/* 
 * Direct MTD block device access
 *
 * $Id: mtdblock.c,v 1.47 2001/10/02 15:05:11 dwmw2 Exp $
 *
 * 02-nov-2000  Nicolas Pitre           Added read-modify-write with cache
 */

#include <linux/config.h>
#include <linux/types.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/mtd/mtd.h>
#include <linux/mtd/compatmac.h>

#define MAJOR_NR MTD_BLOCK_MAJOR
#define DEVICE_NAME "mtdblock"
#define DEVICE_REQUEST mtdblock_request
#define DEVICE_NR(device) (device)
#define DEVICE_ON(device)
#define DEVICE_OFF(device)
#define DEVICE_NO_RANDOM
#include <linux/blk.h>
/* for old kernels... */
#ifndef QUEUE_EMPTY
#define QUEUE_EMPTY  (!CURRENT)
#endif
#if LINUX_VERSION_CODE < 0x20300
#define QUEUE_PLUGGED (blk_dev[MAJOR_NR].plug_tq.sync)
#else
#define QUEUE_PLUGGED (blk_dev[MAJOR_NR].request_queue.plugged)
#endif

#ifdef CONFIG_DEVFS_FS
#include <linux/devfs_fs_kernel.h>
static void mtd_notify_add(struct mtd_info* mtd);
static void mtd_notify_remove(struct mtd_info* mtd);
static struct mtd_notifier notifier = {
        mtd_notify_add,
        mtd_notify_remove,
        NULL
};
static devfs_handle_t devfs_dir_handle = NULL;
static devfs_handle_t devfs_rw_handle[MAX_MTD_DEVICES];
#endif

static struct mtdblk_dev {
        struct mtd_info *mtd; /* Locked */
        int count;
        struct semaphore cache_sem;
        unsigned char *cache_data;
        unsigned long cache_offset;
        unsigned int cache_size;
        enum { STATE_EMPTY, STATE_CLEAN, STATE_DIRTY } cache_state;
} *mtdblks[MAX_MTD_DEVICES];

static spinlock_t mtdblks_lock;

static int mtd_sizes[MAX_MTD_DEVICES];
static int mtd_blksizes[MAX_MTD_DEVICES];


/*
 * Cache stuff...
 * 
 * Since typical flash erasable sectors are much larger than what Linux's
 * buffer cache can handle, we must implement read-modify-write on flash
 * sectors for each block write requests.  To avoid over-erasing flash sectors
 * and to speed things up, we locally cache a whole flash sector while it is
 * being written to until a different sector is required.
 */

static void erase_callback(struct erase_info *done)
{
        wait_queue_head_t *wait_q = (wait_queue_head_t *)done->priv;
        wake_up(wait_q);
}

static int erase_write (struct mtd_info *mtd, unsigned long pos, 
                        int len, const char *buf)
{
        struct erase_info erase;
        DECLARE_WAITQUEUE(wait, current);
        wait_queue_head_t wait_q;
        size_t retlen;
        int ret;

        /*
         * First, let's erase the flash block.
         */

        init_waitqueue_head(&wait_q);
        erase.mtd = mtd;
        erase.callback = erase_callback;
        erase.addr = pos;
        erase.len = len;
        erase.priv = (u_long)&wait_q;

        set_current_state(TASK_INTERRUPTIBLE);
        add_wait_queue(&wait_q, &wait);

        ret = MTD_ERASE(mtd, &erase);
        if (ret) {
                set_current_state(TASK_RUNNING);
                remove_wait_queue(&wait_q, &wait);
                printk (KERN_WARNING "mtdblock: erase of region [0x%lx, 0x%x] "
                                     "on \"%s\" failed\n",
                        pos, len, mtd->name);
                return ret;
        }

        schedule();  /* Wait for erase to finish. */
        remove_wait_queue(&wait_q, &wait);

        /*
         * Next, writhe data to flash.
         */

        ret = MTD_WRITE (mtd, pos, len, &retlen, buf);
        if (ret)
                return ret;
        if (retlen != len)
                return -EIO;
        return 0;
}


static int write_cached_data (struct mtdblk_dev *mtdblk)
{
        struct mtd_info *mtd = mtdblk->mtd;
        int ret;

        if (mtdblk->cache_state != STATE_DIRTY)
                return 0;

