Re: [PATCH v3 02/13] block: use return status of bdrv_append()

[Markus Armbruster]

Kevin Wolf <kwolf@redhat.com> writes:

> Am 16.10.2020 um 19:10 hat Vladimir Sementsov-Ogievskiy geschrieben:
>> Now bdrv_append returns status and we can drop all the local_err things
>> around it.
>> 
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> Reviewed-by: Greg Kurz <groug@kaod.org>
>> Reviewed-by: Alberto Garcia <berto@igalia.com>
>> ---
>>  block.c                     |  5 +----
>>  block/backup-top.c          | 20 ++++++++------------
>>  block/commit.c              |  5 +----
>>  block/mirror.c              |  6 ++----
>>  blockdev.c                  |  4 +---
>>  tests/test-bdrv-graph-mod.c |  6 +++---
>>  6 files changed, 16 insertions(+), 30 deletions(-)
>> 
>> diff --git a/block.c b/block.c
>> index b05fbff42d..7b6818c681 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -3161,7 +3161,6 @@ static BlockDriverState 
>> *bdrv_append_temp_snapshot(BlockDriverState *bs,
>>      int64_t total_size;
>>      QemuOpts *opts = NULL;
>>      BlockDriverState *bs_snapshot = NULL;
>> -    Error *local_err = NULL;
>>      int ret;
>>  
>>      /* if snapshot, we create a temporary backing file and open it
>> @@ -3208,9 +3207,7 @@ static BlockDriverState 
>> *bdrv_append_temp_snapshot(BlockDriverState *bs,
>>       * order to be able to return one, we have to increase
>>       * bs_snapshot's refcount here */
>>      bdrv_ref(bs_snapshot);
>> -    bdrv_append(bs_snapshot, bs, &local_err);
>> -    if (local_err) {
>> -        error_propagate(errp, local_err);
>> +    if (bdrv_append(bs_snapshot, bs, errp) < 0) {
>
> We generally avoid calling functions with side effects inside a
> comparison. Let's use the usual pattern:
>
>     ret = bdrv_append(bs_snapshot, bs, errp);
>     if (ret < 0) {
>         ...
>     }

I'd also advice against buring side effects too deep, but calling a
function in a failure-checking conditional is pretty benign.  It's also
common:

    $ git-grep 'if ([a-z].*) < 0) {'

coughs up several hundred instances.

That said, there is none in block.c.  Local consistency matters.

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