// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (c) International Business Machines Corp., 2006
 *
 * Author: Artem Bityutskiy (Битюцкий Артём), Joern Engel
 */

/*
 * This is a small driver which implements fake MTD devices on top of UBI
 * volumes. This sounds strange, but it is in fact quite useful to make
 * MTD-oriented software (including all the legacy software) work on top of
 * UBI.
 *
 * Gluebi emulates MTD devices of "MTD_UBIVOLUME" type. Their minimal I/O unit
 * size (@mtd->writesize) is equivalent to the UBI minimal I/O unit. The
 * eraseblock size is equivalent to the logical eraseblock size of the volume.
 */

#include <linux/err.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/math64.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/mtd/ubi.h>
#include <linux/mtd/mtd.h>
#include "ubi-media.h"

#define err_msg(fmt, ...)                                   \
        pr_err("gluebi (pid %d): %s: " fmt "\n",            \
               current->pid, __func__, ##__VA_ARGS__)

/**
 * struct gluebi_device - a gluebi device description data structure.
 * @mtd: emulated MTD device description object
 * @refcnt: gluebi device reference count
 * @desc: UBI volume descriptor
 * @ubi_num: UBI device number this gluebi device works on
 * @vol_id: ID of UBI volume this gluebi device works on
 * @list: link in a list of gluebi devices
 */
struct gluebi_device {
        struct mtd_info mtd;
        int refcnt;
        struct ubi_volume_desc *desc;
        int ubi_num;
        int vol_id;
        struct list_head list;
};

/* List of all gluebi devices */
static LIST_HEAD(gluebi_devices);
static DEFINE_MUTEX(devices_mutex);

/**
 * find_gluebi_nolock - find a gluebi device.
 * @ubi_num: UBI device number
 * @vol_id: volume ID
 *
 * This function seraches for gluebi device corresponding to UBI device
 * @ubi_num and UBI volume @vol_id. Returns the gluebi device description
 * object in case of success and %NULL in case of failure. The caller has to
 * have the &devices_mutex locked.
 */
static struct gluebi_device *find_gluebi_nolock(int ubi_num, int vol_id)
{
        struct gluebi_device *gluebi;

        list_for_each_entry(gluebi, &gluebi_devices, list)
                if (gluebi->ubi_num == ubi_num && gluebi->vol_id == vol_id)
                        return gluebi;
        return NULL;
}

/**
 * gluebi_get_device - get MTD device reference.
 * @mtd: the MTD device description object
 *
 * This function is called every time the MTD device is being opened and
 * implements the MTD get_device() operation. Returns zero in case of success
 * and a negative error code in case of failure.
 */
static int gluebi_get_device(struct mtd_info *mtd)
{
        struct gluebi_device *gluebi;
        int ubi_mode = UBI_READONLY;

        if (mtd->flags & MTD_WRITEABLE)
                ubi_mode = UBI_READWRITE;

        gluebi = container_of(mtd, struct gluebi_device, mtd);
        mutex_lock(&devices_mutex);
        if (gluebi->refcnt > 0) {
                /*
                 * The MTD device is already referenced and this is just one
                 * more reference. MTD allows many users to open the same
                 * volume simultaneously and do not distinguish between
                 * readers/writers/exclusive/meta openers as UBI does. So we do
                 * not open the UBI volume again - just increase the reference
                 * counter and return.
                 */
                gluebi->refcnt += 1;
                mutex_unlock(&devices_mutex);
                return 0;
        }

        /*
         * This is the first reference to this UBI volume via the MTD device
         * interface. Open the corresponding volume in read-write mode.
         */
        gluebi->desc = ubi_open_volume(gluebi->ubi_num, gluebi->vol_id,
                                       ubi_mode);
        if (IS_ERR(gluebi->desc)) {
                mutex_unlock(&devices_mutex);
                return PTR_ERR(gluebi->desc);
        }
        gluebi->refcnt += 1;
        mutex_unlock(&devices_mutex);
        return 0;
}

