ext4: make trim/discard optional (and off by default)

It is anticipated that when sb_issue_discard starts doing
real work on trim-capable devices, we may see issues.  Make
this mount-time optional, and default it to off until we know
that things are working out OK.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 13 insertions, 1 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index f2d5ec77c1e9..2b382f6f80c1 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -899,6 +899,9 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
         if (test_opt(sb, NO_AUTO_DA_ALLOC))
                 seq_puts(seq, ",noauto_da_alloc");
 
+        if (test_opt(sb, DISCARD))
+                seq_puts(seq, ",discard");
+
         ext4_show_quota_options(seq, sb);
 
         return 0;
@@ -1079,7 +1082,8 @@ enum {
         Opt_usrquota, Opt_grpquota, Opt_i_version,
         Opt_stripe, Opt_delalloc, Opt_nodelalloc,
         Opt_block_validity, Opt_noblock_validity,
-        Opt_inode_readahead_blks, Opt_journal_ioprio
+        Opt_inode_readahead_blks, Opt_journal_ioprio,
+        Opt_discard, Opt_nodiscard,
 };
 
 static const match_table_t tokens = {
@@ -1144,6 +1148,8 @@ static const match_table_t tokens = {
         {Opt_auto_da_alloc, "auto_da_alloc=%u"},
         {Opt_auto_da_alloc, "auto_da_alloc"},
         {Opt_noauto_da_alloc, "noauto_da_alloc"},
+        {Opt_discard, "discard"},
+        {Opt_nodiscard, "nodiscard"},
         {Opt_err, NULL},
 };
 
@@ -1565,6 +1571,12 @@ set_qf_format:
                         else
                                 set_opt(sbi->s_mount_opt,NO_AUTO_DA_ALLOC);
                         break;
+                case Opt_discard:
+                        set_opt(sbi->s_mount_opt, DISCARD);
+                        break;
+                case Opt_nodiscard:
+                        clear_opt(sbi->s_mount_opt, DISCARD);
+                        break;
                 default:
                         ext4_msg(sb, KERN_ERR,
                                "Unrecognized mount option \"%s\" "