on backing feature. 5. Permission relation are simplified. With old scheme we have to share write permission on target child of copy-before-write, otherwise backing link conflicts with copy-before-write file child write permissions. With new scheme we don't have backing link, and copy-before-write node may have unshared access to temporary node. (Not realized in this commit, will be in future). 6. Having control on fleecing reads we'll be able to implement alternative behavior on failed copy-before-write operations. Currently we just break guest request (that's a historical behavior of backup). But in some scenarios it's a bad behavior: better is to drop the backup as failed but don't break guest request. With new scheme we can simply unset some bits in a bitmap on CBW failure and further fleecing reads will -EACCES, or something like this. (Not implemented in this commit, will be in future) Additional application for this is implementing timeout for CBW operations. Iotest 257 output is updated, as two more bitmaps now live in copy-before-write filter. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20220303194349.2304213-13-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2022-03-03 20:43:45 +01:00
/*
* Do copy-before-write operation.
*
* On failure guest request must be failed too.
*
* On success, we also wait for all in-flight fleecing read requests in source
* node, and it's guaranteed that after cbw_do_copy_before_write() successful
* return there are no such requests and they will never appear.
*/
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
static coroutine_fn int cbw_do_copy_before_write(BlockDriverState *bs,
uint64_t offset, uint64_t bytes, BdrvRequestFlags flags)
{
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
BDRVCopyBeforeWriteState *s = bs->opaque;
block: copy-before-write: realize snapshot-access API Current scheme of image fleecing looks like this: [guest] [NBD export] | | |root | root v v [copy-before-write] -----> [temp.qcow2] | target | |file |backing v | [active disk] <-------------+ - On guest writes copy-before-write filter copies old data from active disk to temp.qcow2. So fleecing client (NBD export) when reads changed regions from temp.qcow2 image and unchanged from active disk through backing link. This patch makes possible new image fleecing scheme: [guest] [NBD export] | | | root | root v file v [copy-before-write]<------[snapshot-access] | | | file | target v v [active-disk] [temp.img] - copy-before-write does CBW operations and also provides snapshot-access API. The API may be accessed through snapshot-access driver. Benefits of new scheme: 1. Access control: if remote client try to read data that not covered by original dirty bitmap used on copy-before-write open, client gets -EACCES. 2. Discard support: if remote client do DISCARD, this additionally to discarding data in temp.img informs block-copy process to not copy these clusters. Next read from discarded area will return -EACCES. This is significant thing: when fleecing user reads data that was not yet copied to temp.img, we can avoid copying it on further guest write. 3. Synchronisation between client reads and block-copy write is more efficient. In old scheme we just rely on BDRV_REQ_SERIALISING flag used for writes to temp.qcow2. New scheme is less blocking: - fleecing reads are never blocked: if data region is untouched or in-flight, we just read from active-disk, otherwise we read from temp.img - writes to temp.img are not blocked by fleecing reads - still, guest writes of-course are blocked by in-flight fleecing reads, that currently read from active-disk - it's the minimum necessary blocking 4. Temporary image may be of any format, as we don't rely on backing feature. 5. Permission relation are simplified. With old scheme we have to share write permission on target child of copy-before-write, otherwise backing link conflicts with copy-before-write file child write permissions. With new scheme we don't have backing link, and copy-before-write node may have unshared access to temporary node. (Not realized in this commit, will be in future). 6. Having control on fleecing reads we'll be able to implement alternative behavior on failed copy-before-write operations. Currently we just break guest request (that's a historical behavior of backup). But in some scenarios it's a bad behavior: better is to drop the backup as failed but don't break guest request. With new scheme we can simply unset some bits in a bitmap on CBW failure and further fleecing reads will -EACCES, or something like this. (Not implemented in this commit, will be in future) Additional application for this is implementing timeout for CBW operations. Iotest 257 output is updated, as two more bitmaps now live in copy-before-write filter. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20220303194349.2304213-13-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2022-03-03 20:43:45 +01:00
int ret;
uint64_t off, end;
int64_t cluster_size = block_copy_cluster_size(s->bcs);
if (flags & BDRV_REQ_WRITE_UNCHANGED) {
return 0;
}
off = QEMU_ALIGN_DOWN(offset, cluster_size);
end = QEMU_ALIGN_UP(offset + bytes, cluster_size);
