[ Linux Busybox ] nandwrite 命令解析

文章目录

    • 相关结构体
    • nandwrite 函数实现
    • nandwrite 实现流程图


文件路径:busybox-1.20.2/miscutils/nandwrite.c

相关结构体

MTD 相关信息结构体

struct mtd_info_user {
    __u8 type;              // MTD 设备类型
    __u32 flags;            // MTD设备属性标志
    __u32 size;             // mtd设备的大小
    __u32 erasesize;        // MTD设备的擦除单元大小,对于 NandFlash来说就是 Block的大小
    __u32 writesize;        // MTD设备的读写单元大小,对于 NandFlash来说就是page 的大小
    __u32 oobsize;          // oob区域大小
    __u64 padding;          // 有效的oob区域大小
};

nandwrite 函数实现

假如要将 mtd2 拷贝到 mtd3 分区中,使用的命令是:nandwrite /dev/mtd3 /dev/mtd2

int nandwrite_main(int argc UNUSED_PARAM, char **argv)
{
    /* Buffer for OOB data */
    unsigned char *oobbuf;
    unsigned opts;
    int fd;
    ssize_t cnt;
    unsigned mtdoffset, meminfo_writesize, blockstart, limit;
    unsigned end_addr = ~0;
    struct mtd_info_user meminfo;
    struct mtd_oob_buf oob;
    unsigned char *filebuf;
    const char *opt_s = "0", *opt_f = "-", *opt_l;

    if (IS_NANDDUMP) {                            // 从命令行获取参数
        opt_complementary = "=1";
        opts = getopt32(argv, "os:bf:l:", &opt_s, &opt_f, &opt_l);
    } else { /* nandwrite */
        opt_complementary = "-1:?2";
        opts = getopt32(argv, "ps:", &opt_s);
    }
    argv += optind;

    if (IS_NANDWRITE && argv[1])                    // argv[1]为  /dev/mtd2
        opt_f = argv[1];
    if (!LONE_DASH(opt_f)) {                        // 判断输入的参数是否为文件,根据命令为文件添加权限
        int tmp_fd = xopen(opt_f,
            IS_NANDDUMP ? O_WRONLY | O_TRUNC | O_CREAT : O_RDONLY
        );
        xmove_fd(tmp_fd, IS_NANDDUMP ? STDOUT_FILENO : STDIN_FILENO);   // 将文件内容放在标准输出或者标准输入中。
    }

    fd = xopen(argv[0], O_RDWR);        // 打开文件,argv[0]为/dev/mtd3
    xioctl(fd, MEMGETINFO, &meminfo);    // 获取内存信息

    mtdoffset = xstrtou(opt_s, 0);            // 获取mtd偏移量,默认为0
    if (IS_NANDDUMP && (opts & OPT_l)) {
        unsigned length = xstrtou(opt_l, 0);
        if (length < meminfo.size - mtdoffset)
            end_addr = mtdoffset + length;
    }

    /* Pull it into a CPU register (hopefully) - smaller code that way */
    meminfo_writesize = meminfo.writesize;        // 获取每次写入内存的大小(一般为页大小)

    if (mtdoffset & (meminfo_writesize - 1))        // 判断写入的地址是否页对齐
        bb_error_msg_and_die("start address is not page aligned");

    filebuf = xmalloc(meminfo_writesize);            // 根据每次写入的大小分配buf和oob内存
    oobbuf = xmalloc(meminfo.oobsize);

    oob.start  = 0;                    // 开始地址
    oob.length = meminfo.oobsize;        // oob大小
    oob.ptr    = oobbuf;                // oob值

    blockstart = mtdoffset & ~(meminfo.erasesize - 1);        // 获得块起始地址
    if (blockstart != mtdoffset) {
        unsigned tmp;
        /* mtdoffset is in the middle of an erase block, verify that
         * this block is OK. Advance mtdoffset only if this block is
         * bad.
         */
        tmp = next_good_eraseblock(fd, &meminfo, blockstart);
        if (tmp != blockstart) {
            /* bad block(s), advance mtdoffset */
            if (IS_NANDDUMP & !(opts & OPT_b)) {
                int bad_len = MIN(tmp, end_addr) - mtdoffset;
                dump_bad(&meminfo, bad_len, !(opts & OPT_o));
            }
            mtdoffset = tmp;
        }
    }

