fat: don't use free_clusters for fat32

It seems that the recent Windows changed specification, and it's
undocumented.  Windows doesn't update ->free_clusters correctly.

This patch doesn't use ->free_clusters by default.  (instead, add "usefree"
for forcing to use it)

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Juergen Beisert <juergen127@kreuzholzen.de>
Cc: Andreas Schwab <schwab@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 20 insertions, 4 deletions

diff --git a/Documentation/filesystems/vfat.txt b/Documentation/filesystems/vfat.txt
index 069cb1094300..fcc123ffa252 100644
--- a/Documentation/filesystems/vfat.txt
+++ b/Documentation/filesystems/vfat.txt
@@ -57,6 +57,13 @@ nonumtail=<bool> -- When creating 8.3 aliases, normally the alias will
                  currently exist in the directory, 'longfile.txt' will
                  be the short alias instead of 'longfi~1.txt'. 
                   
+usefree       -- Use the "free clusters" value stored on FSINFO. It'll
+                 be used to determine number of free clusters without
+                 scanning disk. But it's not used by default, because
+                 recent Windows don't update it correctly in some
+                 case. If you are sure the "free clusters" on FSINFO is
+                 correct, by this option you can avoid scanning disk.
+
 quiet         -- Stops printing certain warning messages.
 
 check=s|r|n   -- Case sensitivity checking setting.
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index a8129e82d594..2c55e8dce793 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -825,6 +825,8 @@ static int fat_show_options(struct seq_file *m, struct vfsmount *mnt)
         }
         if (opts->name_check != 'n')
                 seq_printf(m, ",check=%c", opts->name_check);
+        if (opts->usefree)
+                seq_puts(m, ",usefree");
         if (opts->quiet)
                 seq_puts(m, ",quiet");
         if (opts->showexec)
@@ -850,7 +852,7 @@ static int fat_show_options(struct seq_file *m, struct vfsmount *mnt)
 
 enum {
         Opt_check_n, Opt_check_r, Opt_check_s, Opt_uid, Opt_gid,
-        Opt_umask, Opt_dmask, Opt_fmask, Opt_codepage, Opt_nocase,
+        Opt_umask, Opt_dmask, Opt_fmask, Opt_codepage, Opt_usefree, Opt_nocase,
         Opt_quiet, Opt_showexec, Opt_debug, Opt_immutable,
         Opt_dots, Opt_nodots,
         Opt_charset, Opt_shortname_lower, Opt_shortname_win95,
@@ -872,6 +874,7 @@ static match_table_t fat_tokens = {
         {Opt_dmask, "dmask=%o"},
         {Opt_fmask, "fmask=%o"},
         {Opt_codepage, "codepage=%u"},
+        {Opt_usefree, "usefree"},
         {Opt_nocase, "nocase"},
         {Opt_quiet, "quiet"},
         {Opt_showexec, "showexec"},
@@ -951,7 +954,7 @@ static int parse_options(char *options, int is_vfat, int silent, int *debug,
         opts->quiet = opts->showexec = opts->sys_immutable = opts->dotsOK =  0;
         opts->utf8 = opts->unicode_xlate = 0;
         opts->numtail = 1;
-        opts->nocase = 0;
+        opts->usefree = opts->nocase = 0;
         *debug = 0;
 
         if (!options)
@@ -979,6 +982,9 @@ static int parse_options(char *options, int is_vfat, int silent, int *debug,
                 case Opt_check_n:
                         opts->name_check = 'n';
                         break;
+                case Opt_usefree:
+                        opts->usefree = 1;
+                        break;
                 case Opt_nocase:
                         if (!is_vfat)
                                 opts->nocase = 1;
@@ -1304,7 +1310,9 @@ int fat_fill_super(struct super_block *sb, void *data, int silent,
                                le32_to_cpu(fsinfo->signature2),
                                sbi->fsinfo_sector);
                 } else {
-                        sbi->free_clusters = le32_to_cpu(fsinfo->free_clusters);
+                        if (sbi->options.usefree)
+                                sbi->free_clusters =
+                                        le32_to_cpu(fsinfo->free_clusters);
                         sbi->prev_free = le32_to_cpu(fsinfo->next_cluster);
                 }
 
diff --git a/include/linux/msdos_fs.h b/include/linux/msdos_fs.h
index fa253fa73aa3..0e09c005dda8 100644
--- a/include/linux/msdos_fs.h
+++ b/include/linux/msdos_fs.h
@@ -205,7 +205,8 @@ struct fat_mount_options {
                  numtail:1,       /* Does first alias have a numeric '~1' type tail? */
                  atari:1,         /* Use Atari GEMDOS variation of MS-DOS fs */
                  flush:1,         /* write things quickly */
-                 nocase:1;        /* Does this need case conversion? 0=need case conversion*/
+                 nocase:1,        /* Does this need case conversion? 0=need case conversion*/
+                 usefree:1;       /* Use free_clusters for FAT32 */
 };
 
 #define FAT_HASH_BITS   8