block: copy-before-write: realize snapshot-access API Current scheme of image fleecing looks like this: [guest] [NBD export] | | |root | root v v [copy-before-write] -----> [temp.qcow2] | target | |file |backing v | [active disk] <-------------+ - On guest writes copy-before-write filter copies old data from active disk to temp.qcow2. So fleecing client (NBD export) when reads changed regions from temp.qcow2 image and unchanged from active disk through backing link. This patch makes possible new image fleecing scheme: [guest] [NBD export] | | | root | root v file v [copy-before-write]<------[snapshot-access] | | | file | target v v [active-disk] [temp.img] - copy-before-write does CBW operations and also provides snapshot-access API. The API may be accessed through snapshot-access driver. Benefits of new scheme: 1. Access control: if remote client try to read data that not covered by original dirty bitmap used on copy-before-write open, client gets -EACCES. 2. Discard support: if remote client do DISCARD, this additionally to discarding data in temp.img informs block-copy process to not copy these clusters. Next read from discarded area will return -EACCES. This is significant thing: when fleecing user reads data that was not yet copied to temp.img, we can avoid copying it on further guest write. 3. Synchronisation between client reads and block-copy write is more efficient. In old scheme we just rely on BDRV_REQ_SERIALISING flag used for writes to temp.qcow2. New scheme is less blocking: - fleecing reads are never blocked: if data region is untouched or in-flight, we just read from active-disk, otherwise we read from temp.img - writes to temp.img are not blocked by fleecing reads - still, guest writes of-course are blocked by in-flight fleecing reads, that currently read from active-disk - it's the minimum necessary blocking 4. Temporary image may be of any format, as we don't rely on backing feature. 5. Permission relation are simplified. With old scheme we have to share write permission on target child of copy-before-write, otherwise backing link conflicts with copy-before-write file child write permissions. With new scheme we don't have backing link, and copy-before-write node may have unshared access to temporary node. (Not realized in this commit, will be in future). 6. Having control on fleecing reads we'll be able to implement alternative behavior on failed copy-before-write operations. Currently we just break guest request (that's a historical behavior of backup). But in some scenarios it's a bad behavior: better is to drop the backup as failed but don't break guest request. With new scheme we can simply unset some bits in a bitmap on CBW failure and further fleecing reads will -EACCES, or something like this. (Not implemented in this commit, will be in future) Additional application for this is implementing timeout for CBW operations. Iotest 257 output is updated, as two more bitmaps now live in copy-before-write filter. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20220303194349.2304213-13-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2022-03-03 20:43:45 +01:00
ret = block_copy(s->bcs, off, end - off, true);
if (ret < 0) {
return ret;
}
WITH_QEMU_LOCK_GUARD(&s->lock) {
bdrv_set_dirty_bitmap(s->done_bitmap, off, end - off);
reqlist_wait_all(&s->frozen_read_reqs, off, end - off, &s->lock);
}
return 0;
}
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
static int coroutine_fn cbw_co_pdiscard(BlockDriverState *bs,
block: use int64_t instead of int in driver discard handlers We are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). So, convert driver discard handlers bytes parameter to int64_t. The only caller of all updated function is bdrv_co_pdiscard in block/io.c. It is already prepared to work with 64bit requests, but pass at most max(bs->bl.max_pdiscard, INT_MAX) to the driver. Let's look at all updated functions: blkdebug: all calculations are still OK, thanks to bdrv_check_qiov_request(). both rule_check and bdrv_co_pdiscard are 64bit blklogwrites: pass to blk_loc_writes_co_log which is 64bit blkreplay, copy-on-read, filter-compress: pass to bdrv_co_pdiscard, OK copy-before-write: pass to bdrv_co_pdiscard which is 64bit and to cbw_do_copy_before_write which is 64bit file-posix: one handler calls raw_account_discard() is 64bit and both handlers calls raw_do_pdiscard(). Update raw_do_pdiscard, which pass to RawPosixAIOData::aio_nbytes, which is 64bit (and calls raw_account_discard()) gluster: somehow, third argument of glfs_discard_async is size_t. Let's set max_pdiscard accordingly. iscsi: iscsi_allocmap_set_invalid is 64bit, !is_byte_request_lun_aligned is 64bit. list.num is uint32_t. Let's clarify max_pdiscard and pdiscard_alignment. mirror_top: pass to bdrv_mirror_top_do_write() which is 64bit nbd: protocol limitation. max_pdiscard is alredy set strict enough, keep it as is for now. nvme: buf.nlb is uint32_t and we do shift. So, add corresponding limits to nvme_refresh_limits(). preallocate: pass to bdrv_co_pdiscard() which is 64bit. rbd: pass to qemu_rbd_start_co() which is 64bit. qcow2: calculations are still OK, thanks to bdrv_check_qiov_request(), qcow2_cluster_discard() is 64bit. raw-format: raw_adjust_offset() is 64bit, bdrv_co_pdiscard too. throttle: pass to bdrv_co_pdiscard() which is 64bit and to throttle_group_co_io_limits_intercept() which is 64bit as well. test-block-iothread: bytes argument is unused Great! Now all drivers are prepared to handle 64bit discard requests, or else have explicit max_pdiscard limits. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20210903102807.27127-11-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-09-03 12:28:06 +02:00
int64_t offset, int64_t bytes)
{
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
