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 <mre...@redhat.com>
>> ---
>> 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 <vsement...@virtuozzo.com>
>
>> +
>> + /* 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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