support for vfat long filenames

[Ryan Lortie <desrt@desrt.ca>]

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hello.

here's a first go at a patch to implement long filename support for vfat
in libvolume_id.

i'm not on the list, so please keep me cc:'d in on any discussion...

cheers

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--- a/extras/volume_id/lib/fat.c	2007-03-28 14:47:26.000000000 -0400
+++ b/extras/volume_id/lib/fat.c	2007-05-23 02:12:42.000000000 -0400
@@ -16,6 +16,7 @@
 #  include <config.h>
 #endif
 
+#include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -34,6 +35,16 @@
 #define FAT_ATTR_MASK			0x3f
 #define FAT_ENTRY_FREE			0xe5
 
+#define VFAT_LFN_SEQ_MASK		0x3f
+#define VFAT_LFN_SEQ_LAST		0x40
+#define VFAT_LFN_SEQ_MAX		20
+#define VFAT_LFN_CHARS_PER_ENTRY	(5 + 6 + 2)
+#define VFAT_LOWERCASE_NAME		0x10
+#define VFAT_LOWERCASE_EXT		0x08
+
+#define TRUE				1
+#define FALSE				0
+
 struct vfat_super_block {
 	uint8_t		boot_jump[3];
 	uint8_t		sysid[8];
@@ -88,9 +99,10 @@
 struct vfat_dir_entry {
 	uint8_t		name[11];
 	uint8_t		attr;
+	uint8_t		lowercase;
+	uint8_t		fine_time_creat;
 	uint16_t	time_creat;
 	uint16_t	date_creat;
-	uint16_t	time_acc;
 	uint16_t	date_acc;
 	uint16_t	cluster_high;
 	uint16_t	time_write;
@@ -99,6 +111,139 @@
 	uint32_t	size;
 } PACKED;
 