int ret = cbw_do_copy_before_write(bs, offset, bytes, 0);
if (ret < 0) {
return ret;
}
return bdrv_co_pdiscard(bs->file, offset, bytes);
}
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
static int coroutine_fn cbw_co_pwrite_zeroes(BlockDriverState *bs,
block: use int64_t instead of int in driver write_zeroes handlers We are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). So, convert driver write_zeroes handlers bytes parameter to int64_t. The only caller of all updated function is bdrv_co_do_pwrite_zeroes(). bdrv_co_do_pwrite_zeroes() itself is of course OK with widening of callee parameter type. Also, bdrv_co_do_pwrite_zeroes()'s max_write_zeroes is limited to INT_MAX. So, updated functions all are safe, they will not get "bytes" larger than before. Still, let's look through all updated functions, and add assertions to the ones which are actually unprepared to values larger than INT_MAX. For these drivers also set explicit max_pwrite_zeroes limit. Let's go: blkdebug: calculations can't overflow, thanks to bdrv_check_qiov_request() in generic layer. rule_check() and bdrv_co_pwrite_zeroes() both have 64bit argument. blklogwrites: pass to blk_log_writes_co_log() with 64bit argument. blkreplay, copy-on-read, filter-compress: pass to bdrv_co_pwrite_zeroes() which is OK copy-before-write: Calls cbw_do_copy_before_write() and bdrv_co_pwrite_zeroes, both have 64bit argument. file-posix: both handler calls raw_do_pwrite_zeroes, which is updated. In raw_do_pwrite_zeroes() calculations are OK due to bdrv_check_qiov_request(), bytes go to RawPosixAIOData::aio_nbytes which is uint64_t. Check also where that uint64_t gets handed: handle_aiocb_write_zeroes_block() passes a uint64_t[2] to ioctl(BLKZEROOUT), handle_aiocb_write_zeroes() calls do_fallocate() which takes off_t (and we compile to always have 64-bit off_t), as does handle_aiocb_write_zeroes_unmap. All look safe. gluster: bytes go to GlusterAIOCB::size which is int64_t and to glfs_zerofill_async works with off_t. iscsi: Aha, here we deal with iscsi_writesame16_task() that has uint32_t num_blocks argument and iscsi_writesame16_task() has uint16_t argument. Make comments, add assertions and clarify max_pwrite_zeroes calculation. iscsi_allocmap_() functions already has int64_t argument is_byte_request_lun_aligned is simple to update, do it. mirror_top: pass to bdrv_mirror_top_do_write which has uint64_t argument nbd: Aha, here we have protocol limitation, and NBDRequest::len is uint32_t. max_pwrite_zeroes is cleanly set to 32bit value, so we are OK for now. nvme: Again, protocol limitation. And no inherent limit for write-zeroes at all. But from code that calculates cdw12 it's obvious that we do have limit and alignment. Let's clarify it. Also, obviously the code is not prepared to handle bytes=0. Let's handle this case too. trace events already 64bit preallocate: pass to handle_write() and bdrv_co_pwrite_zeroes(), both 64bit. rbd: pass to qemu_rbd_start_co() which is 64bit. qcow2: offset + bytes and alignment still works good (thanks to bdrv_check_qiov_request()), so tail calculation is OK qcow2_subcluster_zeroize() has 64bit argument, should be OK trace events updated qed: qed_co_request wants int nb_sectors. Also in code we have size_t used for request length which may be 32bit. So, let's just keep INT_MAX as a limit (aligning it down to pwrite_zeroes_alignment) and don't care. raw-format: Is OK. raw_adjust_offset and bdrv_co_pwrite_zeroes are both 64bit. throttle: Both throttle_group_co_io_limits_intercept() and bdrv_co_pwrite_zeroes() are 64bit. vmdk: pass to vmdk_pwritev which is 64bit quorum: pass to quorum_co_pwritev() which is 64bit Hooray! At this point all block drivers are prepared to support 64bit write-zero requests, or have explicitly set max_pwrite_zeroes. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20210903102807.27127-8-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> [eblake: use <= rather than < in assertions relying on max_pwrite_zeroes] Signed-off-by: Eric Blake <eblake@redhat.com>
2021-09-03 12:28:03 +02:00
int64_t offset, int64_t bytes, BdrvRequestFlags flags)
{
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
int ret = cbw_do_copy_before_write(bs, offset, bytes, flags);
if (ret < 0) {
return ret;
}
return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
}
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
static coroutine_fn int cbw_co_pwritev(BlockDriverState *bs,
block: use int64_t instead of uint64_t in driver write handlers We are generally moving to int64_t for both offset and bytes parameters on all io paths. Main motivation is realization of 64-bit write_zeroes operation for fast zeroing large disk chunks, up to the whole disk. We chose signed type, to be consistent with off_t (which is signed) and with possibility for signed return type (where negative value means error). So, convert driver write handlers parameters which are already 64bit to signed type. While being here, convert also flags parameter to be BdrvRequestFlags. Now let's consider all callers. Simple git grep '\->bdrv_\(aio\|co\)_pwritev\(_part\)\?' shows that's there three callers of driver function: bdrv_driver_pwritev() and bdrv_driver_pwritev_compressed() in block/io.c, both pass int64_t, checked by bdrv_check_qiov_request() to be non-negative. qcow2_save_vmstate() does bdrv_check_qiov_request(). Still, the functions may be called directly, not only by drv->... Let's check: git grep '\.bdrv_\(aio\|co\)_pwritev\(_part\)\?