fat: add config option to set UTF-8 mount option by default

FAT has long supported its own default file name encoding config
setting, separate from CONFIG_NLS_DEFAULT.

However, if UTF-8 encoded file names are desired FAT character set
should not be set to utf8 since this would make file names case
sensitive even if case insensitive matching is requested.  Instead,
"utf8" mount options should be provided to enable UTF-8 file names in
FAT file system.

Unfortunately, there was no possibility to set the default value of this
option so on UTF-8 system "utf8" mount option had to be added manually
to most FAT mounts.

This patch adds config option to set such default value.
Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
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>

Documentation/filesystems/vfat.txt

@@ -56,9 +56,10 @@ iocharset=<name> -- Character set to use for converting between the
 		 you should consider the following option instead.
 
 utf8=<bool>   -- UTF-8 is the filesystem safe version of Unicode that
-		 is used by the console.  It can be enabled for the
-		 filesystem with this option. If 'uni_xlate' gets set,
-		 UTF-8 gets disabled.
+		 is used by the console. It can be enabled or disabled
+		 for the filesystem with this option.
+		 If 'uni_xlate' gets set, UTF-8 gets disabled.
+		 By default, FAT_DEFAULT_UTF8 setting is used.
 
 uni_xlate=<bool> -- Translate unhandled Unicode characters to special
 		 escaped sequences.  This would let you backup and

fs/fat/Kconfig

@@ -93,8 +93,24 @@ config FAT_DEFAULT_IOCHARSET
 	  that most of your FAT filesystems use, and can be overridden
 	  with the "iocharset" mount option for FAT filesystems.
 	  Note that "utf8" is not recommended for FAT filesystems.
-	  If unsure, you shouldn't set "utf8" here.
+	  If unsure, you shouldn't set "utf8" here - select the next option
+	  instead if you would like to use UTF-8 encoded file names by default.
 	  See <file:Documentation/filesystems/vfat.txt> for more information.
 
 	  Enable any character sets you need in File Systems/Native Language
 	  Support.
+
+config FAT_DEFAULT_UTF8
+	bool "Enable FAT UTF-8 option by default"
+	depends on VFAT_FS
+	default n
+	help
+	  Set this if you would like to have "utf8" mount option set
+	  by default when mounting FAT filesystems.
+
+	  Even if you say Y here can always disable UTF-8 for
+	  particular mount by adding "utf8=0" to mount options.
+
+	  Say Y if you use UTF-8 encoding for file names, N otherwise.
+
+	  See <file:Documentation/filesystems/vfat.txt> for more information.

fs/fat/inode.c

@@ -1127,7 +1127,7 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
 	}
 	opts->name_check = 'n';
 	opts->quiet = opts->showexec = opts->sys_immutable = opts->dotsOK =  0;
-	opts->utf8 = opts->unicode_xlate = 0;
+	opts->unicode_xlate = 0;
 	opts->numtail = 1;
 	opts->usefree = opts->nocase = 0;
 	opts->tz_set = 0;
@@ -1135,6 +1135,8 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
 	opts->errors = FAT_ERRORS_RO;
 	*debug = 0;
 
+	opts->utf8 = IS_ENABLED(CONFIG_FAT_DEFAULT_UTF8) && is_vfat;
+
 	if (!options)
 		goto out;