This is a new patch for VFAT long filename support, replacing the one

that I posted last month. It retains a lot more functionality then the

previous patch.
A FAQ will be posted immediately after this patch to answer the

questions that were raised from the previous discussion.
Cheers, Tridge
------------
When VFAT_FS_DUALNAMES is disabled we avoid the creation of 8.3 short

filenames for files on VFAT filesystems that require a long name. The

patch uses a pattern of 11 bytes in the directory entry which contains

invalid characters such that it cannot be considered to be a valid short

filename.
Signed-off-by: Andrew Tridgell

Acked-by: Dave Kleikamp

Acked-by: Paul E. McKenney

---

 fs/fat/Kconfig      |   20 +++++++++++++++++

 fs/fat/dir.c        |   15 ++++++-------

 fs/fat/namei_vfat.c |   59 +++++++++++++++++++++++++++++++++++++++++++++++++++

 3 files changed, 86 insertions(+), 8 deletions(-)
diff --git a/fs/fat/Kconfig b/fs/fat/Kconfig

index 182f9ff..907a5de 100644

--- a/fs/fat/Kconfig

+++ b/fs/fat/Kconfig

@@ -74,6 +74,26 @@ config VFAT_FS

 	  To compile this as a module, choose M here: the module will be called

 	  vfat.
+config VFAT_FS_DUALNAMES

+	bool "VFAT dual names support"

+	depends on VFAT_FS

+	help

+	  This option provides support for dual filenames on VFAT filesystems.

+	  If this option is disabled then file creation will either put

+	  a short (8.3) name or a long name on the file, but never both.

+	  The field where a shortname would normally go is filled with

+	  invalid characters such that it cannot be considered a valid

+	  short filename.

+

+	  That means that long filenames created with this option

+	  disabled will not be accessible at all to operating systems

+	  that do not understand the VFAT extensions.

+

+	  Users considering enabling this option should consider the implications

+	  of any patents that may exist on dual filenames in VFAT.

+

+	  If unsure, say N

+

 config FAT_DEFAULT_CODEPAGE

 	int "Default codepage for FAT"

 	depends on MSDOS_FS || VFAT_FS

diff --git a/fs/fat/dir.c b/fs/fat/dir.c

index 38ff75a..cd5d3ec 100644

--- a/fs/fat/dir.c

+++ b/fs/fat/dir.c

@@ -420,14 +420,13 @@ parse_record:

 			}

 			i += chl;

 		}

-		if (!last_u)

-			continue;

-

-		/* Compare shortname */

-		bufuname[last_u] = 0x0000;

-		len = fat_uni_to_x8(sbi, bufuname, bufname, sizeof(bufname));

-		if (fat_name_match(sbi, name, name_len, bufname, len))

-			goto found;

+		if (last_u) {

+			/* Compare shortname */

+			bufuname[last_u] = 0x0000;

+			len = fat_uni_to_x8(sbi, bufuname, bufname, sizeof(bufname));

+			if (fat_name_match(sbi, name, name_len, bufname, len))

+				goto found;

+		}
 		if (nr_slots) {

 			void *longname = unicode + FAT_MAX_UNI_CHARS;

diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c

index 73471b7..894f44d 100644

--- a/fs/fat/namei_vfat.c

+++ b/fs/fat/namei_vfat.c

@@ -22,6 +22,7 @@

 #include

 #include

 #include

+#include

 #include "fat.h"
 /*

@@ -586,6 +587,59 @@ xlate_to_uni(const unsigned char *name, int len, unsigned char *outname,

 	return 0;

 }
+#ifndef CONFIG_VFAT_FS_DUALNAMES

+/*

+ * build a 11 byte 8.3 buffer which is not a short filename. We want 11

+ * bytes which:

+ *    - will be seen as a constant string to all APIs on Linux and Windows

+ *    - cannot be matched with wildcard patterns

+ *    - cannot be used to access the file

+ *    - has a low probability of collision within a directory

+ *    - has an invalid 3 byte extension

+ *    - contains at least one non-space and non-nul byte

+ */

+static void vfat_build_dummy_83_buffer(struct inode *dir, char *msdos_name)

+{

+	u32 rand_num = random32() & 0x3FFFFFFF;

+	int i;

+

+	/* a value of zero would leave us with only nul and spaces,

+	 * which would not work with older linux systems

+	 */

+	if (rand_num == 0)

+		rand_num = 1;

+

+	/* we start with a space followed by nul as spaces at the

+	 * start of an entry are trimmed in FAT, which means that

+	 * starting the 11 bytes with 0x20 0x00 gives us a value which

+	 * cannot be used to access the file. It also means that the

+	 * value as seen from all Windows and Linux APIs is a constant

+	 */

+	msdos_name[0]  = ' ';

+	msdos_name[1]  = 0;

+

+	/* we use / and 2 nul bytes for the extension. These are

+	 * invalid in FAT and mean that utilities that show the

+	 * directory show no extension, but still work via the long

+	 * name for old Linux kernels

+	 */

+	msdos_name[8]  = '/';

+	msdos_name[9]  = 0;

+	msdos_name[10] = 0;

+

+	/*

+	 * fill the remaining 6 bytes with random invalid values

+	 * This gives us a low collision rate, which means a low

+	 * chance of problems with chkdsk.exe and WindowsXP

+	 */

+	for (i = 2; i < 8; i++) {

+		msdos_name[i] = rand_num & 0x1F;

+		rand_num >>= 5;

+	}

+}

+#endif

+

+

 static int vfat_build_slots(struct inode *dir, const unsigned char *name,

 			    int len, int is_dir, int cluster,

 			    struct timespec *ts,

@@ -628,6 +682,11 @@ static int vfat_build_slots(struct inode *dir, const unsigned char *name,

 		goto shortname;

 	}
+#ifndef CONFIG_VFAT_FS_DUALNAMES

+	vfat_build_dummy_83_buffer(dir, msdos_name);

+	lcase = 0;

+#endif

+

 	/* build the entry of long file name */

 	cksum = fat_checksum(msdos_name);
--

1.6.0.4
--

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