Re: [Qemu-devel] [PATCH] nvme: Make nvme_init error handling code more readable

[Fam Zheng <famz@redhat.com>]

On Fri, 05/25 07:47, Markus Armbruster wrote:
> Fam Zheng <famz@redhat.com> 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 <famz@redhat.com>
> >> > ---
> >> >  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.

> 
> 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.

Fam