Re: [Qemu-devel] [PATCH] raw-posix: Fix .bdrv_co_get_block_status() for unaligned image size

[Wen Congyang <wency@cn.fujitsu.com>]

On 06/09/2015 04:55 PM, Kevin Wolf wrote:
> Image files with an unaligned image size have a final hole that starts
> at EOF, i.e. in the middle of a sector. Currently, *pnum == 0 is
> returned when checking the status of this sector. In qemu-img, this
> triggers an assertion failure.
> 
> In order to fix this, one type for the sector that contains EOF must be
> found. Treating a hole as data is safe, so this patch rounds the
> calculated number of data sectors up, so that a partial sector at EOF is
> treated as a full data sector.
> 
> This fixes https://bugzilla.redhat.com/show_bug.cgi?id=1229394
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/raw-posix.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index 2990e95..44ade8c 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -1848,8 +1848,9 @@ static int64_t coroutine_fn raw_co_get_block_status(BlockDriverState *bs,
>          *pnum = nb_sectors;
>          ret = BDRV_BLOCK_DATA;
>      } else if (data == start) {
> -        /* On a data extent, compute sectors to the end of the extent.  */
> -        *pnum = MIN(nb_sectors, (hole - start) / BDRV_SECTOR_SIZE);
> +        /* On a data extent, compute sectors to the end of the extent,
> +         * possibly including a partial sector at EOF. */

Not only for EOF. If the hole and start are in the same sector, (hole - start) / BDRV_SECTOR_SIZE
will be 0

> +        *pnum = MIN(nb_sectors, DIV_ROUND_UP(hole - start, BDRV_SECTOR_SIZE));
>          ret = BDRV_BLOCK_DATA;
>      } else {
>          /* On a hole, compute sectors to the beginning of the next extent.  */
> 

So, if start is hole, data and  start are in the same sector, (data - start) / BDRV_SECTOR_SIZE
will be 0, you also need to fix it here.

Thanks
Wen Congyang