qemu-e2k/tests/qemu-iotests/223.out

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QA output created by 223
=== Create partially sparse image, then add dirty bitmaps ===
Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=4194304
wrote 2097152/2097152 bytes at offset 1048576
2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
Testing:
QMP_VERSION
{"return": {}}
{"return": {}}
{"return": {}}
{"return": {}}
{"return": {}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
=== Write part of the file under active bitmap ===
wrote 512/512 bytes at offset 512
512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 2097152/2097152 bytes at offset 2097152
2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== End dirty bitmaps, and start serving image over NBD ===
{"execute":"qmp_capabilities"}
{"return": {}}
{"execute":"blockdev-add",
"arguments":{"driver":"IMGFMT", "node-name":"n",
"file":{"driver":"file", "filename":"TEST_DIR/t.IMGFMT"}}}
{"return": {}}
{"execute":"block-dirty-bitmap-disable",
"arguments":{"node":"n", "name":"b"}}
{"return": {}}
=== Set up NBD with normal access ===
{"execute":"nbd-server-add",
"arguments":{"device":"n"}}
{"error": {"class": "GenericError", "desc": "NBD server not running"}}
{"execute":"nbd-server-start",
"arguments":{"addr":{"type":"unix",
"data":{"path":"SOCK_DIR/nbd"}}}}
{"return": {}}
{"execute":"nbd-server-start",
"arguments":{"addr":{"type":"unix",
"data":{"path":"SOCK_DIR/nbd1"}}}}
{"error": {"class": "GenericError", "desc": "NBD server already running"}}
exports available: 0
{"execute":"nbd-server-add",
"arguments":{"device":"n", "bitmap":"b"}}
{"return": {}}
{"execute":"nbd-server-add",
"arguments":{"device":"nosuch"}}
{"error": {"class": "GenericError", "desc": "Cannot find device='nosuch' nor node-name='nosuch'"}}
{"execute":"nbd-server-add",
"arguments":{"device":"n"}}
{"error": {"class": "GenericError", "desc": "Block export id 'n' is already in use"}}
{"execute":"nbd-server-add",
"arguments":{"device":"n", "name":"n2",
"bitmap":"b2"}}
{"error": {"class": "GenericError", "desc": "Enabled bitmap 'b2' incompatible with readonly export"}}
{"execute":"nbd-server-add",
"arguments":{"device":"n", "name":"n2",
"bitmap":"b3"}}
{"error": {"class": "GenericError", "desc": "Bitmap 'b3' is not found"}}
{"execute":"nbd-server-add",
"arguments":{"device":"n", "name":"n2", "writable":true,
"description":"some text", "bitmap":"b2"}}
{"return": {}}
exports available: 2
export: 'n'
size: 4194304
flags: 0x58f ( readonly flush fua df multi cache )
min block: 1
opt block: 4096
max block: 33554432
available meta contexts: 2
base:allocation
qemu:dirty-bitmap:b
export: 'n2'
description: some text
size: 4194304
flags: 0xced ( flush fua trim zeroes df cache fast-zero )
min block: 1
opt block: 4096
max block: 33554432
available meta contexts: 2
base:allocation
qemu:dirty-bitmap:b2
=== Contrast normal status to large granularity dirty-bitmap ===
read 512/512 bytes at offset 512
512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 524288/524288 bytes at offset 524288
512 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 1048576/1048576 bytes at offset 1048576
1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 2097152/2097152 bytes at offset 2097152
2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
qemu-img: Make unallocated part of backing chain obvious in map The recently-added NBD context qemu:allocation-depth is able to distinguish between locally-present data (even when that data is sparse) [shown as depth 1 over NBD], and data that could not be found anywhere in the backing chain [shown as depth 0]; and the libnbd project was recently patched to give the human-readable name "absent" to an allocation-depth of 0. But qemu-img map --output=json predates that addition, and has the unfortunate behavior that all portions of the backing chain that resolve without finding a hit in any backing layer report the same depth as the final backing layer. This makes it harder to reconstruct a qcow2 backing chain using just 'qemu-img map' output, especially when using "backing":null to artificially limit a backing chain, because it is impossible to distinguish between a QCOW2_CLUSTER_UNALLOCATED (which defers to a [missing] backing file) and a QCOW2_CLUSTER_ZERO_PLAIN cluster (which would override any backing file), since both types of clusters otherwise show as "data":false,"zero":true" (but note that we can distinguish a QCOW2_CLUSTER_ZERO_ALLOCATED, which would also have an "offset": listing). The task of reconstructing a qcow2 chain was made harder in commit 0da9856851 (nbd: server: Report holes for raw images), because prior to that point, it was possible to abuse NBD's block status command to see which portions of a qcow2 file resulted in BDRV_BLOCK_ALLOCATED (showing up as NBD_STATE_ZERO in isolation) vs. missing from the chain (showing up as NBD_STATE_ZERO|NBD_STATE_HOLE); but now qemu reports more accurate sparseness information over NBD. An obvious solution is to make 'qemu-img map --output=json' add an additional "present":false designation to any cluster lacking an allocation anywhere in the chain, without any change to the "depth" parameter to avoid breaking existing clients. The iotests have several examples where this distinction demonstrates the additional accuracy. Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20210701190655.2131223-3-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [eblake: fix more iotest fallout] Signed-off-by: Eric Blake <eblake@redhat.com>
