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qemu-e2k/block/qcow2-snapshot.c
Eric Blake d2cb36af2b qcow2: Discard/zero clusters by byte count 
Passing a byte offset, but sector count, when we ultimately
want to operate on cluster granularity, is madness.  Clean up
the external interfaces to take both offset and count as bytes,
while still keeping the assertion added previously that the
caller must align the values to a cluster.  Then rename things
to make sure backports don't get confused by changed units:
instead of qcow2_discard_clusters() and qcow2_zero_clusters(),
we now have qcow2_cluster_discard() and qcow2_cluster_zeroize().

The internal functions still operate on clusters at a time, and
return an int for number of cleared clusters; but on an image
with 2M clusters, a single L2 table holds 256k entries that each
represent a 2M cluster, totalling well over INT_MAX bytes if we
ever had a request for that many bytes at once.  All our callers
currently limit themselves to 32-bit bytes (and therefore fewer
clusters), but by making this function 64-bit clean, we have one
less place to clean up if we later improve the block layer to
support 64-bit bytes through all operations (with the block layer
auto-fragmenting on behalf of more-limited drivers), rather than
the current state where some interfaces are artificially limited
to INT_MAX at a time.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 20170507000552.20847-13-eblake@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
2017-05-11 14:28:07 +02:00

739 lines
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/*
* Block driver for the QCOW version 2 format
*
* Copyright (c) 2004-2006 Fabrice Bellard
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "qemu/osdep.h"
#include "qapi/error.h"
#include "block/block_int.h"
#include "block/qcow2.h"
#include "qemu/bswap.h"
#include "qemu/error-report.h"
#include "qemu/cutils.h"
void qcow2_free_snapshots(BlockDriverState *bs)
{
BDRVQcow2State *s = bs->opaque;
int i;
for(i = 0; i < s->nb_snapshots; i++) {
g_free(s->snapshots[i].name);
g_free(s->snapshots[i].id_str);
}
g_free(s->snapshots);
s->snapshots = NULL;
s->nb_snapshots = 0;
}
int qcow2_read_snapshots(BlockDriverState *bs)
{
BDRVQcow2State *s = bs->opaque;
QCowSnapshotHeader h;
QCowSnapshotExtraData extra;
QCowSnapshot *sn;
int i, id_str_size, name_size;
int64_t offset;
uint32_t extra_data_size;
int ret;
if (!s->nb_snapshots) {
s->snapshots = NULL;
s->snapshots_size = 0;
return 0;
}
offset = s->snapshots_offset;
s->snapshots = g_new0(QCowSnapshot, s->nb_snapshots);
for(i = 0; i < s->nb_snapshots; i++) {
/* Read statically sized part of the snapshot header */
offset = align_offset(offset, 8);
ret = bdrv_pread(bs->file, offset, &h, sizeof(h));
if (ret < 0) {
goto fail;
}
offset += sizeof(h);
sn = s->snapshots + i;
sn->l1_table_offset = be64_to_cpu(h.l1_table_offset);
sn->l1_size = be32_to_cpu(h.l1_size);
sn->vm_state_size = be32_to_cpu(h.vm_state_size);
sn->date_sec = be32_to_cpu(h.date_sec);
sn->date_nsec = be32_to_cpu(h.date_nsec);
sn->vm_clock_nsec = be64_to_cpu(h.vm_clock_nsec);
extra_data_size = be32_to_cpu(h.extra_data_size);
id_str_size = be16_to_cpu(h.id_str_size);
name_size = be16_to_cpu(h.name_size);
/* Read extra data */
ret = bdrv_pread(bs->file, offset, &extra,
MIN(sizeof(extra), extra_data_size));
if (ret < 0) {
goto fail;
}
offset += extra_data_size;
if (extra_data_size >= 8) {
sn->vm_state_size = be64_to_cpu(extra.vm_state_size_large);
}
if (extra_data_size >= 16) {
