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Re: [Qemu-devel] [PATCH v3 05/15] block/mirror: don't install backing ch
From: |
John Snow |
Subject: |
Re: [Qemu-devel] [PATCH v3 05/15] block/mirror: don't install backing chain on abort |
Date: |
Tue, 4 Sep 2018 15:15:42 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 |
On 09/03/2018 05:24 AM, Max Reitz wrote:
> On 2018-09-01 00:28, John Snow wrote:
>> In cases where we abort the block/mirror job, there's no point in
>> installing the new backing chain before we finish aborting.
>>
>> Move this to the "success" portion of mirror_exit.
>>
>> Signed-off-by: John Snow <address@hidden>
>> ---
>> block/mirror.c | 27 ++++++++++++++-------------
>> 1 file changed, 14 insertions(+), 13 deletions(-)
>>
>> diff --git a/block/mirror.c b/block/mirror.c
>> index cba555b4ef..c164fee883 100644
>> --- a/block/mirror.c
>> +++ b/block/mirror.c
>> @@ -642,16 +642,6 @@ static void mirror_exit(Job *job)
>> * required before it could become a backing file of target_bs. */
>> bdrv_child_try_set_perm(mirror_top_bs->backing, 0, BLK_PERM_ALL,
>> &error_abort);
>> - if (s->backing_mode == MIRROR_SOURCE_BACKING_CHAIN) {
>> - BlockDriverState *backing = s->is_none_mode ? src : s->base;
>> - if (backing_bs(target_bs) != backing) {
>> - bdrv_set_backing_hd(target_bs, backing, &local_err);
>> - if (local_err) {
>> - error_report_err(local_err);
>> - ret = -EPERM;
>> - }
>> - }
>> - }
>>
>> if (s->to_replace) {
>> replace_aio_context = bdrv_get_aio_context(s->to_replace);
>> @@ -659,9 +649,18 @@ static void mirror_exit(Job *job)
>> }
>>
>> if (s->should_complete && ret == 0) {
>> - BlockDriverState *to_replace = src;
>> - if (s->to_replace) {
>> - to_replace = s->to_replace;
>> + BlockDriverState *to_replace = s->to_replace ? s->to_replace : src;
>> +
>> + if (s->backing_mode == MIRROR_SOURCE_BACKING_CHAIN) {
>> + BlockDriverState *backing = s->is_none_mode ? src : s->base;
>> + if (backing_bs(target_bs) != backing) {
>> + bdrv_set_backing_hd(target_bs, backing, &local_err);
>> + if (local_err) {
>> + error_report_err(local_err);
>> + ret = -EPERM;
>> + goto clean;
>> + }
>> + }
>> }
>>
>> if (bdrv_get_flags(target_bs) != bdrv_get_flags(to_replace)) {
>
> Testing shows that on post-READY cancel, s->should_complete is 0 (which
> makes sense, because all the rest in this path is about replacing
> to_replace by target_bs, which we don't want to do on cancel), so this
> would not be executed.
>
> However, I think we do want to give the target the correct backing chain
> when the job is canceled this way (as I suppose there are ways to keep
> the target around even with drive-mirror).
>
> So we should attach the backing chain whenever ret == 0, not just when
> s->should_complete is true.
>
> Max
>
Ah, thank you for saving me from myself. I got too excited to have
everything under that one conditional.
post-script: I really, really hate the "fake cancel" we've implemented
for mirror. It makes the job logic so much worse.
--js
>> @@ -678,6 +677,8 @@ static void mirror_exit(Job *job)
>> ret = -EPERM;
>> }
>> }
>> +
>> + clean:
>> if (s->to_replace) {
>> bdrv_op_unblock_all(s->to_replace, s->replace_blocker);
>> error_free(s->replace_blocker);
>>
>
>