\s*=' | \ awk '{print $4}' | sed 's/,//' | sed 's/&//' | sort | uniq | \ while read func; do git grep "$func(" | \ grep -v "$func(BlockDriverState"; done shows several callers: qcow2: qcow2_co_truncate() write at most up to @offset, which is checked in generic qcow2_co_truncate() by bdrv_check_request(). qcow2_co_pwritev_compressed_task() pass the request (or part of the request) that already went through normal write path, so it should be OK qcow: qcow_co_pwritev_compressed() pass int64_t, it's updated by this patch quorum: quorum_co_pwrite_zeroes() pass int64_t and int - OK throttle: throttle_co_pwritev_compressed() pass int64_t, it's updated by this patch vmdk: vmdk_co_pwritev_compressed() pass int64_t, it's updated by this patch Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20210903102807.27127-5-vsementsov@virtuozzo.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com>
2021-09-03 12:28:00 +02:00
int64_t offset,
int64_t bytes,
QEMUIOVector *qiov,
BdrvRequestFlags flags)
{
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
int ret = cbw_do_copy_before_write(bs, offset, bytes, flags);
if (ret < 0) {
return ret;
}
return bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
}
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
static int coroutine_fn cbw_co_flush(BlockDriverState *bs)
{
if (!bs->file) {
return 0;
}
return bdrv_co_flush(bs->file->bs);
}
block: copy-before-write: realize snapshot-access API Current scheme of image fleecing looks like this: [guest] [NBD export] | | |root | root v v [copy-before-write] -----> [temp.qcow2] | target | |file |backing v | [active disk] <-------------+ - On guest writes copy-before-write filter copies old data from active disk to temp.qcow2. So fleecing client (NBD export) when reads changed regions from temp.qcow2 image and unchanged from active disk through backing link. This patch makes possible new image fleecing scheme: [guest] [NBD export] | | | root | root v file v [copy-before-write]<------[snapshot-access] | | | file | target v v [active-disk] [temp.img] - copy-before-write does CBW operations and also provides snapshot-access API. The API may be accessed through snapshot-access driver. Benefits of new scheme: 1. Access control: if remote client try to read data that not covered by original dirty bitmap used on copy-before-write open, client gets -EACCES. 2. Discard support: if remote client do DISCARD, this additionally to discarding data in temp.img informs block-copy process to not copy these clusters. Next read from discarded area will return -EACCES. This is significant thing: when fleecing user reads data that was not yet copied to temp.img, we can avoid copying it on further guest write. 3. Synchronisation between client reads and block-copy write is more efficient. In old scheme we just rely on BDRV_REQ_SERIALISING flag used for writes to temp.qcow2. New scheme is less blocking: - fleecing reads are never blocked: if data region is untouched or in-flight, we just read from active-disk, otherwise we read from temp.img - writes to temp.img are not blocked by fleecing reads - still, guest writes of-course are blocked by in-flight fleecing reads, that currently read from active-disk - it's the minimum necessary blocking 4. Temporary image may be of any format, as we don't rely on backing feature. 5. Permission relation are simplified. With old scheme we have to share write permission on target child of copy-before-write, otherwise backing link conflicts with copy-before-write file child write permissions. With new scheme we don't have backing link, and copy-before-write node may have unshared access to temporary node. (Not realized in this commit, will be in future). 6. Having control on fleecing reads we'll be able to implement alternative behavior on failed copy-before-write operations. Currently we just break guest request (that's a historical behavior of backup). But in some scenarios it's a bad behavior: better is to drop the backup as failed but don't break guest request. With new scheme we can simply unset some bits in a bitmap on CBW failure and further fleecing reads will -EACCES, or something like this. (Not implemented in this commit, will be in future) Additional application for this is implementing timeout for CBW operations. Iotest 257 output is updated, as two more bitmaps now live in copy-before-write filter. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20220303194349.2304213-13-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2022-03-03 20:43:45 +01:00
/*
* If @offset not accessible - return NULL.
*
* Otherwise, set @pnum to some bytes that accessible from @file (@file is set
* to bs->file or to s->target). Return newly allocated BlockReq object that
* should be than passed to cbw_snapshot_read_unlock().
*
* It's guaranteed that guest writes will not interact in the region until
* cbw_snapshot_read_unlock() called.
*/
static BlockReq *cbw_snapshot_read_lock(BlockDriverState *bs,
int64_t offset, int64_t bytes,
int64_t *pnum, BdrvChild **file)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
BlockReq *req = g_new(BlockReq, 1);
bool done;
QEMU_LOCK_GUARD(&s->lock);
if (bdrv_dirty_bitmap_next_zero(s->access_bitmap, offset, bytes) != -1) {
g_free(req);
return NULL;
}
done = bdrv_dirty_bitmap_status(s->done_bitmap, offset, bytes, pnum);
if (done) {
/*
* Special invalid BlockReq, that is handled in
* cbw_snapshot_read_unlock(). We don't need to lock something to read
* from s->target.