2021-07-01 21:06:55 +02:00
[{ "start": 0, "length": 4096, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
{ "start": 4096, "length": 1044480, "depth": 0, "present": true, "zero": true, "data": false, "offset": OFFSET},
{ "start": 1048576, "length": 3145728, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET}]
[{ "start": 0, "length": 65536, "depth": 0, "present": false, "zero": false, "data": false},
{ "start": 65536, "length": 2031616, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
{ "start": 2097152, "length": 2097152, "depth": 0, "present": false, "zero": false, "data": false}]
=== Contrast to small granularity dirty-bitmap ===
qemu-img: Make unallocated part of backing chain obvious in map The recently-added NBD context qemu:allocation-depth is able to distinguish between locally-present data (even when that data is sparse) [shown as depth 1 over NBD], and data that could not be found anywhere in the backing chain [shown as depth 0]; and the libnbd project was recently patched to give the human-readable name "absent" to an allocation-depth of 0. But qemu-img map --output=json predates that addition, and has the unfortunate behavior that all portions of the backing chain that resolve without finding a hit in any backing layer report the same depth as the final backing layer. This makes it harder to reconstruct a qcow2 backing chain using just 'qemu-img map' output, especially when using "backing":null to artificially limit a backing chain, because it is impossible to distinguish between a QCOW2_CLUSTER_UNALLOCATED (which defers to a [missing] backing file) and a QCOW2_CLUSTER_ZERO_PLAIN cluster (which would override any backing file), since both types of clusters otherwise show as "data":false,"zero":true" (but note that we can distinguish a QCOW2_CLUSTER_ZERO_ALLOCATED, which would also have an "offset": listing). The task of reconstructing a qcow2 chain was made harder in commit 0da9856851 (nbd: server: Report holes for raw images), because prior to that point, it was possible to abuse NBD's block status command to see which portions of a qcow2 file resulted in BDRV_BLOCK_ALLOCATED (showing up as NBD_STATE_ZERO in isolation) vs. missing from the chain (showing up as NBD_STATE_ZERO|NBD_STATE_HOLE); but now qemu reports more accurate sparseness information over NBD. An obvious solution is to make 'qemu-img map --output=json' add an additional "present":false designation to any cluster lacking an allocation anywhere in the chain, without any change to the "depth" parameter to avoid breaking existing clients. The iotests have several examples where this distinction demonstrates the additional accuracy. Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20210701190655.2131223-3-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [eblake: fix more iotest fallout] Signed-off-by: Eric Blake <eblake@redhat.com>
2021-07-01 21:06:55 +02:00
[{ "start": 0, "length": 512, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
{ "start": 512, "length": 512, "depth": 0, "present": false, "zero": false, "data": false},
{ "start": 1024, "length": 2096128, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
{ "start": 2097152, "length": 2097152, "depth": 0, "present": false, "zero": false, "data": false}]
=== End qemu NBD server ===
{"execute":"nbd-server-remove",
"arguments":{"name":"n"}}
{"return": {}}
{"execute":"nbd-server-remove",
"arguments":{"name":"n2"}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "n"}}
{"return": {}}
{"execute":"nbd-server-remove",
"arguments":{"name":"n2"}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "n2"}}
{"error": {"class": "GenericError", "desc": "Export 'n2' is not found"}}
{"execute":"nbd-server-stop"}
{"return": {}}
{"execute":"nbd-server-stop"}
{"error": {"class": "GenericError", "desc": "NBD server not running"}}
=== Set up NBD with iothread access ===
{"execute":"x-blockdev-set-iothread",
"arguments":{"node-name":"n", "iothread":"io0"}}
{"return": {}}
{"execute":"nbd-server-add",
"arguments":{"device":"n"}}
{"error": {"class": "GenericError", "desc": "NBD server not running"}}
{"execute":"nbd-server-start",
"arguments":{"addr":{"type":"unix",
"data":{"path":"SOCK_DIR/nbd"}}}}
{"return": {}}
