Re: [Qemu-devel] [PATCH 01/11] snapshot: create helper to test that block drivers supports snapshots

[Greg Kurz]

On Wed,  4 Nov 2015 20:19:32 +0300
"Denis V. Lunev" <address@hidden> wrote:

> The patch enforces proper locking for this operation.
> 
> Signed-off-by: Denis V. Lunev <address@hidden>
> CC: Juan Quintela <address@hidden>
> CC: Stefan Hajnoczi <address@hidden>
> CC: Kevin Wolf <address@hidden>
> ---
>  block/snapshot.c         | 27 +++++++++++++++++++++++++++
>  include/block/snapshot.h |  9 +++++++++
>  migration/savevm.c       | 17 ++++-------------
>  3 files changed, 40 insertions(+), 13 deletions(-)
> 
> diff --git a/block/snapshot.c b/block/snapshot.c
> index 89500f2..2ef4545 100644
> --- a/block/snapshot.c
> +++ b/block/snapshot.c
> @@ -356,3 +356,30 @@ 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

s/dataplace/dataplane

> + * when appropriate for appropriate block drivers

Missing ) and anyway the "(take aio_context_acquire..." part more or less
quotes the code and is not needed.

> + *
> + * Returned block driver will be always locked.
> + */
> +
> +bool bdrv_all_can_snapshot(BlockDriverState **first_bad_bs)

Juan suggested bdrv_snapshot_is_possible() and FWIW you already emphasize
that it involves all block drivers in the above comment.

> +{
> +    bool ok = true;
> +    BlockDriverState *bs = NULL;
> +
> +    while ((bs = bdrv_next(bs)) && ok) {
> +        AioContext *ctx = bdrv_get_aio_context(bs);
> +
> +        aio_context_acquire(ctx);
> +        if (bdrv_is_inserted(bs) && !bdrv_is_read_only(bs)) {
> +            ok = bdrv_can_snapshot(bs);
> +        }
> +        aio_context_release(ctx);
> +    }
> +
> +    *first_bad_bs = bs;
> +    return ok;
> +}
> diff --git a/include/block/snapshot.h b/include/block/snapshot.h
> index 770d9bb..0a3cf0d 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
> + *
> + */

This comment is not needed here, already in block/snapshot.c

> +bool bdrv_all_can_snapshot(BlockDriverState **first_bad_bs);
> +
>  #endif
> diff --git a/migration/savevm.c b/migration/savevm.c
> index dbcc39a..3ac3f07 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_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();

Reviewed-by: Greg Kurz <address@hidden>