[Libguestfs] [nbdkit PATCH] offset, partition: Fix .extents with non-zero offset

[Richard W.M. Jones]

On Wed, Aug 28, 2019 at 11:38:15AM -0500, Eric Blake wrote:
> When querying the extents of the underlying plugin, we should only
> translate the starting offset, and let the plugin report for at least
> as many bytes as our range permits.  Otherwise, short-changing the
> range causes bad behavior such as returning 0 extents, or even failing
> the creation of an extents tracker:
> 
> $ cat script
> case "$1" in
>     get_size) echo 1m;;
>     can_extents) ;;
>     extents) echo 0 1m;;
>     *) exit 2 ;;
> esac
> $ nbdkit -U - --filter=offset sh script offset=64k \
>   --run 'qemu-io -r -f raw -c map $nbd'
> nbdkit: sh[1]: error: extents: plugin must return at least one extent
> 896 KiB (0xe0000) bytes     allocated at offset 0 bytes (0x0)
> nbdkit: sh[1]: error: extents: plugin must return at least one extent
> qemu-io: Failed to get allocation status: Invalid argument
> $ nbdkit -U - --filter=offset sh script offset=640k \
>   --run 'qemu-io -r -f raw -c map $nbd'
> nbdkit: sh[1]: error: nbdkit_extents_new: start (655360) >= end (393216)
> qemu-io: Failed to get allocation status: Invalid argument
> 
> Fixes: 1a5e2d9c, 624abb36
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
> 
> At least we're catching this now before 1.14.
> 
>  docs/nbdkit-filter.pod        | 2 +-
>  filters/offset/offset.c       | 4 ++--
>  filters/partition/partition.c | 3 +--
>  3 files changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/docs/nbdkit-filter.pod b/docs/nbdkit-filter.pod
> index 6e2bea61..cfd664eb 100644
> --- a/docs/nbdkit-filter.pod
> +++ b/docs/nbdkit-filter.pod
> @@ -560,7 +560,7 @@ from the layer below.  Without error checking it would look like this:
>     int64_t size;
> 
>     size = next_ops->get_size (nxdata);
> -   extents2 = nbdkit_extents_new (offset + shift, size - shift);
> +   extents2 = nbdkit_extents_new (offset + shift, size);
>     next_ops->extents (nxdata, count, offset + shift, flags, extents2, err);
>     for (i = 0; i < nbdkit_extents_count (extents2); ++i) {
>       e = nbdkit_get_extent (extents2, i);
> diff --git a/filters/offset/offset.c b/filters/offset/offset.c
> index efe5c6d1..00122770 100644
> --- a/filters/offset/offset.c
> +++ b/filters/offset/offset.c
> @@ -140,9 +140,9 @@ offset_extents (struct nbdkit_next_ops *next_ops, void *nxdata,
>    size_t i;
>    CLEANUP_EXTENTS_FREE struct nbdkit_extents *extents2 = NULL;
>    struct nbdkit_extent e;
> -  int64_t real_size = next_ops->get_size (nxdata);
> +  int64_t real_size = range >= 0 ? offset + range : next_ops->get_size (nxdata);
> 
> -  extents2 = nbdkit_extents_new (offs + offset, real_size - offset);
> +  extents2 = nbdkit_extents_new (offs + offset, real_size);
>    if (extents2 == NULL) {
>      *err = errno;
>      return -1;
> diff --git a/filters/partition/partition.c b/filters/partition/partition.c
> index 56ad05e2..b1b1945d 100644
> --- a/filters/partition/partition.c
> +++ b/filters/partition/partition.c
> @@ -230,9 +230,8 @@ partition_extents (struct nbdkit_next_ops *next_ops, void *nxdata,
>    size_t i;
>    CLEANUP_EXTENTS_FREE struct nbdkit_extents *extents2 = NULL;
>    struct nbdkit_extent e;
> -  int64_t real_size = next_ops->get_size (nxdata);
> 
> -  extents2 = nbdkit_extents_new (offs + h->offset, real_size - h->offset);
> +  extents2 = nbdkit_extents_new (offs + h->offset, h->offset + h->range);
>    if (extents2 == NULL) {
>      *err = errno;
>      return -1;
> -- 

Yup, ACK.

Thanks,

Rich.

-- 
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