{"execute":"nbd-server-start",
"arguments":{"addr":{"type":"unix",
"data":{"path":"SOCK_DIR/nbd1"}}}}
{"error": {"class": "GenericError", "desc": "NBD server already running"}}
exports available: 0
{"execute":"nbd-server-add",
"arguments":{"device":"n", "bitmap":"b"}}
{"return": {}}
{"execute":"nbd-server-add",
"arguments":{"device":"nosuch"}}
{"error": {"class": "GenericError", "desc": "Cannot find device='nosuch' nor node-name='nosuch'"}}
{"execute":"nbd-server-add",
"arguments":{"device":"n"}}
{"error": {"class": "GenericError", "desc": "Block export id 'n' is already in use"}}
{"execute":"nbd-server-add",
"arguments":{"device":"n", "name":"n2",
"bitmap":"b2"}}
nbd: Only require disabled bitmap for read-only exports Our initial implementation of x-nbd-server-add-bitmap put in a restriction because of incremental backups: in that usage, we are exporting one qcow2 file (the temporary overlay target of a blockdev-backup sync:none job) and a dirty bitmap owned by a second qcow2 file (the source of the blockdev-backup, which is the backing file of the temporary). While both qcow2 files are still writable (the target in order to capture copy-on-write of old contents, and the source in order to track live guest writes in the meantime), the NBD client expects to see constant data, including the dirty bitmap. An enabled bitmap in the source would be modified by guest writes, which is at odds with the NBD export being a read-only constant view, hence the initial code choice of enforcing a disabled bitmap (the intent is that the exposed bitmap was disabled in the same transaction that started the blockdev-backup job, although we don't want to track enough state to actually enforce that). However, consider the case of a bitmap contained in a read-only node (including when the bitmap is found in a backing layer of the active image). Because the node can't be modified, the bitmap won't change due to writes, regardless of whether it is still enabled. Forbidding the export unless the bitmap is disabled is awkward, paritcularly since we can't change the bitmap to be disabled (because the node is read-only). Alternatively, consider the case of live storage migration, where management directs the destination to create a writable NBD server, then performs a drive-mirror from the source to the target, prior to doing the rest of the live migration. Since storage migration can be time-consuming, it may be wise to let the destination include a dirty bitmap to track which portions it has already received, where even if the migration is interrupted and restarted, the source can query the destination block status in order to potentially minimize re-sending data that has not changed in the meantime on a second attempt. Such code has not been written, and might not be trivial (after all, a cluster being marked dirty in the bitmap does not necessarily guarantee it has the desired contents), but it makes sense that letting an active dirty bitmap be exposed and changing alongside writes may prove useful in the future. Solve both issues by gating the restriction against a disabled bitmap to only happen when the caller has requested a read-only export, and where the BDS that owns the bitmap (whether or not it is the BDS handed to nbd_export_new() or from its backing chain) is still writable. We could drop the check altogether (if management apps are prepared to deal with a changing bitmap even on a read-only image), but for now keeping a check for the read-only case still stands a chance of preventing management errors. Update iotest 223 to show the looser behavior by leaving a bitmap enabled the whole run; note that we have to tear down and re-export a node when handling an error. Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20190111194720.15671-4-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
2019-01-11 20:47:15 +01:00
{"error": {"class": "GenericError", "desc": "Enabled bitmap 'b2' incompatible with readonly export"}}
{"execute":"nbd-server-add",
"arguments":{"device":"n", "name":"n2",
"bitmap":"b3"}}
nbd: Allow bitmap export during QMP nbd-server-add With the experimental x-nbd-server-add-bitmap command, there was a window of time where an NBD client could see the export but not the associated dirty bitmap, which can cause a client that planned on using the dirty bitmap to be forced to treat the entire image as dirty as a safety fallback. Furthermore, if the QMP client successfully exports a disk but then fails to add the bitmap, it has to take on the burden of removing the export. Since we don't allow changing the exposed dirty bitmap (whether to a different bitmap, or removing advertisement of the bitmap), it is nicer to make the bitmap tied to the export at the time the export is created, with automatic failure to export if the bitmap is not available. The experimental command included