    cnt = -1;
    limit = MIN(meminfo.size, end_addr);                // 获取写入总空间,meminfo.size为mtd总空间大小
    while (mtdoffset < limit) {                            // 循环往mtd写入数值,直到超出mtd总空间大小
        int input_fd = IS_NANDWRITE ? STDIN_FILENO : fd;    // 若为IS_NANDWRITE指令,将输入input_fd指向标准输入,输出output_fd指向文件
        int output_fd = IS_NANDWRITE ? fd : STDOUT_FILENO;

        blockstart = mtdoffset & ~(meminfo.erasesize - 1);   // 获得块起始地址
        if (blockstart == mtdoffset) {                // 若是对齐的,开始检测坏块
            /* starting a new eraseblock */
            mtdoffset = next_good_eraseblock(fd, &meminfo, blockstart);         // 检测坏块,若检测到跳过,具体实现见下面一个函数
            if (IS_NANDWRITE)
                printf("Writing at 0x%08x\n", mtdoffset);
            else if (mtdoffset > blockstart) {
                int bad_len = MIN(mtdoffset, limit) - blockstart;
                dump_bad(&meminfo, bad_len, !(opts & OPT_o));
            }
            if (mtdoffset >= limit)        // 偏移量超出mtd总大小跳出
                break;
        }
        xlseek(fd, mtdoffset, SEEK_SET);    // 将读写位置移到文件开头

        /* get some more data from input */
        cnt = full_read(input_fd, filebuf, meminfo_writesize);    // 从获取标准输入中获取数据,大小为内存写入的大小,数据保存在filebuf
        if (cnt == 0) {
            /* even with -p, we do not pad past the end of input
             * (-p only zero-pads last incomplete page)
             */
            break;
        }
        if (cnt < meminfo_writesize) {            // 从标准输出中获取到数据的大小 若小于 写入的标准大小
            if (IS_NANDDUMP)
                bb_error_msg_and_die("short read");
            if (!(opts & OPT_p))
                bb_error_msg_and_die("input size is not rounded up to page size, "
                        "use -p to zero pad");
            /* zero pad to end of write block */
            memset(filebuf + cnt, 0, meminfo_writesize - cnt);    // 在数据后面填充0
        }
        xwrite(output_fd, filebuf, meminfo_writesize);        // 将filebuf数据拷贝到 mtd中

        if (IS_NANDDUMP && !(opts & OPT_o)) {
            /* Dump OOB data */
            oob.start = mtdoffset;
            xioctl(fd, MEMREADOOB, &oob);
            xwrite(output_fd, oobbuf, meminfo.oobsize);
        }

        mtdoffset += meminfo_writesize;            // 指向下个要写入的地址
        if (cnt < meminfo_writesize)                // 若本次获取数据的量小于写入的大小,则跳出
            break;
    }

    if (IS_NANDWRITE && cnt != 0) {         // 填满了整个MTD,但是我们在输入时达到EOF了吗
        /* We filled entire MTD, but did we reach EOF on input? */
        if (full_read(STDIN_FILENO, filebuf, meminfo_writesize) != 0) {
            /* no */
            bb_error_msg_and_die("not enough space in MTD device");
        }
    }

    if (ENABLE_FEATURE_CLEAN_UP) {
        free(filebuf);
        close(fd);
    }

    return EXIT_SUCCESS;
}

标准输出输出定义

#define  STDIN_FILENO   0  /* Standard input.  */
#define  STDOUT_FILENO  1  /* Standard output.  */
#define  STDERR_FILENO  2  /* Standard error output.  */

检测坏块实现

static unsigned next_good_eraseblock(int fd, struct mtd_info_user *meminfo,
        unsigned block_offset)
{
    while (1) {            // 循环检测,便于跳过坏块
        loff_t offs;

        if (block_offset >= meminfo->size) {                // 1、传入的块偏移量大于等于mtd总大小
            if (IS_NANDWRITE)
                bb_error_msg_and_die("not enough space in MTD device");
            return block_offset; /* let the caller exit */    // 返回
        }
        offs = block_offset;
        if (xioctl(fd, MEMGETBADBLOCK, &offs) == 0)        // 2、判断是否为坏块
            return block_offset;                           // 若不是返回地址
        /* ioctl returned 1 => "bad block" */
        if (IS_NANDWRITE)                                    // 若是坏块跳过,并指向下一块的地址检测
            printf("Skipping bad block at 0x%08x\n", block_offset);
        block_offset += meminfo->erasesize;
    }
}

nandwrite 实现流程图

[ Linux Busybox ] nandwrite 命令解析_第1张图片

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