Re: [PATCH v2 fixed 03/16] util: vfio-helpers: Remove Error parameter from qemu_vfio_undo_mapping()

[Peter Xu <peterx@redhat.com>]

On Wed, Feb 12, 2020 at 02:42:41PM +0100, David Hildenbrand wrote:
> Everybody discards the error. Let's error_report() instead so this error
> doesn't get lost.
> 
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Eduardo Habkost <ehabkost@redhat.com>
> Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

IMHO error_setg() should be preferred comparing to error_report()
because it has a context to be delivered to the caller, so the error
has a better chance to be used in a better way (e.g., QMP only
supports error_setg()).

A better solution is that we deliver the error upper.  For example,
qemu_vfio_dma_map() is one caller of qemu_vfio_undo_mapping, if you
see the callers of qemu_vfio_dma_map() you'll notice most of them has
Error** defined (e.g., nvme_init_queue).  Then we can link all of them
up.

Another lazy solution (and especially if vfio-helpers are still mostly
used only by advanced users) is we can simply pass in &error_abort for
the three callers then they won't be missed...

Thanks,

> ---
>  util/vfio-helpers.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/util/vfio-helpers.c b/util/vfio-helpers.c
> index d6332522c1..13dd962d95 100644
> --- a/util/vfio-helpers.c
> +++ b/util/vfio-helpers.c
> @@ -540,8 +540,7 @@ static int qemu_vfio_do_mapping(QEMUVFIOState *s, void *host, size_t size,
>  /**
>   * Undo the DMA mapping from @s with VFIO, and remove from mapping list.
>   */
> -static void qemu_vfio_undo_mapping(QEMUVFIOState *s, IOVAMapping *mapping,
> -                                   Error **errp)
> +static void qemu_vfio_undo_mapping(QEMUVFIOState *s, IOVAMapping *mapping)
>  {
>      int index;
>      struct vfio_iommu_type1_dma_unmap unmap = {
> @@ -556,7 +555,7 @@ static void qemu_vfio_undo_mapping(QEMUVFIOState *s, IOVAMapping *mapping,
>      assert(QEMU_IS_ALIGNED(mapping->size, qemu_real_host_page_size));
>      assert(index >= 0 && index < s->nr_mappings);
>      if (ioctl(s->container, VFIO_IOMMU_UNMAP_DMA, &unmap)) {
> -        error_setg(errp, "VFIO_UNMAP_DMA failed: %d", -errno);
> +        error_report("VFIO_UNMAP_DMA failed: %d", -errno);
>      }
>      memmove(mapping, &s->mappings[index + 1],
>              sizeof(s->mappings[0]) * (s->nr_mappings - index - 1));
> @@ -621,7 +620,7 @@ int qemu_vfio_dma_map(QEMUVFIOState *s, void *host, size_t size,
>              assert(qemu_vfio_verify_mappings(s));
>              ret = qemu_vfio_do_mapping(s, host, size, iova0);
>              if (ret) {
> -                qemu_vfio_undo_mapping(s, mapping, NULL);
> +                qemu_vfio_undo_mapping(s, mapping);
>                  goto out;
>              }
>              s->low_water_mark += size;
> @@ -681,7 +680,7 @@ void qemu_vfio_dma_unmap(QEMUVFIOState *s, void *host)
>      if (!m) {
>          goto out;
>      }
> -    qemu_vfio_undo_mapping(s, m, NULL);
> +    qemu_vfio_undo_mapping(s, m);
>  out:
>      qemu_mutex_unlock(&s->lock);
>  }
> @@ -698,7 +697,7 @@ void qemu_vfio_close(QEMUVFIOState *s)
>          return;
>      }
>      while (s->nr_mappings) {
> -        qemu_vfio_undo_mapping(s, &s->mappings[s->nr_mappings - 1], NULL);
> +        qemu_vfio_undo_mapping(s, &s->mappings[s->nr_mappings - 1]);
>      }
>      ram_block_notifier_remove(&s->ram_notifier);
>      qemu_vfio_reset(s);
> -- 
> 2.24.1
> 
> 

-- 
Peter Xu