nilfs2: add nodiscard mount option

Nilfs has "discard" mount option which issues discard/TRIM commands to
underlying block device, but it lacks a complementary option and has
no way to disable the feature through remount.

This adds "nodiscard" option to resolve this imbalance.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

2 files changed, 9 insertions, 4 deletions

diff --git a/Documentation/filesystems/nilfs2.txt b/Documentation/filesystems/nilfs2.txt
index 54f61c0ff442..d5c0cef38a71 100644
--- a/Documentation/filesystems/nilfs2.txt
+++ b/Documentation/filesystems/nilfs2.txt
@@ -77,9 +77,10 @@ norecovery		Disable recovery of the filesystem on mount.
                         This disables every write access on the device for
                         read-only mounts or snapshots.  This option will fail
                         for r/w mounts on an unclean volume.
-discard                 Issue discard/TRIM commands to the underlying block
-                        device when blocks are freed.  This is useful for SSD
-                        devices and sparse/thinly-provisioned LUNs.
+discard                 This enables/disables the use of discard/TRIM commands.
+nodiscard(*)            The discard/TRIM commands are sent to the underlying
+                        block device when blocks are freed.  This is useful
+                        for SSD devices and sparse/thinly-provisioned LUNs.
 
 NILFS2 usage
 ============
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index 13b0e955c028..9da12211aac1 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -604,7 +604,7 @@ static const struct export_operations nilfs_export_ops = {
 enum {
         Opt_err_cont, Opt_err_panic, Opt_err_ro,
         Opt_barrier, Opt_nobarrier, Opt_snapshot, Opt_order, Opt_norecovery,
-        Opt_discard, Opt_err,
+        Opt_discard, Opt_nodiscard, Opt_err,
 };
 
 static match_table_t tokens = {
@@ -617,6 +617,7 @@ static match_table_t tokens = {
         {Opt_order, "order=%s"},
         {Opt_norecovery, "norecovery"},
         {Opt_discard, "discard"},
+        {Opt_nodiscard, "nodiscard"},
         {Opt_err, NULL}
 };
 
@@ -676,6 +677,9 @@ static int parse_options(char *options, struct super_block *sb)
                 case Opt_discard:
                         nilfs_set_opt(sbi, DISCARD);
                         break;
+                case Opt_nodiscard:
+                        nilfs_clear_opt(sbi, DISCARD);
+                        break;
                 default:
                         printk(KERN_ERR
                                "NILFS: Unrecognized mount option \"%s\"\n", p);