[PATCH] ext3: Add "-o bh" option

This patch adds "-o bh" option to force use of buffer_heads.  This option
is needed when we make "nobh" as default - and if we run into problems.

Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

Documentation/filesystems/ext3.txt

@@ -113,6 +113,14 @@ noquota
 grpquota
 usrquota
 
+bh		(*)	ext3 associates buffer heads to data pages to
+nobh			(a) cache disk block mapping information
+			(b) link pages into transaction to provide
+			    ordering guarantees.
+			"bh" option forces use of buffer heads.
+			"nobh" option tries to avoid associating buffer
+			heads (supported only for "writeback" mode).
+
 
 Specification
 =============

fs/ext3/super.c

@@ -630,7 +630,7 @@ enum {
 	Opt_resgid, Opt_resuid, Opt_sb, Opt_err_cont, Opt_err_panic, Opt_err_ro,
 	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_reservation, Opt_noreservation, Opt_noload, Opt_nobh, Opt_bh,
 	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,
@@ -666,6 +666,7 @@ static match_table_t tokens = {
 	{Opt_noreservation, "noreservation"},
 	{Opt_noload, "noload"},
 	{Opt_nobh, "nobh"},
+	{Opt_bh, "bh"},
 	{Opt_commit, "commit=%u"},
 	{Opt_journal_update, "journal=update"},
 	{Opt_journal_inum, "journal=%u"},
@@ -1014,6 +1015,9 @@ clear_qf_name:
 		case Opt_nobh:
 			set_opt(sbi->s_mount_opt, NOBH);
 			break;
+		case Opt_bh:
+			clear_opt(sbi->s_mount_opt, NOBH);
+			break;
 		default:
 			printk (KERN_ERR
 				"EXT3-fs: Unrecognized mount option \"%s\" "