"Denis V. Lunev" <d...@openvz.org> wrote:
> The patch enforces proper locking for this operation.
>
> Signed-off-by: Denis V. Lunev <d...@openvz.org>
> CC: Stefan Hajnoczi <stefa...@redhat.com>
> CC: Juan Quintela <quint...@redhat.com>
> ---
> Patches are compile-tested only. Sent to check the approach, naming and
> functions placement. Functions are returning bad BlockDriver via
> parameter to make clear distinction when I'll have to return BS to write.
>
> block/snapshot.c | 35 +++++++++++++++++++++++++++++++++++
> include/block/snapshot.h | 9 +++++++++
> migration/savevm.c | 17 ++++-------------
> 3 files changed, 48 insertions(+), 13 deletions(-)
>
> diff --git a/block/snapshot.c b/block/snapshot.c
> index 89500f2..6b5ce4e 100644
> --- a/block/snapshot.c
> +++ b/block/snapshot.c
> @@ -25,6 +25,7 @@
> #include "block/snapshot.h"
> #include "block/block_int.h"
> #include "qapi/qmp/qerror.h"
> +#include "monitor/monitor.h"
You don't need the monitor here O:-)
>
> QemuOptsList internal_snapshot_opts = {
> .name = "snapshot",
> @@ -356,3 +357,37 @@ int
> bdrv_snapshot_load_tmp_by_id_or_name(BlockDriverState *bs,
>
> return ret;
> }
> +
> +
> +/* Group operations. All block drivers are involved.
> + * These functions will properly handle dataplace (take aio_context_acquire
> + * when appropriate for appropriate block drivers
> + *
> + * Returned block driver will be always locked.
> + */
> +
> +bool bdrv_snapshot_all_can_snapshot(BlockDriverState **first_bad_bs)
bdrv_snapshot_is_possible???
> +{
> + BlockDriverState *bs;
> +
> + while ((bs = bdrv_next(bs))) {
> + bool ok;
> + AioContext *ctx = bdrv_get_aio_context(bs);
> +
> + if (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
> + continue;
> + }
> +
> + aio_context_acquire(ctx);
I think that you should get the lock before the bdrv_is_inserted, but
who am I to know for sure O:-)
> + ok = bdrv_can_snapshot(bs);
> + aio_context_release(ctx);
> +
> + if (!ok) {
> + *first_bad_bs = bs;
> + return false;
> + }
> + }
> +
> + *first_bad_bs = NULL;
> + return true;
> +}
> diff --git a/include/block/snapshot.h b/include/block/snapshot.h
> index 770d9bb..61b4b5d 100644
> --- a/include/block/snapshot.h
> +++ b/include/block/snapshot.h
> @@ -75,4 +75,13 @@ int bdrv_snapshot_load_tmp(BlockDriverState *bs,
> int bdrv_snapshot_load_tmp_by_id_or_name(BlockDriverState *bs,
> const char *id_or_name,
> Error **errp);
> +
> +
> +/* Group operations. All block drivers are involved.
> + * These functions will properly handle dataplace (take aio_context_acquire
> + * when appropriate for appropriate block drivers
> + *
> + */
> +bool bdrv_snapshot_all_can_snapshot(BlockDriverState **first_bad_bs);
> +
> #endif
> diff --git a/migration/savevm.c b/migration/savevm.c
> index dbcc39a..91ba0bf 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1290,19 +1290,10 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
> const char *name = qdict_get_try_str(qdict, "name");
> Error *local_err = NULL;
>
> - /* Verify if there is a device that doesn't support snapshots and is
> writable */
> - bs = NULL;
> - while ((bs = bdrv_next(bs))) {
> -
> - if (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
> - continue;
> - }
> -
> - if (!bdrv_can_snapshot(bs)) {
> - monitor_printf(mon, "Device '%s' is writable but does not
> support snapshots.\n",
> - bdrv_get_device_name(bs));
> - return;
> - }
> + if (bdrv_snapshot_all_can_snapshot(&bs)) {
> + monitor_printf(mon, "Device '%s' is writable but does not "
> + "support snapshots.\n", bdrv_get_device_name(bs));
> + return;
> }
>
> bs = find_vmstate_bs();
ok with the savevm.c changes.
