linux-ext4 - [PATCH] libext2fs: Always swab MMP block on BE machines

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Date:	Fri, 30 Sep 2011 12:41:26 -0700
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: [PATCH] libext2fs: Always swab MMP block on BE machines

The MMP code in libext2fs tries to gate MMP block swab'ing with this test:

#ifdef EXT2FS_ENABLE_SWAPFS
if (fs->super->s_magic == ext2fs_swab16(EXT2_SUPER_MAGIC))

However, EXT2FS_ENABLE_SWAPFS never seems to be defined anywhere (all possible
#define's were cleaned out of e2fsprogs ages ago), and even if any still
existed, the field fs->super->s_magic is always in host byteorder, so the test
always fails.  So, we can change the #ifdef to WORDS_BIGENDIAN (which is
conditionally defined on BE platforms) and get rid of the broken if test.

(This fix came up while testing the metadata checksumming patchset)

Signed-off-by: Darrick J. Wong <djwong@...ibm.com>
---

 lib/ext2fs/mmp.c |   15 ++++++---------
 1 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/lib/ext2fs/mmp.c b/lib/ext2fs/mmp.c
index ed6ee42..91f4fb2 100644
--- a/lib/ext2fs/mmp.c
+++ b/lib/ext2fs/mmp.c
@@ -91,9 +91,8 @@ errcode_t ext2fs_mmp_read(ext2_filsys fs, blk64_t mmp_blk, void *buf)
 	}

 	mmp_cmp = fs->mmp_cmp;
-#ifdef EXT2FS_ENABLE_SWAPFS
-	if (fs->flags & EXT2_FLAG_SWAP_BYTES)
-		ext2fs_swap_mmp(mmp_cmp);
+#ifdef WORDS_BIGENDIAN
+	ext2fs_swap_mmp(mmp_cmp);
 #endif

 	if (buf != NULL && buf != fs->mmp_cmp)
@@ -122,18 +121,16 @@ errcode_t ext2fs_mmp_write(ext2_filsys fs, blk64_t mmp_blk, void *buf)
 	    fs->super->s_mmp_block > ext2fs_blocks_count(fs->super))
 		return EXT2_ET_MMP_BAD_BLOCK;

-#ifdef EXT2FS_ENABLE_SWAPFS
-	if (fs->super->s_magic == ext2fs_swab16(EXT2_SUPER_MAGIC))
-		ext2fs_swap_mmp(mmp_s);
+#ifdef WORDS_BIGENDIAN
+	ext2fs_swap_mmp(mmp_s);
 #endif

 	/* I was tempted to make this use O_DIRECT and the mmp_fd, but
 	 * this caused no end of grief, while leaving it as-is works. */
 	retval = io_channel_write_blk64(fs->io, mmp_blk, -fs->blocksize, buf);

-#ifdef EXT2FS_ENABLE_SWAPFS
-	if (fs->super->s_magic == ext2fs_swab16(EXT2_SUPER_MAGIC))
-		ext2fs_swap_mmp(mmp_s);
+#ifdef WORDS_BIGENDIAN
+	ext2fs_swap_mmp(mmp_s);
 #endif

 	/* Make sure the block gets to disk quickly */
--
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