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

["Denis V. Lunev" <den@openvz.org>]

On 11/05/2015 09:26 AM, Greg Kurz wrote:
> On Wed,  4 Nov 2015 20:19:32 +0300
> "Denis V. Lunev" <den@openvz.org> wrote:
>
>> The patch enforces proper locking for this operation.
>>
>> Signed-off-by: Denis V. Lunev <den@openvz.org>
>> CC: Juan Quintela <quintela@redhat.com>
>> CC: Stefan Hajnoczi <stefanha@redhat.com>
>> CC: Kevin Wolf <kwolf@redhat.com>
>> ---
>>   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
it is better to have it twice.


>> +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 <gkurz@linux.vnet.ibm.com>
>
Thank you for spelling check.