一、 步骤六：U-boot支持yaffs格式的文件下载
前面我们已经移植、修改好了基于cramfs格式的根文件系统，本节我们来修改u-boot的源码，使之支持yaffs格式的根文件系统。
cramfs与yaffs文件系统的区别：
通常一个Nnad Flash存储设备由若干块组成，1个块由若干页组成。
一般128MB以下容量的Nand Flash芯片，一页大小为528B，被依次分为2个256B的主数据区和16B的额外空间；128MB以上容量的Nand Flash芯片，一页大小通常为2KB。
由于Nand Flash出现位反转的概率较大，一般在读写时需要使用ECC进行错误检验和恢复。
Yaffs/yaffs2文件系统的设计充分考虑到Nand Flash以页为存取单位等的特点，将文件组织成固定大小的段(Chunk)。以528B的页为例，Yaffs/yaffs2文件系统使用前512B存储数据和16B的额外空间存放数据的ECC和文件系统的组织信息等(称为OOB数据)。通过OOB数据，不但能实现错误检测和坏块处理，同时还可以避免加载时对整个存储介质的扫描，加快了文件系统的加载速度。以下是Yaffs/yaffs2文件系统页的结构说明：
Yaffs页结构说明
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = ====
字节 用途
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = ====
0 - 511 存储数据(分为两个半部)
512 - 515 系统信息
516 数据状态字
517 块状态字
518 - 519 系统信息
520 - 522 后半部256字节的ECC
523 - 524 系统信息
525 - 527 前半部256字节的ECC
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = ====
好了，在了解Nand Flash组成和Yaffs/yaffs2文件系统结构后，我们再回到u-boot中。目前，在u-boot中已经有对Cramfs、Jffs2等文件系统的读写支持，但与带有数据校验等功能的OOB区的Yaffs/Yaffs2文件系统相比，他们是将所有文件数据简单的以线性表形式组织的。所以，我们只 要在此基础上通过修改u-boot的Nand Flash读写命令，增加处理00B区域数据的功能，即可以实现对Yaffs/Yaffs2文件系统的读写支持。
我们需要按照以下步骤修改：
1) 在include/configs/unsp2440.h中添加yaffs2烧写宏定义
#define CONFIG_MTD_NAND_YAFFS 1 //定义一个管理对Yaffs2支持的宏
2) 增加yaffs烧写命令：
#gedit common/cmd_nand.c //在U_BOOT_CMD中添加
U_BOOT_CMD(nand, CONFIG_SYS_MAXARGS, 1, do_nand,
"NAND sub-system",
"info - show available NAND devices/n"
"nand device [dev] - show or set current device/n"
"nand read - addr off|partition size/n"
"nand write - addr off|partition size/n"
" read/write 'size' bytes starting at offset 'off'/n"
" to/from memory address 'addr', skipping bad blocks./n"
#if defined(CONFIG_MTD_NAND_YAFFS)
"nand_write[.yaffs2] -addr of | partition size - write 'size' byte yaffs image/n"
"starting at offset off'from memory address addr'(.yaffs2 for 2048+64 NAND)/n"
#endif
"nand erase [clean] [off size] - erase 'size' bytes from/n"
"offset 'off' (entire device if not specified)/n"
。。。。
#endif
);
3) 在该文件中对nand操作的do_nand函数中添加yaffs2对nand的操作，如下
if (strncmp(cmd, "read", 4) == 0 || strncmp(cmd, "write", 5) == 0)
{
int read;
if (argc < 4)
goto usage;
addr = (ulong)simple_strtoul(argv[2], NULL, 16);
read = strncmp(cmd, "read", 4) == 0; /* 1 = read, 0 = write */
printf("/nNAND %s: ", read ? "read" : "write");
if (arg_off_size(argc - 3, argv + 3, nand, &off, &size) != 0)
return 1;
s = strchr(cmd, '.');
if (!s || !strcmp(s, ".jffs2") ||!strcmp(s, ".e") || !strcmp(s, ".i"))
{
if (read)
ret = nand_read_skip_bad(nand, off, &size, (u_char *)addr);
else
ret = nand_write_skip_bad(nand, off, &size, (u_char *)addr);
}
#if defined(CONFIG_MTD_NAND_YAFFS)
