[PATCH] update max_sectors documentation

[linux-2.6/mini2440.git] / drivers / block / loop.c

/*
 *  linux/drivers/block/loop.c
 *
 *  Written by Theodore Ts'o, 3/29/93
 *
 * Copyright 1993 by Theodore Ts'o.  Redistribution of this file is
 * permitted under the GNU General Public License.
 *
 * DES encryption plus some minor changes by Werner Almesberger, 30-MAY-1993
 * more DES encryption plus IDEA encryption by Nicholas J. Leon, June 20, 1996
 *
 * Modularized and updated for 1.1.16 kernel - Mitch Dsouza 28th May 1994
 * Adapted for 1.3.59 kernel - Andries Brouwer, 1 Feb 1996
 *
 * Fixed do_loop_request() re-entrancy - Vincent.Renardias@waw.com Mar 20, 1997
 *
 * Added devfs support - Richard Gooch <rgooch@atnf.csiro.au> 16-Jan-1998
 *
 * Handle sparse backing files correctly - Kenn Humborg, Jun 28, 1998
 *
 * Loadable modules and other fixes by AK, 1998
 *
 * Make real block number available to downstream transfer functions, enables
 * CBC (and relatives) mode encryption requiring unique IVs per data block.
 * Reed H. Petty, rhp@draper.net
 *
 * Maximum number of loop devices now dynamic via max_loop module parameter.
 * Russell Kroll <rkroll@exploits.org> 19990701
 *
 * Maximum number of loop devices when compiled-in now selectable by passing
 * max_loop=<1-255> to the kernel on boot.
 * Erik I. Bolsø, <eriki@himolde.no>, Oct 31, 1999
 *
 * Completely rewrite request handling to be make_request_fn style and
 * non blocking, pushing work to a helper thread. Lots of fixes from
 * Al Viro too.
 * Jens Axboe <axboe@suse.de>, Nov 2000
 *
 * Support up to 256 loop devices
 * Heinz Mauelshagen <mge@sistina.com>, Feb 2002
 *
 * Support for falling back on the write file operation when the address space
 * operations prepare_write and/or commit_write are not available on the
 * backing filesystem.
 * Anton Altaparmakov, 16 Feb 2005
 *
 * Still To Fix:
 * - Advisory locking is ignored here.
 * - Should use an own CAP_* category instead of CAP_SYS_ADMIN
 *
 */

#include <linux/config.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/stat.h>
#include <linux/errno.h>
#include <linux/major.h>
#include <linux/wait.h>
#include <linux/blkdev.h>
#include <linux/blkpg.h>
#include <linux/init.h>
#include <linux/devfs_fs_kernel.h>
#include <linux/smp_lock.h>
#include <linux/swap.h>
#include <linux/slab.h>
#include <linux/loop.h>
#include <linux/suspend.h>
#include <linux/writeback.h>
#include <linux/buffer_head.h>          /* for invalidate_bdev() */
#include <linux/completion.h>
#include <linux/highmem.h>
#include <linux/gfp.h>

#include <asm/uaccess.h>

static int max_loop = 8;
static struct loop_device *loop_dev;
static struct gendisk **disks;

/*
 * Transfer functions
 */
static int transfer_none(struct loop_device *lo, int cmd,
                         struct page *raw_page, unsigned raw_off,
                         struct page *loop_page, unsigned loop_off,
                         int size, sector_t real_block)
{
        char *raw_buf = kmap_atomic(raw_page, KM_USER0) + raw_off;
        char *loop_buf = kmap_atomic(loop_page, KM_USER1) + loop_off;

        if (cmd == READ)
                memcpy(loop_buf, raw_buf, size);
        else
                memcpy(raw_buf, loop_buf, size);

        kunmap_atomic(raw_buf, KM_USER0);
        kunmap_atomic(loop_buf, KM_USER1);
        cond_resched();
        return 0;
}

static int transfer_xor(struct loop_device *lo, int cmd,
                        struct page *raw_page, unsigned raw_off,
                        struct page *loop_page, unsigned loop_off,
                        int size, sector_t real_block)
{
        char *raw_buf = kmap_atomic(raw_page, KM_USER0) + raw_off;
        char *loop_buf = kmap_atomic(loop_page, KM_USER1) + loop_off;
        char *in, *out, *key;
        int i, keysize;

        if (cmd == READ) {
                in = raw_buf;
                out = loop_buf;
        } else {
                in = loop_buf;
                out = raw_buf;
        }

