[PATCH] fat: make discard a mount option

[Christoph Hellwig <hch@lst.de>]

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>

Index: linux-2.6/fs/fat/fat.h
===================================================================
--- linux-2.6.orig/fs/fat/fat.h	2009-11-18 13:47:49.380003970 +0100
+++ linux-2.6/fs/fat/fat.h	2009-11-18 13:48:13.169014622 +0100
@@ -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
Index: linux-2.6/fs/fat/fatent.c
===================================================================
--- linux-2.6.orig/fs/fat/fatent.c	2009-11-18 13:48:24.102254108 +0100
+++ linux-2.6/fs/fat/fatent.c	2009-11-18 13:49:14.338033708 +0100
@@ -573,8 +573,11 @@ int fat_free_clusters(struct inode *inod
 		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);
+			if (sbi->options.discard) {
+				sb_issue_discard(sb,
+					fat_clus_to_blknr(sbi, first_cl),
+					nr_clus * sbi->sec_per_clus);
+			}
 			first_cl = cluster;
 		}
 
Index: linux-2.6/fs/fat/inode.c
===================================================================
--- linux-2.6.orig/fs/fat/inode.c	2009-11-18 13:46:40.484256340 +0100
+++ linux-2.6/fs/fat/inode.c	2009-11-18 13:47:39.457256306 +0100
@@ -871,7 +871,7 @@ 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 = {
@@ -910,6 +910,7 @@ static const match_table_t fat_tokens = 
 	{Opt_obsolate, "cvf_format=%20s"},
 	{Opt_obsolate, "cvf_options=%100s"},
 	{Opt_obsolate, "posix"},
+	{Opt_discard, "discard"},
 	{Opt_err, NULL},
 };
 static const match_table_t msdos_tokens = {
@@ -1136,6 +1137,9 @@ static int parse_options(char *options, 
 		case Opt_rodir:
 			opts->rodir = 1;
 			break;
+		case Opt_discard:
+			opts->discard = 1;
+			break;
 
 		/* obsolete mount options */
 		case Opt_obsolate: