linux-ext4 - [PATCH] libext2fs: don't swap extent-based journal backup on read

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Message-ID: <4AF9D0F8.6020609@redhat.com>
Date:	Tue, 10 Nov 2009 14:45:44 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	ext4 development <linux-ext4@...r.kernel.org>
Subject: [PATCH] libext2fs: don't swap extent-based journal backup on read

The f_illitable_flexbg test was failing on ppc, because
e2fsck_move_ext3_journal is doing a direct memcmp of i_block with 
s_jnl_blocks, and failing.

This is because we don't swap extent data on read from disk; rather
we do it when we access the extents.  However, ext2fs_swap_super
was swapping s_jnl_blocks unconditionally, so these didn't match.

Looks like we need to treat s_jnl_blocks the same as i_block, and
swap it on access, not on read.  Except for the last i_size bit...

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

diff --git a/lib/ext2fs/swapfs.c b/lib/ext2fs/swapfs.c
index 42bc01e..38f5f9b 100644
--- a/lib/ext2fs/swapfs.c
+++ b/lib/ext2fs/swapfs.c
@@ -73,9 +73,19 @@ void ext2fs_swap_super(struct ext2_super_block * sb)
 	sb->s_kbytes_written = ext2fs_swab64(sb->s_kbytes_written);
 	for (i=0; i < 4; i++)
 		sb->s_hash_seed[i] = ext2fs_swab32(sb->s_hash_seed[i]);
+
+	/* if journal backup is for a valid extent-based journal... */
+	if (!ext2fs_extent_header_verify(sb->s_jnl_blocks,
+					 sizeof(sb->s_jnl_blocks))) {
+		/* ... swap only the journal i_size */
+		sb->s_jnl_blocks[16] = ext2fs_swab32(sb->s_jnl_blocks[16]);
+		/* and the extent data is not swapped on read */
+		return;
+	}
+
+	/* direct/indirect journal: swap it all */
 	for (i=0; i < 17; i++)
 		sb->s_jnl_blocks[i] = ext2fs_swab32(sb->s_jnl_blocks[i]);
-
 }
 
 void ext2fs_swap_group_desc(struct ext2_group_desc *gdp)


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