        DEBUG(MTD_DEBUG_LEVEL2, "mtdblock: writing cached data for \"%s\" "
                        "at 0x%lx, size 0x%x\n", mtd->name, 
                        mtdblk->cache_offset, mtdblk->cache_size);
        
        ret = erase_write (mtd, mtdblk->cache_offset, 
                           mtdblk->cache_size, mtdblk->cache_data);
        if (ret)
                return ret;

        /*
         * Here we could argably set the cache state to STATE_CLEAN.
         * However this could lead to inconsistency since we will not 
         * be notified if this content is altered on the flash by other 
         * means.  Let's declare it empty and leave buffering tasks to
         * the buffer cache instead.
         */
        mtdblk->cache_state = STATE_EMPTY;
        return 0;
}


static int do_cached_write (struct mtdblk_dev *mtdblk, unsigned long pos, 
                            int len, const char *buf)
{
        struct mtd_info *mtd = mtdblk->mtd;
        unsigned int sect_size = mtdblk->cache_size;
        size_t retlen;
        int ret;

        DEBUG(MTD_DEBUG_LEVEL2, "mtdblock: write on \"%s\" at 0x%lx, size 0x%x\n",
                mtd->name, pos, len);
        
        if (!sect_size)
                return MTD_WRITE (mtd, pos, len, &retlen, buf);

        while (len > 0) {
                unsigned long sect_start = (pos/sect_size)*sect_size;
                unsigned int offset = pos - sect_start;
                unsigned int size = sect_size - offset;
                if( size > len ) 
                        size = len;

                if (size == sect_size) {
                        /* 
                         * We are covering a whole sector.  Thus there is no
                         * need to bother with the cache while it may still be
                         * useful for other partial writes.
                         */
                        ret = erase_write (mtd, pos, size, buf);
                        if (ret)
                                return ret;
                } else {
                        /* Partial sector: need to use the cache */

                        if (mtdblk->cache_state == STATE_DIRTY &&
                            mtdblk->cache_offset != sect_start) {
                                ret = write_cached_data(mtdblk);
                                if (ret) 
                                        return ret;
                        }

                        if (mtdblk->cache_state == STATE_EMPTY ||
                            mtdblk->cache_offset != sect_start) {
                                /* fill the cache with the current sector */
                                mtdblk->cache_state = STATE_EMPTY;
                                ret = MTD_READ(mtd, sect_start, sect_size, &retlen, mtdblk->cache_data);
                                if (ret)
                                        return ret;
                                if (retlen != sect_size)
                                        return -EIO;

                                mtdblk->cache_offset = sect_start;
                                mtdblk->cache_size = sect_size;
                                mtdblk->cache_state = STATE_CLEAN;
                        }

                        /* write data to our local cache */
                        memcpy (mtdblk->cache_data + offset, buf, size);
                        mtdblk->cache_state = STATE_DIRTY;
                }

                buf += size;
                pos += size;
                len -= size;
        }

        return 0;
}


static int do_cached_read (struct mtdblk_dev *mtdblk, unsigned long pos, 
                           int len, char *buf)
{
        struct mtd_info *mtd = mtdblk->mtd;
        unsigned int sect_size = mtdblk->cache_size;
        size_t retlen;
        int ret;

        DEBUG(MTD_DEBUG_LEVEL2, "mtdblock: read on \"%s\" at 0x%lx, size 0x%x\n", 
                        mtd->name, pos, len);
        
        if (!sect_size)
                return MTD_READ (mtd, pos, len, &retlen, buf);

        while (len > 0) {
                unsigned long sect_start = (pos/sect_size)*sect_size;
                unsigned int offset = pos - sect_start;
                unsigned int size = sect_size - offset;
                if (size > len) 
                        size = len;

                /*
                 * Check if the requested data is already cached
                 * Read the requested amount of data from our internal cache if it
                 * contains what we want, otherwise we read the data directly
                 * from flash.
                 */
                if (mtdblk->cache_state != STATE_EMPTY &&
                    mtdblk->cache_offset == sect_start) {
                        memcpy (buf, mtdblk->cache_data + offset, size);
                } else {
                        ret = MTD_READ (mtd, pos, size, &retlen, buf);
                        if (ret)
                                return ret;
                        if (retlen != size)
                                return -EIO;
                }

                buf += size;
                pos += size;
                len -= size;
        }

        return 0;
}



static int mtdblock_open(struct inode *inode, struct file *file)
{
        struct mtdblk_dev *mtdblk;
        struct mtd_info *mtd;
        int dev;

