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。