ext4: Add auto_da_alloc mount option

Add a mount option which allows the user to disable automatic
allocation of blocks whose allocation by delayed allocation when the
file was originally truncated or when the file is renamed over an
existing file.  This feature is intended to save users from the
effects of naive application writers, but it reduces the effectiveness
of the delayed allocation code.  This mount option disables this
safety feature, which may be desirable for prodcutions systems where
the risk of unclean shutdowns or unexpected system crashes is low.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ext4.h

@@ -549,7 +549,7 @@ do {									       \
 #define EXT4_MOUNT_NO_UID32		0x02000  /* Disable 32-bit UIDs */
 #define EXT4_MOUNT_XATTR_USER		0x04000	/* Extended user attributes */
 #define EXT4_MOUNT_POSIX_ACL		0x08000	/* POSIX Access Control Lists */
-#define EXT4_MOUNT_RESERVATION		0x10000	/* Preallocation */
+#define EXT4_MOUNT_NO_AUTO_DA_ALLOC	0x10000	/* No auto delalloc mapping */
 #define EXT4_MOUNT_BARRIER		0x20000 /* Use block barriers */
 #define EXT4_MOUNT_NOBH			0x40000 /* No bufferheads */
 #define EXT4_MOUNT_QUOTA		0x80000 /* Some quota option set */

fs/ext4/inode.c

@@ -3908,7 +3908,7 @@ void ext4_truncate(struct inode *inode)
 	if (!ext4_can_truncate(inode))
 		return;
 
-	if (inode->i_size == 0)
+	if (inode->i_size == 0 && !test_opt(inode->i_sb, NO_AUTO_DA_ALLOC))
 		ei->i_state |= EXT4_STATE_DA_ALLOC_CLOSE;
 
 	if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {

fs/ext4/namei.c

@@ -2497,7 +2497,8 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 		ext4_mark_inode_dirty(handle, new_inode);
 		if (!new_inode->i_nlink)
 			ext4_orphan_add(handle, new_inode);
-		force_da_alloc = 1;
+		if (!test_opt(new_dir->i_sb, NO_AUTO_DA_ALLOC))
+			force_da_alloc = 1;
 	}
 	retval = 0;
 

fs/ext4/super.c

@@ -816,8 +816,6 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
 	if (!test_opt(sb, POSIX_ACL) && (def_mount_opts & EXT4_DEFM_ACL))
 		seq_puts(seq, ",noacl");
 #endif
-	if (!test_opt(sb, RESERVATION))
-		seq_puts(seq, ",noreservation");
 	if (sbi->s_commit_interval != JBD2_DEFAULT_MAX_COMMIT_AGE*HZ) {
 		seq_printf(seq, ",commit=%u",
 			   (unsigned) (sbi->s_commit_interval / HZ));
@@ -868,6 +866,9 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
 	if (test_opt(sb, DATA_ERR_ABORT))
 		seq_puts(seq, ",data_err=abort");
 
+	if (test_opt(sb, NO_AUTO_DA_ALLOC))
+		seq_puts(seq, ",auto_da_alloc=0");
+
 	ext4_show_quota_options(seq, sb);
 	return 0;
 }
@@ -1017,7 +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_reservation, Opt_noreservation, Opt_noload, Opt_nobh, Opt_bh,
+	Opt_auto_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,
@@ -1052,8 +1053,6 @@ static const match_table_t tokens = {
 	{Opt_nouser_xattr, "nouser_xattr"},
 	{Opt_acl, "acl"},
 	{Opt_noacl, "noacl"},
-	{Opt_reservation, "reservation"},
-	{Opt_noreservation, "noreservation"},
 	{Opt_noload, "noload"},
 	{Opt_nobh, "nobh"},
 	{Opt_bh, "bh"},
@@ -1088,6 +1087,7 @@ static const match_table_t tokens = {
 	{Opt_nodelalloc, "nodelalloc"},
 	{Opt_inode_readahead_blks, "inode_readahead_blks=%u"},
 	{Opt_journal_ioprio, "journal_ioprio=%u"},
+	{Opt_auto_da_alloc, "auto_da_alloc=%u"},
 	{Opt_err, NULL},
 };
 
@@ -1220,12 +1220,6 @@ static int parse_options(char *options, struct super_block *sb,
 			       "not supported\n");
 			break;
 #endif
-		case Opt_reservation:
-			set_opt(sbi->s_mount_opt, RESERVATION);
-			break;
-		case Opt_noreservation:
-			clear_opt(sbi->s_mount_opt, RESERVATION);
-			break;
 		case Opt_journal_update:
 			/* @@@ FIXME */
 			/* Eventually we will want to be able to create
@@ -1491,6 +1485,14 @@ static int parse_options(char *options, struct super_block *sb,
 			*journal_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE,
 							    option);
 			break;
+		case Opt_auto_da_alloc:
+			if (match_int(&args[0], &option))
+				return 0;
+			if (option)
+				clear_opt(sbi->s_mount_opt, NO_AUTO_DA_ALLOC);
+			else
+				set_opt(sbi->s_mount_opt,NO_AUTO_DA_ALLOC);
+			break;
 		default:
 			printk(KERN_ERR
 			       "EXT4-fs: Unrecognized mount option \"%s\" "
@@ -2306,7 +2308,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	sbi->s_min_batch_time = EXT4_DEF_MIN_BATCH_TIME;
 	sbi->s_max_batch_time = EXT4_DEF_MAX_BATCH_TIME;
 
-	set_opt(sbi->s_mount_opt, RESERVATION);
 	set_opt(sbi->s_mount_opt, BARRIER);
 
 	/*