[PATCH] ext3: external journal device as a mount option

The patch below adds a new mount option to allow the external journal
device to be specified.

The syntax is as follows:
# mount -t ext3 -o journal_dev=0x0820 ...
where 0x0820 means major=8 and minor=32.
Signed-off-by: Johann Lombardi <johann.lombardi@bull.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

Documentation/filesystems/ext3.txt

@@ -22,6 +22,11 @@ journal=inum		When a journal already exists, this option is
 			the inode which will represent the ext3 file
 			system's journal file.
 
+journal_dev=devnum	When the external journal device's major/minor numbers
+			have changed, this option allows to specify the new
+			journal location. The journal device is identified
+			through its new major/minor numbers encoded in devnum.
+
 noload			Don't load the journal on mounting.
 
 data=journal		All data are committed into the journal prior

fs/ext3/super.c

@@ -43,7 +43,8 @@
 #include "acl.h"
 #include "namei.h"
 
-static int ext3_load_journal(struct super_block *, struct ext3_super_block *);
+static int ext3_load_journal(struct super_block *, struct ext3_super_block *,
+			     unsigned long journal_devnum);
 static int ext3_create_journal(struct super_block *, struct ext3_super_block *,
 			       int);
 static void ext3_commit_super (struct super_block * sb,
@@ -628,7 +629,7 @@ enum {
 	Opt_nouid32, Opt_nocheck, Opt_debug, Opt_oldalloc, Opt_orlov,
 	Opt_user_xattr, Opt_nouser_xattr, Opt_acl, Opt_noacl,
 	Opt_reservation, Opt_noreservation, Opt_noload, Opt_nobh,
-	Opt_commit, Opt_journal_update, Opt_journal_inum,
+	Opt_commit, Opt_journal_update, Opt_journal_inum, Opt_journal_dev,
 	Opt_abort, Opt_data_journal, Opt_data_ordered, Opt_data_writeback,
 	Opt_usrjquota, Opt_grpjquota, Opt_offusrjquota, Opt_offgrpjquota,
 	Opt_jqfmt_vfsold, Opt_jqfmt_vfsv0, Opt_quota, Opt_noquota,
@@ -666,6 +667,7 @@ static match_table_t tokens = {
 	{Opt_commit, "commit=%u"},
 	{Opt_journal_update, "journal=update"},
 	{Opt_journal_inum, "journal=%u"},
+	{Opt_journal_dev, "journal_dev=%u"},
 	{Opt_abort, "abort"},
 	{Opt_data_journal, "data=journal"},
 	{Opt_data_ordered, "data=ordered"},
@@ -705,8 +707,9 @@ static unsigned long get_sb_block(void **data)
 	return sb_block;
 }
 
-static int parse_options (char * options, struct super_block *sb,
-			  unsigned long * inum, unsigned long *n_blocks_count, int is_remount)
+static int parse_options (char *options, struct super_block *sb,
+			  unsigned long *inum, unsigned long *journal_devnum,
+			  unsigned long *n_blocks_count, int is_remount)
 {
 	struct ext3_sb_info *sbi = EXT3_SB(sb);
 	char * p;
@@ -839,6 +842,16 @@ static int parse_options (char * options, struct super_block *sb,
 				return 0;
 			*inum = option;
 			break;
+		case Opt_journal_dev:
+			if (is_remount) {
+				printk(KERN_ERR "EXT3-fs: cannot specify "
+				       "journal on remount\n");
+				return 0;
+			}
+			if (match_int(&args[0], &option))
+				return 0;
+			*journal_devnum = option;
+			break;
 		case Opt_noload:
 			set_opt (sbi->s_mount_opt, NOLOAD);
 			break;
@@ -1331,6 +1344,7 @@ static int ext3_fill_super (struct super_block *sb, void *data, int silent)
 	unsigned long logic_sb_block;
 	unsigned long offset = 0;
 	unsigned long journal_inum = 0;
+	unsigned long journal_devnum = 0;
 	unsigned long def_mount_opts;
 	struct inode *root;
 	int blocksize;
@@ -1411,7 +1425,8 @@ static int ext3_fill_super (struct super_block *sb, void *data, int silent)
 
 	set_opt(sbi->s_mount_opt, RESERVATION);
 
-	if (!parse_options ((char *) data, sb, &journal_inum, NULL, 0))
+	if (!parse_options ((char *) data, sb, &journal_inum, &journal_devnum,
+			    NULL, 0))
 		goto failed_mount;
 
 	sb->s_flags = (sb->s_flags & ~MS_POSIXACL) |
@@ -1622,7 +1637,7 @@ static int ext3_fill_super (struct super_block *sb, void *data, int silent)
 	 */
 	if (!test_opt(sb, NOLOAD) &&
 	    EXT3_HAS_COMPAT_FEATURE(sb, EXT3_FEATURE_COMPAT_HAS_JOURNAL)) {
-		if (ext3_load_journal(sb, es))
+		if (ext3_load_journal(sb, es, journal_devnum))
 			goto failed_mount2;
 	} else if (journal_inum) {
 		if (ext3_create_journal(sb, es, journal_inum))
@@ -1902,15 +1917,24 @@ out_bdev:
 	return NULL;
 }
 
-static int ext3_load_journal(struct super_block * sb,
-			     struct ext3_super_block * es)
+static int ext3_load_journal(struct super_block *sb,
+			     struct ext3_super_block *es,
+			     unsigned long journal_devnum)
 {
 	journal_t *journal;
 	int journal_inum = le32_to_cpu(es->s_journal_inum);
-	dev_t journal_dev = new_decode_dev(le32_to_cpu(es->s_journal_dev));
+	dev_t journal_dev;
 	int err = 0;
 	int really_read_only;
 
+	if (journal_devnum &&
+	    journal_devnum != le32_to_cpu(es->s_journal_dev)) {
+		printk(KERN_INFO "EXT3-fs: external journal device major/minor "
+			"numbers have changed\n");
+		journal_dev = new_decode_dev(journal_devnum);
+	} else
+		journal_dev = new_decode_dev(le32_to_cpu(es->s_journal_dev));
+
 	really_read_only = bdev_read_only(sb->s_bdev);
 
 	/*
@@ -1969,6 +1993,16 @@ static int ext3_load_journal(struct super_block * sb,
 
 	EXT3_SB(sb)->s_journal = journal;
 	ext3_clear_journal_err(sb, es);
+
+	if (journal_devnum &&
+	    journal_devnum != le32_to_cpu(es->s_journal_dev)) {
+		es->s_journal_dev = cpu_to_le32(journal_devnum);
+		sb->s_dirt = 1;
+
+		/* Make sure we flush the recovery flag to disk. */
+		ext3_commit_super(sb, es, 1);
+	}
+
 	return 0;
 }
 
@@ -2197,7 +2231,7 @@ static int ext3_remount (struct super_block * sb, int * flags, char * data)
 	/*
 	 * Allow the "check" option to be passed as a remount option.
 	 */
-	if (!parse_options(data, sb, NULL, &n_blocks_count, 1)) {
+	if (!parse_options(data, sb, NULL, NULL, &n_blocks_count, 1)) {
 		err = -EINVAL;
 		goto restore_opts;
 	}