Android 4.4 -- blkid命令支持exfat格式U盘显示信息(UUID、LABEL等)_blkid -s label 乱码

一、前言

最近客户反馈一个问题，就是Android系统的机顶盒插上exfat格式的U盘后，获取不到UUID这个信息。
/system/vold/中已经添加对exfat格式U盘的支持，并且通过df命令能够看到U盘已经挂载上，但是执行blkid时，并未显示exfat格式U盘信息。

二、问题分析

1. 执行blkid /dev/block/sda1命令(sda1为U盘挂载点)，若U盘格式为vfat的，则能够正常显示，若U盘格式为exfat的，则不能显示。
2. 问题应该出在blkid命令不健全导致的，可以补充一部分代码，让其能够显示出来。

三、解决方法

1. 需要修改的代码在external/e2fsprogs/lib/blkid路径下。
2. e2fsprogs是一个Ext2（及Ext3/4）文件系统工具（Ext2Filesystems Utilities），它包含了诸如创建、修复、配置、调试ext2文件系统等的标准工具。e2fsprogs是开放源代码软件 ，遵从GPLv2或LGPLv2。
3. codechina上有e2fsprogs的开源代码，里面已经添加对exfat的相应支持，我们可以在这个里面搜寻相应的修改同步过来。
4. 里面主要修改了两个文件，probe.c和probe.h。

四、代码修改

下面是针对exfat格式的设备修改的，代码如下：

From 05cf6cbb92bf6d65ef0480053ddcc4a625f0e86b Mon Sep 17 00:00:00 2001
From: Amosstan
Date: Tue, 6 Jul 2021 16:02:38 +0800
Subject: [PATCH] aaa

---
 external/e2fsprogs/lib/blkid/probe.c | 131 +++++++++++++++++++++++++++
 external/e2fsprogs/lib/blkid/probe.h |  41 +++++++++
 2 files changed, 172 insertions(+)

diff --git a/external/e2fsprogs/lib/blkid/probe.c b/external/e2fsprogs/lib/blkid/probe.c
index 1867129..36f5ca3 100644
--- a/external/e2fsprogs/lib/blkid/probe.c
+++ b/external/e2fsprogs/lib/blkid/probe.c
@@ -1158,6 +1158,38 @@ static void unicode_16be_to_utf8(unsigned char *str, int out_len,
 	str[j] = '\0';
 }
 
+static void unicode_16le_to_utf8(unsigned char *str, int out_len,
+				 const unsigned char *buf, int in_len)
+{
+	int i, j;
+	unsigned int c;
+
+	for (i = j = 0; i + 2 <= in_len; i += 2) {
+		c = (buf[i+1] << 8) | buf[i];
+		if (c == 0) {
+			str[j] = '\0';
+			break;
+		} else if (c < 0x80) {
+			if (j+1 >= out_len)
+				break;
+			str[j++] = (unsigned char) c;
+		} else if (c < 0x800) {
+			if (j+2 >= out_len)
+				break;
+			str[j++] = (unsigned char) (0xc0 | (c >> 6));
+			str[j++] = (unsigned char) (0x80 | (c & 0x3f));
+		} else {
+			if (j+3 >= out_len)
+				break;
+			str[j++] = (unsigned char) (0xe0 | (c >> 12));
+			str[j++] = (unsigned char) (0x80 | ((c >> 6) & 0x3f));
+			str[j++] = (unsigned char) (0x80 | (c & 0x3f));
+		}
+	}
+	str[j] = '\0';
+}
+
+
 static int probe_hfs(struct blkid_probe *probe __BLKID_ATTR((unused)),
 			 struct blkid_magic *id __BLKID_ATTR((unused)),
 			 unsigned char *buf)
@@ -1383,6 +1415,104 @@ static int probe_btrfs(struct blkid_probe *probe,
 	set_uuid(probe->dev, bs->fsid, 0);
 	return 0;
 }
+
+static uint64_t exfat_block_to_offset(const struct exfat_super_block *sb,
+                                      uint64_t block)
+{
+    return block << sb->block_bits;
+}
+
+static uint64_t exfat_cluster_to_block(const struct exfat_super_block *sb,
+                                       uint32_t cluster)
+{
+    return sb->cluster_block_start +
+            ((uint64_t)(cluster - EXFAT_FIRST_DATA_CLUSTER) << sb->bpc_bits);
+}
+
+static uint64_t exfat_cluster_to_offset(const struct exfat_super_block *sb,
+                                        uint32_t cluster)
+{
+    return exfat_block_to_offset(sb, exfat_cluster_to_block(sb, cluster));
+}
+
+static uint32_t exfat_next_cluster(struct blkid_probe *probe,
+                                   const struct exfat_super_block *sb,
+                                   uint32_t cluster)
+{
+    uint32_t *next;
+    uint64_t offset;
+
+    offset = exfat_block_to_offset(sb, sb->fat_block_start)
+            + (uint64_t) cluster * sizeof (cluster);
+    next = (uint32_t *)get_buffer(probe, offset, sizeof (uint32_t));
+
+    return next ? *next : 0;
+}
+
+static struct exfat_entry_label *find_exfat_entry_label(
+    struct blkid_probe *probe, const struct exfat_super_block *sb)
+{
+    uint32_t cluster = sb->rootdir_cluster;
+    uint64_t offset = exfat_cluster_to_offset(sb, cluster);
+    uint8_t *entry;
+    const size_t max_iter = 10000;
+    size_t i = 0;
+
+    for (; i < max_iter; ++i) {
+        entry = (uint8_t *)get_buffer(probe, offset, EXFAT_ENTRY_SIZE);
+        if (!entry)
+            return NULL;
+        if (entry[0] == EXFAT_ENTRY_EOD)
+            return NULL;
+        if (entry[0] == EXFAT_ENTRY_LABEL)
+            return (struct exfat_entry_label*) entry;
+
+        offset += EXFAT_ENTRY_SIZE;
+        if (offset % CLUSTER_SIZE(sb) == 0) {
+            cluster = exfat_next_cluster(probe, sb, cluster);
+            if (cluster < EXFAT_FIRST_DATA_CLUSTER)
+                return NULL;
+            if (cluster > EXFAT_LAST_DATA_CLUSTER)
+                return NULL;
+            offset = exfat_cluster_to_offset(sb, cluster);
+        }
+    }
+
+    return NULL;
+}
+
+static int probe_exfat(struct blkid_probe *probe,
+		       struct blkid_magic *id __BLKID_ATTR((unused)),
+                       unsigned char *buf)
+{
+    struct exfat_super_block *sb;
+    struct exfat_entry_label *label;
+    char uuid[40];
+
+    sb = (struct exfat_super_block *)buf;
+    if (!sb || CLUSTER_SIZE(sb) == 0) {
+        DBG(DEBUG_PROBE, printf("bad exfat superblock.\n"));
+        return errno ? - errno : 1;
+    }
+
+    label = find_exfat_entry_label(probe, sb);
+    if (label) {
+        unsigned char utf8_label[128];
+        unicode_16le_to_utf8(utf8_label, sizeof(utf8_label), label->name, label->length * 2);
+        blkid_set_tag(probe->dev, "LABEL", (char *) utf8_label, 0);
+    } else {
+        blkid_set_tag(probe->dev, "LABEL", "disk", 4);
+    }
+
+    memset(uuid, 0, sizeof (uuid));
+    snprintf(uuid, sizeof (uuid), "%02hhX%02hhX-%02hhX%02hhX",
+             sb->volume_serial[3], sb->volume_serial[2],
+             sb->volume_serial[1], sb->volume_serial[0]);
+    blkid_set_tag(probe->dev, "UUID", uuid, strlen(uuid));
+
+    return 0;
+}
+
 /*
  * Various filesystem magics that we can check for.  Note that kboff and
  * sboff are in kilobytes and bytes respectively.  All magics are in
@@ -1482,6 +1612,7 @@ static struct blkid_magic type_array[] = {
   { "lvm2pv",	 1,  0x018,  8, "LVM2 001",		probe_lvm2 },
   { "lvm2pv",	 1,  0x218,  8, "LVM2 001",		probe_lvm2 },
   { "btrfs",	 64,  0x40,  8, "_BHRfS_M",		probe_btrfs },
+  { "exfat",     0,      3,  8, "EXFAT   ",             probe_exfat },
   {   NULL,	 0,	 0,  0, NULL,			NULL }
 };
 
