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

雨点打透心脏的1/2处 2022-10-10 12:56 513阅读 0赞

### 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

[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。

[codechina]: https://codechina.csdn.net/mirrors/tytso/e2fsprogs