*/
*req = (BlockReq) {.offset = -1, .bytes = -1};
*file = s->target;
} else {
reqlist_init_req(&s->frozen_read_reqs, req, offset, bytes);
*file = bs->file;
}
return req;
}
static void cbw_snapshot_read_unlock(BlockDriverState *bs, BlockReq *req)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
if (req->offset == -1 && req->bytes == -1) {
g_free(req);
return;
}
QEMU_LOCK_GUARD(&s->lock);
reqlist_remove_req(req);
g_free(req);
}
static coroutine_fn int
cbw_co_preadv_snapshot(BlockDriverState *bs, int64_t offset, int64_t bytes,
QEMUIOVector *qiov, size_t qiov_offset)
{
BlockReq *req;
BdrvChild *file;
int ret;
/* TODO: upgrade to async loop using AioTask */
while (bytes) {
int64_t cur_bytes;
req = cbw_snapshot_read_lock(bs, offset, bytes, &cur_bytes, &file);
if (!req) {
return -EACCES;
}
ret = bdrv_co_preadv_part(file, offset, cur_bytes,
qiov, qiov_offset, 0);
cbw_snapshot_read_unlock(bs, req);
if (ret < 0) {
return ret;
}
bytes -= cur_bytes;
offset += cur_bytes;
qiov_offset += cur_bytes;
}
return 0;
}
static int coroutine_fn
cbw_co_snapshot_block_status(BlockDriverState *bs,
bool want_zero, int64_t offset, int64_t bytes,
int64_t *pnum, int64_t *map,
BlockDriverState **file)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
BlockReq *req;
int ret;
int64_t cur_bytes;
BdrvChild *child;
req = cbw_snapshot_read_lock(bs, offset, bytes, &cur_bytes, &child);
if (!req) {
return -EACCES;
}
ret = bdrv_block_status(child->bs, offset, cur_bytes, pnum, map, file);
if (child == s->target) {
/*
* We refer to s->target only for areas that we've written to it.
* And we can not report unallocated blocks in s->target: this will
* break generic block-status-above logic, that will go to
* copy-before-write filtered child in this case.
*/
assert(ret & BDRV_BLOCK_ALLOCATED);
}
cbw_snapshot_read_unlock(bs, req);
return ret;
}
static int coroutine_fn cbw_co_pdiscard_snapshot(BlockDriverState *bs,
int64_t offset, int64_t bytes)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
WITH_QEMU_LOCK_GUARD(&s->lock) {
bdrv_reset_dirty_bitmap(s->access_bitmap, offset, bytes);
}
block_copy_reset(s->bcs, offset, bytes);
return bdrv_co_pdiscard(s->target, offset, bytes);
}
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
static void cbw_refresh_filename(BlockDriverState *bs)
{
pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
bs->file->bs->filename);
}
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
static void cbw_child_perm(BlockDriverState *bs, BdrvChild *c,
BdrvChildRole role,
BlockReopenQueue *reopen_queue,
uint64_t perm, uint64_t shared,
uint64_t *nperm, uint64_t *nshared)
{
if (!(role & BDRV_CHILD_FILTERED)) {
/*
* Target child
*
* Share write to target (child_file), to not interfere
* with guest writes to its disk which may be in target backing chain.
* Can't resize during a backup block job because we check the size
* only upfront.
*/
*nshared = BLK_PERM_ALL & ~BLK_PERM_RESIZE;
*nperm = BLK_PERM_WRITE;
} else {
/* Source child */
bdrv_default_perms(bs, c, role, reopen_queue,
perm, shared, nperm, nshared);
if (!QLIST_EMPTY(&bs->parents)) {
if (perm & BLK_PERM_WRITE) {
*nperm = *nperm | BLK_PERM_CONSISTENT_READ;
}
*nshared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
}
}
}
static bool cbw_parse_bitmap_option(QDict *options, BdrvDirtyBitmap **bitmap,
Error **errp)
{
QDict *bitmap_qdict = NULL;
BlockDirtyBitmap *bmp_param = NULL;
Visitor *v = NULL;
bool ret = false;
*bitmap = NULL;
qdict_extract_subqdict(options, &bitmap_qdict, "bitmap.");
if (!qdict_size(bitmap_qdict)) {
ret = true;
goto out;
}
v = qobject_input_visitor_new_flat_confused(bitmap_qdict, errp);
if (!v) {
goto out;
}
visit_type_BlockDirtyBitmap(v, NULL, &bmp_param, errp);
if (!bmp_param) {
goto out;
}
*bitmap = block_dirty_bitmap_lookup(bmp_param->node, bmp_param->name, NULL,
errp);
if (!*bitmap) {
goto out;
}
ret = true;
out:
qapi_free_BlockDirtyBitmap(bmp_param);
visit_free(v);
qobject_unref(bitmap_qdict);
return ret;
}
static int cbw_open(BlockDriverState *bs, QDict *options, int flags,
Error **errp)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
BdrvDirtyBitmap *bitmap = NULL;
block: copy-before-write: realize snapshot-access API Current scheme of image fleecing looks like this: [guest] [NBD export] | | |root | root v v [copy-before-write] -----> [temp.qcow2] | target | |file |backing v | [active disk] <-------------+ - On guest writes copy-before-write filter copies old data from active disk to temp.qcow2. So fleecing client (NBD export) when reads changed regions from temp.qcow2 image and unchanged from active disk through backing link. This patch makes possible new image fleecing scheme: [guest] [NBD export] | | | root | root v file v [copy-before-write]<------[snapshot-access] | | | file | target v v [active-disk] [temp.img] - copy-before-write does CBW operations and also provides snapshot-access API. The API may be accessed through snapshot-access driver. Benefits of new scheme: 1. Access control: if remote client try to read data that not covered by original dirty bitmap used on copy-before-write open, client gets -EACCES. 2. Discard support: if remote client do DISCARD, this additionally to discarding data in temp.img informs block-copy process to not copy these clusters. Next read from discarded area will return -EACCES. This is significant thing: when fleecing user reads data that was not yet copied to temp.img, we can avoid copying it on further guest write. 