From: Kevin Wolf <kwolf@redhat.com>
To: Markus Armbruster <armbru@redhat.com>
Cc: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
berto@igalia.com, stefanha@redhat.com, qemu-block@nongnu.org,
Greg Kurz <groug@kaod.org>,
qemu-devel@nongnu.org, pavel.dovgaluk@ispras.ru,
pbonzini@redhat.com, den@openvz.org, mreitz@redhat.com,
jsnow@redhat.com, ari@tuxera.com
Subject: Re: [PATCH v3 02/13] block: use return status of bdrv_append()
Date: Mon, 19 Oct 2020 18:10:26 +0200 [thread overview]
Message-ID: <20201019161026.GF6508@merkur.fritz.box> (raw)
In-Reply-To: <87v9f62p8o.fsf@dusky.pond.sub.org>
Am 19.10.2020 um 17:45 hat Markus Armbruster geschrieben:
> 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.
Actually, after looking at the rest of the series, I also need to be a
bit more specific: We do have boolean if (!foo()), it's just the
negative errno ones that aren't very common in the block layer.
And the reason why it's not very common is probably that 0/-errno is
very common in the block layer and a check for < 0 just throws the
specific errno away. We had a lot of such code, which was wrong because
it lost information instead of passing the real error to the caller.
I guess this is the real origin of the block layer habits to avoid it.
Kevin
next prev parent reply other threads:[~2020-10-19 16:21 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-16 17:10 [PATCH v3 00/13] block: deal with errp: part I Vladimir Sementsov-Ogievskiy
2020-10-16 17:10 ` [PATCH v3 01/13] block: return status from bdrv_append and friends Vladimir Sementsov-Ogievskiy
2020-10-19 11:50 ` Kevin Wolf
2020-10-16 17:10 ` [PATCH v3 02/13] block: use return status of bdrv_append() Vladimir Sementsov-Ogievskiy
2020-10-19 12:13 ` Kevin Wolf
2020-10-19 15:45 ` Markus Armbruster
2020-10-19 16:10 ` Kevin Wolf [this message]
2020-10-16 17:10 ` [PATCH v3 03/13] block: check return value of bdrv_open_child and drop error propagation Vladimir Sementsov-Ogievskiy
2020-10-16 17:10 ` [PATCH v3 04/13] blockdev: fix drive_backup_prepare() missed error Vladimir Sementsov-Ogievskiy
2020-10-16 17:10 ` [PATCH v3 05/13] block: drop extra error propagation for bdrv_set_backing_hd Vladimir Sementsov-Ogievskiy
2020-10-16 17:10 ` [PATCH v3 06/13] block/mirror: drop extra error propagation in commit_active_start() Vladimir Sementsov-Ogievskiy
2020-10-16 17:10 ` [PATCH v3 07/13] blockjob: return status from block_job_set_speed() Vladimir Sementsov-Ogievskiy
2020-10-16 17:10 ` [PATCH v3 08/13] block/qcow2: qcow2_get_specific_info(): drop error propagation Vladimir Sementsov-Ogievskiy
2020-10-16 17:10 ` [PATCH v3 09/13] block/qcow2-bitmap: improve qcow2_load_dirty_bitmaps() interface Vladimir Sementsov-Ogievskiy
2020-10-16 17:10 ` [PATCH v3 10/13] block/qcow2-bitmap: return status from qcow2_store_persistent_dirty_bitmaps Vladimir Sementsov-Ogievskiy
2020-10-16 17:10 ` [PATCH v3 11/13] block/qcow2: read_cache_sizes: return status value Vladimir Sementsov-Ogievskiy
2020-10-16 17:10 ` [PATCH v3 12/13] block/qcow2: simplify qcow2_co_invalidate_cache() Vladimir Sementsov-Ogievskiy
2020-10-19 13:06 ` Kevin Wolf
2020-10-20 12:46 ` Vladimir Sementsov-Ogievskiy
2020-10-16 17:10 ` [PATCH v3 13/13] block/qed: bdrv_qed_do_open: deal with errp Vladimir Sementsov-Ogievskiy
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