an optional 'bitmap-export-name' field for remapping the name exposed over NBD to be different from the bitmap name stored on disk. However, my libvirt demo code for implementing differential backups on top of persistent bitmaps did not need to take advantage of that feature (it is instead possible to create a new temporary bitmap with the desired name, use block-dirty-bitmap-merge to merge one or more persistent bitmaps into the temporary, then associate the temporary with the NBD export, if control is needed over the exported bitmap name). Hence, I'm not copying that part of the experiment over to the stable addition. For more details on the libvirt demo, see https://www.redhat.com/archives/libvir-list/2018-October/msg01254.html, https://kvmforum2018.sched.com/event/FzuB/facilitating-incremental-backup-eric-blake-red-hat This patch focuses on the user interface, and reduces (but does not completely eliminate) the window where an NBD client can see the export but not the dirty bitmap, with less work to clean up after errors. Later patches will add further cleanups now that this interface is declared stable via a single QMP command, including removing the race window. Update test 223 to use the new interface. Signed-off-by: Eric Blake <eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20190111194720.15671-6-eblake@redhat.com>
2019-01-11 20:47:17 +01:00
{"error": {"class": "GenericError", "desc": "Bitmap 'b3' is not found"}}
{"execute":"nbd-server-add",
"arguments":{"device":"n", "name":"n2", "writable":true,
"description":"some text", "bitmap":"b2"}}
{"return": {}}
exports available: 2
export: 'n'
size: 4194304
nbd: Improve per-export flag handling in server When creating a read-only image, we are still advertising support for TRIM and WRITE_ZEROES to the client, even though the client should not be issuing those commands. But seeing this requires looking across multiple functions: All callers to nbd_export_new() passed a single flag based solely on whether the export allows writes. Later, we then pass a constant set of flags to nbd_negotiate_options() (namely, the set of flags which we always support, at least for writable images), which is then further dynamically modified with NBD_FLAG_SEND_DF based on client requests for structured options. Finally, when processing NBD_OPT_EXPORT_NAME or NBD_OPT_EXPORT_GO we bitwise-or the original caller's flag with the runtime set of flags we've built up over several functions. Let's refactor things to instead compute a baseline of flags as soon as possible which gets shared between multiple clients, in nbd_export_new(), and changing the signature for the callers to pass in a simpler bool rather than having to figure out flags. We can then get rid of the 'myflags' parameter to various functions, and instead refer to client for everything we need (we still have to perform a bitwise-OR for NBD_FLAG_SEND_DF during NBD_OPT_EXPORT_NAME and NBD_OPT_EXPORT_GO, but it's easier to see what is being computed). This lets us quit advertising senseless flags for read-only images, as well as making the next patch for exposing FAST_ZERO support easier to write. Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20190823143726.27062-2-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [eblake: improve commit message, update iotest 223]
2019-08-23 16:37:22 +02:00
flags: 0x58f ( readonly flush fua df multi cache )
nbd/server: Advertise actual minimum block size Both NBD_CMD_BLOCK_STATUS and structured NBD_CMD_READ will split their reply according to bdrv_block_status() boundaries. If the block device has a request_alignment smaller than 512, but we advertise a block alignment of 512 to the client, then this can result in the server reply violating client expectations by reporting a smaller region of the export than what the client is permitted to address (although this is less of an issue for qemu 4.0 clients, given recent client patches to overlook our non-compliance at EOF). Since it's always better to be strict in what we send, it is worth advertising the actual minimum block limit rather than blindly rounding it up to 512. Note that this patch is not foolproof - it is still possible to provoke non-compliant server behavior using: $ qemu-nbd --image-opts driver=blkdebug,align=512,image.driver=file,image.filename=/path/to/non-aligned-file That is arguably a bug in the blkdebug driver (it should never pass back block status smaller than its alignment, even if it has to make multiple bdrv_get_status calls and determine the least-common-denominator status among the group to return). It may also be possible to observe issues with a backing layer with smaller alignment than the active layer, although so far I have been unable to write a reliable iotest for that scenario (but again, an issue like that could be argued to be a bug in the block layer, or