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From: Dave Chinner <david@fromorbit.com>
To: xfs@oss.sgi.com
Subject: [PATCH 27/30] libxfs: work around do_div() not handling 32 bit numerators
Date: Wed, 30 Oct 2013 15:31:18 +1100	[thread overview]
Message-ID: <1383107481-28937-28-git-send-email-david@fromorbit.com> (raw)
In-Reply-To: <1383107481-28937-1-git-send-email-david@fromorbit.com>

From: Dave Chinner <dchinner@redhat.com>

The libxfs dquot buffer code uses do_div() with a 32 bit numerator.
This gives incorrect results as do_div() passes the numerator by
reference as a pointer to a 64 bit value. Hence it does the division
using 32 bits of garbage gives the wrong result. The kernel code
handles 32 bit numerators just fine, so this patch is a temporary
workaround in the dquot buffer code until we fix do_div() to handle
32 bit numerators correctly.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 libxfs/xfs_dquot_buf.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/libxfs/xfs_dquot_buf.c b/libxfs/xfs_dquot_buf.c
index 620d9d3..ce6b09c 100644
--- a/libxfs/xfs_dquot_buf.c
+++ b/libxfs/xfs_dquot_buf.c
@@ -18,18 +18,28 @@
  */
 #include "xfs.h"
 
+/*
+ * XXX: the userspace implementation of the do_div() macro does not handle 32
+ * bit numerators properly as it passes it by reference as a pointer to a 64 bit
+ * variable and dereferences it as such. Hence the result is way, way off
+ * because it uses 32 bits of garbage for the upper 32 bits of the numerator.
+ *
+ * This is being left here as a reminder that we need to fix do_div() in
+ * userspace as every time we do a libxfs kernel/userspace diff we'll see this
+ * comment.
+ */
 int
 xfs_calc_dquots_per_chunk(
 	struct xfs_mount	*mp,
 	unsigned int		nbblks)	/* basic block units */
 {
-	unsigned int	ndquots;
+	uint64_t	ndquots;
 
 	ASSERT(nbblks > 0);
 	ndquots = BBTOB(nbblks);
 	do_div(ndquots, sizeof(xfs_dqblk_t));
 
-	return ndquots;
+	return (int)ndquots;
 }
 
 /*
-- 
1.8.4.rc3

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  parent reply	other threads:[~2013-10-30  4:31 UTC|newest]

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-10-30  4:30 [PATCH 00/30 V3] xfsprogs: CRC write support for xfs_db Dave Chinner
2013-10-30  4:30 ` [PATCH 01/30] xfsprogs: fix automatic dependency generation Dave Chinner
2013-10-31 14:44   ` Christoph Hellwig
2013-10-30  4:30 ` [PATCH 02/30] xfs: fix some minor sparse warnings Dave Chinner
2013-10-31 14:44   ` Christoph Hellwig
2013-10-30  4:30 ` [PATCH 03/30] xfs: create a shared header file for format-related information Dave Chinner
2013-10-31 14:45   ` Christoph Hellwig
2013-10-30  4:30 ` [PATCH 04/30] xfs: split dquot buffer operations out Dave Chinner
2013-10-31 14:45   ` Christoph Hellwig
2013-10-30  4:30 ` [PATCH 05/30] xfs: decouple inode and bmap btree header files Dave Chinner
2013-10-31 14:45   ` Christoph Hellwig
2013-10-30  4:30 ` [PATCH 06/30] libxfs: unify xfs_btree.c with kernel code Dave Chinner
2013-10-31 14:46   ` Christoph Hellwig
2013-10-30  4:30 ` [PATCH 07/30] libxfs: bmap btree owner swap support Dave Chinner
2013-10-31 14:47   ` Christoph Hellwig
2013-10-30  4:30 ` [PATCH 08/30] libxfs: xfs_rtalloc.c becomes xfs_rtbitmap.c Dave Chinner
2013-10-31 14:48   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 09/30] libxfs: bring across inode buffer readahead verifier changes Dave Chinner
2013-10-31 14:48   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 10/30] libxfs: Minor cleanup and bug fix sync Dave Chinner
2013-10-31 14:48   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 11/30] xfs: remove newlines from strings passed to __xfs_printk Dave Chinner
2013-10-31 14:49   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 12/30] xfs: fix the wrong new_size/rnew_size at xfs_iext_realloc_direct() Dave Chinner
2013-10-31 14:49   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 13/30] xfs: fix node forward in xfs_node_toosmall Dave Chinner
2013-10-31 14:49   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 14/30] xfs: don't emit corruption noise on fs probes Dave Chinner
2013-10-31 14:49   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 15/30] db: separate out straight buffer IO from map based IO Dave Chinner
2013-10-31 14:56   ` Christoph Hellwig
2013-10-31 21:50     ` Dave Chinner
2013-11-01 12:51       ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 16/30] db: rewrite bbmap to use xfs_buf_map Dave Chinner
2013-10-31 15:06   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 17/30] db: rewrite IO engine to use libxfs Dave Chinner
2013-10-31 15:10   ` Christoph Hellwig
2013-10-31 21:59     ` Dave Chinner
2013-10-30  4:31 ` [PATCH 18/30] db: introduce verifier support into set_cur Dave Chinner
2013-11-01 13:07   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 19/30] db: indicate if the CRC on a buffer is correct or not Dave Chinner
2013-11-01 13:09   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 20/30] db: verify and calculate inode CRCs Dave Chinner
2013-11-04  9:05   ` Christoph Hellwig
2013-11-05  0:18     ` Dave Chinner
2013-10-30  4:31 ` [PATCH 21/30] db: verify and calculate dquot CRCs Dave Chinner
2013-11-04  9:06   ` Christoph Hellwig
2013-11-05  0:25     ` Dave Chinner
2013-10-30  4:31 ` [PATCH 22/30] db: add a special directory buffer verifier Dave Chinner
2013-11-04  9:07   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 23/30] db: add a special attribute " Dave Chinner
2013-11-04  9:07   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 24/30] db: re-enable write support for v5 filesystems Dave Chinner
2013-11-04  9:07   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 25/30] libxfs: fix root inode handling inconsistencies Dave Chinner
2013-10-30 10:23   ` Christoph Hellwig
2013-10-30 21:59     ` Dave Chinner
2013-10-31  4:13       ` [PATCH 25/30 V2] " Dave Chinner
2013-10-31 15:00         ` Christoph Hellwig
2013-10-31 22:04           ` Dave Chinner
2013-11-01 13:03             ` Christoph Hellwig
2013-11-04 23:22               ` Dave Chinner
2013-11-05  9:05                 ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 26/30] xfs_db: avoid libxfs buffer lookup warnings Dave Chinner
2013-11-04  9:12   ` Christoph Hellwig
2013-11-05  0:52     ` Dave Chinner
2013-11-05  9:06       ` Christoph Hellwig
2013-10-30  4:31 ` Dave Chinner [this message]
2013-11-04  9:16   ` [PATCH 27/30] libxfs: work around do_div() not handling 32 bit numerators Christoph Hellwig
2013-11-05  1:55     ` Dave Chinner
2013-10-30  4:31 ` [PATCH 28/30] db: enable metadump on CRC filesystems Dave Chinner
2013-11-04  9:18   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 29/30] xfs: support larger inode clusters on v5 filesystems Dave Chinner
2013-11-04  9:18   ` Christoph Hellwig
2013-10-30  4:31 ` [PATCH 30/30] xfsprogs: kill experimental warnings for " Dave Chinner
2013-11-04  9:19   ` Christoph Hellwig

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