On 25.09.19 14:39, Vladimir Sementsov-Ogievskiy wrote: > 20.09.2019 18:27, Max Reitz wrote: >> After a couple of follow-up patches, this function will replace >> bdrv_recurse_is_first_non_filter() in check_to_replace_node(). >> >> bdrv_recurse_is_first_non_filter() is both not sufficiently specific for >> check_to_replace_node() (it allows cases that should not be allowed, >> like replacing child nodes of quorum with dissenting data that have more >> parents than just quorum), and it is too restrictive (it is perfectly >> fine to replace filters). >> >> Signed-off-by: Max Reitz <[email protected]> >> --- >> include/block/block_int.h | 10 ++++++++++ >> block.c | 38 ++++++++++++++++++++++++++++++++++++++ >> 2 files changed, 48 insertions(+) >> >> diff --git a/include/block/block_int.h b/include/block/block_int.h >> index 5fd4f17d93..0be7d12f04 100644 >> --- a/include/block/block_int.h >> +++ b/include/block/block_int.h >> @@ -103,6 +103,13 @@ struct BlockDriver { >> */ >> bool (*bdrv_recurse_is_first_non_filter)(BlockDriverState *bs, >> BlockDriverState *candidate); >> + /* >> + * Return true if @to_replace can be replaced by a BDS with the >> + * same data as @bs without it affecting @bs's behavior (that is, >> + * without it being visible to @bs's parents). >> + */ >> + bool (*bdrv_recurse_can_replace)(BlockDriverState *bs, >> + BlockDriverState *to_replace); >> >> int (*bdrv_probe)(const uint8_t *buf, int buf_size, const char >> *filename); >> int (*bdrv_probe_device)(const char *filename); >> @@ -1254,6 +1261,9 @@ void bdrv_format_default_perms(BlockDriverState *bs, >> BdrvChild *c, >> uint64_t perm, uint64_t shared, >> uint64_t *nperm, uint64_t *nshared); >> >> +bool bdrv_recurse_can_replace(BlockDriverState *bs, >> + BlockDriverState *to_replace); >> + >> /* >> * Default implementation for drivers to pass bdrv_co_block_status() to >> * their file. >> diff --git a/block.c b/block.c >> index 7d99ca692c..a2deca4ac9 100644 >> --- a/block.c >> +++ b/block.c >> @@ -6206,6 +6206,44 @@ bool >> bdrv_recurse_is_first_non_filter(BlockDriverState *bs, >> return false; >> } >> >> +/* >> + * This function checks whether the given @to_replace is allowed to be >> + * replaced by a node that always shows the same data as @bs. This is >> + * used for example to verify whether the mirror job can replace >> + * @to_replace by the target mirrored from @bs. >> + * To be replaceable, @bs and @to_replace may either be guaranteed to >> + * always show the same data (because they are only connected through >> + * filters), or some driver may allow replacing one of its children >> + * because it can guarantee that this child's data is not visible at >> + * all (for example, for dissenting quorum children that have no other >> + * parents). >> + */ >> +bool bdrv_recurse_can_replace(BlockDriverState *bs, >> + BlockDriverState *to_replace) >> +{ >> + if (!bs || !bs->drv) { >> + return false; >> + } >> + >> + if (bs == to_replace) { >> + return true; >> + } >> + >> + /* For filters, we can recurse on our own */ >> + if (bs->drv->is_filter) { >> + BdrvChild *child = bs->file ?: bs->backing; > > then, maybe asset(!bs->drv->bdrv_recurse_can_replace)
It’s actually the other way around. As you find yourself, blkverify is
a filter and has its own implementation. That is entirely correct
because we cannot recurse to just bs->file in blkverify's case. So we
should first invoke the driver-specific function, and then have the
generic filter code.
Max
>> + return bdrv_recurse_can_replace(child->bs, to_replace);
>> + }
>
> or, this may be filter-skipping loop instead of recursion, like
>
> while (bs && bs->drv && bs->drv->is_filter) {
> bs = (bs->file ?: bs->backing)->bs;
> }
>
> at function start.
>
> either way:
>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <[email protected]>
>
>> +
>> + /* See what the driver can do */
>> + if (bs->drv->bdrv_recurse_can_replace) {
>> + return bs->drv->bdrv_recurse_can_replace(bs, to_replace);
>> + }
>> +
>> + /* Safe default */
>> + return false;
>> +}
>> +
>> BlockDriverState *check_to_replace_node(BlockDriverState *parent_bs,
>> const char *node_name, Error
>> **errp)
>> {
>>
>
>
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