        DEBUG(MTD_DEBUG_LEVEL1,"mtdblock_open\n");
        
        if (!inode)
                return -EINVAL;
        
        dev = MINOR(inode->i_rdev);
        if (dev >= MAX_MTD_DEVICES)
                return -EINVAL;

        mtd = get_mtd_device(NULL, dev);
        if (!mtd)
                return -ENODEV;
        if (MTD_ABSENT == mtd->type) {
                put_mtd_device(mtd);
                return -ENODEV;
        }
        
        spin_lock(&mtdblks_lock);

        /* If it's already open, no need to piss about. */
        if (mtdblks[dev]) {
                mtdblks[dev]->count++;
                spin_unlock(&mtdblks_lock);
                return 0;
        }
        
        /* OK, it's not open. Try to find it */

        /* First we have to drop the lock, because we have to
           to things which might sleep.
        */
        spin_unlock(&mtdblks_lock);

        mtdblk = kmalloc(sizeof(struct mtdblk_dev), GFP_KERNEL);
        if (!mtdblk) {
                put_mtd_device(mtd);
                return -ENOMEM;
        }
        memset(mtdblk, 0, sizeof(*mtdblk));
        mtdblk->count = 1;
        mtdblk->mtd = mtd;

        init_MUTEX (&mtdblk->cache_sem);
        mtdblk->cache_state = STATE_EMPTY;
        if ((mtdblk->mtd->flags & MTD_CAP_RAM) != MTD_CAP_RAM &&
            mtdblk->mtd->erasesize) {
                mtdblk->cache_size = mtdblk->mtd->erasesize;
                mtdblk->cache_data = vmalloc(mtdblk->mtd->erasesize);
                if (!mtdblk->cache_data) {
                        put_mtd_device(mtdblk->mtd);
                        kfree(mtdblk);
                        return -ENOMEM;
                }
        }

        /* OK, we've created a new one. Add it to the list. */

        spin_lock(&mtdblks_lock);

        if (mtdblks[dev]) {
                /* Another CPU made one at the same time as us. */
                mtdblks[dev]->count++;
                spin_unlock(&mtdblks_lock);
                put_mtd_device(mtdblk->mtd);
                vfree(mtdblk->cache_data);
                kfree(mtdblk);
                return 0;
        }

        mtdblks[dev] = mtdblk;
        mtd_sizes[dev] = mtdblk->mtd->size/1024;
        if (mtdblk->mtd->erasesize)
                mtd_blksizes[dev] = mtdblk->mtd->erasesize;
        if (mtd_blksizes[dev] > PAGE_SIZE)
                mtd_blksizes[dev] = PAGE_SIZE;
        set_device_ro (inode->i_rdev, !(mtdblk->mtd->flags & MTD_WRITEABLE));
        
        spin_unlock(&mtdblks_lock);
        
        DEBUG(MTD_DEBUG_LEVEL1, "ok\n");

        return 0;
}

static release_t mtdblock_release(struct inode *inode, struct file *file)
{
        int dev;
        struct mtdblk_dev *mtdblk;
        DEBUG(MTD_DEBUG_LEVEL1, "mtdblock_release\n");

        if (inode == NULL)
                release_return(-ENODEV);

        invalidate_device(inode->i_rdev, 1);

        dev = MINOR(inode->i_rdev);
        mtdblk = mtdblks[dev];

        down(&mtdblk->cache_sem);
        write_cached_data(mtdblk);
        up(&mtdblk->cache_sem);

        spin_lock(&mtdblks_lock);
        if (!--mtdblk->count) {
                /* It was the last usage. Free the device */
                mtdblks[dev] = NULL;
                spin_unlock(&mtdblks_lock);
                if (mtdblk->mtd->sync)
                        mtdblk->mtd->sync(mtdblk->mtd);
                put_mtd_device(mtdblk->mtd);
                vfree(mtdblk->cache_data);
                kfree(mtdblk);
        } else {
                spin_unlock(&mtdblks_lock);
        }