sn->disk_size = be64_to_cpu(extra.disk_size);
} else {
sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
}
/* Read snapshot ID */
sn->id_str = g_malloc(id_str_size + 1);
ret = bdrv_pread(bs->file, offset, sn->id_str, id_str_size);
if (ret < 0) {
goto fail;
}
offset += id_str_size;
sn->id_str[id_str_size] = '\0';
/* Read snapshot name */
sn->name = g_malloc(name_size + 1);
ret = bdrv_pread(bs->file, offset, sn->name, name_size);
if (ret < 0) {
goto fail;
}
offset += name_size;
sn->name[name_size] = '\0';
if (offset - s->snapshots_offset > QCOW_MAX_SNAPSHOTS_SIZE) {
ret = -EFBIG;
goto fail;
}
}
assert(offset - s->snapshots_offset <= INT_MAX);
s->snapshots_size = offset - s->snapshots_offset;
return 0;
fail:
qcow2_free_snapshots(bs);
return ret;
}
/* add at the end of the file a new list of snapshots */
static int qcow2_write_snapshots(BlockDriverState *bs)
{
BDRVQcow2State *s = bs->opaque;
QCowSnapshot *sn;
QCowSnapshotHeader h;
QCowSnapshotExtraData extra;
int i, name_size, id_str_size, snapshots_size;
struct {
uint32_t nb_snapshots;
uint64_t snapshots_offset;
} QEMU_PACKED header_data;
int64_t offset, snapshots_offset = 0;
int ret;
/* compute the size of the snapshots */
offset = 0;
for(i = 0; i < s->nb_snapshots; i++) {
sn = s->snapshots + i;
offset = align_offset(offset, 8);
offset += sizeof(h);
offset += sizeof(extra);
offset += strlen(sn->id_str);
offset += strlen(sn->name);
if (offset > QCOW_MAX_SNAPSHOTS_SIZE) {
ret = -EFBIG;
goto fail;
}
}
assert(offset <= INT_MAX);
snapshots_size = offset;
/* Allocate space for the new snapshot list */
snapshots_offset = qcow2_alloc_clusters(bs, snapshots_size);
offset = snapshots_offset;
if (offset < 0) {
ret = offset;
goto fail;
}
ret = bdrv_flush(bs);
if (ret < 0) {
goto fail;
}
/* The snapshot list position has not yet been updated, so these clusters
* must indeed be completely free */
ret = qcow2_pre_write_overlap_check(bs, 0, offset, snapshots_size);
if (ret < 0) {
goto fail;
}
/* Write all snapshots to the new list */
for(i = 0; i < s->nb_snapshots; i++) {
sn = s->snapshots + i;
memset(&h, 0, sizeof(h));
h.l1_table_offset = cpu_to_be64(sn->l1_table_offset);
h.l1_size = cpu_to_be32(sn->l1_size);
/* If it doesn't fit in 32 bit, older implementations should treat it
* as a disk-only snapshot rather than truncate the VM state */
if (sn->vm_state_size <= 0xffffffff) {
h.vm_state_size = cpu_to_be32(sn->vm_state_size);
}
h.date_sec = cpu_to_be32(sn->date_sec);
h.date_nsec = cpu_to_be32(sn->date_nsec);
h.vm_clock_nsec = cpu_to_be64(sn->vm_clock_nsec);
h.extra_data_size = cpu_to_be32(sizeof(extra));
memset(&extra, 0, sizeof(extra));
extra.vm_state_size_large = cpu_to_be64(sn->vm_state_size);
extra.disk_size = cpu_to_be64(sn->disk_size);
id_str_size = strlen(sn->id_str);
name_size = strlen(sn->name);
assert(id_str_size <= UINT16_MAX && name_size <= UINT16_MAX);
h.id_str_size = cpu_to_be16(id_str_size);
h.name_size = cpu_to_be16(name_size);
offset = align_offset(offset, 8);
ret = bdrv_pwrite(bs->file, offset, &h, sizeof(h));
if (ret < 0) {
goto fail;
}
offset += sizeof(h);
ret = bdrv_pwrite(bs->file, offset, &extra, sizeof(extra));
if (ret < 0) {
goto fail;
}
offset += sizeof(extra);
ret = bdrv_pwrite(bs->file, offset, sn->id_str, id_str_size);
if (ret < 0) {
goto fail;
}
offset += id_str_size;
ret = bdrv_pwrite(bs->file, offset, sn->name, name_size);
if (ret < 0) {
goto fail;
}
offset += name_size;
}
/*
* Update the header to point to the new snapshot table. This requires the
* new table and its refcounts to be stable on disk.