3. Synchronisation between client reads and block-copy write is more efficient. In old scheme we just rely on BDRV_REQ_SERIALISING flag used for writes to temp.qcow2. New scheme is less blocking: - fleecing reads are never blocked: if data region is untouched or in-flight, we just read from active-disk, otherwise we read from temp.img - writes to temp.img are not blocked by fleecing reads - still, guest writes of-course are blocked by in-flight fleecing reads, that currently read from active-disk - it's the minimum necessary blocking 4. Temporary image may be of any format, as we don't rely on backing feature. 5. Permission relation are simplified. With old scheme we have to share write permission on target child of copy-before-write, otherwise backing link conflicts with copy-before-write file child write permissions. With new scheme we don't have backing link, and copy-before-write node may have unshared access to temporary node. (Not realized in this commit, will be in future). 6. Having control on fleecing reads we'll be able to implement alternative behavior on failed copy-before-write operations. Currently we just break guest request (that's a historical behavior of backup). But in some scenarios it's a bad behavior: better is to drop the backup as failed but don't break guest request. With new scheme we can simply unset some bits in a bitmap on CBW failure and further fleecing reads will -EACCES, or something like this. (Not implemented in this commit, will be in future) Additional application for this is implementing timeout for CBW operations. Iotest 257 output is updated, as two more bitmaps now live in copy-before-write filter. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20220303194349.2304213-13-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2022-03-03 20:43:45 +01:00
int64_t cluster_size;
bs->file = bdrv_open_child(NULL, options, "file", bs, &child_of_bds,
BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
false, errp);
if (!bs->file) {
return -EINVAL;
}
s->target = bdrv_open_child(NULL, options, "target", bs, &child_of_bds,
BDRV_CHILD_DATA, false, errp);
if (!s->target) {
return -EINVAL;
}
if (!cbw_parse_bitmap_option(options, &bitmap, errp)) {
return -EINVAL;
}
bs->total_sectors = bs->file->bs->total_sectors;
bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
(BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
bs->file->bs->supported_zero_flags);
s->bcs = block_copy_state_new(bs->file, s->target, bitmap, errp);
if (!s->bcs) {
error_prepend(errp, "Cannot create block-copy-state: ");
return -EINVAL;
}
block: copy-before-write: realize snapshot-access API Current scheme of image fleecing looks like this: [guest] [NBD export] | | |root | root v v [copy-before-write] -----> [temp.qcow2] | target | |file |backing v | [active disk] <-------------+ - On guest writes copy-before-write filter copies old data from active disk to temp.qcow2. So fleecing client (NBD export) when reads changed regions from temp.qcow2 image and unchanged from active disk through backing link. This patch makes possible new image fleecing scheme: [guest] [NBD export] | | | root | root v file v [copy-before-write]<------[snapshot-access] | | | file | target v v [active-disk] [temp.img] - copy-before-write does CBW operations and also provides snapshot-access API. The API may be accessed through snapshot-access driver. Benefits of new scheme: 1. Access control: if remote client try to read data that not covered by original dirty bitmap used on copy-before-write open, client gets -EACCES. 2. Discard support: if remote client do DISCARD, this additionally to discarding data in temp.img informs block-copy process to not copy these clusters. Next read from discarded area will return -EACCES. This is significant thing: when fleecing user reads data that was not yet copied to temp.img, we can avoid copying it on further guest write. 3. Synchronisation between client reads and block-copy write is more efficient. In old scheme we just rely on BDRV_REQ_SERIALISING flag used for writes to temp.qcow2. New scheme is less blocking: - fleecing reads are never blocked: if data region is untouched or in-flight, we just read from active-disk, otherwise we read from temp.img - writes to temp.img are not blocked by fleecing reads - still, guest writes of-course are blocked by in-flight fleecing reads, that currently read from active-disk - it's the minimum necessary blocking 4. Temporary image may be of any format, as we don't rely on backing feature. 5. Permission relation are simplified. With old scheme we have to share write permission on target child of copy-before-write, otherwise backing link conflicts with copy-before-write file child write permissions. With new scheme we don't have backing link, and copy-before-write node may have unshared access to temporary node. (Not realized in this commit, will be in future). 6. Having control on fleecing reads we'll be able to implement alternative behavior on failed copy-before-write operations. Currently we just break guest request (that's a historical behavior of backup). But in some scenarios it's a bad behavior: better is to drop the backup as failed but don't break guest request. With new scheme we can simply unset some bits in a bitmap on CBW failure and further fleecing reads will -EACCES, or something like this. (Not implemented in this commit, will be in future) Additional application for this is implementing timeout for CBW operations. Iotest 257 output is updated, as two more bitmaps now live in copy-before-write filter. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20220303194349.2304213-13-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2022-03-03 20:43:45 +01:00