+
+struct vfat_lfn_entry {
+	uint8_t		seq;
+	uint16_t	name0[5];
+	uint8_t		attr;
+	uint8_t		reserved;
+	uint8_t		cksum;
+	uint16_t	name1[6];
+	uint16_t	cluster;
+	uint16_t	name2[2];
+} PACKED;
+
+/* output must be at least 3 times longer than input */
+static void
+utf8_from_ucs16 (uint8_t *utf8, uint16_t *ucs16)
+{
+	while (*ucs16) {
+		if (*ucs16 & 0xf800) {
+			/* three-byte encoding */
+			*utf8++ = 0xe0 | ((*ucs16 >> 12) & 0x0f);
+			*utf8++ = 0x80 | ((*ucs16 >>  6) & 0x3f);
+			*utf8++ = 0x80 | ((*ucs16 >>  0) & 0x3f);
+		} else if (*ucs16 & 0xff80) {
+			/* two-byte encoding */
+			*utf8++ = 0xc0 | ((*ucs16 >> 6) & 0x1f);
+			*utf8++ = 0x80 | ((*ucs16 >> 0) & 0x3f);
+		} else {
+			/* ascii */
+			*utf8++ = *ucs16;
+		}
+
+		ucs16++;
+	}
+}
+
+static uint8_t
+fat_lfn_checksum (const uint8_t name[11])
+{
+  uint8_t cksum = 0;
+  int i;
+
+  /* http://en.wikipedia.org/wiki/File_Allocation_Table */
+  for (i = 0; i < 11; i++)
+    cksum = ((cksum & 1) ? 0x80 : 0) + (cksum >> 1) + name[i];
+
+  return cksum;
+}
+
+static int
+fat_read_lfn (struct vfat_dir_entry *dir,
+	      struct vfat_dir_entry *entry,
+	      uint8_t *filename)
+{
+	uint16_t buffer[VFAT_LFN_SEQ_MAX*VFAT_LFN_CHARS_PER_ENTRY];
+	uint8_t expected_seq = 1;
+	uint8_t cksum;
+	int len = 0;
+
+	cksum = fat_lfn_checksum (entry->name);
+
+	while (--entry >= dir)
+	{
+		struct vfat_lfn_entry *lfn = (struct vfat_lfn_entry *) entry;
+		unsigned int i;
+
+		if (expected_seq > VFAT_LFN_SEQ_MAX)
+			break;
+
+		if ((lfn->attr & FAT_ATTR_MASK) != FAT_ATTR_LONG_NAME)
+			break;
+
+		if (lfn->cksum != cksum)
+			break;
+
+		if ((lfn->seq & VFAT_LFN_SEQ_MASK) != expected_seq++)
+			break;
+
+		if (lfn->cluster != 0)
+			break;
+
+		/* extra paranoia */
+		assert (((char *) &buffer[len]) - ((char *) &buffer[0]) +
+			sizeof lfn->name0 +
+			sizeof lfn->name1 +
+			sizeof lfn->name2 <= sizeof buffer);
+
+		for (i = 0; i < sizeof lfn->name0 / sizeof (uint16_t); i++)
+			buffer[len++] = le16_to_cpu (lfn->name0[i]);
+		for (i = 0; i < sizeof lfn->name1 / sizeof (uint16_t); i++)
+			buffer[len++] = le16_to_cpu (lfn->name1[i]);
+		for (i = 0; i < sizeof lfn->name2 / sizeof (uint16_t); i++)
+			buffer[len++] = le16_to_cpu (lfn->name2[i]);
+
+		if (lfn->seq & VFAT_LFN_SEQ_LAST)
+		{
+			/* length is 255 including null terminator */
+			buffer[255] = '\0';
+
+			if (expected_seq <= VFAT_LFN_SEQ_MAX)
+				buffer[len] = '\0';
+
+			utf8_from_ucs16 (filename, buffer);
+
+			return TRUE;
+		}
+	}
+
+	return FALSE;
+}
+
+static uint8_t *
+fat_read_filename (struct vfat_dir_entry *dir, struct vfat_dir_entry *entry)
+{
+	static uint8_t filename[3*255];
+        int i;
+
+	/* check if maybe we have LFN entries */
+	if (fat_read_lfn (dir, entry, filename))
+		return filename;
+
+	/* else, read the normal 8.3 name */
+	for (i = 0; i < 11; i++) {
+		if (entry->lowercase & ((i < 8) ? VFAT_LOWERCASE_NAME :
+		    				  VFAT_LOWERCASE_EXT))
+			filename[i] = tolower (entry->name[i]);
+		else
+			filename[i] = entry->name[i];
+	}
+
+	return filename;
+}
+
+
 static uint8_t *get_attr_volume_id(struct vfat_dir_entry *dir, unsigned int count)
 {
 	unsigned int i;
@@ -124,7 +269,7 @@
 				continue;
 
 			dbg("found ATTR_VOLUME_ID id in root dir");
-			return dir[i].name;
+			return fat_read_filename (dir, &dir[i]);
 		}
 
 		dbg("skip dir entry");
@@ -282,8 +427,13 @@
 		return -1;
 
 	if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
-		volume_id_set_label_raw(id, label, 11);
-		volume_id_set_label_string(id, label, 11);
+		int length = strlen ((char *) label);
+
+		if (length > 64)
+			length = 64;
+
+		volume_id_set_label_raw(id, label, length);
+		volume_id_set_label_string(id, label, length);
 	} else if (memcmp(vs->type.fat.label, "NO NAME    ", 11) != 0) {
 		volume_id_set_label_raw(id, vs->type.fat.label, 11);
 		volume_id_set_label_string(id, vs->type.fat.label, 11);
@@ -360,8 +510,13 @@
 		return -1;
 
 	if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
-		volume_id_set_label_raw(id, label, 11);
-		volume_id_set_label_string(id, label, 11);
+		int length = strlen ((char *) label);
+
+		if (length > 64)
+			length = 64;
+
+		volume_id_set_label_raw(id, label, length);
+		volume_id_set_label_string(id, label, length);
 	} else if (memcmp(vs->type.fat32.label, "NO NAME    ", 11) != 0) {
 		volume_id_set_label_raw(id, vs->type.fat32.label, 11);
 		volume_id_set_label_string(id, vs->type.fat32.label, 11);

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