/**
 * gluebi_put_device - put MTD device reference.
 * @mtd: the MTD device description object
 *
 * This function is called every time the MTD device is being put. Returns
 * zero in case of success and a negative error code in case of failure.
 */
static void gluebi_put_device(struct mtd_info *mtd)
{
        struct gluebi_device *gluebi;

        gluebi = container_of(mtd, struct gluebi_device, mtd);
        mutex_lock(&devices_mutex);
        gluebi->refcnt -= 1;
        if (gluebi->refcnt == 0)
                ubi_close_volume(gluebi->desc);
        mutex_unlock(&devices_mutex);
}

/**
 * gluebi_read - read operation of emulated MTD devices.
 * @mtd: MTD device description object
 * @from: absolute offset from where to read
 * @len: how many bytes to read
 * @retlen: count of read bytes is returned here
 * @buf: buffer to store the read data
 *
 * This function returns zero in case of success and a negative error code in
 * case of failure.
 */
static int gluebi_read(struct mtd_info *mtd, loff_t from, size_t len,
                       size_t *retlen, unsigned char *buf)
{
        int err = 0, lnum, offs, bytes_left;
        struct gluebi_device *gluebi;

        gluebi = container_of(mtd, struct gluebi_device, mtd);
        lnum = div_u64_rem(from, mtd->erasesize, &offs);
        bytes_left = len;
        while (bytes_left) {
                size_t to_read = mtd->erasesize - offs;

                if (to_read > bytes_left)
                        to_read = bytes_left;

                err = ubi_read(gluebi->desc, lnum, buf, offs, to_read);
                if (err)
                        break;

                lnum += 1;
                offs = 0;
                bytes_left -= to_read;
                buf += to_read;
        }

        *retlen = len - bytes_left;
        return err;
}

/**
 * gluebi_write - write operation of emulated MTD devices.
 * @mtd: MTD device description object
 * @to: absolute offset where to write
 * @len: how many bytes to write
 * @retlen: count of written bytes is returned here
 * @buf: buffer with data to write
 *
 * This function returns zero in case of success and a negative error code in
 * case of failure.
 */
static int gluebi_write(struct mtd_info *mtd, loff_t to, size_t len,
                        size_t *retlen, const u_char *buf)
{
        int err = 0, lnum, offs, bytes_left;
        struct gluebi_device *gluebi;

        gluebi = container_of(mtd, struct gluebi_device, mtd);
        lnum = div_u64_rem(to, mtd->erasesize, &offs);

        if (len % mtd->writesize || offs % mtd->writesize)
                return -EINVAL;

        bytes_left = len;
        while (bytes_left) {
                size_t to_write = mtd->erasesize - offs;

                if (to_write > bytes_left)
                        to_write = bytes_left;

                err = ubi_leb_write(gluebi->desc, lnum, buf, offs, to_write);
                if (err)
                        break;

                lnum += 1;
                offs = 0;
                bytes_left -= to_write;
                buf += to_write;
        }

        *retlen = len - bytes_left;
        return err;
}

/**
 * gluebi_erase - erase operation of emulated MTD devices.
 * @mtd: the MTD device description object
 * @instr: the erase operation description
 *
 * This function calls the erase callback when finishes. Returns zero in case
 * of success and a negative error code in case of failure.
 */
static int gluebi_erase(struct mtd_info *mtd, struct erase_info *instr)
{
        int err, i, lnum, count;
        struct gluebi_device *gluebi;

        if (mtd_mod_by_ws(instr->addr, mtd) || mtd_mod_by_ws(instr->len, mtd))
                return -EINVAL;

        lnum = mtd_div_by_eb(instr->addr, mtd);
        count = mtd_div_by_eb(instr->len, mtd);
        gluebi = container_of(mtd, struct gluebi_device, mtd);

        for (i = 0; i < count - 1; i++) {
                err = ubi_leb_unmap(gluebi->desc, lnum + i);
                if (err)
                        goto out_err;
        }
        /*
         * MTD erase operations are synchronous, so we have to make sure the
         * physical eraseblock is wiped out.
         *
         * Thus, perform leb_erase instead of leb_unmap operation - leb_erase
         * will wait for the end of operations
         */
        err = ubi_leb_erase(gluebi->desc, lnum + i);
        if (err)
                goto out_err;

        return 0;

out_err:
        instr->fail_addr = (long long)lnum * mtd->erasesize;
        return err;
}