*/
ret = bdrv_flush(bs);
if (ret < 0) {
goto fail;
}
QEMU_BUILD_BUG_ON(offsetof(QCowHeader, snapshots_offset) !=
offsetof(QCowHeader, nb_snapshots) + sizeof(header_data.nb_snapshots));
header_data.nb_snapshots = cpu_to_be32(s->nb_snapshots);
header_data.snapshots_offset = cpu_to_be64(snapshots_offset);
ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
&header_data, sizeof(header_data));
if (ret < 0) {
goto fail;
}
/* free the old snapshot table */
qcow2_free_clusters(bs, s->snapshots_offset, s->snapshots_size,
QCOW2_DISCARD_SNAPSHOT);
s->snapshots_offset = snapshots_offset;
s->snapshots_size = snapshots_size;
return 0;
fail:
if (snapshots_offset > 0) {
qcow2_free_clusters(bs, snapshots_offset, snapshots_size,
QCOW2_DISCARD_ALWAYS);
}
return ret;
}
static void find_new_snapshot_id(BlockDriverState *bs,
char *id_str, int id_str_size)
{
BDRVQcow2State *s = bs->opaque;
QCowSnapshot *sn;
int i;
unsigned long id, id_max = 0;
for(i = 0; i < s->nb_snapshots; i++) {
sn = s->snapshots + i;
id = strtoul(sn->id_str, NULL, 10);
if (id > id_max)
id_max = id;
}
snprintf(id_str, id_str_size, "%lu", id_max + 1);
}
static int find_snapshot_by_id_and_name(BlockDriverState *bs,
const char *id,
const char *name)
{
BDRVQcow2State *s = bs->opaque;
int i;
if (id && name) {
for (i = 0; i < s->nb_snapshots; i++) {
if (!strcmp(s->snapshots[i].id_str, id) &&
!strcmp(s->snapshots[i].name, name)) {
return i;
}
}
} else if (id) {
for (i = 0; i < s->nb_snapshots; i++) {
if (!strcmp(s->snapshots[i].id_str, id)) {
return i;
}
}
} else if (name) {
for (i = 0; i < s->nb_snapshots; i++) {
if (!strcmp(s->snapshots[i].name, name)) {
return i;
}
}
}
return -1;
}
static int find_snapshot_by_id_or_name(BlockDriverState *bs,
const char *id_or_name)
{
int ret;
ret = find_snapshot_by_id_and_name(bs, id_or_name, NULL);
if (ret >= 0) {
return ret;
}
return find_snapshot_by_id_and_name(bs, NULL, id_or_name);
}
/* if no id is provided, a new one is constructed */
int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
{
BDRVQcow2State *s = bs->opaque;
QCowSnapshot *new_snapshot_list = NULL;
QCowSnapshot *old_snapshot_list = NULL;
QCowSnapshot sn1, *sn = &sn1;
int i, ret;
uint64_t *l1_table = NULL;
int64_t l1_table_offset;
if (s->nb_snapshots >= QCOW_MAX_SNAPSHOTS) {
return -EFBIG;
}
memset(sn, 0, sizeof(*sn));
/* Generate an ID */
find_new_snapshot_id(bs, sn_info->id_str, sizeof(sn_info->id_str));
/* Check that the ID is unique */
if (find_snapshot_by_id_and_name(bs, sn_info->id_str, NULL) >= 0) {
return -EEXIST;
}
/* Populate sn with passed data */
sn->id_str = g_strdup(sn_info->id_str);
sn->name = g_strdup(sn_info->name);
sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
sn->vm_state_size = sn_info->vm_state_size;
sn->date_sec = sn_info->date_sec;
sn->date_nsec = sn_info->date_nsec;
sn->vm_clock_nsec = sn_info->vm_clock_nsec;
/* Allocate the L1 table of the snapshot and copy the current one there. */
l1_table_offset = qcow2_alloc_clusters(bs, s->l1_size * sizeof(uint64_t));
if (l1_table_offset < 0) {
ret = l1_table_offset;
goto fail;
}
sn->l1_table_offset = l1_table_offset;
sn->l1_size = s->l1_size;
l1_table = g_try_new(uint64_t, s->l1_size);
if (s->l1_size && l1_table == NULL) {
ret = -ENOMEM;
goto fail;
}
for(i = 0; i < s->l1_size; i++) {
l1_table[i] = cpu_to_be64(s->l1_table[i]);
}
ret = qcow2_pre_write_overlap_check(bs, 0, sn->l1_table_offset,
s->l1_size * sizeof(uint64_t));
if (ret < 0) {
goto fail;
}
ret = bdrv_pwrite(bs->file, sn->l1_table_offset, l1_table,
s->l1_size * sizeof(uint64_t));
if (ret < 0) {
goto fail;
}
g_free(l1_table);
l1_table = NULL;
/*
* Increase the refcounts of all clusters and make sure everything is
* stable on disk before updating the snapshot table to contain a pointer
* to the new L1 table.
