不过，对于之前的版本的Linux的kernel来说，使用mtd-util的话，一定要配套，主要是后来新的linux的版本，开始支持mtd的大小，即nand的大小，大于4GB，对应的linux内核中的mtd层的有些变量，就必须从u32升级成u64，才可以支持。

对应的mtd的util中一些变量，也是要和你当前linux版本的mtd匹配。

简单说就是，无论你用哪个版本的Linux内核，如果要去用mtd-util的话，那么两者的版本要一直，即查看linux内核中的mtd的一些头文件，主要是include\mtd\mtd-abi.h和你的mtd-util中的include\mtd\mtd-abi.h,两个要一致。

否则，就会出现我之前遇到的问题，当然linux内核是u64版本的，支持nand flash大于4GB的，而用的mtd-util中的变量的定义，却还是u32，所以肯定会出错的。

为了同一套mtd-util工具即支持u32又支持u64，我定义了一个宏来切换，下面贴出来，供需要的人参考：

加了宏以支持u32和u64的mtd-abi.h文件

mtd-util中的include\mtd\mtd-abi.h：

/*
 * Portions of MTD ABI definition which are shared by kernel and user space
 */

#ifndef __MTD_ABI_H__
#define __MTD_ABI_H__

#include <linux/types.h>

/* from u32 to u64 to support >4GB */
#define U64_VERSION   		  1

struct erase_info_user {
#if U64_VERSION
	__u64 start;
	__u64 length;
#else
	__u32 start;
	__u32 length;
#endif
};

struct mtd_oob_buf {
#if U64_VERSION
	__u64 start;
#else
	__u32 start;
#endif
	__u32 length;
	unsigned char __user *ptr;
};

#define MTD_ABSENT		0
#define MTD_RAM			1
#define MTD_ROM			2
#define MTD_NORFLASH		3
#define MTD_NANDFLASH		4
#define MTD_DATAFLASH		6
#define MTD_UBIVOLUME		7

#define MTD_WRITEABLE		0x400	/* Device is writeable */
#define MTD_BIT_WRITEABLE	0x800	/* Single bits can be flipped */
#define MTD_NO_ERASE		0x1000	/* No erase necessary */
#define MTD_STUPID_LOCK		0x2000	/* Always locked after reset */

// Some common devices / combinations of capabilities
#define MTD_CAP_ROM		0
#define MTD_CAP_RAM		(MTD_WRITEABLE | MTD_BIT_WRITEABLE | MTD_NO_ERASE)
#define MTD_CAP_NORFLASH	(MTD_WRITEABLE | MTD_BIT_WRITEABLE)
#define MTD_CAP_NANDFLASH	(MTD_WRITEABLE)

/* ECC byte placement */
#define MTD_NANDECC_OFF		0	// Switch off ECC (Not recommended)
#define MTD_NANDECC_PLACE	1	// Use the given placement in the structure (YAFFS1 legacy mode)
#define MTD_NANDECC_AUTOPLACE	2	// Use the default placement scheme
#define MTD_NANDECC_PLACEONLY	3	// Use the given placement in the structure (Do not store ecc result on read)
#define MTD_NANDECC_AUTOPL_USR 	4	// Use the given autoplacement scheme rather than using the default

#define MTD_MAX_OOBFREE_ENTRIES	8

/* This constant declares the max. oobsize / page, which
 * is supported now. If you add a chip with bigger oobsize/page
 * adjust this accordingly.
 */
#define MTD_NAND_MAX_PAGESIZE	8192
/*
 * for special chip, page/oob is 4K/218,
 * so here alloc more than 256+256 for 8192 pagesize for future special chip like that
 */
#define MTD_NAND_MAX_OOBSIZE		(256 + 256)

/* OTP mode selection */
#define MTD_OTP_OFF		0
#define MTD_OTP_FACTORY	1
#define MTD_OTP_USER		2

struct mtd_info_user {
	__u8 type;
	__u32 flags;
#if U64_VERSION
	__u64 size;	 // Total size of the MTD
#else
	__u32 size;	 // Total size of the MTD
#endif
	__u32 erasesize;
	__u32 writesize;
	__u32 oobsize;   // Amount of OOB data per block (e.g. 16)
	/* The below two fields are obsolete and broken, do not use them
	 * (TODO: remove at some point) */
	__u32 ecctype;
	__u32 eccsize;
};

struct region_info_user {
#if U64_VERSION
	__u64 offset;		/* At which this region starts,
					 * from the beginning of the MTD */
#else
	__u32 offset;		/* At which this region starts,
					 * from the beginning of the MTD */
#endif
	__u32 erasesize;		/* For this region */
	__u32 numblocks;		/* Number of blocks in this region */
	__u32 regionindex;
};

struct otp_info {
	__u32 start;
	__u32 length;
	__u32 locked;
};