diff --git a/external/e2fsprogs/lib/blkid/probe.h b/external/e2fsprogs/lib/blkid/probe.h
index 37fc9c0..2c6acea 100644
--- a/external/e2fsprogs/lib/blkid/probe.h
+++ b/external/e2fsprogs/lib/blkid/probe.h
@@ -14,6 +14,8 @@
 #ifndef _BLKID_PROBE_H
 #define _BLKID_PROBE_H
 
+#include <stdint.h>
+
 #include <blkid/blkid_types.h>
 
 struct blkid_magic;
@@ -725,6 +727,45 @@ struct btrfs_super_block {
 	__u8 sys_chunk_array[BTRFS_SYSTEM_CHUNK_ARRAY_SIZE];
 } __attribute__ ((__packed__));
 
+struct exfat_super_block {
+    uint8_t jump[3];
+    uint8_t oem_name[8];
+    uint8_t __unused1[53];
+    uint64_t block_start;
+    uint64_t block_count;
+    uint32_t fat_block_start;
+    uint32_t fat_block_count;
+    uint32_t cluster_block_start;
+    uint32_t cluster_count;
+    uint32_t rootdir_cluster;
+    uint8_t volume_serial[4];
+    struct {
+        uint8_t vermin;
+        uint8_t vermaj;
+    } version;
+    uint16_t volume_state;
+    uint8_t block_bits;
+    uint8_t bpc_bits;
+    uint8_t fat_count;
+    uint8_t drive_no;
+    uint8_t allocated_percent;
+}  __attribute__ ((__packed__));
+
+struct exfat_entry_label {
+    uint8_t type;
+    uint8_t length;
+    uint8_t name[30];
+} __attribute__ ((__packed__));
+
+#define BLOCK_SIZE(sb)   (1 << (sb)->block_bits)
+#define CLUSTER_SIZE(sb) (BLOCK_SIZE(sb) << (sb)->bpc_bits)
+
+#define EXFAT_FIRST_DATA_CLUSTER 2
+#define EXFAT_LAST_DATA_CLUSTER  0xffffff6
+#define EXFAT_ENTRY_SIZE         32
+
+#define EXFAT_ENTRY_EOD   0x00
+#define EXFAT_ENTRY_LABEL 0x83
 /*
  * Byte swap functions
  */
-- 
2.17.1


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229

codechina上的提交id号：

1. AOSP: blkid: add support to recognize exfat to blkid.
   I870e59a14b6bcd8b45562cdd02c2502d60a9eeff
2. AOSP: blkid: Resolve to the exFAT uuid change on reboot.
   I376ed9fe1ba1b7f3d367d78cc5e2bb8ea9cc2d13
3. AOSP: blkid: Correct the label name for exfat
   Ib16204c75c2cdf675d480e9c66f484bb3c51108e
   可根据上面的修改来同步到自己的代码上。