[Libguestfs] [PATCH nbdkit 7/8] vddk: Implement extents.

[Eric Blake]

On 3/20/19 5:11 PM, Richard W.M. Jones wrote:
> This uses a new API VixDiskLib_QueryAllocatedBlocks provided in
> VDDK >= 6.7.
> 
> Thanks: Martin Kletzander.
> ---
>  plugins/vddk/vddk-structs.h |  15 +++-
>  plugins/vddk/vddk.c         | 138 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 152 insertions(+), 1 deletion(-)
> 

> +static int
> +vddk_extents (void *handle, uint32_t count, uint64_t offset, uint32_t flags,
> +              struct nbdkit_extents *extents)
> +{
> +  struct vddk_handle *h = handle;
> +  bool req_one = flags & NBDKIT_FLAG_REQ_ONE;
> +  uint64_t position, end, start_sector;
> +
> +  position = offset;
> +
...
> +
> +    for (i = 0; i < block_list->numBlocks; ++i) {
> +      uint64_t offset, length;
> +
> +      offset = block_list->blocks[i].offset * VIXDISKLIB_SECTOR_SIZE;
> +      length = block_list->blocks[i].length * VIXDISKLIB_SECTOR_SIZE;
> +
> +      /* The query returns blocks.  We must insert holes between the
> +       * blocks as necessary.
> +       */
> +      if (position < offset) {
> +        if (nbdkit_add_extent (extents,
> +                               offset, length,
> +                               NBDKIT_EXTENT_HOLE | NBDKIT_EXTENT_ZERO) == -1)
> +          goto error_in_add;
> +      }
> +
> +      if (nbdkit_add_extent (extents,
> +                             offset, length, 0 /* allocated data */) == -1) {
> +      error_in_add:
> +        DEBUG_CALL ("VixDiskLib_FreeBlockList", "block_list");
> +        VixDiskLib_FreeBlockList (block_list);
> +        return -1;
> +      }
> +
> +      position = offset + length;

This inner loop might be long; you could add this:

if (req_one)
  break;

> +    }
> +    DEBUG_CALL ("VixDiskLib_FreeBlockList", "block_list");
> +    VixDiskLib_FreeBlockList (block_list);
> +
> +    start_sector += nr_sectors;
> +
> +    if (req_one)
> +      break;

just as you break the outer loop here, to make REQ_ONE slightly faster.

Otherwise looks sane. m not in a position to test it, but if 'qemu-img
map --output=json nbd://...' pointing to your server matches what you
expect for vddk, that's a good sign.

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

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