/*
 * block2mtd.c - create an mtd from a block device
 *
 * Copyright (C) 2001,2002      Simon Evans <spse@secret.org.uk>
 * Copyright (C) 2004-2006      Joern Engel <joern@wh.fh-wedel.de>
 *
 * Licence: GPL
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

/*
 * When the first attempt at device initialization fails, we may need to
 * wait a little bit and retry. This timeout, by default 3 seconds, gives
 * device time to start up. Required on BCM2708 and a few other chipsets.
 */
#define MTD_DEFAULT_TIMEOUT     3

#include <linux/module.h>
#include <linux/delay.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/bio.h>
#include <linux/pagemap.h>
#include <linux/list.h>
#include <linux/init.h>
#include <linux/mtd/mtd.h>
#include <linux/mutex.h>
#include <linux/mount.h>
#include <linux/slab.h>
#include <linux/major.h>

/* Maximum number of comma-separated items in the 'block2mtd=' parameter */
#define BLOCK2MTD_PARAM_MAX_COUNT 3

/* Info for the block device */
struct block2mtd_dev {
        struct list_head list;
        struct block_device *blkdev;
        struct mtd_info mtd;
        struct mutex write_mutex;
};


/* Static info about the MTD, used in cleanup_module */
static LIST_HEAD(blkmtd_device_list);


static struct page *page_read(struct address_space *mapping, pgoff_t index)
{
        return read_mapping_page(mapping, index, NULL);
}

/* erase a specified part of the device */
static int _block2mtd_erase(struct block2mtd_dev *dev, loff_t to, size_t len)
{
        struct address_space *mapping = dev->blkdev->bd_inode->i_mapping;
        struct page *page;
        pgoff_t index = to >> PAGE_SHIFT;       // page index
        int pages = len >> PAGE_SHIFT;
        u_long *p;
        u_long *max;

        while (pages) {
                page = page_read(mapping, index);
                if (IS_ERR(page))
                        return PTR_ERR(page);

                max = page_address(page) + PAGE_SIZE;
                for (p=page_address(page); p<max; p++)
                        if (*p != -1UL) {
                                lock_page(page);
                                memset(page_address(page), 0xff, PAGE_SIZE);
                                set_page_dirty(page);
                                unlock_page(page);
                                balance_dirty_pages_ratelimited(mapping);
                                break;
                        }

                put_page(page);
                pages--;
                index++;
        }
        return 0;
}
static int block2mtd_erase(struct mtd_info *mtd, struct erase_info *instr)
{
        struct block2mtd_dev *dev = mtd->priv;
        size_t from = instr->addr;
        size_t len = instr->len;
        int err;

        mutex_lock(&dev->write_mutex);
        err = _block2mtd_erase(dev, from, len);
        mutex_unlock(&dev->write_mutex);
        if (err)
                pr_err("erase failed err = %d\n", err);

        return err;
}


static int block2mtd_read(struct mtd_info *mtd, loff_t from, size_t len,
                size_t *retlen, u_char *buf)
{
        struct block2mtd_dev *dev = mtd->priv;
        struct page *page;
        pgoff_t index = from >> PAGE_SHIFT;
        int offset = from & (PAGE_SIZE-1);
        int cpylen;

        while (len) {
                if ((offset + len) > PAGE_SIZE)
                        cpylen = PAGE_SIZE - offset;    // multiple pages
                else
                        cpylen = len;   // this page
                len = len - cpylen;

                page = page_read(dev->blkdev->bd_inode->i_mapping, index);
                if (IS_ERR(page))
                        return PTR_ERR(page);

                memcpy(buf, page_address(page) + offset, cpylen);
                put_page(page);

                if (retlen)
                        *retlen += cpylen;
                buf += cpylen;
                offset = 0;
                index++;
        }
        return 0;
}


/* write data to the underlying device */
static int _block2mtd_write(struct block2mtd_dev *dev, const u_char *buf,
                loff_t to, size_t len, size_t *retlen)
{
        struct page *page;
        struct address_space *mapping = dev->blkdev->bd_inode->i_mapping;
        pgoff_t index = to >> PAGE_SHIFT;       // page index
        int offset = to & ~PAGE_MASK;   // page offset
        int cpylen;

        while (len) {
                if ((offset+len) > PAGE_SIZE)
                        cpylen = PAGE_SIZE - offset;    // multiple pages
                else
                        cpylen = len;                   // this page
                len = len - cpylen;

                page = page_read(mapping, index);
                if (IS_ERR(page))
                        return PTR_ERR(page);

                if (memcmp(page_address(page)+offset, buf, cpylen)) {
                        lock_page(page);
                        memcpy(page_address(page) + offset, buf, cpylen);
                        set_page_dirty(page);
                        unlock_page(page);
                        balance_dirty_pages_ratelimited(mapping);
                }
                put_page(page);

                if (retlen)
                        *retlen += cpylen;

                buf += cpylen;
                offset = 0;
                index++;
        }
        return 0;
}


static int block2mtd_write(struct mtd_info *mtd, loff_t to, size_t len,
                size_t *retlen, const u_char *buf)
{
        struct block2mtd_dev *dev = mtd->priv;
        int err;

        mutex_lock(&dev->write_mutex);
        err = _block2mtd_write(dev, buf, to, len, retlen);
        mutex_unlock(&dev->write_mutex);
        if (err > 0)
                err = 0;
        return err;
}


