Linux Kernel（10.2）- mtd partitions

在drivers/mtd/devices/mtdram.c中可以知道，透過add_mtd_device()/del_mtd_device()新增和刪除mtd device，但是並沒有規劃partition，在這邊將介紹add_mtd_partitions()/del_mtd_partitions()讓您可以透過這兩個函數為mtd切割partition。
此範例為drivers/mtd/devices/mtdram.c內容來修改而成（紅色粗體為修改部份）。

/*
 * mtdram - a test mtd device
 * Author: Alexander Larsson 
 *
 * Copyright (c) 1999 Alexander Larsson 
 * Copyright (c) 2005 Joern Engel 
 *
 * This code is GPL
 *
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/ioport.h>
#include <linux/vmalloc.h>
#include <linux/init.h>
#include <linux/mtd/compatmac.h>
#include <linux/mtd/mtd.h>
#include <linux/mtd/mtdram.h>
#include <linux/mtd/partitions.h>

static unsigned long total_size = CONFIG_MTDRAM_TOTAL_SIZE;
static unsigned long erase_size = CONFIG_MTDRAM_ERASE_SIZE;
#define MTDRAM_TOTAL_SIZE (total_size * 1024)
#define MTDRAM_ERASE_SIZE (erase_size * 1024)

static struct mtd_partition brook_partitions[] = {
    {
        .name = "part-1",
        .size = 0x00100000,
        .offset = 0x0000000
    }, {
        .name = "part-2",
        .size = 0x00100000,
        .offset = MTDPART_OFS_APPEND,
        .mask_flags = MTD_WRITEABLE
    }, {
        .name = "part-3",
        .offset = MTDPART_OFS_APPEND,
    }，
};

#ifdef MODULE
module_param(total_size, ulong, 0);
MODULE_PARM_DESC(total_size, "Total device size in KiB");
module_param(erase_size, ulong, 0);
MODULE_PARM_DESC(erase_size, "Device erase block size in KiB");
#endif

// We could store these in the mtd structure, but we only support 1 device..
static struct mtd_info *mtd_info;

static int ram_erase(struct mtd_info *mtd, struct erase_info *instr)
{
    if (instr->addr + instr->len > mtd->size)
        return -EINVAL;

    memset((char *)mtd->priv + instr->addr, 0xff, instr->len);

    instr->state = MTD_ERASE_DONE;
    mtd_erase_callback(instr);

    return 0;
}

static int ram_point(struct mtd_info *mtd, loff_t from, size_t len,
        size_t *retlen, void **virt, resource_size_t *phys)
{
    if (from + len > mtd->size)
        return -EINVAL;

    /* can we return a physical address with this driver? */
    if (phys)
        return -EINVAL;

    *virt = mtd->priv + from;
    *retlen = len;。
    return 0;
}

static void ram_unpoint(struct mtd_info *mtd, loff_t from, size_t len)
{
}

/*
 * Allow NOMMU mmap() to directly map the device (if not NULL)
 * - return the address to which the offset maps
 * - return -ENOSYS to indicate refusal to do the mapping
 */
static unsigned long ram_get_unmapped_area(struct mtd_info *mtd,
                       unsigned long len,
                       unsigned long offset,
                       unsigned long flags)
{
    return (unsigned long) mtd->priv + offset;
}

static int ram_read(struct mtd_info *mtd, loff_t from, size_t len,
        size_t *retlen, u_char *buf)
{
    if (from + len > mtd->size)
        return -EINVAL;

    memcpy(buf, mtd->priv + from, len);

    *retlen = len;
    return 0;
}

static int ram_write(struct mtd_info *mtd, loff_t to, size_t len,
        size_t *retlen, const u_char *buf)
{
    if (to + len > mtd->size)
        return -EINVAL;

    memcpy((char *)mtd->priv + to, buf, len);

    *retlen = len;
    return 0;
}

static void __exit cleanup_mtdram(void)
{
    if (mtd_info) {
        del_mtd_partitions(mtd_info);
        vfree(mtd_info->priv);
        kfree(mtd_info);
    }
}

int mtdram_init_device(struct mtd_info *mtd, void *mapped_address,
        unsigned long size, char *name)
{
    memset(mtd, 0, sizeof(*mtd));

