Re: [Qemu-devel] [PATCH v5 06/16] block/mirror: conservative mirror_exit refactor

[John Snow]

On 09/06/2018 12:57 PM, Jeff Cody wrote:
> On Thu, Sep 06, 2018 at 09:02:15AM -0400, John Snow wrote:
>> For purposes of minimum code movement, refactor the mirror_exit
>> callback to use the post-finalization callbacks in a trivial way.
>>
>> Signed-off-by: John Snow <address@hidden>
>> ---
>>  block/mirror.c | 39 ++++++++++++++++++++++++++++-----------
>>  1 file changed, 28 insertions(+), 11 deletions(-)
>>
>> diff --git a/block/mirror.c b/block/mirror.c
>> index bd3e908710..a92b4702c5 100644
>> --- a/block/mirror.c
>> +++ b/block/mirror.c
>> @@ -79,6 +79,7 @@ typedef struct MirrorBlockJob {
>>      int max_iov;
>>      bool initial_zeroing_ongoing;
>>      int in_active_write_counter;
>> +    bool prepared;
>>  } MirrorBlockJob;
>>  
>>  typedef struct MirrorBDSOpaque {
>> @@ -607,7 +608,7 @@ static void mirror_wait_for_all_io(MirrorBlockJob *s)
>>      }
>>  }
>>  
>> -static void mirror_exit(Job *job)

/**
 * mirror_exit_common: handle both abort() and prepare() cases.
 * for .prepare, returns 0 on success and -errno on failure.
 * for .abort cases, denoted by abort = true, MUST return 0.
 */

>> +static int mirror_exit_common(Job *job)
>>  {
>>      MirrorBlockJob *s = container_of(job, MirrorBlockJob, common.job);
>>      BlockJob *bjob = &s->common;
>> @@ -617,7 +618,13 @@ static void mirror_exit(Job *job)
>>      BlockDriverState *target_bs = blk_bs(s->target);
>>      BlockDriverState *mirror_top_bs = s->mirror_top_bs;
>>      Error *local_err = NULL;
>> -    int ret = job->ret;
>> +    bool abort = job->ret < 0;
>> +    int ret = 0;
>> +
>> +    if (s->prepared) {
>> +        return 0;
>> +    }
>> +    s->prepared = true;
>>  
>>      bdrv_release_dirty_bitmap(src, s->dirty_bitmap);
>>  
>> @@ -642,7 +649,7 @@ 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 (ret == 0 && s->backing_mode == MIRROR_SOURCE_BACKING_CHAIN) {
>> +    if (!abort && 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);
>> @@ -658,11 +665,8 @@ static void mirror_exit(Job *job)
>>          aio_context_acquire(replace_aio_context);
>>      }
>>  
>> -    if (s->should_complete && ret == 0) {
>> -        BlockDriverState *to_replace = src;
>> -        if (s->to_replace) {
>> -            to_replace = s->to_replace;
>> -        }
>> +    if (s->should_complete && !abort) {
>> +        BlockDriverState *to_replace = s->to_replace ?: src;
>>  
>>          if (bdrv_get_flags(target_bs) != bdrv_get_flags(to_replace)) {
>>              bdrv_reopen(target_bs, bdrv_get_flags(to_replace), NULL);
>> @@ -711,7 +715,18 @@ static void mirror_exit(Job *job)
>>      bdrv_unref(mirror_top_bs);
>>      bdrv_unref(src);
>>  
>> -    job->ret = ret;
>> +    return ret;
>> +}
>> +
>> +static int mirror_prepare(Job *job)
>> +{
>> +    return mirror_exit_common(job);
>> +}
>> +
>> +static void mirror_abort(Job *job)
>> +{
>> +    int ret = mirror_exit_common(job);
>> +    assert(ret == 0);
> 
> Not something to hold the series up, but in case a v6 is called for due to
> other changes: I think it may be worth a comment in mirror_exit_common()
> that if abort is true, and we don't return success, QEMU will hit an assert.
> Mainly to prevent someone from including a call with a potential error
> return in the abort path in the future.
> 
> Reviewed-by: Jeff Cody <address@hidden>
> 

Yeah, I should have added a comment, like the one you read before you
got to this comment, by the very nature of how email works.

--js