[PATCH] xfs: simplify xfs_calc_dquots_per_chunk

[PATCH] xfs: simplify xfs_calc_dquots_per_chunk

[Eric Sandeen]

ndquots is a 32-bit value, and we don't care
about the remainder; there is no reason to use do_div
here, it seems to be the result of a decade+ historical
accident.

Worse, the do_div implementation in userspace breaks
when fed a 32-bit dividend, so we commented it out there
in any case.

Change to simple division, and then we can change
userspace to match, and mandate a 64-bit dividend in
the do_div() in userspace as well.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
--- 

tested w/ ./check -g quota

diff --git a/fs/xfs/libxfs/xfs_dquot_buf.c b/fs/xfs/libxfs/xfs_dquot_buf.c
index ac9a003..747085b 100644
--- a/fs/xfs/libxfs/xfs_dquot_buf.c
+++ b/fs/xfs/libxfs/xfs_dquot_buf.c
@@ -35,13 +35,8 @@
 xfs_calc_dquots_per_chunk(
 	unsigned int		nbblks)	/* basic block units */
 {
-	unsigned int	ndquots;
-
 	ASSERT(nbblks > 0);
-	ndquots = BBTOB(nbblks);
-	do_div(ndquots, sizeof(xfs_dqblk_t));
-
-	return ndquots;
+	return BBTOB(nbblks) / sizeof(xfs_dqblk_t);
 }
 
 /*

Re: [PATCH] xfs: simplify xfs_calc_dquots_per_chunk

[Darrick J. Wong]

On Wed, Apr 05, 2017 at 04:03:17PM -0500, Eric Sandeen wrote:
> ndquots is a 32-bit value, and we don't care
> about the remainder; there is no reason to use do_div
> here, it seems to be the result of a decade+ historical
> accident.
> 
> Worse, the do_div implementation in userspace breaks
> when fed a 32-bit dividend, so we commented it out there
> in any case.
> 
> Change to simple division, and then we can change
> userspace to match, and mandate a 64-bit dividend in
> the do_div() in userspace as well.

This looks fine since nbblks is (unsigned int) and BBTOB doesn't cast to
a 64-bit quantity, therefore 64-bit division isn't ncessary.  This
passes compilation on i386 and armhf, so I guess I'll go test it.

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> --- 
> 
> tested w/ ./check -g quota
> 
> diff --git a/fs/xfs/libxfs/xfs_dquot_buf.c b/fs/xfs/libxfs/xfs_dquot_buf.c
> index ac9a003..747085b 100644
> --- a/fs/xfs/libxfs/xfs_dquot_buf.c
> +++ b/fs/xfs/libxfs/xfs_dquot_buf.c
> @@ -35,13 +35,8 @@
>  xfs_calc_dquots_per_chunk(
>  	unsigned int		nbblks)	/* basic block units */
>  {
> -	unsigned int	ndquots;
> -
>  	ASSERT(nbblks > 0);
> -	ndquots = BBTOB(nbblks);
> -	do_div(ndquots, sizeof(xfs_dqblk_t));
> -
> -	return ndquots;
> +	return BBTOB(nbblks) / sizeof(xfs_dqblk_t);
>  }
>  
>  /*
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html