    /* Setup the MTD structure */
    mtd->name = name;
    mtd->type = MTD_RAM;
    mtd->flags = MTD_CAP_RAM;
    mtd->size = size;
    mtd->writesize = 1;
    mtd->erasesize = MTDRAM_ERASE_SIZE;
    mtd->priv = mapped_address;

    mtd->owner = THIS_MODULE;
    mtd->erase = ram_erase;
    mtd->point = ram_point;
    mtd->unpoint = ram_unpoint;
    mtd->get_unmapped_area = ram_get_unmapped_area;
    mtd->read = ram_read;
    mtd->write = ram_write;

    if (add_mtd_partitions(mtd, brook_partitions,
                ARRAY_SIZE(brook_partitions))) {
        return -EIO;
    }

    return 0;
}

static int __init init_mtdram(void)
{
    void *addr;
    int err;

    if (!total_size)
        return -EINVAL;

    /* Allocate some memory */
    mtd_info = kmalloc(sizeof(struct mtd_info), GFP_KERNEL);
    if (!mtd_info)
        return -ENOMEM;

    addr = vmalloc(MTDRAM_TOTAL_SIZE);
    if (!addr) {
        kfree(mtd_info);
        mtd_info = NULL;
        return -ENOMEM;
    }
    err = mtdram_init_device(mtd_info, addr, 
                  MTDRAM_TOTAL_SIZE, "brook_flash");
    if (err) {
        vfree(addr);
        kfree(mtd_info);
        mtd_info = NULL;
        return err;
    }
    memset(mtd_info->priv, 0xff, MTDRAM_TOTAL_SIZE);
    return err;
}

module_init(init_mtdram);
module_exit(cleanup_mtdram);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Alexander Larsson >alexl@redhat.com>");
MODULE_DESCRIPTION("Simulated MTD driver for testing");

如果要切割partitions就必須要提供partitions的資訊，於是我們就宣告了一個名為brook_partitions的static struct mtd_partition，然後將原本呼叫add_mtd_device()/del_mtd_device()分別改成add_mtd_partitions()/del_mtd_partitions()就大功告成了。

Linux Kernel（10.1）- drivers/mtd/devices/mtdram.c

MTD的基本介紹可以參考MTD - Memory Technology Devices，這篇文章要透過drivers/mtd/devices/mtdram.c來了解mtd的driver如何運作。

static unsigned long total_size = CONFIG_MTDRAM_TOTAL_SIZE;
#define MTDRAM_TOTAL_SIZE (total_size * 1024)

#ifdef MODULE
module_param(total_size, ulong, 0);
MODULE_PARM_DESC(total_size, "Total device size in KiB");
#endif

static int __init init_mtdram(void)
{
 void *addr;
 int err;

 if (!total_size)
  return -EINVAL;

 /* Allocate some memory */
 mtd_info = kmalloc(sizeof(struct mtd_info), GFP_KERNEL);
 if (!mtd_info)
  return -ENOMEM;

 addr = vmalloc(MTDRAM_TOTAL_SIZE);
 if (!addr) {
  kfree(mtd_info);
  mtd_info = NULL;
  return -ENOMEM;
 }
 err = mtdram_init_device(mtd_info, addr,
                   MTDRAM_TOTAL_SIZE, "mtdram test device");
 if (err) {
  vfree(addr);
  kfree(mtd_info);
  mtd_info = NULL;
  return err;
 }
 memset(mtd_info->priv, 0xff, MTDRAM_TOTAL_SIZE);
 return err;
}

首先，看到init_mtdram()，在該function中，我們分配一塊記憶體給mtd_info，以及一塊v-memory給稍候模擬的flash用，接著就呼叫mtdram_init_device()進行mtd的註冊動作，（一個mtd partition需要一個mtd_info來存放所需的資訊），init_mtdram()後面就將mtd_info->priv（即v-memory）的內容全部設成0xff，這是因為一個空的flash裡面預設就是0xff。

int mtdram_init_device(struct mtd_info *mtd, void *mapped_address,
  unsigned long size, char *name)
{
 memset(mtd, 0, sizeof(*mtd));