/**
 * gluebi_create - create a gluebi device for an UBI volume.
 * @di: UBI device description object
 * @vi: UBI volume description object
 *
 * This function is called when a new UBI volume is created in order to create
 * corresponding fake MTD device. Returns zero in case of success and a
 * negative error code in case of failure.
 */
static int gluebi_create(struct ubi_device_info *di,
                         struct ubi_volume_info *vi)
{
        struct gluebi_device *gluebi, *g;
        struct mtd_info *mtd;

        gluebi = kzalloc_obj(struct gluebi_device);
        if (!gluebi)
                return -ENOMEM;

        mtd = &gluebi->mtd;
        mtd->name = kmemdup(vi->name, vi->name_len + 1, GFP_KERNEL);
        if (!mtd->name) {
                kfree(gluebi);
                return -ENOMEM;
        }

        gluebi->vol_id = vi->vol_id;
        gluebi->ubi_num = vi->ubi_num;
        mtd->type = MTD_UBIVOLUME;
        if (!di->ro_mode)
                mtd->flags = MTD_WRITEABLE;
        mtd->owner      = THIS_MODULE;
        mtd->writesize  = di->min_io_size;
        mtd->erasesize  = vi->usable_leb_size;
        mtd->_read       = gluebi_read;
        mtd->_write      = gluebi_write;
        mtd->_erase      = gluebi_erase;
        mtd->_get_device = gluebi_get_device;
        mtd->_put_device = gluebi_put_device;

        /*
         * In case of dynamic a volume, MTD device size is just volume size. In
         * case of a static volume the size is equivalent to the amount of data
         * bytes.
         */
        if (vi->vol_type == UBI_DYNAMIC_VOLUME)
                mtd->size = (unsigned long long)vi->usable_leb_size * vi->size;
        else
                mtd->size = vi->used_bytes;

        /* Just a sanity check - make sure this gluebi device does not exist */
        mutex_lock(&devices_mutex);
        g = find_gluebi_nolock(vi->ubi_num, vi->vol_id);
        if (g)
                err_msg("gluebi MTD device %d form UBI device %d volume %d already exists",
                        g->mtd.index, vi->ubi_num, vi->vol_id);
        mutex_unlock(&devices_mutex);

        if (mtd_device_register(mtd, NULL, 0)) {
                err_msg("cannot add MTD device");
                kfree(mtd->name);
                kfree(gluebi);
                return -ENFILE;
        }

        mutex_lock(&devices_mutex);
        list_add_tail(&gluebi->list, &gluebi_devices);
        mutex_unlock(&devices_mutex);
        return 0;
}

/**
 * gluebi_remove - remove a gluebi device.
 * @vi: UBI volume description object
 *
 * This function is called when an UBI volume is removed and it removes
 * corresponding fake MTD device. Returns zero in case of success and a
 * negative error code in case of failure.
 */
static int gluebi_remove(struct ubi_volume_info *vi)
{
        int err = 0;
        struct mtd_info *mtd;
        struct gluebi_device *gluebi;

        mutex_lock(&devices_mutex);
        gluebi = find_gluebi_nolock(vi->ubi_num, vi->vol_id);
        if (!gluebi) {
                err_msg("got remove notification for unknown UBI device %d volume %d",
                        vi->ubi_num, vi->vol_id);
                err = -ENOENT;
        } else if (gluebi->refcnt)
                err = -EBUSY;
        else
                list_del(&gluebi->list);
        mutex_unlock(&devices_mutex);
        if (err)
                return err;

        mtd = &gluebi->mtd;
        err = mtd_device_unregister(mtd);
        if (err) {
                err_msg("cannot remove fake MTD device %d, UBI device %d, volume %d, error %d",
                        mtd->index, gluebi->ubi_num, gluebi->vol_id, err);
                mutex_lock(&devices_mutex);
                list_add_tail(&gluebi->list, &gluebi_devices);
                mutex_unlock(&devices_mutex);
                return err;
        }