/* sync the device - wait until the write queue is empty */
static void block2mtd_sync(struct mtd_info *mtd)
{
        struct block2mtd_dev *dev = mtd->priv;
        sync_blockdev(dev->blkdev);
        return;
}


static void block2mtd_free_device(struct block2mtd_dev *dev)
{
        if (!dev)
                return;

        kfree(dev->mtd.name);

        if (dev->blkdev) {
                invalidate_mapping_pages(dev->blkdev->bd_inode->i_mapping,
                                        0, -1);
                blkdev_put(dev->blkdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
        }

        kfree(dev);
}


static struct block2mtd_dev *add_device(char *devname, int erase_size,
                char *label, int timeout)
{
#ifndef MODULE
        int i;
#endif
        const fmode_t mode = FMODE_READ | FMODE_WRITE | FMODE_EXCL;
        struct block_device *bdev;
        struct block2mtd_dev *dev;
        char *name;

        if (!devname)
                return NULL;

        dev = kzalloc(sizeof(struct block2mtd_dev), GFP_KERNEL);
        if (!dev)
                return NULL;

        /* Get a handle on the device */
        bdev = blkdev_get_by_path(devname, mode, dev);

#ifndef MODULE
        /*
         * We might not have the root device mounted at this point.
         * Try to resolve the device name by other means.
         */
        for (i = 0; IS_ERR(bdev) && i <= timeout; i++) {
                dev_t devt;

                if (i)
                        /*
                         * Calling wait_for_device_probe in the first loop
                         * was not enough, sleep for a bit in subsequent
                         * go-arounds.
                         */
                        msleep(1000);
                wait_for_device_probe();

                devt = name_to_dev_t(devname);
                if (!devt)
                        continue;
                bdev = blkdev_get_by_dev(devt, mode, dev);
        }
#endif

        if (IS_ERR(bdev)) {
                pr_err("error: cannot open device %s\n", devname);
                goto err_free_block2mtd;
        }
        dev->blkdev = bdev;

        if (MAJOR(bdev->bd_dev) == MTD_BLOCK_MAJOR) {
                pr_err("attempting to use an MTD device as a block device\n");
                goto err_free_block2mtd;
        }

        if ((long)dev->blkdev->bd_inode->i_size % erase_size) {
                pr_err("erasesize must be a divisor of device size\n");
                goto err_free_block2mtd;
        }

        mutex_init(&dev->write_mutex);

        /* Setup the MTD structure */
        /* make the name contain the block device in */
        if (!label)
                name = kasprintf(GFP_KERNEL, "block2mtd: %s", devname);
        else
                name = kstrdup(label, GFP_KERNEL);
        if (!name)
                goto err_destroy_mutex;

        dev->mtd.name = name;

        dev->mtd.size = dev->blkdev->bd_inode->i_size & PAGE_MASK;
        dev->mtd.erasesize = erase_size;
        dev->mtd.writesize = 1;
        dev->mtd.writebufsize = PAGE_SIZE;
        dev->mtd.type = MTD_RAM;
        dev->mtd.flags = MTD_CAP_RAM;
        dev->mtd._erase = block2mtd_erase;
        dev->mtd._write = block2mtd_write;
        dev->mtd._sync = block2mtd_sync;
        dev->mtd._read = block2mtd_read;
        dev->mtd.priv = dev;
        dev->mtd.owner = THIS_MODULE;

        if (mtd_device_register(&dev->mtd, NULL, 0)) {
                /* Device didn't get added, so free the entry */
                goto err_destroy_mutex;
        }

        list_add(&dev->list, &blkmtd_device_list);
        pr_info("mtd%d: [%s] erase_size = %dKiB [%d]\n",
                dev->mtd.index,
                label ? label : dev->mtd.name + strlen("block2mtd: "),
                dev->mtd.erasesize >> 10, dev->mtd.erasesize);
        return dev;

err_destroy_mutex:
        mutex_destroy(&dev->write_mutex);
err_free_block2mtd:
        block2mtd_free_device(dev);
        return NULL;
}