*/
ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1);
if (ret < 0) {
goto fail;
}
/* Append the new snapshot to the snapshot list */
new_snapshot_list = g_new(QCowSnapshot, s->nb_snapshots + 1);
if (s->snapshots) {
memcpy(new_snapshot_list, s->snapshots,
s->nb_snapshots * sizeof(QCowSnapshot));
old_snapshot_list = s->snapshots;
}
s->snapshots = new_snapshot_list;
s->snapshots[s->nb_snapshots++] = *sn;
ret = qcow2_write_snapshots(bs);
if (ret < 0) {
g_free(s->snapshots);
s->snapshots = old_snapshot_list;
s->nb_snapshots--;
goto fail;
}
g_free(old_snapshot_list);
/* The VM state isn't needed any more in the active L1 table; in fact, it
* hurts by causing expensive COW for the next snapshot. */
qcow2_cluster_discard(bs, qcow2_vm_state_offset(s),
align_offset(sn->vm_state_size, s->cluster_size),
QCOW2_DISCARD_NEVER, false);
#ifdef DEBUG_ALLOC
{
BdrvCheckResult result = {0};
qcow2_check_refcounts(bs, &result, 0);
}
#endif
return 0;
fail:
g_free(sn->id_str);
g_free(sn->name);
g_free(l1_table);
return ret;
}
/* copy the snapshot 'snapshot_name' into the current disk image */
int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
{
BDRVQcow2State *s = bs->opaque;
QCowSnapshot *sn;
int i, snapshot_index;
int cur_l1_bytes, sn_l1_bytes;
int ret;
uint64_t *sn_l1_table = NULL;
/* Search the snapshot */
snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
if (snapshot_index < 0) {
return -ENOENT;
}
sn = &s->snapshots[snapshot_index];
if (sn->disk_size != bs->total_sectors * BDRV_SECTOR_SIZE) {
error_report("qcow2: Loading snapshots with different disk "
"size is not implemented");
ret = -ENOTSUP;
goto fail;
}
/*
* Make sure that the current L1 table is big enough to contain the whole
* L1 table of the snapshot. If the snapshot L1 table is smaller, the
* current one must be padded with zeros.
*/
ret = qcow2_grow_l1_table(bs, sn->l1_size, true);
if (ret < 0) {
goto fail;
}
cur_l1_bytes = s->l1_size * sizeof(uint64_t);
sn_l1_bytes = sn->l1_size * sizeof(uint64_t);
/*
* Copy the snapshot L1 table to the current L1 table.
*
* Before overwriting the old current L1 table on disk, make sure to
* increase all refcounts for the clusters referenced by the new one.
* Decrease the refcount referenced by the old one only when the L1
* table is overwritten.
*/
sn_l1_table = g_try_malloc0(cur_l1_bytes);
if (cur_l1_bytes && sn_l1_table == NULL) {
ret = -ENOMEM;
goto fail;
}
ret = bdrv_pread(bs->file, sn->l1_table_offset,
sn_l1_table, sn_l1_bytes);
if (ret < 0) {
goto fail;
}
ret = qcow2_update_snapshot_refcount(bs, sn->l1_table_offset,
sn->l1_size, 1);
if (ret < 0) {
goto fail;
}
ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_ACTIVE_L1,
s->l1_table_offset, cur_l1_bytes);
if (ret < 0) {
goto fail;
}
ret = bdrv_pwrite_sync(bs->file, s->l1_table_offset, sn_l1_table,
cur_l1_bytes);
if (ret < 0) {
goto fail;
}
/*
* Decrease refcount of clusters of current L1 table.
*
* At this point, the in-memory s->l1_table points to the old L1 table,
* whereas on disk we already have the new one.
*
* qcow2_update_snapshot_refcount special cases the current L1 table to use
* the in-memory data instead of really using the offset to load a new one,
* which is why this works.
*/
ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
s->l1_size, -1);
/*
* Now update the in-memory L1 table to be in sync with the on-disk one. We
* need to do this even if updating refcounts failed.
*/
for(i = 0;i < s->l1_size; i++) {
s->l1_table[i] = be64_to_cpu(sn_l1_table[i]);
}
if (ret < 0) {
goto fail;
}
g_free(sn_l1_table);
sn_l1_table = NULL;
/*
* Update QCOW_OFLAG_COPIED in the active L1 table (it may have changed
* when we decreased the refcount of the old snapshot.
