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>

1 files changed, 13 insertions, 12 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index b9aefce..45d07cf 100644
--- a/fs/ext4/super.c
+++ b/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 @@ set_qf_format:
 			*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);
 
 	/*