qcow2: Save disk size in snapshot header

This allows that different snapshots of an image can have different
sizes, which is a requirement for enabling image resizing even with
images that have internal snapshots.

We don't do the actual support for it now, but make sure that the
additional field is present and not completely ignored in all version 3
images. When trying to load a snapshot of different size, it returns
an error.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 17 insertions, 0 deletions

diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 7d3fde5..42f971b 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -48,6 +48,7 @@ typedef struct QEMU_PACKED QCowSnapshotHeader {
 
 typedef struct QEMU_PACKED QCowSnapshotExtraData {
     uint64_t vm_state_size_large;
+    uint64_t disk_size;
 } QCowSnapshotExtraData;
 
 void qcow2_free_snapshots(BlockDriverState *bs)
@@ -117,6 +118,12 @@ int qcow2_read_snapshots(BlockDriverState *bs)
             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);
@@ -197,6 +204,7 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
 
         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);
@@ -330,6 +338,7 @@ int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
     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;
@@ -426,6 +435,13 @@ int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
     }
     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
diff --git a/block/qcow2.h b/block/qcow2.h
index e4ac366..ddb976a 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -78,6 +78,7 @@ typedef struct QCowSnapshot {
     uint32_t l1_size;
     char *id_str;
     char *name;
+    uint64_t disk_size;
     uint64_t vm_state_size;
     uint32_t date_sec;
     uint32_t date_nsec;