 /* Setup the MTD structure */
 mtd->name = name;
 mtd->type = MTD_RAM;
 mtd->flags = MTD_CAP_RAM;
 mtd->size = size;
 mtd->writesize = 1;
 mtd->erasesize = MTDRAM_ERASE_SIZE;
 mtd->priv = mapped_address;

 mtd->owner = THIS_MODULE;
 mtd->erase = ram_erase;
 mtd->point = ram_point;
 mtd->unpoint = ram_unpoint;
 mtd->get_unmapped_area = ram_get_unmapped_area;
 mtd->read = ram_read;
 mtd->write = ram_write;

 if (add_mtd_device(mtd)) {
  return -EIO;
 }

 return 0;
}

在mtdram_init_device()主要是填mtd_info相關資訊，然後呼叫add_mtd_device()進行註冊mtd的動作。呼叫del_mtd_device()進行移除mtd的工作。
point()/unpoint()可以參考http://www.linux-mtd.infradead.org/faq/general.html#L_point。

#ifdef MODULE
module_param(total_size, ulong, 0);
MODULE_PARM_DESC(total_size, "Total device size in KiB");
module_param(erase_size, ulong, 0);
MODULE_PARM_DESC(erase_size, "Device erase block size in KiB");
#endif

// We could store these in the mtd structure, but we only support 1 device.
static struct mtd_info *mtd_info;

static int ram_erase(struct mtd_info *mtd, struct erase_info *instr)
{
 if (instr->addr + instr->len > mtd->size)
  return -EINVAL;

 memset((char *)mtd->priv + instr->addr, 0xff, instr->len);

 instr->state = MTD_ERASE_DONE;
 mtd_erase_callback(instr);

 return 0;
}

static int ram_point(struct mtd_info *mtd, loff_t from, size_t len,
  size_t *retlen, void **virt, resource_size_t *phys)
{
 if (from + len > mtd->size)
  return -EINVAL;

 /* can we return a physical address with this driver? */
 if (phys)
  return -EINVAL;

 *virt = mtd->priv + from;
 *retlen = len;
 return 0;
}

static void ram_unpoint(struct mtd_info *mtd, loff_t from, size_t len)
{
}

/*
 * Allow NOMMU mmap() to directly map the device (if not NULL)
 * - return the address to which the offset maps
 * - return -ENOSYS to indicate refusal to do the mapping
 */
static unsigned long ram_get_unmapped_area(struct mtd_info *mtd,
        unsigned long len,
        unsigned long offset,
        unsigned long flags)
{
 return (unsigned long) mtd->priv + offset;
}

static int ram_read(struct mtd_info *mtd, loff_t from, size_t len,
  size_t *retlen, u_char *buf)
{
 if (from + len > mtd->size)
  return -EINVAL;

 memcpy(buf, mtd->priv + from, len);

 *retlen = len;
 return 0;
}

static int ram_write(struct mtd_info *mtd, loff_t to, size_t len,
  size_t *retlen, const u_char *buf)
{
 if (to + len > mtd->size)
  return -EINVAL;

 memcpy((char *)mtd->priv + to, buf, len);

 *retlen = len;
 return 0;
}

剩下的read()/write()/erase()都是copy from/to memory和清成0xff，所以您可以發現讀寫NOR flash和讀寫memory差不多。

Linux Kernel（10）- MTD - Memory Technology Devices

說到MTD您就不得不親自拜訪一下MTD的官網(http://www.linux-mtd.infradead.org/)，傳統上UNIX將device分成兩大類，char device和block device，char device就像鍵盤，可以讀資料，但卻不能做seek，也沒有固定大小，而block就像硬碟一樣，可以隨機存取某個位置(seek)。而MTD並不是char device也不是block device，因此建立了新的device類別，稱為MTD。
MTD subsystem提供一個抽象層（FTL）來存取flash device（如NAN、OneNAND、NOR等等），而我們一般用的USB flash因為有IC控制，以Linux的角度看起來就像block device，而不是一個原生的(raw) flash。

一般PC都不會接這些raw flash，不過我們可以透過一些simulate來練習這些device。
在insmod mtd.ko之後我可以透過/proc/mtd得知目前有哪些MTD，因為我們系統當然沒有MTD的device，所以可以insmod mtdram.ko安裝一個虛擬的MTD。

如果要能mount raw flash，還必須透過block device的介面存取，所以在安裝一下mtdblock.ko吧。

利用，mkfs.jffs2建立一個jffs2的image，再利用flashcp將image燒錄到flash中，最後就可以mount來用啦。

這一張圖是利用dd將flash的資料備份下來，再利用flashcp還原資料。