[PATCHv2] fat: add config option to set UTF-8 mount option by default

[Maciej S. Szmigiero]

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@xxxxxxxxxxxxxxxxxxxxx>
---
Changes from v1: use IS_ENABLED() macro to simplify code

 Documentation/filesystems/vfat.txt |  7 ++++---
 fs/fat/Kconfig                     | 18 +++++++++++++++++-
 fs/fat/inode.c                     |  4 +++-
 3 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/Documentation/filesystems/vfat.txt b/Documentation/filesystems/vfat.txt
index 223c32171dcc..cf51360e3a9f 100644
--- a/Documentation/filesystems/vfat.txt
+++ b/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
diff --git a/fs/fat/Kconfig b/fs/fat/Kconfig
index 182f9ffe2b51..3ff1772f612e 100644
--- a/fs/fat/Kconfig
+++ b/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.
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index a5599052116c..226281068a46 100644
--- a/fs/fat/inode.c
+++ b/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;