        DEBUG(MTD_DEBUG_LEVEL1, "ok\n");

        release_return(0);
}  


/* 
 * This is a special request_fn because it is executed in a process context 
 * to be able to sleep independently of the caller.  The io_request_lock 
 * is held upon entry and exit.
 * The head of our request queue is considered active so there is no need 
 * to dequeue requests before we are done.
 */
static void handle_mtdblock_request(void)
{
        struct request *req;
        struct mtdblk_dev *mtdblk;
        unsigned int res;

        for (;;) {
                INIT_REQUEST;
                req = CURRENT;
                spin_unlock_irq(&io_request_lock);
                mtdblk = mtdblks[MINOR(req->rq_dev)];
                res = 0;

                if (MINOR(req->rq_dev) >= MAX_MTD_DEVICES)
                        panic(__FUNCTION__": minor out of bound");

                if ((req->sector + req->current_nr_sectors) > (mtdblk->mtd->size >> 9))
                        goto end_req;

                // Handle the request
                switch (req->cmd)
                {
                        int err;

                        case READ:
                        down(&mtdblk->cache_sem);
                        err = do_cached_read (mtdblk, req->sector << 9, 
                                        req->current_nr_sectors << 9,
                                        req->buffer);
                        up(&mtdblk->cache_sem);
                        if (!err)
                                res = 1;
                        break;

                        case WRITE:
                        // Read only device
                        if ( !(mtdblk->mtd->flags & MTD_WRITEABLE) ) 
                                break;

                        // Do the write
                        down(&mtdblk->cache_sem);
                        err = do_cached_write (mtdblk, req->sector << 9,
                                        req->current_nr_sectors << 9, 
                                        req->buffer);
                        up(&mtdblk->cache_sem);
                        if (!err)
                                res = 1;
                        break;
                }

end_req:
                spin_lock_irq(&io_request_lock);
                end_request(res);
        }
}

static volatile int leaving = 0;
static DECLARE_MUTEX_LOCKED(thread_sem);
static DECLARE_WAIT_QUEUE_HEAD(thr_wq);

int mtdblock_thread(void *dummy)
{
        struct task_struct *tsk = current;
        DECLARE_WAITQUEUE(wait, tsk);

        tsk->session = 1;
        tsk->pgrp = 1;
        /* we might get involved when memory gets low, so use PF_MEMALLOC */
        tsk->flags |= PF_MEMALLOC;
        strcpy(tsk->comm, "mtdblockd");
        tsk->tty = NULL;
        spin_lock_irq(&tsk->sigmask_lock);
        sigfillset(&tsk->blocked);
        recalc_sigpending(tsk);
        spin_unlock_irq(&tsk->sigmask_lock);
        exit_mm(tsk);
        exit_files(tsk);
        exit_sighand(tsk);
        exit_fs(tsk);

        while (!leaving) {
                add_wait_queue(&thr_wq, &wait);
                set_current_state(TASK_INTERRUPTIBLE);
                spin_lock_irq(&io_request_lock);
                if (QUEUE_EMPTY || QUEUE_PLUGGED) {
                        spin_unlock_irq(&io_request_lock);
                        schedule();
                        remove_wait_queue(&thr_wq, &wait); 
                } else {
                        remove_wait_queue(&thr_wq, &wait); 
                        set_current_state(TASK_RUNNING);
                        handle_mtdblock_request();
                        spin_unlock_irq(&io_request_lock);
                }
        }

        up(&thread_sem);
        return 0;
}

#if LINUX_VERSION_CODE < 0x20300
#define RQFUNC_ARG void
#else
#define RQFUNC_ARG request_queue_t *q
#endif

static void mtdblock_request(RQFUNC_ARG)
{
        /* Don't do anything, except wake the thread if necessary */
        wake_up(&thr_wq);
}


static int mtdblock_ioctl(struct inode * inode, struct file * file,
                      unsigned int cmd, unsigned long arg)
{
        struct mtdblk_dev *mtdblk;

        mtdblk = mtdblks[MINOR(inode->i_rdev)];