#define MEMGETINFO		_IOR('M', 1, struct mtd_info_user)
#define MEMERASE		_IOW('M', 2, struct erase_info_user)
#define MEMWRITEOOB		_IOWR('M', 3, struct mtd_oob_buf)
#define MEMREADOOB		_IOWR('M', 4, struct mtd_oob_buf)
#define MEMLOCK			_IOW('M', 5, struct erase_info_user)
#define MEMUNLOCK		_IOW('M', 6, struct erase_info_user)
#define MEMGETREGIONCOUNT	_IOR('M', 7, int)
#define MEMGETREGIONINFO	_IOWR('M', 8, struct region_info_user)
#define MEMSETOOBSEL		_IOW('M', 9, struct nand_oobinfo)
#define MEMGETOOBSEL		_IOR('M', 10, struct nand_oobinfo)
#define MEMGETBADBLOCK		_IOW('M', 11, __kernel_loff_t)
#define MEMSETBADBLOCK		_IOW('M', 12, __kernel_loff_t)
#define OTPSELECT		_IOR('M', 13, int)
#define OTPGETREGIONCOUNT	_IOW('M', 14, int)
#define OTPGETREGIONINFO	_IOW('M', 15, struct otp_info)
#define OTPLOCK			_IOR('M', 16, struct otp_info)
#define ECCGETLAYOUT		_IOR('M', 17, struct nand_ecclayout)
#define ECCGETSTATS		_IOR('M', 18, struct mtd_ecc_stats)
#define MTDFILEMODE		_IO('M', 19)
/*
 * set/clear prepare oob support
 * usage:
 * 1. set prep_oob_support
 * 2. call write_oob will only prepare, not actually write
 * 3. clear prep_oob_support 
 * 4. write_page will use the previously prepared oob buffer, then clear it automatically
 */
#define SETPREPAREOOB		_IOWR('M', 20, int)
#define CLEARPREPAREOOB	_IOWR('M', 21, int)

/*
 * Obsolete legacy interface. Keep it in order not to break userspace
 * interfaces
 */
struct nand_oobinfo {
	__u32 useecc;
	__u32 eccbytes;
	__u32 oobfree[MTD_MAX_OOBFREE_ENTRIES][2];
	__u32 eccpos[MTD_NAND_MAX_OOBSIZE];
};

struct nand_oobfree {
	__u32 offset;
	__u32 length;
};

/*
 * ECC layout control structure. Exported to userspace for
 * diagnosis and to allow creation of raw images
 */
struct nand_ecclayout {
	__u32 eccbytes;
	__u32 eccpos[MTD_NAND_MAX_OOBSIZE];
	__u32 oobavail;
	struct nand_oobfree oobfree[MTD_MAX_OOBFREE_ENTRIES];
};

/**
 * struct mtd_ecc_stats - error correction stats
 *
 * @corrected:	number of corrected bits
 * @failed:	number of uncorrectable errors
 * @badblocks:	number of bad blocks in this partition
 * @bbtblocks:	number of blocks reserved for bad block tables
 */
struct mtd_ecc_stats {
	__u32 corrected;
	__u32 failed;
	__u32 badblocks;
	__u32 bbtblocks;
};

/*
 * Read/write file modes for access to MTD
 */
enum mtd_file_modes {
	MTD_MODE_NORMAL = MTD_OTP_OFF,
	MTD_MODE_OTP_FACTORY = MTD_OTP_FACTORY,
	MTD_MODE_OTP_USER = MTD_OTP_USER,
	MTD_MODE_RAW,
};

#endif /* __MTD_ABI_H__ */
                

所谓的ramdisk，我个人也不是非常熟悉。

只是对更不熟悉的人解释一下，可以简单理解为把你的内存划分出来，当做一块分区使用

所以这个小分区，说白了就是内存。所以，读写速度很快，也和nand 或nor flash无关，不会影响到Nand或Nor的升级。

一般来说，多数都是将ramdisk挂载到/tmp下面的，所以，如果你啥都不熟悉，直接把相关文件拷贝到/tmp，即可。

更多的，关于ramdisk或tmpfs，自己google吧。