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

[Kevin Wolf]

Am 09.06.2015 um 11:47 hat Wen Congyang geschrieben:
> 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 <address@hidden>
> > ---
> >  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.

At first, I thought the same. But how would you ever get a hole that
starts in the middle of a sector? You would have to have a filesystem
with a block size smaller than 512. I don't think that it exists.

Kevin