qcow2 v3 requires every snapshot table entry to have two extra data
fields: The 64-bit VM state size, and the virtual disk size.  Both are
optional for v2 images, so they may not be present.

qcow2_upgrade() therefore should update the snapshot table to ensure all
entries have these extra data fields.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1727347
Reported-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2.c | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 190a3874c1..2219639e11 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -4759,7 +4759,9 @@ static int qcow2_upgrade(BlockDriverState *bs, int target_version,
                          Error **errp)
 {
     BDRVQcow2State *s = bs->opaque;
+    bool need_snapshot_update;
     int current_version = s->qcow_version;
+    int i;
     int ret;
 
     /* This is qcow2_upgrade(), not qcow2_downgrade() */
@@ -4768,7 +4770,33 @@ static int qcow2_upgrade(BlockDriverState *bs, int target_version,
     /* There are no other versions (yet) that you can upgrade to */
     assert(target_version == 3);
 
-    status_cb(bs, 0, 1, cb_opaque);
+    status_cb(bs, 0, 2, cb_opaque);
+
+    /*
+     * In v2, snapshots do not need to have extra data.  v3 requires
+     * the 64-bit VM state size and the virtual disk size to be
+     * present.
+     * qcow2_write_snapshots() will always write the list in the
+     * v3-compliant format.
+     */
+    need_snapshot_update = false;
+    for (i = 0; i < s->nb_snapshots; i++) {
+        if (s->snapshots[i].extra_data_size <
+            sizeof_field(QCowSnapshotExtraData, vm_state_size_large) +
+            sizeof_field(QCowSnapshotExtraData, disk_size))
+        {
+            need_snapshot_update = true;
+            break;
+        }
+    }
+    if (need_snapshot_update) {
+        ret = qcow2_write_snapshots(bs);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to update the snapshot table");
+            return ret;
+        }
+    }
+    status_cb(bs, 1, 2, cb_opaque);
 
     s->qcow_version = target_version;
     ret = qcow2_update_header(bs);
@@ -4777,7 +4805,7 @@ static int qcow2_upgrade(BlockDriverState *bs, int target_version,
         error_setg_errno(errp, -ret, "Failed to update the image header");
         return ret;
     }
-    status_cb(bs, 1, 1, cb_opaque);
+    status_cb(bs, 2, 2, cb_opaque);
 
     return 0;
 }
-- 
2.21.0

On 8/19/19 1:55 PM, Max Reitz wrote:
> qcow2 v3 requires every snapshot table entry to have two extra data
> fields: The 64-bit VM state size, and the virtual disk size.  Both are
> optional for v2 images, so they may not be present.
> 
> qcow2_upgrade() therefore should update the snapshot table to ensure all
> entries have these extra data fields.
> 
> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1727347
> Reported-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qcow2.c | 32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
> 

> @@ -4768,7 +4770,33 @@ static int qcow2_upgrade(BlockDriverState *bs, int target_version,
>      /* There are no other versions (yet) that you can upgrade to */
>      assert(target_version == 3);
>  
> -    status_cb(bs, 0, 1, cb_opaque);
> +    status_cb(bs, 0, 2, cb_opaque);
> +
> +    /*
> +     * In v2, snapshots do not need to have extra data.  v3 requires
> +     * the 64-bit VM state size and the virtual disk size to be
> +     * present.
> +     * qcow2_write_snapshots() will always write the list in the
> +     * v3-compliant format.
> +     */
> +    need_snapshot_update = false;
> +    for (i = 0; i < s->nb_snapshots; i++) {
> +        if (s->snapshots[i].extra_data_size <
> +            sizeof_field(QCowSnapshotExtraData, vm_state_size_large) +
> +            sizeof_field(QCowSnapshotExtraData, disk_size))

sizeof(extra) would be more concise than two sizeof_field() added
together, but might cause problems if we later expand the size of extra
for other reasons, but don't revisit this code.  So I actually like what
you did here.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org