uboot do_load函数分析

load mmc       0:2      0x10000000   /boot/zImage
     argv[1]   argv[2]                           argv[4]

int do_load(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[],
		int fstype)
{
	unsigned long addr;
	const char *addr_str;
	const char *filename;
	loff_t bytes;
	loff_t pos;
	loff_t len_read;
	int ret;
	unsigned long time;
	char *ep;

	if (argc < 2)
		return CMD_RET_USAGE;
	if (argc > 7)
		return CMD_RET_USAGE;

	if (fs_set_blk_dev(argv[1], (argc >= 3) ? argv[2] : NULL, fstype)) //fs_set_blk_dev("mmc", "0:2", FS_TYPE_ANY)
		return 1;

	if (argc >= 4) {
		addr = simple_strtoul(argv[3], &ep, 16);//得到内存地址  0x10000000
		if (ep == argv[3] || *ep != '\0')
			return CMD_RET_USAGE;
	} else {
		addr_str = env_get("loadaddr");
		if (addr_str != NULL)
			addr = simple_strtoul(addr_str, NULL, 16);
		else
			addr = CONFIG_SYS_LOAD_ADDR;
	}
	if (argc >= 5) {
		filename = argv[4];//得到文件名   /boot/zImage
	} else {
		filename = env_get("bootfile");
		if (!filename) {
			puts("** No boot file defined **\n");
			return 1;
		}
	}
	if (argc >= 6)
		bytes = simple_strtoul(argv[5], NULL, 16);  //读多少字节
	else
		bytes = 0;
	if (argc >= 7)
		pos = simple_strtoul(argv[6], NULL, 16); //从文件的偏移地址处读取
	else
		pos = 0;

	time = get_timer(0);
	ret = fs_read(filename, addr, pos, bytes, &len_read);
	time = get_timer(time);
	if (ret < 0)
		return 1;

	printf("%llu bytes read in %lu ms", len_read, time);// len_read是实际读到的
	if (time > 0) {
		puts(" (");
		print_size(div_u64(len_read, time) * 1000, "/s");
		puts(")");
	}
	puts("\n");

	env_set_hex("fileaddr", addr);
	env_set_hex("filesize", len_read);

	return 0;
}