        key = lo->lo_encrypt_key;
        keysize = lo->lo_encrypt_key_size;
        for (i = 0; i < size; i++)
                *out++ = *in++ ^ key[(i & 511) % keysize];

        kunmap_atomic(raw_buf, KM_USER0);
        kunmap_atomic(loop_buf, KM_USER1);
        cond_resched();
        return 0;
}

static int xor_init(struct loop_device *lo, const struct loop_info64 *info)
{
        if (unlikely(info->lo_encrypt_key_size <= 0))
                return -EINVAL;
        return 0;
}

static struct loop_func_table none_funcs = {
        .number = LO_CRYPT_NONE,
        .transfer = transfer_none,
};      

static struct loop_func_table xor_funcs = {
        .number = LO_CRYPT_XOR,
        .transfer = transfer_xor,
        .init = xor_init
};      

/* xfer_funcs[0] is special - its release function is never called */
static struct loop_func_table *xfer_funcs[MAX_LO_CRYPT] = {
        &none_funcs,
        &xor_funcs
};

static loff_t get_loop_size(struct loop_device *lo, struct file *file)
{
        loff_t size, offset, loopsize;

        /* Compute loopsize in bytes */
        size = i_size_read(file->f_mapping->host);
        offset = lo->lo_offset;
        loopsize = size - offset;
        if (lo->lo_sizelimit > 0 && lo->lo_sizelimit < loopsize)
                loopsize = lo->lo_sizelimit;

        /*
         * Unfortunately, if we want to do I/O on the device,
         * the number of 512-byte sectors has to fit into a sector_t.
         */
        return loopsize >> 9;
}

static int
figure_loop_size(struct loop_device *lo)
{
        loff_t size = get_loop_size(lo, lo->lo_backing_file);
        sector_t x = (sector_t)size;

        if (unlikely((loff_t)x != size))
                return -EFBIG;

        set_capacity(disks[lo->lo_number], x);
        return 0;                                       
}

static inline int
lo_do_transfer(struct loop_device *lo, int cmd,
               struct page *rpage, unsigned roffs,
               struct page *lpage, unsigned loffs,
               int size, sector_t rblock)
{
        if (unlikely(!lo->transfer))
                return 0;

        return lo->transfer(lo, cmd, rpage, roffs, lpage, loffs, size, rblock);
}

/**
 * do_lo_send_aops - helper for writing data to a loop device
 *
 * This is the fast version for backing filesystems which implement the address
 * space operations prepare_write and commit_write.
 */
static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec,
                int bsize, loff_t pos, struct page *page)
{
        struct file *file = lo->lo_backing_file; /* kudos to NFsckingS */
        struct address_space *mapping = file->f_mapping;
        struct address_space_operations *aops = mapping->a_ops;
        pgoff_t index;
        unsigned offset, bv_offs;
        int len, ret;

        mutex_lock(&mapping->host->i_mutex);
        index = pos >> PAGE_CACHE_SHIFT;
        offset = pos & ((pgoff_t)PAGE_CACHE_SIZE - 1);
        bv_offs = bvec->bv_offset;
        len = bvec->bv_len;
        while (len > 0) {
                sector_t IV;
                unsigned size;
                int transfer_result;

                IV = ((sector_t)index << (PAGE_CACHE_SHIFT - 9))+(offset >> 9);
                size = PAGE_CACHE_SIZE - offset;
                if (size > len)
                        size = len;
                page = grab_cache_page(mapping, index);
                if (unlikely(!page))
                        goto fail;
                ret = aops->prepare_write(file, page, offset,
                                          offset + size);
                if (unlikely(ret)) {
                        if (ret == AOP_TRUNCATED_PAGE) {
                                page_cache_release(page);
                                continue;
                        }
                        goto unlock;
                }
                transfer_result = lo_do_transfer(lo, WRITE, page, offset,
                                bvec->bv_page, bv_offs, size, IV);
                if (unlikely(transfer_result)) {
                        char *kaddr;

