fat: introduce 2 new values for the -o nfs mount option

This patchset eliminates the client side ESTALE errors when a FAT
partition exported over NFS has its dentries evicted from the cache.  The
idea is to find the on-disk location_'i_pos' of the dirent of the inode
that has been evicted and use it to rebuild the inode.

This patch:

Provide two possible values 'stale_rw' and 'nostale_ro' for the -o nfs
mount option.The first one allows all file operations but does not reduce
ESTALE errors on memory constrained systems.  The second one eliminates
ESTALE errors but mounts the filesystem as read-only.  Not specifying a
value defaults to 'stale_rw'.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ravishankar N <ravi.n1@samsung.com>
Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 7 deletions

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index acf6e479b44..93fbc8a7f09 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -814,8 +814,6 @@ static int fat_show_options(struct seq_file *m, struct dentry *root)
 		seq_puts(m, ",usefree");
 	if (opts->quiet)
 		seq_puts(m, ",quiet");
-	if (opts->nfs)
-		seq_puts(m, ",nfs");
 	if (opts->showexec)
 		seq_puts(m, ",showexec");
 	if (opts->sys_immutable)
@@ -849,6 +847,10 @@ static int fat_show_options(struct seq_file *m, struct dentry *root)
 		seq_puts(m, ",errors=panic");
 	else
 		seq_puts(m, ",errors=remount-ro");
+	if (opts->nfs == FAT_NFS_NOSTALE_RO)
+		seq_puts(m, ",nfs=nostale_ro");
+	else if (opts->nfs)
+		seq_puts(m, ",nfs=stale_rw");
 	if (opts->discard)
 		seq_puts(m, ",discard");
 
@@ -865,7 +867,7 @@ enum {
 	Opt_uni_xl_no, Opt_uni_xl_yes, Opt_nonumtail_no, Opt_nonumtail_yes,
 	Opt_obsolete, Opt_flush, Opt_tz_utc, Opt_rodir, Opt_err_cont,
 	Opt_err_panic, Opt_err_ro, Opt_discard, Opt_nfs, Opt_time_offset,
-	Opt_err,
+	Opt_nfs_stale_rw, Opt_nfs_nostale_ro, Opt_err,
 };
 
 static const match_table_t fat_tokens = {
@@ -895,7 +897,9 @@ static const match_table_t fat_tokens = {
 	{Opt_err_panic, "errors=panic"},
 	{Opt_err_ro, "errors=remount-ro"},
 	{Opt_discard, "discard"},
-	{Opt_nfs, "nfs"},
+	{Opt_nfs_stale_rw, "nfs"},
+	{Opt_nfs_stale_rw, "nfs=stale_rw"},
+	{Opt_nfs_nostale_ro, "nfs=nostale_ro"},
 	{Opt_obsolete, "conv=binary"},
 	{Opt_obsolete, "conv=text"},
 	{Opt_obsolete, "conv=auto"},
@@ -1092,6 +1096,12 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
 		case Opt_err_ro:
 			opts->errors = FAT_ERRORS_RO;
 			break;
+		case Opt_nfs_stale_rw:
+			opts->nfs = FAT_NFS_STALE_RW;
+			break;
+		case Opt_nfs_nostale_ro:
+			opts->nfs = FAT_NFS_NOSTALE_RO;
+			break;
 
 		/* msdos specific */
 		case Opt_dots:
@@ -1150,9 +1160,6 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
 		case Opt_discard:
 			opts->discard = 1;
 			break;
-		case Opt_nfs:
-			opts->nfs = 1;
-			break;
 
 		/* obsolete mount options */
 		case Opt_obsolete:
@@ -1183,6 +1190,8 @@ out:
 		opts->allow_utime = ~opts->fs_dmask & (S_IWGRP | S_IWOTH);
 	if (opts->unicode_xlate)
 		opts->utf8 = 0;
+	if (opts->nfs == FAT_NFS_NOSTALE_RO)
+		sb->s_flags |= MS_RDONLY;
 
 	return 0;
 }