fat: modify 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.

One of the reasons for this error is lack of permanent inode numbers on
FAT which makes it difficult to construct persistent file handles.  This
can be overcome by using fat_encode_fh() that include i_pos in file
handle.

Once the i_pos is available, it is only a matter of reading the directory
entries from the disk clusters to locate the matching entry and rebuild
the corresponding inode.

We reached the conclusion support stable inode's read-only export first
after discussing with OGAWA and Bruce.  And will make it writable with
some operation(unlink and rename) limitation next time.

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>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 623f36f0423bf0e7fb584945868089e5a6746482..955784e6a9931d9e653688e18269497a8b786b23 100644 (file)
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -23,6 +23,9 @@
 #define FAT_ERRORS_PANIC       2      /* panic on error */
 #define FAT_ERRORS_RO          3      /* remount r/o on error */
 
+#define FAT_NFS_STALE_RW       1      /* NFS RW support, can cause ESTALE */
+#define FAT_NFS_NOSTALE_RO     2      /* NFS RO support, no ESTALE issue */
+
 struct fat_mount_options {
        kuid_t fs_uid;
        kgid_t fs_gid;
@@ -33,6 +36,7 @@ struct fat_mount_options {
        unsigned short shortname;  /* flags for shortname display/create rule */
        unsigned char name_check;  /* r = relaxed, n = normal, s = strict */
        unsigned char errors;      /* On error: continue, panic, remount-ro */
+       unsigned char nfs;         /* NFS support: nostale_ro, stale_rw */
        unsigned short allow_utime;/* permission for setting the [am]time */
        unsigned quiet:1,          /* set = fake successful chmods and chowns */
                 showexec:1,       /* set = only set x bit for com/exe/bat */
@@ -47,8 +51,7 @@ struct fat_mount_options {
                 usefree:1,        /* Use free_clusters for FAT32 */
                 tz_utc:1,         /* Filesystem timestamps are in UTC */
                 rodir:1,          /* allow ATTR_RO for directory */
-                discard:1,        /* Issue discard requests on deletions */
-                nfs:1;            /* Do extra work needed for NFS export */
+                discard:1;        /* Issue discard requests on deletions */
 };
 
 #define FAT_HASH_BITS  8

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 5bafaad0053059502b33219c1c1e2b8deb0e5e58..40f0ef0e8d37019ed63f3b116dac68be7a835466 100644 (file)
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -754,8 +754,6 @@ 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)
@@ -785,6 +783,10 @@ 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");
 
@@ -800,7 +802,8 @@ 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_obsolete, Opt_flush, Opt_tz_utc, Opt_rodir, Opt_err_cont,
-       Opt_err_panic, Opt_err_ro, Opt_discard, Opt_nfs, Opt_err,
+       Opt_err_panic, Opt_err_ro, Opt_discard, Opt_nfs_stale_rw,
+       Opt_nfs_nostale_ro, Opt_err,
 };
 
 static const match_table_t fat_tokens = {
@@ -829,7 +832,9 @@ 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"},
@@ -1017,6 +1022,12 @@ 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:
@@ -1075,9 +1086,6 @@ 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:
@@ -1108,6 +1116,8 @@ 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;
 }