/* This function works similar to reguler strtoul.  In addition, it
 * allows some suffixes for a more human-readable number format:
 * ki, Ki, kiB, KiB     - multiply result with 1024
 * Mi, MiB              - multiply result with 1024^2
 * Gi, GiB              - multiply result with 1024^3
 */
static int ustrtoul(const char *cp, char **endp, unsigned int base)
{
        unsigned long result = simple_strtoul(cp, endp, base);
        switch (**endp) {
        case 'G' :
                result *= 1024;
                fallthrough;
        case 'M':
                result *= 1024;
                fallthrough;
        case 'K':
        case 'k':
                result *= 1024;
        /* By dwmw2 editorial decree, "ki", "Mi" or "Gi" are to be used. */
                if ((*endp)[1] == 'i') {
                        if ((*endp)[2] == 'B')
                                (*endp) += 3;
                        else
                                (*endp) += 2;
                }
        }
        return result;
}


static int parse_num(size_t *num, const char *token)
{
        char *endp;
        size_t n;

        n = (size_t) ustrtoul(token, &endp, 0);
        if (*endp)
                return -EINVAL;

        *num = n;
        return 0;
}


static inline void kill_final_newline(char *str)
{
        char *newline = strrchr(str, '\n');
        if (newline && !newline[1])
                *newline = 0;
}


#ifndef MODULE
static int block2mtd_init_called = 0;
/* 80 for device, 12 for erase size */
static char block2mtd_paramline[80 + 12];
#endif

static int block2mtd_setup2(const char *val)
{
        /* 80 for device, 12 for erase size, 80 for name, 8 for timeout */
        char buf[80 + 12 + 80 + 8];
        char *str = buf;
        char *token[BLOCK2MTD_PARAM_MAX_COUNT];
        char *name;
        char *label = NULL;
        size_t erase_size = PAGE_SIZE;
        unsigned long timeout = MTD_DEFAULT_TIMEOUT;
        int i, ret;

        if (strnlen(val, sizeof(buf)) >= sizeof(buf)) {
                pr_err("parameter too long\n");
                return 0;
        }

        strcpy(str, val);
        kill_final_newline(str);

        for (i = 0; i < BLOCK2MTD_PARAM_MAX_COUNT; i++)
                token[i] = strsep(&str, ",");

        if (str) {
                pr_err("too many arguments\n");
                return 0;
        }

        if (!token[0]) {
                pr_err("no argument\n");
                return 0;
        }

        name = token[0];
        if (strlen(name) + 1 > 80) {
                pr_err("device name too long\n");
                return 0;
        }

        /* Optional argument when custom label is used */
        if (token[1] && strlen(token[1])) {
                ret = parse_num(&erase_size, token[1]);
                if (ret) {
                        pr_err("illegal erase size\n");
                        return 0;
                }
        }

        if (token[2]) {
                label = token[2];
                pr_info("Using custom MTD label '%s' for dev %s\n", label, name);
        }

        add_device(name, erase_size, label, timeout);

        return 0;
}


static int block2mtd_setup(const char *val, const struct kernel_param *kp)
{
#ifdef MODULE
        return block2mtd_setup2(val);
#else
        /* If more parameters are later passed in via
           /sys/module/block2mtd/parameters/block2mtd
           and block2mtd_init() has already been called,
           we can parse the argument now. */

        if (block2mtd_init_called)
                return block2mtd_setup2(val);

        /* During early boot stage, we only save the parameters
           here. We must parse them later: if the param passed
           from kernel boot command line, block2mtd_setup() is
           called so early that it is not possible to resolve
           the device (even kmalloc() fails). Deter that work to
           block2mtd_setup2(). */

        strlcpy(block2mtd_paramline, val, sizeof(block2mtd_paramline));

        return 0;
#endif
}


module_param_call(block2mtd, block2mtd_setup, NULL, NULL, 0200);
MODULE_PARM_DESC(block2mtd, "Device to use. \"block2mtd=<dev>[,[<erasesize>][,<label>]]\"");

static int __init block2mtd_init(void)
{
        int ret = 0;

#ifndef MODULE
        if (strlen(block2mtd_paramline))
                ret = block2mtd_setup2(block2mtd_paramline);
        block2mtd_init_called = 1;
#endif

        return ret;
}


static void block2mtd_exit(void)
{
        struct list_head *pos, *next;

        /* Remove the MTD devices */
        list_for_each_safe(pos, next, &blkmtd_device_list) {
                struct block2mtd_dev *dev = list_entry(pos, typeof(*dev), list);
                block2mtd_sync(&dev->mtd);
                mtd_device_unregister(&dev->mtd);
                mutex_destroy(&dev->write_mutex);
                pr_info("mtd%d: [%s] removed\n",
                        dev->mtd.index,
                        dev->mtd.name + strlen("block2mtd: "));
                list_del(&dev->list);
                block2mtd_free_device(dev);
        }
}

late_initcall(block2mtd_init);
module_exit(block2mtd_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Joern Engel <joern@lazybastard.org>");
MODULE_DESCRIPTION("Emulate an MTD using a block device");