f2fs: add barrier mount option

This patch adds a mount option, barrier, in f2fs.
The barrier option is the opposite of nobarrier.
If this option is set, cache_flush commands are allowed to be issued.
Signed-off-by: Yangtao Li <frank.li@vivo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Documentation/filesystems/f2fs.rst

@@ -154,6 +154,8 @@ nobarrier		 This option can be used if underlying storage guarantees
 			 If this option is set, no cache_flush commands are issued
 			 but f2fs still guarantees the write ordering of all the
 			 data writes.
+barrier		 If this option is set, cache_flush commands are allowed to be
+			 issued.
 fastboot		 This option is used when a system wants to reduce mount
 			 time as much as possible, even though normal performance
 			 can be sacrificed.

fs/f2fs/super.c

@@ -111,6 +111,7 @@ enum {
 	Opt_noinline_dentry,
 	Opt_flush_merge,
 	Opt_noflush_merge,
+	Opt_barrier,
 	Opt_nobarrier,
 	Opt_fastboot,
 	Opt_extent_cache,
@@ -187,6 +188,7 @@ static match_table_t f2fs_tokens = {
 	{Opt_noinline_dentry, "noinline_dentry"},
 	{Opt_flush_merge, "flush_merge"},
 	{Opt_noflush_merge, "noflush_merge"},
+	{Opt_barrier, "barrier"},
 	{Opt_nobarrier, "nobarrier"},
 	{Opt_fastboot, "fastboot"},
 	{Opt_extent_cache, "extent_cache"},
@@ -807,6 +809,9 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
 		case Opt_nobarrier:
 			set_opt(sbi, NOBARRIER);
 			break;
+		case Opt_barrier:
+			clear_opt(sbi, NOBARRIER);
+			break;
 		case Opt_fastboot:
 			set_opt(sbi, FASTBOOT);
 			break;
@@ -1940,6 +1945,8 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 		seq_puts(seq, ",flush_merge");
 	if (test_opt(sbi, NOBARRIER))
 		seq_puts(seq, ",nobarrier");
+	else
+		seq_puts(seq, ",barrier");
 	if (test_opt(sbi, FASTBOOT))
 		seq_puts(seq, ",fastboot");
 	if (test_opt(sbi, EXTENT_CACHE))