else if(s!=NULL & (!strcmp(s,".yaffs2")))
{
nand->rw_oob = 1;
nand->skipfirstblk = 1; //写入yaffs，不支持读入
ret = nand_write_skip_bad(nand,off,&size,(u_char *)addr);
nand->skipfirstblk = 0;
nand->rw_oob = 0;
}
#endif
else if (!strcmp(s, ".oob"))
。。。。
4) 在include/linux/mtd/mtd.h头文件的mtd_info结构体中添加上面用到rw_oob和skipfirstblk数据成员，如下：
struct mtd_info
{
u_char type;
u_int32_t flags;
uint64_t size; /* Total size of the MTD */
#if defined(CONFIG_MTD_NAND_YAFFS)
u_char rw_oob;
u_char skipfirstblk;
#endif
。。。。
}
5) 在nand_write_skip_bad函数中添加对Nand OOB的相关操作，如下：
#gedit drivers/mtd/nand/nand_util.c //在nand_write_skip_bad函数中添加
int nand_write_skip_bad(nand_info_t *nand, loff_t offset, size_t *length,u_char *buffer)
{
int rval;
size_t left_to_write = *length;
size_t len_incl_bad;
u_char *p_buffer = buffer;
#if defined(CONFIG_MTD_NAND_YAFFS) //addr yaffs2 file system support
if(nand->rw_oob == 1)
{
size_t oobsize = nand->oobsize; //定义oobsize的大小
size_t datasize = nand->writesize;//可用的数据的大小
int datapages = 0;
//长度不是528整数倍，认为数据出错。文件大小必须要是（512+16）的整数倍
if(((*length)%(nand->oobsize + nand->writesize))!=0)
{
printf("Attempt to write error length data!/n");
return -EINVAL;
}
datapages = *length/(datasize + oobsize);
*length = datapages * datasize;
left_to_write = *length;
}
#endif
/* Reject writes, which are not page aligned */
if ((offset & (nand->writesize - 1)) != 0 ||
(*length & (nand->writesize - 1)) != 0) {
printf ("Attempt to write non page aligned data/n");
return -EINVAL;
}
len_incl_bad = get_len_incl_bad (nand, offset, *length);
if ((offset + len_incl_bad) > nand->size)
{
printf ("Attempt to write outside the flash area/n");
return -EINVAL;
}
if (len_incl_bad == *length) {
rval = nand_write (nand, offset, length, buffer);
if (rval != 0)
printf ("NAND write to offset %llx failed %d/n",
offset, rval);
return rval;
}
#if !defined(CONFIG_MTD_NAND_YAFFS)
if(len_ind_bad == *length)
{
rval = nand_write(nand,offset,length,buffer);
if(rval!=0)
printf("NAND write to offset %llx failed %d/n",offset,rval);
return rval;
}
#endif
while (left_to_write > 0) {
size_t block_offset = offset & (nand->erasesize - 1);
size_t write_size;
WATCHDOG_RESET ();
if (nand_block_isbad (nand, offset & ~(nand->erasesize - 1))) {
printf ("Skip bad block 0xllx/n",
offset & ~(nand->erasesize - 1));
offset += nand->erasesize - block_offset;
continue;
}
#if defined(CONFIG_MTD_NAND_YAFFS)
if(nand->skipfirstblk==1)
{
nand->skipfirstblk =0;
printf("skip first good block %llx/n",offset &~(nand->erasesize-1));
offset += nand->erasesize - block_offset;
continue;
}
#endif
if (left_to_write < (nand->erasesize - block_offset))
write_size = left_to_write;
