Re: [PATCH] 9pfs: Fix divide by zero bug

[Christian Schoenebeck <qemu_oss@crudebyte.com>]

On Freitag, 22. November 2019 21:00:34 CET Dan Schatzberg wrote:
> Some filesystems may return 0s in statfs (trivially, a FUSE filesystem
> can do so). QEMU should handle this gracefully and just behave the
> same as if statfs failed.

Is that actually legal in non-error cases? Shouldn't a driver without a block 
size concept return 512 according to POSIX?

> Signed-off-by: Dan Schatzberg <dschatzberg@fb.com>
> ---
>  hw/9pfs/9p.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index 37abcdb71e..520177f40c 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -1834,8 +1834,10 @@ static int32_t coroutine_fn get_iounit(V9fsPDU *pdu,
> V9fsPath *path) * and as well as less than (client msize - P9_IOHDRSZ))
>       */
>      if (!v9fs_co_statfs(pdu, path, &stbuf)) {
> -        iounit = stbuf.f_bsize;
> -        iounit *= (s->msize - P9_IOHDRSZ)/stbuf.f_bsize;
> +        if (stbuf.f_bsize) {
> +            iounit = stbuf.f_bsize;
> +            iounit *= (s->msize - P9_IOHDRSZ) / stbuf.f_bsize;
> +        }
>      }
>      if (!iounit) {
>          iounit = s->msize - P9_IOHDRSZ;

Nevertheless, since that will leave iounit initialized with zero and since 
there is already an !ionunit case handling there ...

Acked-by: Christian Schoenebeck <qemu_oss@crudebyte.com>

Best regards,
Christian Schoenebeck