ext4: Regularize mount options

Add support for using the mount options "barrier" and "nobarrier", and
"auto_da_alloc" and "noauto_da_alloc", which is more consistent than
"barrier=<0|1>" or "auto_da_alloc=<0|1>".  Most other ext3/ext4 mount
options use the foo/nofoo naming convention.  We allow the old forms
of these mount options for backwards compatibility.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

Documentation/filesystems/ext4.txt

@@ -183,8 +183,8 @@ commit=nrsec	(*)	Ext4 can be told to sync all its data and metadata
 			performance.
 
 barrier=<0|1(*)>	This enables/disables the use of write barriers in
-			the jbd code.  barrier=0 disables, barrier=1 enables.
+barrier(*)		the jbd code.  barrier=0 disables, barrier=1 enables.
-			This also requires an IO stack which can support
+nobarrier		This also requires an IO stack which can support
 			barriers, and if jbd gets an error on a barrier
 			write, it will disable again with a warning.
 			Write barriers enforce proper on-disk ordering
@@ -192,6 +192,9 @@ barrier=<0|1(*)>	This enables/disables the use of write barriers in
 			safe to use, at some performance penalty.  If
 			your disks are battery-backed in one way or another,
 			disabling barriers may safely improve performance.
+			The mount options "barrier" and "nobarrier" can
+			also be used to enable or disable barriers, for
+			consistency with other ext4 mount options.
 
 inode_readahead=n	This tuning parameter controls the maximum
 			number of inode table blocks that ext4's inode
@@ -313,6 +316,24 @@ journal_ioprio=prio	The I/O priority (from 0 to 7, where 0 is the
 			a slightly higher priority than the default I/O
 			priority.
 
+auto_da_alloc(*)	Many broken applications don't use fsync() when 
+noauto_da_alloc		replacing existing files via patterns such as
+			fd = open("foo.new")/write(fd,..)/close(fd)/
+			rename("foo.new", "foo"), or worse yet,
+			fd = open("foo", O_TRUNC)/write(fd,..)/close(fd).
+			If auto_da_alloc is enabled, ext4 will detect
+			the replace-via-rename and replace-via-truncate
+			patterns and force that any delayed allocation
+			blocks are allocated such that at the next
+			journal commit, in the default data=ordered
+			mode, the data blocks of the new file are forced
+			to disk before the rename() operation is
+			commited.  This provides roughly the same level
+			of guarantees as ext3, and avoids the
+			"zero-length" problem that can happen when a
+			system crashes before the delayed allocation
+			blocks are forced to disk.
+
 Data Mode
 =========
 There are 3 different data modes:

fs/ext4/super.c

@@ -867,7 +867,7 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
 		seq_puts(seq, ",data_err=abort");
 
 	if (test_opt(sb, NO_AUTO_DA_ALLOC))
-		seq_puts(seq, ",auto_da_alloc=0");
+		seq_puts(seq, ",noauto_da_alloc");
 
 	ext4_show_quota_options(seq, sb);
 	return 0;
@@ -1018,7 +1018,7 @@ enum {
 	Opt_resgid, Opt_resuid, Opt_sb, Opt_err_cont, Opt_err_panic, Opt_err_ro,
 	Opt_nouid32, Opt_debug, Opt_oldalloc, Opt_orlov,
 	Opt_user_xattr, Opt_nouser_xattr, Opt_acl, Opt_noacl,
-	Opt_auto_da_alloc, Opt_noload, Opt_nobh, Opt_bh,
+	Opt_auto_da_alloc, Opt_noauto_da_alloc, Opt_noload, Opt_nobh, Opt_bh,
 	Opt_commit, Opt_min_batch_time, Opt_max_batch_time,
 	Opt_journal_update, Opt_journal_dev,
 	Opt_journal_checksum, Opt_journal_async_commit,
@@ -1026,8 +1026,8 @@ enum {
 	Opt_data_err_abort, Opt_data_err_ignore,
 	Opt_usrjquota, Opt_grpjquota, Opt_offusrjquota, Opt_offgrpjquota,
 	Opt_jqfmt_vfsold, Opt_jqfmt_vfsv0, Opt_quota, Opt_noquota,
-	Opt_ignore, Opt_barrier, Opt_err, Opt_resize, Opt_usrquota,
+	Opt_ignore, Opt_barrier, Opt_nobarrier, Opt_err, Opt_resize,
-	Opt_grpquota, Opt_i_version,
+	Opt_usrquota, Opt_grpquota, Opt_i_version,
 	Opt_stripe, Opt_delalloc, Opt_nodelalloc,
 	Opt_inode_readahead_blks, Opt_journal_ioprio
 };
@@ -1080,6 +1080,8 @@ static const match_table_t tokens = {
 	{Opt_quota, "quota"},
 	{Opt_usrquota, "usrquota"},
 	{Opt_barrier, "barrier=%u"},
+	{Opt_barrier, "barrier"},
+	{Opt_nobarrier, "nobarrier"},
 	{Opt_i_version, "i_version"},
 	{Opt_stripe, "stripe=%u"},
 	{Opt_resize, "resize"},
@@ -1088,6 +1090,8 @@ static const match_table_t tokens = {
 	{Opt_inode_readahead_blks, "inode_readahead_blks=%u"},
 	{Opt_journal_ioprio, "journal_ioprio=%u"},
 	{Opt_auto_da_alloc, "auto_da_alloc=%u"},
+	{Opt_auto_da_alloc, "auto_da_alloc"},
+	{Opt_noauto_da_alloc, "noauto_da_alloc"},
 	{Opt_err, NULL},
 };
 
@@ -1422,9 +1426,14 @@ set_qf_format:
 		case Opt_abort:
 			set_opt(sbi->s_mount_opt, ABORT);
 			break;
+		case Opt_nobarrier:
+			clear_opt(sbi->s_mount_opt, BARRIER);
+			break;
 		case Opt_barrier:
-			if (match_int(&args[0], &option))
+			if (match_int(&args[0], &option)) {
-				return 0;
+				set_opt(sbi->s_mount_opt, BARRIER);
+				break;
+			}
 			if (option)
 				set_opt(sbi->s_mount_opt, BARRIER);
 			else
@@ -1485,9 +1494,14 @@ set_qf_format:
 			*journal_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE,
 							    option);
 			break;
+		case Opt_noauto_da_alloc:
+			set_opt(sbi->s_mount_opt,NO_AUTO_DA_ALLOC);
+			break;
 		case Opt_auto_da_alloc:
-			if (match_int(&args[0], &option))
+			if (match_int(&args[0], &option)) {
-				return 0;
+				clear_opt(sbi->s_mount_opt, NO_AUTO_DA_ALLOC);
+				break;
+			}
 			if (option)
 				clear_opt(sbi->s_mount_opt, NO_AUTO_DA_ALLOC);
 			else