以下红色部分就是需要修改的地方，老版本的U-boot需要添加下面的代码才能够增加对yaffs2的支持，新版本的只需添加一个宏就可以增加对yaffs2的支持。

yaffs2文件系统的移植主要涉及到u-boot对yaffs2文件系统的烧写支持、linux内核对yaffs2文件系统的支持，以及yaffs2文件系统的制作，现在我们按照从下到上的顺序来实现各部分的功能。

1、实现u-boot对yaffs/yaffs2文件系统下载的支持。

注意：这里对Nand的操作是基于MTD架构方式。

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ECC523 - 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。

实现u-boot对Yaffs或者Yaffs2文件系统的读写支持步骤如下：

①、在include/configs/smdk2440.h头文件中定义一个管理对Yaffs2支持的宏和开启u-boot中对Nand Flash默认分区的宏，如下：

#define CONFIG_MTD_NAND_YAFFS2   1 //定义一个管理对Yaffs2支持的宏

//开启Nand Flash默认分区，注意此处的分区要和你的内核中的分区保持一致

#define MTDIDS_DEFAULT "nand0=nandflash0"

#define MTDPARTS_DEFAULT "mtdparts=nandflash0:256k(bootloader)," \

                     "128k(params)," \

                     "2m(kernel)," \

                     "-(root)"

 

②、在common/cmd_nand.c 原来对Nand操作的命令集列表中添加Yaffs2对Nand的写命令，如下：//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"

//注意：这里只添加了yaffs2的写命令，因为我们只用u-boot下载(即写)功能，所以我们没有添加yaffs2读的命令

#if defined(CONFIG_MTD_NAND_YAFFS2)

    "nand write[.yaffs2] - addr off|partition size - write `size' byte yaffs image\n"

    " starting at offset off' from memory address addr' (.yaffs2 for 512+16 NAND)\n"

#endif

    "nand erase [clean] [off size] - erase 'size' bytes from\n"     " offset 'off' (entire device if not specified)\n"     "nand bad - show bad blocks\n"     "nand dump[.oob] off - dump page\n"     "nand scrub - really clean NAND erasing bad blocks (UNSAFE)\n"     "nand markbad off [...] - mark bad block(s) at offset (UNSAFE)\n"     "nand biterr off - make a bit error at offset (UNSAFE)" #ifdef CONFIG_CMD_NAND_LOCK_UNLOCK     "\n"     "nand lock [tight] [status]\n"     " bring nand to lock state or display locked pages\n"     "nand unlock [offset] [size] - unlock section" #endif );

接着，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);         }

//添加yaffs2相关操作，注意该处又关联到nand_write_skip_bad函数

#if defined(CONFIG_MTD_NAND_YAFFS2)

        else if (s != NULL && (!strcmp(s, ".yaffs2")))         {             nand->rw_oob = 1;             nand->skipfirstblk = 1;             ret = nand_write_skip_bad(nand,off,&size,(u_char *)addr);             nand->skipfirstblk = 0;             nand->rw_oob = 0;         } #endif

        else if (!strcmp(s, ".oob")) 

        {             /* out-of-band data */             mtd_oob_ops_t ops =              {                 .oobbuf = (u8 *)addr,                 .ooblen = size,                 .mode = MTD_OOB_RAW             };

            if (read)

                ret = nand->read_oob(nand, off, &ops);             else                 ret = nand->write_oob(nand, off, &ops);         }          else          {             printf("Unknown nand command suffix '%s'.\n", s);             return 1;         }

        printf(" %zu bytes %s: %s\n", size, read ? "read" : "written", ret ? "ERROR" : "OK");

        return ret == 0 ? 0 : 1;

    }

③、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：

#if defined(CONFIG_MTD_NAND_YAFFS2)

    u_char rw_oob;

    u_char skipfirstblk;

#endif

 

④、在第二步关联的drivers/mtd/nand/nand_util.c 的nand_write_skip_bad函数中添加对Nand OOB的相关操作，如下：

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_YAFFS2) //add yaffs2 file system support

    if(nand->rw_oob==1)    

    {

        size_t oobsize = nand->oobsize;

        size_t datasize = nand->writesize;

        int datapages = 0;

        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 !defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support

    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;

    }#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 0x%08llx\n",                 offset & ~(nand->erasesize - 1));             offset += nand->erasesize - block_offset;             continue;         }

#if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support

        if(nand->skipfirstblk==1)             {             nand->skipfirstblk=0;             printf ("Skip the 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;

        printf("\rWriting at 0x%llx -- ",offset); //add yaffs2 file system support

        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;

        printf("%d%% is complete.",100-(left_to_write/(*length/100)));         offset += write_size;

#if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support

        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;

}

⑤、在第四步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drivers/mtd/nand/nand_base.c  的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_YAFFS2) //add yaffs2 file system support

    int oldopsmode = 0;

    if(mtd->rw_oob==1)    

    {         int i = 0;        int datapages = 0;

        size_t oobsize = mtd->oobsize;

        size_t datasize = mtd->writesize;

        uint8_t oobtemp[oobsize];

        datapages = len / (datasize);

        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

 

    /* Do not allow reads past end of device */

    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_YAFFS2) //add yaffs2 file system support

    if(mtd->rw_oob!=1)    

    {         chip->ops.oobbuf = NULL;    }     else        {         chip->ops.oobbuf = (uint8_t *)(buf + len);        chip->ops.ooblen = mtd->oobsize;        oldopsmode = chip->ops.mode;        chip->ops.mode = MTD_OOB_RAW;    }#else    chip->ops.oobbuf = NULL;#endif

 

    ret = nand_do_write_ops(mtd, to, &chip->ops);

    *retlen = chip->ops.retlen;

    nand_release_device(mtd);

 

#if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support

    chip->ops.mode = oldopsmode;

#endif

 

    return ret;

}