        kfree(mtd->name);
        kfree(gluebi);
        return 0;
}

/**
 * gluebi_updated - UBI volume was updated notifier.
 * @vi: volume info structure
 *
 * This function is called every time an UBI volume is updated. It does nothing
 * if te volume @vol is dynamic, and changes MTD device size if the
 * volume is static. This is needed because static volumes cannot be read past
 * data they contain. This function returns zero in case of success and a
 * negative error code in case of error.
 */
static int gluebi_updated(struct ubi_volume_info *vi)
{
        struct gluebi_device *gluebi;

        mutex_lock(&devices_mutex);
        gluebi = find_gluebi_nolock(vi->ubi_num, vi->vol_id);
        if (!gluebi) {
                mutex_unlock(&devices_mutex);
                err_msg("got update notification for unknown UBI device %d volume %d",
                        vi->ubi_num, vi->vol_id);
                return -ENOENT;
        }

        if (vi->vol_type == UBI_STATIC_VOLUME)
                gluebi->mtd.size = vi->used_bytes;
        mutex_unlock(&devices_mutex);
        return 0;
}

/**
 * gluebi_resized - UBI volume was re-sized notifier.
 * @vi: volume info structure
 *
 * This function is called every time an UBI volume is re-size. It changes the
 * corresponding fake MTD device size. This function returns zero in case of
 * success and a negative error code in case of error.
 */
static int gluebi_resized(struct ubi_volume_info *vi)
{
        struct gluebi_device *gluebi;

        mutex_lock(&devices_mutex);
        gluebi = find_gluebi_nolock(vi->ubi_num, vi->vol_id);
        if (!gluebi) {
                mutex_unlock(&devices_mutex);
                err_msg("got update notification for unknown UBI device %d volume %d",
                        vi->ubi_num, vi->vol_id);
                return -ENOENT;
        }
        gluebi->mtd.size = vi->used_bytes;
        mutex_unlock(&devices_mutex);
        return 0;
}

/**
 * gluebi_notify - UBI notification handler.
 * @nb: registered notifier block
 * @l: notification type
 * @ns_ptr: pointer to the &struct ubi_notification object
 */
static int gluebi_notify(struct notifier_block *nb, unsigned long l,
                         void *ns_ptr)
{
        struct ubi_notification *nt = ns_ptr;

        switch (l) {
        case UBI_VOLUME_ADDED:
                gluebi_create(&nt->di, &nt->vi);
                break;
        case UBI_VOLUME_REMOVED:
                gluebi_remove(&nt->vi);
                break;
        case UBI_VOLUME_RESIZED:
                gluebi_resized(&nt->vi);
                break;
        case UBI_VOLUME_UPDATED:
                gluebi_updated(&nt->vi);
                break;
        default:
                break;
        }
        return NOTIFY_OK;
}

static struct notifier_block gluebi_notifier = {
        .notifier_call  = gluebi_notify,
};

static int __init ubi_gluebi_init(void)
{
        return ubi_register_volume_notifier(&gluebi_notifier, 0);
}

static void __exit ubi_gluebi_exit(void)
{
        struct gluebi_device *gluebi, *g;

        list_for_each_entry_safe(gluebi, g, &gluebi_devices, list) {
                int err;
                struct mtd_info *mtd = &gluebi->mtd;

                err = mtd_device_unregister(mtd);
                if (err)
                        err_msg("error %d while removing gluebi MTD device %d, UBI device %d, volume %d - ignoring",
                                err, mtd->index, gluebi->ubi_num,
                                gluebi->vol_id);
                kfree(mtd->name);
                kfree(gluebi);
        }
        ubi_unregister_volume_notifier(&gluebi_notifier);
}

module_init(ubi_gluebi_init);
module_exit(ubi_gluebi_exit);
MODULE_DESCRIPTION("MTD emulation layer over UBI volumes");
MODULE_AUTHOR("Artem Bityutskiy, Joern Engel");
MODULE_LICENSE("GPL");