cluster_size = block_copy_cluster_size(s->bcs);
s->done_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp);
if (!s->done_bitmap) {
return -EINVAL;
}
bdrv_disable_dirty_bitmap(s->done_bitmap);
/* s->access_bitmap starts equal to bcs bitmap */
s->access_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp);
if (!s->access_bitmap) {
return -EINVAL;
}
bdrv_disable_dirty_bitmap(s->access_bitmap);
bdrv_dirty_bitmap_merge_internal(s->access_bitmap,
block_copy_dirty_bitmap(s->bcs), NULL,
true);
qemu_co_mutex_init(&s->lock);
QLIST_INIT(&s->frozen_read_reqs);
return 0;
}
static void cbw_close(BlockDriverState *bs)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
block: copy-before-write: realize snapshot-access API Current scheme of image fleecing looks like this: [guest] [NBD export] | | |root | root v v [copy-before-write] -----> [temp.qcow2] | target | |file |backing v | [active disk] <-------------+ - On guest writes copy-before-write filter copies old data from active disk to temp.qcow2. So fleecing client (NBD export) when reads changed regions from temp.qcow2 image and unchanged from active disk through backing link. This patch makes possible new image fleecing scheme: [guest] [NBD export] | | | root | root v file v [copy-before-write]<------[snapshot-access] | | | file | target v v [active-disk] [temp.img] - copy-before-write does CBW operations and also provides snapshot-access API. The API may be accessed through snapshot-access driver. Benefits of new scheme: 1. Access control: if remote client try to read data that not covered by original dirty bitmap used on copy-before-write open, client gets -EACCES. 2. Discard support: if remote client do DISCARD, this additionally to discarding data in temp.img informs block-copy process to not copy these clusters. Next read from discarded area will return -EACCES. This is significant thing: when fleecing user reads data that was not yet copied to temp.img, we can avoid copying it on further guest write. 3. Synchronisation between client reads and block-copy write is more efficient. In old scheme we just rely on BDRV_REQ_SERIALISING flag used for writes to temp.qcow2. New scheme is less blocking: - fleecing reads are never blocked: if data region is untouched or in-flight, we just read from active-disk, otherwise we read from temp.img - writes to temp.img are not blocked by fleecing reads - still, guest writes of-course are blocked by in-flight fleecing reads, that currently read from active-disk - it's the minimum necessary blocking 4. Temporary image may be of any format, as we don't rely on backing feature. 5. Permission relation are simplified. With old scheme we have to share write permission on target child of copy-before-write, otherwise backing link conflicts with copy-before-write file child write permissions. With new scheme we don't have backing link, and copy-before-write node may have unshared access to temporary node. (Not realized in this commit, will be in future). 6. Having control on fleecing reads we'll be able to implement alternative behavior on failed copy-before-write operations. Currently we just break guest request (that's a historical behavior of backup). But in some scenarios it's a bad behavior: better is to drop the backup as failed but don't break guest request. With new scheme we can simply unset some bits in a bitmap on CBW failure and further fleecing reads will -EACCES, or something like this. (Not implemented in this commit, will be in future) Additional application for this is implementing timeout for CBW operations. Iotest 257 output is updated, as two more bitmaps now live in copy-before-write filter. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20220303194349.2304213-13-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2022-03-03 20:43:45 +01:00
bdrv_release_dirty_bitmap(s->access_bitmap);
bdrv_release_dirty_bitmap(s->done_bitmap);
block_copy_state_free(s->bcs);
s->bcs = NULL;
}
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
BlockDriver bdrv_cbw_filter = {
.format_name = "copy-before-write",
.instance_size = sizeof(BDRVCopyBeforeWriteState),
.bdrv_open = cbw_open,
.bdrv_close = cbw_close,
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
.bdrv_co_preadv = cbw_co_preadv,
.bdrv_co_pwritev = cbw_co_pwritev,
.bdrv_co_pwrite_zeroes = cbw_co_pwrite_zeroes,
.bdrv_co_pdiscard = cbw_co_pdiscard,
.bdrv_co_flush = cbw_co_flush,
