Re: [patch 22/23] fs: check for statfs overflow

[Andreas Dilger <adilger@sun.com>]

On May 28, 2008  11:02 +0200, Nick Piggin wrote:
> fs: check for statfs overflow
> 
> Adds a check for an overflow in the filesystem size so if someone is
> checking with statfs() on a 16G hugetlbfs  in a 32bit binary that it
> will report back EOVERFLOW instead of a size of 0.
> 
> Are other places that need a similar check?  I had tried a similar
> check in put_compat_statfs64 too but it didn't seem to generate an
> EOVERFLOW in my test case.
> 
> Signed-off-by: Jon Tollefson <kniht@linux.vnet.ibm.com>
> Signed-off-by: Nick Piggin <npiggin@suse.de>
> ---
> 
>  fs/compat.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> 
> Index: linux-2.6/fs/compat.c
> ===================================================================
> --- linux-2.6.orig/fs/compat.c
> +++ linux-2.6/fs/compat.c
> @@ -197,8 +197,8 @@ static int put_compat_statfs(struct comp
>  {
>  	
>  	if (sizeof ubuf->f_blocks == 4) {
> -		if ((kbuf->f_blocks | kbuf->f_bfree | kbuf->f_bavail) &
> -		    0xffffffff00000000ULL)
> +		if ((kbuf->f_blocks | kbuf->f_bfree | kbuf->f_bavail |
> +		     kbuf->f_bsize | kbuf->f_frsize) & 0xffffffff00000000ULL)
>  			return -EOVERFLOW;

Hmm, doesn't this check break every filesystem > 16TB on 4kB PAGE_SIZE
nodes?  It would be better, IMHO, to scale down f_blocks, f_bfree, and
f_bavail and correspondingly scale up f_bsize to fit into the 32-bit
statfs structure.

We did this for several years with Lustre, as the first installation was
already larger than 16TB on 32-bit clients at the time.  There was never
a problem with statfs returning a larger f_bsize, since applications
generally use the fstat() st_blocksize to determine IO size and not the
statfs() data.

Returning statfs data accurate to within a few kB is better than failing
the request outright, IMHO.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.