[ 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

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/mtd2opt_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/mtd3xioctl(fd, MEMGETINFO, &meminfo);    // 获取内存信息mtdoffset = xstrtou(opt_s, 0);            // 获取mtd偏移量，默认为0if (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filebufif (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;}
}