From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58829) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fM78a-0008BY-3C for qemu-devel@nongnu.org; Fri, 25 May 2018 03:27:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fM78Z-0001Hv-4w for qemu-devel@nongnu.org; Fri, 25 May 2018 03:27:44 -0400 From: Markus Armbruster References: <20180521063516.5479-1-famz@redhat.com> <677208b5-586b-354a-5fd4-67468152510e@redhat.com> <20180525021641.GD12594@lemon.usersys.redhat.com> <87a7soxp5j.fsf@dusky.pond.sub.org> <20180525062503.GE28589@lemon.usersys.redhat.com> Date: Fri, 25 May 2018 09:27:34 +0200 In-Reply-To: <20180525062503.GE28589@lemon.usersys.redhat.com> (Fam Zheng's message of "Fri, 25 May 2018 14:25:03 +0800") Message-ID: <87sh6gurdl.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH] nvme: Make nvme_init error handling code more readable List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng Cc: Kevin Wolf , Paolo Bonzini , qemu-devel@nongnu.org, qemu-block@nongnu.org, Max Reitz Fam Zheng writes: > On Fri, 05/25 07:47, Markus Armbruster wrote: >> Fam Zheng writes: >> >> > On Thu, 05/24 19:16, Paolo Bonzini wrote: >> >> On 21/05/2018 08:35, Fam Zheng wrote: >> >> > Coverity doesn't like the tests under fail label (report CID 1385847). >> >> > Reset the fields so the clean up order is more apparent. >> >> > >> >> > Signed-off-by: Fam Zheng >> >> > --- >> >> > block/nvme.c | 7 +++++++ >> >> > 1 file changed, 7 insertions(+) >> >> > >> >> > diff --git a/block/nvme.c b/block/nvme.c >> >> > index 6f71122bf5..8239b920c8 100644 >> >> > --- a/block/nvme.c >> >> > +++ b/block/nvme.c >> >> > @@ -560,6 +560,13 @@ static int nvme_init(BlockDriverState *bs, const char *device, int namespace, >> >> > qemu_co_queue_init(&s->dma_flush_queue); >> >> > s->nsid = namespace; >> >> > s->aio_context = bdrv_get_aio_context(bs); >> >> > + >> >> > + /* Fields we've not touched should be zero-initialized by block layer >> >> > + * already, but reset them anyway to make the error handling code easier to >> >> > + * reason. */ >> >> > + s->regs = NULL; >> >> > + s->vfio = NULL; >> >> > + >> >> > ret = event_notifier_init(&s->irq_notifier, 0); >> >> > if (ret) { >> >> > error_setg(errp, "Failed to init event notifier"); >> >> > >> >> >> >> I think we should just mark it as a false positive or do something like >> >> >> >> fail_regs: >> >> qemu_vfio_pci_unmap_bar(s->vfio, 0, (void *)s->regs, 0, NVME_BAR_SIZE); >> >> fail_vfio: >> >> qemu_vfio_close(s->vfio); >> >> fail: >> >> g_free(s->queues); >> >> event_notifier_cleanup(&s->irq_notifier); >> >> return ret; >> >> >> >> even though it's a larger patch. >> > >> > And that makes five labels in total, I'm not sure I like it: >> > >> > fail_handler: >> > aio_set_event_notifier(bdrv_get_aio_context(bs), &s->irq_notifier, >> > false, NULL, NULL); >> > fail_queue: >> > nvme_free_queue_pair(bs, s->queues[0]); >> > fail_regs: >> > qemu_vfio_pci_unmap_bar(s->vfio, 0, (void *)s->regs, 0, NVME_BAR_SIZE); >> > fail_vfio: >> > qemu_vfio_close(s->vfio); >> > fail: >> > g_free(s->queues); >> > event_notifier_cleanup(&s->irq_notifier); >> > return ret; >> >> Doesn't look materially worse to me :) > > The labels themselves are not ugly or bad, but the goto statements above will be > harder to manage. Slightly. The difference between three and five feels smaller than say the one between one and three. Admittedly subjective. >> With nice cleanup functions that detect "hasn't been set up" and do >> nothing then, like free(NULL), you can use just one label. Sadly, >> cleanup functions are often not nice that way. > > nvme_free_queue_pair and qemu_vfio_close are cleanup functions and we can > improve them, but to make qemu_vfio_pci_unmap_bar behave similarly is just odd: > it's not a clean up function, at least not for s->vfio. The technique isn't "all or nothing". Reducing the number of labels is nice even when you can't reduce them to one.