volume_id: add LittleFS detection

Add support for LittleFS to blkid. Not included if FEATURE_BLKID_TYPE
is not selected (neither UUID nor label).

LittleFS is a small fail-safe filesystem designed for embedded
systems. It has strong copy-on-write guarantees and storage on disk
is always kept in a valid state. It also provides a form of dynamic
wear levelling for systems that can not fit a full flash translation
layer. (https://github.com/geky/littlefs)

ARM has introduced it in its Mbed OS 5.7, so it starts to gain focus.
(https://os.mbed.com/blog/entry/littlefs-high-integrity-embedded-fs/)

function                                             old     new   delta
volume_id_probe_lfs                                    -      62     +62
fs1                                                   20      24      +4

Signed-off-by: Sven-Göran Bergh <sgb@systemaxion.se>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

util-linux/volume_id/lfs.c

@@ -0,0 +1,62 @@
+/*
+ * volume_id - reads filesystem label and uuid
+ *
+ * Copyright (C) 2018 Sven-Göran Bergh <sgb@systemaxion.se>
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
+ */
+//config:config FEATURE_VOLUMEID_LFS
+//config:	bool "LittleFS filesystem"
+//config:	default y
+//config:	depends on VOLUMEID && FEATURE_BLKID_TYPE
+//config:	help
+//config:	LittleFS is a small fail-safe filesystem designed for embedded
+//config:	systems. It has strong copy-on-write guarantees and storage on disk
+//config:	is always kept in a valid state. It also provides a form of dynamic
+//config:	wear levelling for systems that can not fit a full flash translation
+//config:	layer.
+
+//kbuild:lib-$(CONFIG_FEATURE_VOLUMEID_LFS) += lfs.o
+
+#include "volume_id_internal.h"
+
+#define LFS_SB1_OFFSET		0x10
+#define LFS_MAGIC_NAME		"littlefs"
+#define LFS_MAGIC_LEN		8
+
+// The superblock is stored in the first metadata pair, i.e the first two blocks.
+struct lfs_super_block {	// A block in a metadata pair
+// /* 0x00 */	uint32_t	rev_count;		// Revision count
+// /* 0x04 */	uint32_t	dir_size;		// Directory size
+// /* 0x08 */	uint64_t	tail_ptr;		// Tail pointer
+/* 0x10 */	uint8_t		entry_type;		// Entry type
+/* 0x11 */	uint8_t		entry_len;		// Entry length
+/* 0x12 */	uint8_t		att_len;		// Attribute length
+/* 0x13 */	uint8_t 	name_len;		// Name length
+/* 0x14 */	uint64_t	root_dir;		// Root directory
+/* 0x1C */	uint32_t	block_size;		// Block size
+/* 0x20 */	uint32_t	block_count;		// Block count
+/* 0x24 */	uint16_t	ver_major;		// Version major
+/* 0x26 */	uint16_t	ver_minor;		// Version minor
+/* 0x28 */	uint8_t		magic[LFS_MAGIC_LEN];	// Magic string "littlefs"
+// /* 0x30 */	uint32_t	crc;			// CRC-32 checksum
+} PACKED;
+
+int FAST_FUNC volume_id_probe_lfs(struct volume_id *id /*,uint64_t off*/)
+{
+	struct lfs_super_block *sb;
+
+	// Go for primary super block (ignore second sb)
+	dbg("lfs: probing at offset 0x%x", LFS_SB1_OFFSET);
+	sb = volume_id_get_buffer(id, LFS_SB1_OFFSET, sizeof(*sb));
+
+	if (!sb)
+		return -1;
+
+	if (memcmp(sb->magic, LFS_MAGIC_NAME, LFS_MAGIC_LEN) != 0)
+		return -1;
+
+	IF_FEATURE_BLKID_TYPE(id->type = LFS_MAGIC_NAME);
+
+	return 0;
+}

util-linux/volume_id/volume_id.c

@@ -97,6 +97,9 @@ static const probe_fptr fs1[] = {
 #if ENABLE_FEATURE_VOLUMEID_EXFAT
 	volume_id_probe_exfat,
 #endif
+#if ENABLE_FEATURE_VOLUMEID_LFS
+	volume_id_probe_lfs,
+#endif
 #if ENABLE_FEATURE_VOLUMEID_MAC
 	volume_id_probe_mac_partition_map,
 #endif

util-linux/volume_id/volume_id_internal.h

@@ -187,6 +187,8 @@ int FAST_FUNC volume_id_probe_iso9660(struct volume_id *id /*,uint64_t off*/);
 
 int FAST_FUNC volume_id_probe_jfs(struct volume_id *id /*,uint64_t off*/);
 
+int FAST_FUNC volume_id_probe_lfs(struct volume_id *id /*,uint64_t off*/);
+
 int FAST_FUNC volume_id_probe_linux_swap(struct volume_id *id /*,uint64_t off*/);
 
 int FAST_FUNC volume_id_probe_luks(struct volume_id *id /*,uint64_t off*/);