[PATCH] ext2: errors behaviour fix

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:

EXT2_ERRORS_CONTINUE should be read from the superblock as default value for
error behaviour.  parse_option() should clean the alternative options and
should not change default value taken from the superblock.

Signed-off-by: Vasily Averin <vvs@sw.ru>
Acked-by: Kirill Korotaev <dev@openvz.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/ext2/super.c

@@ -364,7 +364,6 @@ static int parse_options (char * options,
 {
 	char * p;
 	substring_t args[MAX_OPT_ARGS];
-	unsigned long kind = EXT2_MOUNT_ERRORS_CONT;
 	int option;
 
 	if (!options)
@@ -404,13 +403,19 @@ static int parse_options (char * options,
 			/* *sb_block = match_int(&args[0]); */
 			break;
 		case Opt_err_panic:
-			kind = EXT2_MOUNT_ERRORS_PANIC;
+			clear_opt (sbi->s_mount_opt, ERRORS_CONT);
+			clear_opt (sbi->s_mount_opt, ERRORS_RO);
+			set_opt (sbi->s_mount_opt, ERRORS_PANIC);
 			break;
 		case Opt_err_ro:
-			kind = EXT2_MOUNT_ERRORS_RO;
+			clear_opt (sbi->s_mount_opt, ERRORS_CONT);
+			clear_opt (sbi->s_mount_opt, ERRORS_PANIC);
+			set_opt (sbi->s_mount_opt, ERRORS_RO);
 			break;
 		case Opt_err_cont:
-			kind = EXT2_MOUNT_ERRORS_CONT;
+			clear_opt (sbi->s_mount_opt, ERRORS_RO);
+			clear_opt (sbi->s_mount_opt, ERRORS_PANIC);
+			set_opt (sbi->s_mount_opt, ERRORS_CONT);
 			break;
 		case Opt_nouid32:
 			set_opt (sbi->s_mount_opt, NO_UID32);
@@ -489,7 +494,6 @@ static int parse_options (char * options,
 			return 0;
 		}
 	}
-	sbi->s_mount_opt |= kind;
 	return 1;
 }
 
@@ -715,6 +719,8 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
 		set_opt(sbi->s_mount_opt, ERRORS_PANIC);
 	else if (le16_to_cpu(sbi->s_es->s_errors) == EXT2_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);