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qcow2: Keep unknown extra snapshot data

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The qcow2 specification says to ignore unknown extra data fields in
snapshot table entries.  Currently, we discard it whenever we update the
image, which is a bit different from "ignore".

This patch makes the qcow2 driver keep all unknown extra data fields
when updating an image's snapshot table.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20191011152814.14791-5-mreitz@redhat.com
[mreitz: Adjusted comments as proposed by Eric]
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Max Reitz 2019-10-11 17:28:02 +02:00
parent ecf6c7c0c1
commit fcf9a6b728
2 changed files with 58 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

61
block/qcow2-snapshot.c
View File

@ -37,6 +37,7 @@ void qcow2_free_snapshots(BlockDriverState *bs)
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[i].unknown_extra_data);
}
g_free(s->snapshots);
s->snapshots = NULL;
@ -51,7 +52,6 @@ int qcow2_read_snapshots(BlockDriverState *bs, Error **errp)
QCowSnapshot *sn;
int i, id_str_size, name_size;
int64_t offset;
uint32_t extra_data_size;
int ret;
if (!s->nb_snapshots) {
@ -80,31 +80,53 @@ int qcow2_read_snapshots(BlockDriverState *bs, Error **errp)
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);
sn->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 */
if (sn->extra_data_size > QCOW_MAX_SNAPSHOT_EXTRA_DATA) {
ret = -EFBIG;
error_setg(errp, "Too much extra metadata in snapshot table "
"entry %i", i);
goto fail;
}
/* Read known extra data */
ret = bdrv_pread(bs->file, offset, &extra,
MIN(sizeof(extra), extra_data_size));
MIN(sizeof(extra), sn->extra_data_size));
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to read snapshot table");
goto fail;
}
offset += extra_data_size;
offset += MIN(sizeof(extra), sn->extra_data_size);
if (extra_data_size >= endof(QCowSnapshotExtraData,
vm_state_size_large)) {
if (sn->extra_data_size >= endof(QCowSnapshotExtraData,
vm_state_size_large)) {
sn->vm_state_size = be64_to_cpu(extra.vm_state_size_large);
}
if (extra_data_size >= endof(QCowSnapshotExtraData, disk_size)) {
if (sn->extra_data_size >= endof(QCowSnapshotExtraData, disk_size)) {
sn->disk_size = be64_to_cpu(extra.disk_size);
} else {
sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
}
if (sn->extra_data_size > sizeof(extra)) {
/* Store unknown extra data */
size_t unknown_extra_data_size =
sn->extra_data_size - sizeof(extra);
sn->unknown_extra_data = g_malloc(unknown_extra_data_size);
ret = bdrv_pread(bs->file, offset, sn->unknown_extra_data,
unknown_extra_data_size);
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to read snapshot table");
goto fail;
}
offset += unknown_extra_data_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);
@ -162,7 +184,7 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
sn = s->snapshots + i;
offset = ROUND_UP(offset, 8);
offset += sizeof(h);
offset += sizeof(extra);
offset += MAX(sizeof(extra), sn->extra_data_size);
offset += strlen(sn->id_str);
offset += strlen(sn->name);
@ -209,7 +231,8 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
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));
h.extra_data_size = cpu_to_be32(MAX(sizeof(extra),
sn->extra_data_size));
memset(&extra, 0, sizeof(extra));
extra.vm_state_size_large = cpu_to_be64(sn->vm_state_size);
@ -234,6 +257,22 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
}
offset += sizeof(extra);
if (sn->extra_data_size > sizeof(extra)) {
size_t unknown_extra_data_size =
sn->extra_data_size - sizeof(extra);
/* qcow2_read_snapshots() ensures no unbounded allocation */
assert(unknown_extra_data_size <= BDRV_REQUEST_MAX_BYTES);
assert(sn->unknown_extra_data);
ret = bdrv_pwrite(bs->file, offset, sn->unknown_extra_data,
unknown_extra_data_size);
if (ret < 0) {
goto fail;
}
offset += unknown_extra_data_size;
}
ret = bdrv_pwrite(bs->file, offset, sn->id_str, id_str_size);
if (ret < 0) {
goto fail;
@ -376,6 +415,7 @@ int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
sn->date_sec = sn_info->date_sec;
sn->date_nsec = sn_info->date_nsec;
sn->vm_clock_nsec = sn_info->vm_clock_nsec;
sn->extra_data_size = sizeof(QCowSnapshotExtraData);
/* 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));
@ -647,6 +687,7 @@ int qcow2_snapshot_delete(BlockDriverState *bs,
* The snapshot is now unused, clean up. If we fail after this point, we
* won't recover but just leak clusters.
*/
g_free(sn.unknown_extra_data);
g_free(sn.id_str);
g_free(sn.name);

7
block/qcow2.h
View File

@ -61,6 +61,9 @@
* space for snapshot names and IDs */
#define QCOW_MAX_SNAPSHOTS_SIZE (1024 * QCOW_MAX_SNAPSHOTS)
/* Maximum amount of extra data per snapshot table entry to accept */
#define QCOW_MAX_SNAPSHOT_EXTRA_DATA 1024
/* Bitmap header extension constraints */
#define QCOW2_MAX_BITMAPS 65535
#define QCOW2_MAX_BITMAP_DIRECTORY_SIZE (1024 * QCOW2_MAX_BITMAPS)
@ -181,6 +184,10 @@ typedef struct QCowSnapshot {
uint32_t date_sec;
uint32_t date_nsec;
uint64_t vm_clock_nsec;
/* Size of all extra data, including QCowSnapshotExtraData if available */
uint32_t extra_data_size;
/* Data beyond QCowSnapshotExtraData, if any */
void *unknown_extra_data;
} QCowSnapshot;
struct Qcow2Cache;