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Re: [Qemu-block] [PATCH v5 14/42] block: Use CAFs when working with back
From: |
Max Reitz |
Subject: |
Re: [Qemu-block] [PATCH v5 14/42] block: Use CAFs when working with backing chains |
Date: |
Fri, 14 Jun 2019 15:50:23 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 |
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 <address@hidden>
>> ---
>> 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.
>> /* 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. :-)
Max
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- Re: [Qemu-block] [PATCH v5 11/42] block: Add bdrv_supports_compressed_writes(), (continued)
[Qemu-block] [PATCH v5 15/42] block: Re-evaluate backing file handling in reopen, Max Reitz, 2019/06/12
[Qemu-block] [PATCH v5 16/42] block: Use child access functions when flushing, Max Reitz, 2019/06/12