*/
ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
if (ret < 0) {
goto fail;
}
#ifdef DEBUG_ALLOC
{
BdrvCheckResult result = {0};
qcow2_check_refcounts(bs, &result, 0);
}
#endif
return 0;
fail:
g_free(sn_l1_table);
return ret;
}
int qcow2_snapshot_delete(BlockDriverState *bs,
const char *snapshot_id,
const char *name,
Error **errp)
{
BDRVQcow2State *s = bs->opaque;
QCowSnapshot sn;
int snapshot_index, ret;
/* Search the snapshot */
snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
if (snapshot_index < 0) {
error_setg(errp, "Can't find the snapshot");
return -ENOENT;
}
sn = s->snapshots[snapshot_index];
/* Remove it from the snapshot list */
memmove(s->snapshots + snapshot_index,
s->snapshots + snapshot_index + 1,
(s->nb_snapshots - snapshot_index - 1) * sizeof(sn));
s->nb_snapshots--;
ret = qcow2_write_snapshots(bs);
if (ret < 0) {
error_setg_errno(errp, -ret,
"Failed to remove snapshot from snapshot list");
return ret;
}
/*
* The snapshot is now unused, clean up. If we fail after this point, we
* won't recover but just leak clusters.
*/
g_free(sn.id_str);
g_free(sn.name);
/*
* Now decrease the refcounts of clusters referenced by the snapshot and
* free the L1 table.
*/
ret = qcow2_update_snapshot_refcount(bs, sn.l1_table_offset,
sn.l1_size, -1);
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to free the cluster and L1 table");
return ret;
}
qcow2_free_clusters(bs, sn.l1_table_offset, sn.l1_size * sizeof(uint64_t),
QCOW2_DISCARD_SNAPSHOT);
/* must update the copied flag on the current cluster offsets */
ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
if (ret < 0) {
error_setg_errno(errp, -ret,
"Failed to update snapshot status in disk");
return ret;
}
#ifdef DEBUG_ALLOC
{
BdrvCheckResult result = {0};
qcow2_check_refcounts(bs, &result, 0);
}
#endif
return 0;
}
int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
{
BDRVQcow2State *s = bs->opaque;
QEMUSnapshotInfo *sn_tab, *sn_info;
QCowSnapshot *sn;
int i;
if (!s->nb_snapshots) {
*psn_tab = NULL;
return s->nb_snapshots;
}
sn_tab = g_new0(QEMUSnapshotInfo, s->nb_snapshots);
for(i = 0; i < s->nb_snapshots; i++) {
sn_info = sn_tab + i;
sn = s->snapshots + i;
pstrcpy(sn_info->id_str, sizeof(sn_info->id_str),
sn->id_str);
pstrcpy(sn_info->name, sizeof(sn_info->name),
sn->name);
sn_info->vm_state_size = sn->vm_state_size;
sn_info->date_sec = sn->date_sec;
sn_info->date_nsec = sn->date_nsec;
sn_info->vm_clock_nsec = sn->vm_clock_nsec;
}
*psn_tab = sn_tab;
return s->nb_snapshots;
}
int qcow2_snapshot_load_tmp(BlockDriverState *bs,
const char *snapshot_id,
const char *name,
Error **errp)
{
int i, snapshot_index;
BDRVQcow2State *s = bs->opaque;
QCowSnapshot *sn;
uint64_t *new_l1_table;
int new_l1_bytes;
int ret;
assert(bs->read_only);
/* Search the snapshot */
snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
if (snapshot_index < 0) {
error_setg(errp,
"Can't find snapshot");
return -ENOENT;
}
sn = &s->snapshots[snapshot_index];
/* Allocate and read in the snapshot's L1 table */
if (sn->l1_size > QCOW_MAX_L1_SIZE / sizeof(uint64_t)) {
error_setg(errp, "Snapshot L1 table too large");
return -EFBIG;
}
new_l1_bytes = sn->l1_size * sizeof(uint64_t);
new_l1_table = qemu_try_blockalign(bs->file->bs,
align_offset(new_l1_bytes, 512));
if (new_l1_table == NULL) {
return -ENOMEM;
}
ret = bdrv_pread(bs->file, sn->l1_table_offset,
new_l1_table, new_l1_bytes);
if (ret < 0) {
error_setg(errp, "Failed to read l1 table for snapshot");
qemu_vfree(new_l1_table);
return ret;
}
/* Switch the L1 table */
qemu_vfree(s->l1_table);
s->l1_size = sn->l1_size;
s->l1_table_offset = sn->l1_table_offset;
s->l1_table = new_l1_table;
for(i = 0;i < s->l1_size; i++) {
be64_to_cpus(&s->l1_table[i]);
}
return 0;
}
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