fat: make discard a mount option

Currently shipping discard capable SSDs and arrays have rather sub-optimal
implementations of the command and can the use of it can cause massive
slowdowns.  Make issueing these commands option as it's already in btrfs
and gfs2.

Signed-off-by: Christoph Hellwig <hch@lst.de>
[hirofumi@mail.parknet.co.jp: tweaks, and add "discard" to fat_show_options]
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

3 files changed, 24 insertions, 12 deletions

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 7db0979c6b7..e6efdfa0f6d 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -44,7 +44,8 @@ struct fat_mount_options {
                  nocase:1,        /* Does this need case conversion? 0=need case conversion*/
                  usefree:1,       /* Use free_clusters for FAT32 */
                  tz_utc:1,        /* Filesystem timestamps are in UTC */
-                 rodir:1;         /* allow ATTR_RO for directory */
+                 rodir:1,         /* allow ATTR_RO for directory */
+                 discard:1;       /* Issue discard requests on deletions */
 };
 
 #define FAT_HASH_BITS   8
diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c
index a81037721a6..81184d3b75a 100644
--- a/fs/fat/fatent.c
+++ b/fs/fat/fatent.c
@@ -566,16 +566,21 @@ int fat_free_clusters(struct inode *inode, int cluster)
                         goto error;
                 }
 
-                /* 
-                 * Issue discard for the sectors we no longer care about,
-                 * batching contiguous clusters into one request
-                 */
-                if (cluster != fatent.entry + 1) {
-                        int nr_clus = fatent.entry - first_cl + 1;
-
-                        sb_issue_discard(sb, fat_clus_to_blknr(sbi, first_cl),
-                                         nr_clus * sbi->sec_per_clus);
-                        first_cl = cluster;
+                if (sbi->options.discard) {
+                        /*
+                         * Issue discard for the sectors we no longer
+                         * care about, batching contiguous clusters
+                         * into one request
+                         */
+                        if (cluster != fatent.entry + 1) {
+                                int nr_clus = fatent.entry - first_cl + 1;
+
+                                sb_issue_discard(sb,
+                                        fat_clus_to_blknr(sbi, first_cl),
+                                        nr_clus * sbi->sec_per_clus);
+
+                                first_cl = cluster;
+                        }
                 }
 
                 ops->ent_put(&fatent, FAT_ENT_FREE);
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 76b7961ab66..14da530b05c 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -858,6 +858,8 @@ static int fat_show_options(struct seq_file *m, struct vfsmount *mnt)
                 seq_puts(m, ",errors=panic");
         else
                 seq_puts(m, ",errors=remount-ro");
+        if (opts->discard)
+                seq_puts(m, ",discard");
 
         return 0;
 }
@@ -871,7 +873,7 @@ enum {
         Opt_shortname_winnt, Opt_shortname_mixed, Opt_utf8_no, Opt_utf8_yes,
         Opt_uni_xl_no, Opt_uni_xl_yes, Opt_nonumtail_no, Opt_nonumtail_yes,
         Opt_obsolate, Opt_flush, Opt_tz_utc, Opt_rodir, Opt_err_cont,
-        Opt_err_panic, Opt_err_ro, Opt_err,
+        Opt_err_panic, Opt_err_ro, Opt_discard, Opt_err,
 };
 
 static const match_table_t fat_tokens = {
@@ -899,6 +901,7 @@ static const match_table_t fat_tokens = {
         {Opt_err_cont, "errors=continue"},
         {Opt_err_panic, "errors=panic"},
         {Opt_err_ro, "errors=remount-ro"},
+        {Opt_discard, "discard"},
         {Opt_obsolate, "conv=binary"},
         {Opt_obsolate, "conv=text"},
         {Opt_obsolate, "conv=auto"},
@@ -1136,6 +1139,9 @@ static int parse_options(char *options, int is_vfat, int silent, int *debug,
                 case Opt_rodir:
                         opts->rodir = 1;
                         break;
+                case Opt_discard:
+                        opts->discard = 1;
+                        break;
 
                 /* obsolete mount options */
                 case Opt_obsolate: