On 14.06.19 16:31, Vladimir Sementsov-Ogievskiy wrote: > 14.06.2019 16:50, Max Reitz wrote: >> On 14.06.19 15:26, Vladimir Sementsov-Ogievskiy wrote: >>> 13.06.2019 1:09, Max Reitz wrote: >>>> Use child access functions when iterating through backing chains so >>>> filters do not break the chain. >>>> >>>> Signed-off-by: Max Reitz <[email protected]> >>>> --- >>>> block.c | 40 ++++++++++++++++++++++++++++------------ >>>> 1 file changed, 28 insertions(+), 12 deletions(-) >>>> >>>> diff --git a/block.c b/block.c >>>> index 11f37983d9..505b3e9a01 100644 >>>> --- a/block.c >>>> +++ b/block.c >> >> [...] >> >>>> @@ -4273,11 +4274,18 @@ int bdrv_change_backing_file(BlockDriverState *bs, >>>> BlockDriverState *bdrv_find_overlay(BlockDriverState *active, >>>> BlockDriverState *bs) >>>> { >>>> - while (active && bs != backing_bs(active)) { >>>> - active = backing_bs(active); >>>> + bs = bdrv_skip_rw_filters(bs); >>>> + active = bdrv_skip_rw_filters(active); >>>> + >>>> + while (active) { >>>> + BlockDriverState *next = bdrv_backing_chain_next(active); >>>> + if (bs == next) { >>>> + return active; >>>> + } >>>> + active = next; >>>> } >>>> >>>> - return active; >>>> + return NULL; >>>> } >>> >>> Semantics changed for this function. >>> It is used in two places >>> 1. from bdrv_find_base wtih @bs=NULL, it should be unchanged, as I hope we >>> will never have >>> filter node as a bottom of some valid chain >>> >>> 2. from qmp_block_commit, only to check op-blocker... hmmm. I really don't >>> understand, >>> why do we check BLOCK_OP_TYPE_COMMIT_TARGET on top_bs overlay.. top_bs >>> overlay is out of the job, >>> what is this check for? >> >> There is a loop before this check which checks that the same blocker is >> not set on any nodes between top and base (both inclusive). I guess >> non-active commit checks the node above @top, too, because its backing >> file will change. > > So in this case frozen chain works better.
Perhaps. The op blockers are in this weird state anyway. I don’t think
we even need them any more, because the permissions were intended to
replace them (they were originally called “fine-grained op blockers”, I
seem to remember).
I dare not touch them.
>>>> /* Given a BDS, searches for the base layer. */
>>
>> [...]
>>
>>>> @@ -5149,7 +5165,7 @@ BlockDriverState
>>>> *bdrv_find_backing_image(BlockDriverState *bs,
>>>> char *backing_file_full_ret;
>>>>
>>>> if (strcmp(backing_file, curr_bs->backing_file) == 0) {
>>>
>>> hmm, interesting, what bs->backing_file now means? It's strange enough to
>>> store such field on
>>> bds, when we have backing link anyway..
>>
>> Patch 37 has you covered. :-)
>>
>
> Hmm, if it has removed this field, but it doesn't)
Because it’s needed. (Just not in the current form, but that’s what 37
is for.)
> So, we finished with some object, called "overlay", but it is not an overlay
> of bs, it's overlay of
> first non-implicit filtered node in bs backing chain, it may be found by
> bdrv_find_overlay() helper (which is
> almost unused and my be safely dropped), and filename of this "overlay" is
> stored in bs->backing_file string
> variable, keeping in mind that bs->backing is pointer to backing child of bs
> which is completely another thing?
I don’t quite see what you mean. There is no “overlay” in this function.
> Oh, no, everything related to filename-based backing chain logic is not for
> me o_O. If something doesn't work
> with filename-based logic users should use node-names..
In theory yes, but that isn’t an option for qemu-img commit, for example.
> And I'd prefer to deprecate filename based interfaces at all.
Me too.
https://lists.nongnu.org/archive/html/qemu-devel/2014-09/msg04878.html
:-/
Max
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