δΊ 2013-2-27 21:58, Markus Armbruster ει:
> Wenchao Xia <xiaw...@linux.vnet.ibm.com> writes:
>
>> Compared to bdrv_can_snapshot(), this function return whether
>> bs* is ready to read snapshot info from instead of write. If yes,
>> caller can then query snapshot information, but taking snapshot
>> is not always possible for that *bs may be read only.
>>
>> Signed-off-by: Wenchao Xia <xiaw...@linux.vnet.ibm.com>
>> Reviewed-by: Eric Blake <ebl...@redhat.com>
>> ---
>> block.c | 19 +++++++++++++++++++
>> include/block/block.h | 1 +
>> 2 files changed, 20 insertions(+), 0 deletions(-)
>>
>> diff --git a/block.c b/block.c
>> index 50dab8e..19c2d7b 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -3058,6 +3058,25 @@ bool bdrv_debug_is_suspended(BlockDriverState *bs,
>> const char *tag)
>> /**************************************************************/
>> /* handling of snapshots */
>>
>> +/* return whether internal snapshot can be read on @bs */
>> +bool bdrv_can_read_snapshot(BlockDriverState *bs)
>> +{
>> + BlockDriver *drv = bs->drv;
>> + if (!drv || !bdrv_is_inserted(bs)) {
>> + return false;
>> + }
>> +
>> + if (!drv->bdrv_snapshot_create) {
>> + if (bs->file != NULL) {
>> + return bdrv_can_read_snapshot(bs->file);
>> + }
>> + return false;
>> + }
>> +
>> + return true;
>> +}
>
> Looks like
>
> bdrv_can_read_snapshot(bs) && !bdrv_is_read_only(bs) == bdrv_can_snapshot(bs)
>
> Correct?
>
not equal, it is tricky for that recusively check is done inside
bdrv_can_snapshot(bs), that is why I did not use a common internal
static function.
>> +
>> +/* return whether internal snapshot can be write on @bs */
>
> "be written".
>
> Or more succinctly:
>
> /* Can @bs take a snapshot? */
>
OK, this seems better.
>> int bdrv_can_snapshot(BlockDriverState *bs)
>> {
>> BlockDriver *drv = bs->drv;
>> diff --git a/include/block/block.h b/include/block/block.h
>> index 5c3b911..4c48052 100644
>> --- a/include/block/block.h
>> +++ b/include/block/block.h
>> @@ -321,6 +321,7 @@ void bdrv_get_full_backing_filename(BlockDriverState *bs,
>> char *dest, size_t sz);
>> BlockInfo *bdrv_query_info(BlockDriverState *s);
>> BlockStats *bdrv_query_stats(const BlockDriverState *bs);
>> +bool bdrv_can_read_snapshot(BlockDriverState *bs);
>> int bdrv_can_snapshot(BlockDriverState *bs);
>> int bdrv_is_snapshot(BlockDriverState *bs);
>> BlockDriverState *bdrv_snapshots(void);
>
--
Best Regards
Wenchao Xia
