[Libguestfs] [PATCH nbdkit 4/8] offset: Implement mapping of extents.

[Eric Blake]

On 3/20/19 5:11 PM, Richard W.M. Jones wrote:
> Allows you to safely use nbdkit-offset-filter on top of a plugin
> supporting extents.
> ---
>  filters/offset/offset.c | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)

If we don't change our minds on the interface in patch 1, then this
looks correct.

> +/* Extents. */
> +static int
> +offset_extents (struct nbdkit_next_ops *next_ops, void *nxdata,
> +                void *handle, uint32_t count, uint64_t offs, uint32_t flags,
> +                struct nbdkit_extents *extents, int *err)
> +{
> +  size_t i;
> +  struct nbdkit_extents *extents2;
> +  struct nbdkit_extent e;
> +
> +  extents2 = nbdkit_extents_new (offs + offset);
> +  if (extents2 == NULL) {
> +    *err = errno;
> +    return -1;
> +  }

Ouch - nbdkit_extents_new() returns NULL for 'start >= INT64_MAX'
without setting errno. Of course, that failure path should be
unreachable here, but if you are going to assign *err based on errno,
then we have to make sure patch 1 guarantees sane errno settings on all
failure paths.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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