| Message ID | 20250130171240.286878-3-kwolf@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | block: Managing inactive nodes (QSD migration) | expand |
On Thu, Jan 30, 2025 at 06:12:33PM +0100, Kevin Wolf wrote: > Putting an active block node on top of an inactive one is strictly > speaking an invalid configuration and the next patch will turn it into a > hard error. > > However, taking a snapshot while disk images are inactive after > completing migration has an important use case: After migrating to a > file, taking an external snapshot is what is needed to take a full VM > snapshot. > > In order for this to keep working after the later patches, change > creating a snapshot such that it automatically inactivates an overlay > that is added on top of an already inactive node. > > Signed-off-by: Kevin Wolf <kwolf@redhat.com> > --- > blockdev.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/blockdev.c b/blockdev.c index 218024497b..eb2517f1dd 100644 --- a/blockdev.c +++ b/blockdev.c @@ -1497,6 +1497,22 @@ static void external_snapshot_action(TransactionAction *action, return; } + /* + * Older QEMU versions have allowed adding an active parent node to an + * inactive child node. This is unsafe in the general case, but there is an + * important use case, which is taking a VM snapshot with migration to file + * and then adding an external snapshot while the VM is still stopped and + * images are inactive. Requiring the user to explicitly create the overlay + * as inactive would break compatibility, so just do it automatically here + * to keep this working. + */ + if (bdrv_is_inactive(state->old_bs) && !bdrv_is_inactive(state->new_bs)) { + ret = bdrv_inactivate(state->new_bs, errp); + if (ret < 0) { + return; + } + } + ret = bdrv_append(state->new_bs, state->old_bs, errp); if (ret < 0) { return;
Putting an active block node on top of an inactive one is strictly speaking an invalid configuration and the next patch will turn it into a hard error. However, taking a snapshot while disk images are inactive after completing migration has an important use case: After migrating to a file, taking an external snapshot is what is needed to take a full VM snapshot. In order for this to keep working after the later patches, change creating a snapshot such that it automatically inactivates an overlay that is added on top of an already inactive node. Signed-off-by: Kevin Wolf <kwolf@redhat.com> --- blockdev.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)