else
write_size = nand->erasesize - block_offset;
rval = nand_write (nand, offset, &write_size, p_buffer);
if (rval != 0)
{
printf ("NAND write to offset %llx failed %d/n",
offset, rval);
*length -= left_to_write;
return rval;
}
left_to_write -= write_size;
offset += write_size;
//p_buffer += write_size;
#if defined(CONFIG_MTD_NAND_YAFFS)
if(nand->rw_oob ==1)
{
p_buffer +=write_size+(write_size/nand->writesize*nand->oobsize);
}
else
{
p_buffer +=write_size;
}
#else
p_buffer += write_size;
#endif
}
return 0;
}
6) 在nand_write_skip_bad函数中我们看到又对nand_write函数进行了访问，所以这一步是到nand_write函数中添加对yaffs2的支持，如下
static int nand_write(struct mtd_info *mtd, loff_t to, size_t len,size_t *retlen, const uint8_t *buf)
{
struct nand_chip *chip = mtd->priv;
int ret;
#if defined(CONFIG_MTD_NAND_YAFFS)
int oldopsmode = 0;
if(mtd->rw_oob==1)
{
int i=0;
int datapages = 0;
size_t oobsize = mtd->oobsize;//定义oobsize的大小
size_t datasize = mtd->writesize;//定义正常的数据区的大小
uint8_t oobtemp[oobsize];
datapages = len /(datasize); //传进来的len是没有包括oob的数据长度
for(i=0;i<(datapages);i++)
{
memcpy((void *)oobtemp,(void *)(buf + datasize *(i + 1)),oobsize);
memmove((void *)(buf + datasize *(i+1)),(void *)(buf + datasize *(i+1) + oobsize),(datapages -(i+1))*(datasize) + (datapages -1) *oobsize);
memcpy((void *)(buf +(datapages) *(datasize + oobsize) -oobsize),(void *)(oobtemp),oobsize);
}
}
#endif
if ((to + len) > mtd->size)
return -EINVAL;
if (!len)
return 0;
nand_get_device(chip, mtd, FL_WRITING);
chip->ops.len = len;
chip->ops.datbuf = (uint8_t *)buf;
#if defined(CONFIG_MTD_NAND_YAFFS)
if(mtd->rw_oob!=1)
{
chip->ops.oobbuf = NULL;
}
else
{
chip->ops.oobbuf = (uint8_t *)(buf+len);
//将oob缓存的指针指向buf的后段，即oob数据区的起始地址。
chip->ops.ooblen = mtd->oobsize;
oldopsmode = chip->ops.mode;
chip->ops.mode = MTD_OOB_RAW;
//将写入模式改为直接书写oob区，即写入数据时，不进行ECC校验的计算和写入。
//（yaffs映像的oob数据中，本身就带有ECC校验）
}
#else
chip->ops.oobbuf = NULL;
#endif
//chip->ops.oobbuf = NULL;
ret = nand_do_write_ops(mtd, to, &chip->ops);
*retlen = chip->ops.retlen;
nand_release_device(mtd);
#if defined(CONFIG_MTD_NAND_YAFFS) //add yaffs2 file system support
chip->ops.mode = oldopsmode; #endif
return ret;
}
OK，对yaffs2支持的代码已修改完毕，重新编译u-boot并下载到nand中，启动开发板，在u-boot的命令行输入:nand help查看nand的命令，可以看到多了一个nand write[.yaffs2]的命令，这个就是用来下载yaffs2文件系统到nand中的命令了。
7) 使用nand write[.yaffs2]命令把事前制作好的yaffs2文件系统下载到Nand Flash中
#tftp 0x33000000 172.20.223.63:rootfs.yaffs //用tftp将yaffs2文件系统下载到内存的0x33000000位置
#nand erase 0x350000 0x3cac000 //擦除Nand的文件系统分区
#nand write.yaffs2 0x30000000 0x250000 0x658170
//将内存中的yaffs2文件系统写入Nand的文件系统分区，注意这里的0x658170是yaffs2文件系统的实际大小，且必须能被528整除才可以