something where we need a flag to bdrv_block_status() to state whether the result must be aligned to the current layer's limits or can be subdivided for accuracy when chasing backing files). Anyways, as blkdebug is not normally used, and as this patch makes our server more interoperable with qemu 3.1 clients, it is worth applying now, even while we still work on a larger patch series for the 4.1 timeframe to have byte-accurate file lengths. Note that the iotests output changes - for 223 and 233, we can see the server's better granularity advertisement; and for 241, the three test cases have the following effects: - natural alignment: the server's smaller alignment is now advertised, and the hole reported at EOF is now the right result; we've gotten rid of the server's non-compliance - forced server alignment: the server still advertises 512 bytes, but still sends a mid-sector hole. This is still a server compliance bug, which needs to be fixed in the block layer in a later patch; output does not change because the client is already being tolerant of the non-compliance - forced client alignment: the server's smaller alignment means that the client now sees the server's status change mid-sector without any protocol violations, but the fact that the map shows an unaligned mid-sector hole is evidence of the block layer problems with aligned block status, to be fixed in a later patch Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20190329042750.14704-7-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [eblake: rebase to enhanced iotest 241 coverage]
2019-03-31 03:36:36 +02:00
min block: 1
opt block: 4096
max block: 33554432
available meta contexts: 2
base:allocation
qemu:dirty-bitmap:b
export: 'n2'
description: some text
size: 4194304
flags: 0xced ( flush fua trim zeroes df cache fast-zero )
nbd/server: Advertise actual minimum block size Both NBD_CMD_BLOCK_STATUS and structured NBD_CMD_READ will split their reply according to bdrv_block_status() boundaries. If the block device has a request_alignment smaller than 512, but we advertise a block alignment of 512 to the client, then this can result in the server reply violating client expectations by reporting a smaller region of the export than what the client is permitted to address (although this is less of an issue for qemu 4.0 clients, given recent client patches to overlook our non-compliance at EOF). Since it's always better to be strict in what we send, it is worth advertising the actual minimum block limit rather than blindly rounding it up to 512. Note that this patch is not foolproof - it is still possible to provoke non-compliant server behavior using: $ qemu-nbd --image-opts driver=blkdebug,align=512,image.driver=file,image.filename=/path/to/non-aligned-file That is arguably a bug in the blkdebug driver (it should never pass back block status smaller than its alignment, even if it has to make multiple bdrv_get_status calls and determine the least-common-denominator status among the group to return). It may also be possible to observe issues with a backing layer with smaller alignment than the active layer, although so far I have been unable to write a reliable iotest for that scenario (but again, an issue like that could be argued to be a bug in the block layer, or something where we need a flag to bdrv_block_status() to state whether the result must be aligned to the current layer's limits or can be subdivided for accuracy when chasing backing files). Anyways, as blkdebug is not normally used, and as this patch makes our server more interoperable with qemu 3.1 clients, it is worth applying now, even while we still work on a larger patch series for the 4.1 timeframe to have byte-accurate file lengths. Note that the iotests output changes - for 223 and 233, we can see the server's better granularity advertisement; and for 241, the three test cases have the following effects: - natural alignment: the server's smaller alignment is now advertised, and the hole reported at EOF is now the right result; we've gotten rid of the server's non-compliance - forced server alignment: the server still advertises 512 bytes, but still sends a mid-sector hole. This is still a server compliance bug, which needs to be fixed in the block layer in a later patch; output does not change because the client is already being tolerant of the non-compliance - forced client alignment: the server's smaller alignment means that the client now sees the server's status change mid-sector without any protocol violations, but the fact that the map shows an unaligned mid-sector hole is evidence of the block layer problems with aligned block status, to be fixed in a later patch Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20190329042750.14704-7-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [eblake: rebase to enhanced iotest 241 coverage]