#ifdef PARANOIA
        if (!mtdblk)
                BUG();
#endif

        switch (cmd) {
        case BLKGETSIZE:   /* Return device size */
                return put_user((mtdblk->mtd->size >> 9), (unsigned long *) arg);
        case BLKGETSIZE64:
                return put_user((u64)mtdblk->mtd->size, (u64 *)arg);
                
        case BLKFLSBUF:
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,2,0)
                if(!capable(CAP_SYS_ADMIN))
                        return -EACCES;
#endif
                fsync_dev(inode->i_rdev);
                invalidate_buffers(inode->i_rdev);
                down(&mtdblk->cache_sem);
                write_cached_data(mtdblk);
                up(&mtdblk->cache_sem);
                if (mtdblk->mtd->sync)
                        mtdblk->mtd->sync(mtdblk->mtd);
                return 0;

        default:
                return -EINVAL;
        }
}

#if LINUX_VERSION_CODE < 0x20326
static struct file_operations mtd_fops =
{
        open: mtdblock_open,
        ioctl: mtdblock_ioctl,
        release: mtdblock_release,
        read: block_read,
        write: block_write
};
#else
static struct block_device_operations mtd_fops = 
{
        owner: THIS_MODULE,
        open: mtdblock_open,
        release: mtdblock_release,
        ioctl: mtdblock_ioctl
};
#endif

#ifdef CONFIG_DEVFS_FS
/* Notification that a new device has been added. Create the devfs entry for
 * it. */

static void mtd_notify_add(struct mtd_info* mtd)
{
        char name[8];

        if (!mtd || mtd->type == MTD_ABSENT)
                return;

        sprintf(name, "%d", mtd->index);
        devfs_rw_handle[mtd->index] = devfs_register(devfs_dir_handle, name,
                        DEVFS_FL_DEFAULT, MTD_BLOCK_MAJOR, mtd->index,
                        S_IFBLK | S_IRUGO | S_IWUGO,
                        &mtd_fops, NULL);
}

static void mtd_notify_remove(struct mtd_info* mtd)
{
        if (!mtd || mtd->type == MTD_ABSENT)
                return;

        devfs_unregister(devfs_rw_handle[mtd->index]);
}
#endif

int __init init_mtdblock(void)
{
        int i;

        spin_lock_init(&mtdblks_lock);
#ifdef CONFIG_DEVFS_FS
        if (devfs_register_blkdev(MTD_BLOCK_MAJOR, DEVICE_NAME, &mtd_fops))
        {
                printk(KERN_NOTICE "Can't allocate major number %d for Memory Technology Devices.\n",
                        MTD_BLOCK_MAJOR);
                return -EAGAIN;
        }

        devfs_dir_handle = devfs_mk_dir(NULL, DEVICE_NAME, NULL);
        register_mtd_user(&notifier);
#else
        if (register_blkdev(MAJOR_NR,DEVICE_NAME,&mtd_fops)) {
                printk(KERN_NOTICE "Can't allocate major number %d for Memory Technology Devices.\n",
                       MTD_BLOCK_MAJOR);
                return -EAGAIN;
        }
#endif
        
        /* We fill it in at open() time. */
        for (i=0; i< MAX_MTD_DEVICES; i++) {
                mtd_sizes[i] = 0;
                mtd_blksizes[i] = BLOCK_SIZE;
        }
        init_waitqueue_head(&thr_wq);
        /* Allow the block size to default to BLOCK_SIZE. */
        blksize_size[MAJOR_NR] = mtd_blksizes;
        blk_size[MAJOR_NR] = mtd_sizes;
        
        blk_init_queue(BLK_DEFAULT_QUEUE(MAJOR_NR), &mtdblock_request);
        kernel_thread (mtdblock_thread, NULL, CLONE_FS|CLONE_FILES|CLONE_SIGHAND);
        return 0;
}

static void __exit cleanup_mtdblock(void)
{
        leaving = 1;
        wake_up(&thr_wq);
        down(&thread_sem);
#ifdef CONFIG_DEVFS_FS
        unregister_mtd_user(&notifier);
        devfs_unregister(devfs_dir_handle);
        devfs_unregister_blkdev(MTD_BLOCK_MAJOR, DEVICE_NAME);
#else
        unregister_blkdev(MAJOR_NR,DEVICE_NAME);
#endif
        blk_cleanup_queue(BLK_DEFAULT_QUEUE(MAJOR_NR));
        blksize_size[MAJOR_NR] = NULL;
        blk_size[MAJOR_NR] = NULL;
}

module_init(init_mtdblock);
module_exit(cleanup_mtdblock);


MODULE_LICENSE("GPL");
MODULE_AUTHOR("Nicolas Pitre <nico@cam.org> et al.");
MODULE_DESCRIPTION("Caching read/erase/writeback block device emulation access to MTD devices");