Re: [Qemu-devel] [PATCH] block/raw-posix: use seek_hole ahead of fiemap

[Markus Armbruster <armbru@redhat.com>]

Please copy Kevin & Stefan for block patches.  Doing that for you.  I
also copy Max, who left his fingerprints on commit 4f11aa8.

Tony Breeds <tony@bakeyournoodle.com> writes:

> The command
>   qemu-img convert -O raw inputimage.qcow2 outputimage.raw
>
> intermittently creates corrupted output images, when the input image is not yet fully synchronized to disk.  This patch preferese the use of seek_hole checks to determine if the sector is present in the disk image.
>
> While we're there modify try_fiemap() to set FIEMAP_FLAG_SYNC.
>
> Reported-By: Michael Steffens <michael_steffens@posteo.de>
> CC: Pádraig Brady <pbrady@redhat.com>
> Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
> ---
>  block/raw-posix.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index a253697..b438c54 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -1472,7 +1472,7 @@ static int64_t try_fiemap(BlockDriverState *bs, off_t start, off_t *data,
>  
>      f.fm.fm_start = start;
>      f.fm.fm_length = (int64_t)nb_sectors * BDRV_SECTOR_SIZE;
> -    f.fm.fm_flags = 0;
> +    f.fm.fm_flags = FIEMAP_FLAG_SYNC;
>      f.fm.fm_extent_count = 1;
>      f.fm.fm_reserved = 0;
>      if (ioctl(s->fd, FS_IOC_FIEMAP, &f) == -1) {
> @@ -1561,9 +1561,9 @@ static int64_t coroutine_fn raw_co_get_block_status(BlockDriverState *bs,
>  
>      start = sector_num * BDRV_SECTOR_SIZE;
>  
> -    ret = try_fiemap(bs, start, &data, &hole, nb_sectors, pnum);
> +    ret = try_seek_hole(bs, start, &data, &hole, pnum);
>      if (ret < 0) {
> -        ret = try_seek_hole(bs, start, &data, &hole, pnum);
> +        ret = try_fiemap(bs, start, &data, &hole, nb_sectors, pnum);
>          if (ret < 0) {
>              /* Assume everything is allocated. */
>              data = 0;