2019-03-31 03:36:36 +02:00
min block: 1
opt block: 4096
max block: 33554432
available meta contexts: 2
base:allocation
qemu:dirty-bitmap:b2
=== Contrast normal status to large granularity dirty-bitmap ===
read 512/512 bytes at offset 512
512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 524288/524288 bytes at offset 524288
512 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 1048576/1048576 bytes at offset 1048576
1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 2097152/2097152 bytes at offset 2097152
2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
qemu-img: Make unallocated part of backing chain obvious in map The recently-added NBD context qemu:allocation-depth is able to distinguish between locally-present data (even when that data is sparse) [shown as depth 1 over NBD], and data that could not be found anywhere in the backing chain [shown as depth 0]; and the libnbd project was recently patched to give the human-readable name "absent" to an allocation-depth of 0. But qemu-img map --output=json predates that addition, and has the unfortunate behavior that all portions of the backing chain that resolve without finding a hit in any backing layer report the same depth as the final backing layer. This makes it harder to reconstruct a qcow2 backing chain using just 'qemu-img map' output, especially when using "backing":null to artificially limit a backing chain, because it is impossible to distinguish between a QCOW2_CLUSTER_UNALLOCATED (which defers to a [missing] backing file) and a QCOW2_CLUSTER_ZERO_PLAIN cluster (which would override any backing file), since both types of clusters otherwise show as "data":false,"zero":true" (but note that we can distinguish a QCOW2_CLUSTER_ZERO_ALLOCATED, which would also have an "offset": listing). The task of reconstructing a qcow2 chain was made harder in commit 0da9856851 (nbd: server: Report holes for raw images), because prior to that point, it was possible to abuse NBD's block status command to see which portions of a qcow2 file resulted in BDRV_BLOCK_ALLOCATED (showing up as NBD_STATE_ZERO in isolation) vs. missing from the chain (showing up as NBD_STATE_ZERO|NBD_STATE_HOLE); but now qemu reports more accurate sparseness information over NBD. An obvious solution is to make 'qemu-img map --output=json' add an additional "present":false designation to any cluster lacking an allocation anywhere in the chain, without any change to the "depth" parameter to avoid breaking existing clients. The iotests have several examples where this distinction demonstrates the additional accuracy. Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20210701190655.2131223-3-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [eblake: fix more iotest fallout] Signed-off-by: Eric Blake <eblake@redhat.com>
2021-07-01 21:06:55 +02:00
[{ "start": 0, "length": 4096, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
{ "start": 4096, "length": 1044480, "depth": 0, "present": true, "zero": true, "data": false, "offset": OFFSET},
{ "start": 1048576, "length": 3145728, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET}]
[{ "start": 0, "length": 65536, "depth": 0, "present": false, "zero": false, "data": false},
{ "start": 65536, "length": 2031616, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
{ "start": 2097152, "length": 2097152, "depth": 0, "present": false, "zero": false, "data": false}]
=== Contrast to small granularity dirty-bitmap ===
qemu-img: Make unallocated part of backing chain obvious in map The recently-added NBD context qemu:allocation-depth is able to distinguish between locally-present data (even when that data is sparse) [shown as depth 1 over NBD], and data that could not be found anywhere in the backing chain [shown as depth 0]; and the libnbd project was recently patched to give the human-readable name "absent" to an allocation-depth of 0. But qemu-img map --output=json predates that addition, and has the unfortunate behavior that all portions of the backing chain that resolve without finding a hit in any backing layer report the same depth as the final backing layer. This makes it harder to reconstruct a qcow2 backing chain using just 'qemu-img map' output, especially when using "backing":null to artificially limit a backing chain, because it is impossible to distinguish between a QCOW2_CLUSTER_UNALLOCATED (which defers to a [missing] backing file) and a QCOW2_CLUSTER_ZERO_PLAIN cluster (which would override any backing file), since both types of clusters otherwise show as "data":false,"zero":true" (but note that we can distinguish a QCOW2_CLUSTER_ZERO_ALLOCATED, which would also have an "offset": listing). The task of reconstructing a qcow2 chain was made harder in commit 0da9856851 (nbd: server: Report holes for raw images), because prior to that point, it was possible to abuse NBD's block status command to see which portions of a qcow2 file resulted in BDRV_BLOCK_ALLOCATED (showing up as NBD_STATE_ZERO in isolation) vs. missing from the chain (showing up as NBD_STATE_ZERO|NBD_STATE_HOLE); but now qemu reports more accurate sparseness information over NBD. An obvious solution is to make 'qemu-img map --output=json' add an additional "present":false designation to any cluster lacking an allocation anywhere in the chain, without any change to the "depth" parameter to avoid breaking existing clients. The iotests have several examples where this distinction demonstrates the additional accuracy. Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20210701190655.2131223-3-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [eblake: fix more iotest fallout] Signed-off-by: Eric Blake <eblake@redhat.com>
2021-07-01 21:06:55 +02:00
[{ "start": 0, "length": 512, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
{ "start": 512, "length": 512, "depth": 0, "present": false, "zero": false, "data": false},
{ "start": 1024, "length": 2096128, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
{ "start": 2097152, "length": 2097152, "depth": 0, "present": false, "zero": false, "data": false}]
=== End qemu NBD server ===
{"execute":"nbd-server-remove",
"arguments":{"name":"n"}}
{"return": {}}
{"execute":"nbd-server-remove",
"arguments":{"name":"n2"}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "n"}}
{"return": {}}
{"execute":"nbd-server-remove",
"arguments":{"name":"n2"}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "n2"}}
{"error": {"class": "GenericError", "desc": "Export 'n2' is not found"}}
{"execute":"nbd-server-stop"}
{"return": {}}
{"execute":"nbd-server-stop"}
{"error": {"class": "GenericError", "desc": "NBD server not running"}}
{"execute":"quit"}
{"return": {}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
=== Use qemu-nbd as server ===
qemu-img: Make unallocated part of backing chain obvious in map The recently-added NBD context qemu:allocation-depth is able to distinguish between locally-present data (even when that data is sparse) [shown as depth 1 over NBD], and data that could not be found anywhere in the backing chain [shown as depth 0]; and the libnbd project was recently patched to give the human-readable name "absent" to an allocation-depth of 0. But qemu-img map --output=json predates that addition, and has the unfortunate behavior that all portions of the backing chain that resolve without finding a hit in any backing layer report the same depth as the final backing layer. This makes it harder to reconstruct a qcow2 backing chain using just 'qemu-img map' output, especially when using "backing":null to artificially limit a backing chain, because it is impossible to distinguish between a QCOW2_CLUSTER_UNALLOCATED (which defers to a [missing] backing file) and a QCOW2_CLUSTER_ZERO_PLAIN cluster (which would override any backing file), since both types of clusters otherwise show as "data":false,"zero":true" (but note that we can distinguish a QCOW2_CLUSTER_ZERO_ALLOCATED, which would also have an "offset": listing). The task of reconstructing a qcow2 chain was made harder in commit 0da9856851 (nbd: server: Report holes for raw images), because prior to that point, it was possible to abuse NBD's block status command to see which portions of a qcow2 file resulted in BDRV_BLOCK_ALLOCATED (showing up as NBD_STATE_ZERO in isolation) vs. missing from the chain (showing up as NBD_STATE_ZERO|NBD_STATE_HOLE); but now qemu reports more accurate sparseness information over NBD. An obvious solution is to make 'qemu-img map --output=json' add an additional "present":false designation to any cluster lacking an allocation anywhere in the chain, without any change to the "depth" parameter to avoid breaking existing clients. The iotests have several examples where this distinction demonstrates the additional accuracy. Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20210701190655.2131223-3-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [eblake: fix more iotest fallout] Signed-off-by: Eric Blake <eblake@redhat.com>
2021-07-01 21:06:55 +02:00
[{ "start": 0, "length": 65536, "depth": 0, "present": false, "zero": false, "data": false},
{ "start": 65536, "length": 2031616, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
{ "start": 2097152, "length": 2097152, "depth": 0, "present": false, "zero": false, "data": false}]
[{ "start": 0, "length": 512, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
{ "start": 512, "length": 512, "depth": 0, "present": false, "zero": false, "data": false},
{ "start": 1024, "length": 11321, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET}]
[{ "start": 12345, "length": 2084807, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
{ "start": 2097152, "length": 2097152, "depth": 0, "present": false, "zero": false, "data": false}]
*** done