linux-ext4 - [patch 036/100] ext4: errors behaviour fix

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Date:	Wed, 11 Oct 2006 01:21:21 -0700
From:	akpm@...l.org
To:	torvalds@...l.org
Cc:	akpm@...l.org, dim@...nvz.org, dev@...nvz.org,
	linux-ext4@...r.kernel.org, vvs@...ru
Subject: [patch 036/100] ext4: errors behaviour fix

From: Dmitry Mishin <dim@...nvz.org>

Current error behaviour for ext2 and ext3 filesystems does not fully
correspond to the documentation and should be fixed.

According to man 8 mount, ext2 and ext3 file systems allow to set one of 3
different on-errors behaviours:

---- start of quote man 8 mount ----

errors=continue / errors=remount-ro / errors=panic

    Define the behaviour when an error is encountered.  (Either ignore
    errors and just mark the file system erroneous and continue, or remount
    the file system read-only, or panic and halt the system.) The default is
    set in the filesystem superblock, and can be changed using tune2fs(8).

---- end of quote ----

However EXT3_ERRORS_CONTINUE is not read from the superblock, and thus
ERRORS_CONT is not saved on the sbi->s_mount_opt.  It leads to the incorrect
handle of errors on ext3.

Then we've checked corresponding code in ext2 and discovered that it is buggy
as well:

- EXT2_ERRORS_CONTINUE is not read from the superblock (the same);

- parse_option() does not clean the alternative values and thus something
  like (ERRORS_CONT|ERRORS_RO) can be set;

- if options are omitted, parse_option() does not set any of these options.

Therefore it is possible to set any combination of these options on the ext2:

- none of them may be set: EXT2_ERRORS_CONTINUE on superblock / empty mount
  options;

- any of them may be set using mount options;

- 2 any options may be set: by using EXT2_ERRORS_RO/EXT2_ERRORS_PANIC on the
  superblock and other value in mount options;

- and finally all three options may be set by adding third option in remount.

Currently ext2 uses these values only in ext2_error() and it is not leading to
any noticeable troubles.  However somebody may be discouraged when he will try
to workaround EXT2_ERRORS_PANIC on the superblock by using errors=continue in
mount options.


This patch:

EXT4_ERRORS_CONTINUE should be taken from the superblock as default value for
error behaviour.

Signed-off-by:	Dmitry Mishin <dim@...nvz.org>
Acked-by: Vasily Averin <vvs@...ru>
Acked-by: Kirill Korotaev <dev@...nvz.org>
Cc: <linux-ext4@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...l.org>
---

 fs/ext4/super.c |    2 ++
 1 file changed, 2 insertions(+)

diff -puN fs/ext4/super.c~ext4-errors-behaviour-fix fs/ext4/super.c
--- a/fs/ext4/super.c~ext4-errors-behaviour-fix
+++ a/fs/ext4/super.c
@@ -1526,6 +1526,8 @@ static int ext4_fill_super (struct super
 		set_opt(sbi->s_mount_opt, ERRORS_PANIC);
 	else if (le16_to_cpu(sbi->s_es->s_errors) == EXT4_ERRORS_RO)
 		set_opt(sbi->s_mount_opt, ERRORS_RO);
+	else
+		set_opt(sbi->s_mount_opt, ERRORS_CONT);
 
 	sbi->s_resuid = le16_to_cpu(es->s_def_resuid);
 	sbi->s_resgid = le16_to_cpu(es->s_def_resgid);
_
-
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