block: copy-before-write: realize snapshot-access API Current scheme of image fleecing looks like this: [guest] [NBD export] | | |root | root v v [copy-before-write] -----> [temp.qcow2] | target | |file |backing v | [active disk] <-------------+ - On guest writes copy-before-write filter copies old data from active disk to temp.qcow2. So fleecing client (NBD export) when reads changed regions from temp.qcow2 image and unchanged from active disk through backing link. This patch makes possible new image fleecing scheme: [guest] [NBD export] | | | root | root v file v [copy-before-write]<------[snapshot-access] | | | file | target v v [active-disk] [temp.img] - copy-before-write does CBW operations and also provides snapshot-access API. The API may be accessed through snapshot-access driver. Benefits of new scheme: 1. Access control: if remote client try to read data that not covered by original dirty bitmap used on copy-before-write open, client gets -EACCES. 2. Discard support: if remote client do DISCARD, this additionally to discarding data in temp.img informs block-copy process to not copy these clusters. Next read from discarded area will return -EACCES. This is significant thing: when fleecing user reads data that was not yet copied to temp.img, we can avoid copying it on further guest write. 3. Synchronisation between client reads and block-copy write is more efficient. In old scheme we just rely on BDRV_REQ_SERIALISING flag used for writes to temp.qcow2. New scheme is less blocking: - fleecing reads are never blocked: if data region is untouched or in-flight, we just read from active-disk, otherwise we read from temp.img - writes to temp.img are not blocked by fleecing reads - still, guest writes of-course are blocked by in-flight fleecing reads, that currently read from active-disk - it's the minimum necessary blocking 4. Temporary image may be of any format, as we don't rely on backing feature. 5. Permission relation are simplified. With old scheme we have to share write permission on target child of copy-before-write, otherwise backing link conflicts with copy-before-write file child write permissions. With new scheme we don't have backing link, and copy-before-write node may have unshared access to temporary node. (Not realized in this commit, will be in future). 6. Having control on fleecing reads we'll be able to implement alternative behavior on failed copy-before-write operations. Currently we just break guest request (that's a historical behavior of backup). But in some scenarios it's a bad behavior: better is to drop the backup as failed but don't break guest request. With new scheme we can simply unset some bits in a bitmap on CBW failure and further fleecing reads will -EACCES, or something like this. (Not implemented in this commit, will be in future) Additional application for this is implementing timeout for CBW operations. Iotest 257 output is updated, as two more bitmaps now live in copy-before-write filter. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20220303194349.2304213-13-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2022-03-03 20:43:45 +01:00
.bdrv_co_preadv_snapshot = cbw_co_preadv_snapshot,
.bdrv_co_pdiscard_snapshot = cbw_co_pdiscard_snapshot,
.bdrv_co_snapshot_block_status = cbw_co_snapshot_block_status,
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
.bdrv_refresh_filename = cbw_refresh_filename,
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
.bdrv_child_perm = cbw_child_perm,
.is_filter = true,
};
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
BlockDriverState *target,
const char *filter_node_name,
BlockCopyState **bcs,
Error **errp)
{
ERRP_GUARD();
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
BDRVCopyBeforeWriteState *state;
BlockDriverState *top;
QDict *opts;
assert(source->total_sectors == target->total_sectors);
GLOBAL_STATE_CODE();
opts = qdict_new();
qdict_put_str(opts, "driver", "copy-before-write");
if (filter_node_name) {
qdict_put_str(opts, "node-name", filter_node_name);
}
qdict_put_str(opts, "file", bdrv_get_node_name(source));
qdict_put_str(opts, "target", bdrv_get_node_name(target));
top = bdrv_insert_node(source, opts, BDRV_O_RDWR, errp);
if (!top) {
return NULL;
}
state = top->opaque;
*bcs = state->bcs;
return top;
}
block: rename backup-top to copy-before-write We are going to convert backup_top to full featured public filter, which can be used in separate of backup job. Start from renaming from "how it used" to "what it does". While updating comments in 283 iotest, drop and rephrase also things about ".active", as this field is now dropped, and filter doesn't have "inactive" mode. Note that this change may be considered as incompatible interface change, as backup-top filter format name was visible through query-block and query-named-block-nodes. Still, consider the following reasoning: 1. backup-top was never documented, so if someone depends on format name (for driver that can't be used other than it is automatically inserted on backup job start), it's a kind of "undocumented feature use". So I think we are free to change it. 2. There is a hope, that there is no such users: it's a lot more native to give a good node-name to backup-top filter if need to operate with it somehow, and don't touch format name. 3. Another "incompatible" change in further commit would be moving copy-before-write filter from using backing child to file child. And this is even more reasonable than renaming: for now all public filters are file-child based. So, it's a risky change, but risk seems small and good interface worth it. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
2021-08-24 10:38:27 +02:00
void bdrv_cbw_drop(BlockDriverState *bs)
{
GLOBAL_STATE_CODE();
bdrv_drop_filter(bs, &error_abort);
bdrv_unref(bs);
}
static void cbw_init(void)
{
bdrv_register(&bdrv_cbw_filter);
}
block_init(cbw_init);