[git commit] volume_id: add exFAT detection

Denys Vlasenko vda.linux at googlemail.com
Tue Nov 13 13:40:37 UTC 2012


commit: http://git.busybox.net/busybox/commit/?id=e4b9451413013388757cf48fbb16d8137ddd1ccb
branch: http://git.busybox.net/busybox/commit/?id=refs/heads/master

function                                             old     new   delta
volume_id_probe_exfat                                  -     294    +294

Signed-off-by: S-G Bergh <sgb at systemasis.org>
Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 util-linux/Config.src                     |    9 ++
 util-linux/volume_id/Kbuild.src           |    1 +
 util-linux/volume_id/exfat.c              |  130 +++++++++++++++++++++++++++++
 util-linux/volume_id/volume_id.c          |    3 +
 util-linux/volume_id/volume_id_internal.h |    2 +
 5 files changed, 145 insertions(+), 0 deletions(-)

diff --git a/util-linux/Config.src b/util-linux/Config.src
index 3355e97..e4516dd 100644
--- a/util-linux/Config.src
+++ b/util-linux/Config.src
@@ -734,6 +734,15 @@ config FEATURE_VOLUMEID_FAT
 	help
 	  TODO
 
+config FEATURE_VOLUMEID_EXFAT
+	bool "exFAT filesystem"
+	default y
+	depends on VOLUMEID
+	help
+	  exFAT (extended FAT) is a proprietary file system designed especially
+	  for flash drives. It has many features from NTFS, but with less
+	  overhead. exFAT is used on most SDXC cards for consumer electronics.
+
 config FEATURE_VOLUMEID_HFS
 	bool "hfs filesystem"
 	default y
diff --git a/util-linux/volume_id/Kbuild.src b/util-linux/volume_id/Kbuild.src
index 39a2d8c..759fdaa 100644
--- a/util-linux/volume_id/Kbuild.src
+++ b/util-linux/volume_id/Kbuild.src
@@ -33,6 +33,7 @@ lib-$(CONFIG_FEATURE_VOLUMEID_LINUXSWAP)        += linux_swap.o
 ### lib-$(CONFIG_FEATURE_VOLUMEID_MSDOS)            += msdos.o
 lib-$(CONFIG_FEATURE_VOLUMEID_NILFS)            += nilfs.o
 lib-$(CONFIG_FEATURE_VOLUMEID_NTFS)             += ntfs.o
+lib-$(CONFIG_FEATURE_VOLUMEID_EXFAT)            += exfat.o
 lib-$(CONFIG_FEATURE_VOLUMEID_REISERFS)         += reiserfs.o
 lib-$(CONFIG_FEATURE_VOLUMEID_UDF)              += udf.o
 ### lib-$(CONFIG_FEATURE_VOLUMEID_UFS)              += ufs.o
diff --git a/util-linux/volume_id/exfat.c b/util-linux/volume_id/exfat.c
new file mode 100644
index 0000000..a38a891
--- /dev/null
+++ b/util-linux/volume_id/exfat.c
@@ -0,0 +1,130 @@
+/*
+ * volume_id - reads filesystem label and uuid
+ *
+ * Copyright (C) 2012 S-G Bergh <sgb at systemasis.org>
+ *
+ *	This library is free software; you can redistribute it and/or
+ *	modify it under the terms of the GNU Lesser General Public
+ *	License as published by the Free Software Foundation; either
+ *	version 2.1 of the License, or (at your option) any later version.
+ *
+ *	This library is distributed in the hope that it will be useful,
+ *	but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ *	Lesser General Public License for more details.
+ *
+ *	You should have received a copy of the GNU Lesser General Public
+ *	License along with this library; if not, write to the Free Software
+ *	Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include "volume_id_internal.h"
+
+#define EXFAT_SB_OFFSET		0
+#define EXFAT_DIR_ENTRY_SZ	32
+#define EXFAT_MAX_DIR_ENTRIES	100
+
+struct exfat_super_block {
+/* 0x00 */	uint8_t		boot_jump[3];
+/* 0x03 */	uint8_t		fs_name[8];
+/* 0x0B */	uint8_t		must_be_zero[53];
+/* 0x40 */	uint64_t	partition_offset;
+/* 0x48 */	uint64_t	volume_length;
+/* 0x50 */	uint32_t	fat_offset;		// Sector address of 1st FAT
+/* 0x54 */	uint32_t	fat_size;		// In sectors
+/* 0x58 */	uint32_t	cluster_heap_offset;	// Sector address of Data Region
+/* 0x5C */	uint32_t	cluster_count;
+/* 0x60 */	uint32_t	root_dir;		// Cluster address of Root Directory
+/* 0x64 */	uint8_t		vol_serial_nr[4];	// Volume ID
+/* 0x68 */	uint16_t	fs_revision;		// VV.MM
+/* 0x6A */	uint16_t	vol_flags;
+/* 0x6C */	uint8_t		bytes_per_sector;	// Power of 2: 9 => 512, 12 => 4096
+/* 0x6D */	uint8_t		sectors_per_cluster;	// Power of 2
+/* 0x6E */	uint8_t		nr_of_fats;		// 2 for TexFAT
+/* 0x6F */	// ...
+} PACKED;
+
+struct exfat_dir_entry {
+/* 0x00 */	uint8_t		entry_type;
+		union {
+			struct volume_label {
+/* 0x01 */			uint8_t		char_count;		// Length of label
+/* 0x02 */			uint16_t	vol_label[11];		// UTF16 string without null termination
+/* 0x18 */			uint8_t		reserved[8];
+/* 0x20 */		} PACKED label;
+			struct volume_guid {
+/* 0x01 */			uint8_t		sec_count;
+/* 0x02 */			uint16_t	set_checksum;
+/* 0x04 */			uint16_t	flags;
+/* 0x06 */			uint8_t		vol_guid[16];
+/* 0x16 */			uint8_t		reserved[10];
+/* 0x20 */		} PACKED guid;
+		} PACKED type;
+} PACKED;
+
+int FAST_FUNC volume_id_probe_exfat(struct volume_id *id /*,uint64_t off*/)
+{
+	struct exfat_super_block *sb;
+	struct exfat_dir_entry *de;
+	unsigned	sector_sz;
+	unsigned	cluster_sz;
+	uint64_t	root_dir_off;
+	unsigned	count;
+	unsigned	need_lbl_guid;
+
+	// Primary super block
+	dbg("exFAT: probing at offset 0x%x", EXFAT_SB_OFFSET);
+	sb = volume_id_get_buffer(id, EXFAT_SB_OFFSET, sizeof(*sb));
+
+	if (!sb)
+		return -1;
+
+	if (memcmp(sb->fs_name, "EXFAT   ", 8) != 0)
+		return -1;
+
+	sector_sz = 1 << sb->bytes_per_sector;
+	cluster_sz = sector_sz << sb->sectors_per_cluster;
+	// There are no clusters 0 and 1, so the first cluster is 2.
+	root_dir_off = (uint64_t)EXFAT_SB_OFFSET +
+		// Hmm... should we cast sector_sz/cluster_sz to uint64_t?
+		(le32_to_cpu(sb->cluster_heap_offset)) * sector_sz +
+		(le32_to_cpu(sb->root_dir) - 2) * cluster_sz;
+	dbg("exFAT: sector size 0x%x bytes", sector_sz);
+	dbg("exFAT: cluster size 0x%x bytes", cluster_sz);
+	dbg("exFAT: root dir is at 0x%llx", (long long)root_dir_off);
+
+	// Use DOS uuid as fallback, if no GUID set
+	volume_id_set_uuid(id, sb->vol_serial_nr, UUID_DOS);
+
+	// EXFAT_MAX_DIR_ENTRIES is used as a safety belt.
+	// The Root Directory may hold an unlimited number of entries,
+	// so we do not want to check all. Usually label and GUID
+	// are in the beginning, but there are no guarantees.
+	need_lbl_guid = (1 << 0) | (1 << 1);
+	for (count = 0; count < EXFAT_MAX_DIR_ENTRIES; count++) {
+		de = volume_id_get_buffer(id, root_dir_off + (count * EXFAT_DIR_ENTRY_SZ), EXFAT_DIR_ENTRY_SZ);
+		if (de == NULL)
+			break;
+		if (de->entry_type == 0x00) {
+			// End of Directory Marker
+			dbg("exFAT: End of root directory reached after %u entries", count);
+			break;
+		}
+		if (de->entry_type == 0x83) {
+			// Volume Label Directory Entry
+			volume_id_set_label_unicode16(id, (uint8_t *)de->type.label.vol_label,
+						LE, 2 * de->type.label.char_count);
+			need_lbl_guid &= ~(1 << 0);
+		}
+		if (de->entry_type == 0xA0) {
+			// Volume GUID Directory Entry
+			volume_id_set_uuid(id, de->type.guid.vol_guid, UUID_DCE);
+			need_lbl_guid &= ~(1 << 1);
+		}
+		if (!need_lbl_guid)
+			break;
+	}
+
+	IF_FEATURE_BLKID_TYPE(id->type = "exfat";)
+	return 0;
+}
diff --git a/util-linux/volume_id/volume_id.c b/util-linux/volume_id/volume_id.c
index c1d6152..3c3c698 100644
--- a/util-linux/volume_id/volume_id.c
+++ b/util-linux/volume_id/volume_id.c
@@ -93,6 +93,9 @@ static const probe_fptr fs1[] = {
 #if ENABLE_FEATURE_VOLUMEID_FAT
 	volume_id_probe_vfat,
 #endif
+#if ENABLE_FEATURE_VOLUMEID_EXFAT
+	volume_id_probe_exfat,
+#endif
 #if ENABLE_FEATURE_VOLUMEID_MAC
 	volume_id_probe_mac_partition_map,
 #endif
diff --git a/util-linux/volume_id/volume_id_internal.h b/util-linux/volume_id/volume_id_internal.h
index 1c2e0ff..03dc46f 100644
--- a/util-linux/volume_id/volume_id_internal.h
+++ b/util-linux/volume_id/volume_id_internal.h
@@ -216,6 +216,8 @@ int FAST_FUNC volume_id_probe_nilfs(struct volume_id *id /*,uint64_t off*/);
 
 int FAST_FUNC volume_id_probe_ntfs(struct volume_id *id /*,uint64_t off*/);
 
+int FAST_FUNC volume_id_probe_exfat(struct volume_id *id /*,uint64_t off*/);
+
 int FAST_FUNC volume_id_probe_ocfs2(struct volume_id *id /*,uint64_t off*/);
 
 int FAST_FUNC volume_id_probe_reiserfs(struct volume_id *id /*,uint64_t off*/);


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