                        /*
                         * The transfer failed, but we still write the data to
                         * keep prepare/commit calls balanced.
                         */
                        printk(KERN_ERR "loop: transfer error block %llu\n",
                               (unsigned long long)index);
                        kaddr = kmap_atomic(page, KM_USER0);
                        memset(kaddr + offset, 0, size);
                        kunmap_atomic(kaddr, KM_USER0);
                }
                flush_dcache_page(page);
                ret = aops->commit_write(file, page, offset,
                                         offset + size);
                if (unlikely(ret)) {
                        if (ret == AOP_TRUNCATED_PAGE) {
                                page_cache_release(page);
                                continue;
                        }
                        goto unlock;
                }
                if (unlikely(transfer_result))
                        goto unlock;
                bv_offs += size;
                len -= size;
                offset = 0;
                index++;
                pos += size;
                unlock_page(page);
                page_cache_release(page);
        }
        ret = 0;
out:
        mutex_unlock(&mapping->host->i_mutex);
        return ret;
unlock:
        unlock_page(page);
        page_cache_release(page);
fail:
        ret = -1;
        goto out;
}

/**
 * __do_lo_send_write - helper for writing data to a loop device
 *
 * This helper just factors out common code between do_lo_send_direct_write()
 * and do_lo_send_write().
 */
static int __do_lo_send_write(struct file *file,
                u8 __user *buf, const int len, loff_t pos)
{
        ssize_t bw;
        mm_segment_t old_fs = get_fs();

        set_fs(get_ds());
        bw = file->f_op->write(file, buf, len, &pos);
        set_fs(old_fs);
        if (likely(bw == len))
                return 0;
        printk(KERN_ERR "loop: Write error at byte offset %llu, length %i.\n",
                        (unsigned long long)pos, len);
        if (bw >= 0)
                bw = -EIO;
        return bw;
}

/**
 * do_lo_send_direct_write - helper for writing data to a loop device
 *
 * This is the fast, non-transforming version for backing filesystems which do
 * not implement the address space operations prepare_write and commit_write.
 * It uses the write file operation which should be present on all writeable
 * filesystems.
 */
static int do_lo_send_direct_write(struct loop_device *lo,
                struct bio_vec *bvec, int bsize, loff_t pos, struct page *page)
{
        ssize_t bw = __do_lo_send_write(lo->lo_backing_file,
                        (u8 __user *)kmap(bvec->bv_page) + bvec->bv_offset,
                        bvec->bv_len, pos);
        kunmap(bvec->bv_page);
        cond_resched();
        return bw;
}

/**
 * do_lo_send_write - helper for writing data to a loop device
 *
 * This is the slow, transforming version for filesystems which do not
 * implement the address space operations prepare_write and commit_write.  It
 * uses the write file operation which should be present on all writeable
 * filesystems.
 *
 * Using fops->write is slower than using aops->{prepare,commit}_write in the
 * transforming case because we need to double buffer the data as we cannot do
 * the transformations in place as we do not have direct access to the
 * destination pages of the backing file.
 */
static int do_lo_send_write(struct loop_device *lo, struct bio_vec *bvec,
                int bsize, loff_t pos, struct page *page)
{
        int ret = lo_do_transfer(lo, WRITE, page, 0, bvec->bv_page,
                        bvec->bv_offset, bvec->bv_len, pos >> 9);
        if (likely(!ret))
                return __do_lo_send_write(lo->lo_backing_file,
                                (u8 __user *)page_address(page), bvec->bv_len,
                                pos);
        printk(KERN_ERR "loop: Transfer error at byte offset %llu, "
                        "length %i.\n", (unsigned long long)pos, bvec->bv_len);
        if (ret > 0)
                ret = -EIO;
        return ret;
}

static int lo_send(struct loop_device *lo, struct bio *bio, int bsize,
                loff_t pos)
{
        int (*do_lo_send)(struct loop_device *, struct bio_vec *, int, loff_t,
                        struct page *page);
        struct bio_vec *bvec;
        struct page *page = NULL;
        int i, ret = 0;

        do_lo_send = do_lo_send_aops;
        if (!(lo->lo_flags & LO_FLAGS_USE_AOPS)) {
                do_lo_send = do_lo_send_direct_write;
                if (lo->transfer != transfer_none) {
                        page = alloc_page(GFP_NOIO | __GFP_HIGHMEM);
                        if (unlikely(!page))
                                goto fail;
                        kmap(page);
                        do_lo_send = do_lo_send_write;
                }
        }
        bio_for_each_segment(bvec, bio, i) {
                ret = do_lo_send(lo, bvec, bsize, pos, page);
                if (ret < 0)
                        break;
                pos += bvec->bv_len;
        }
        if (page) {
                kunmap(page);
                __free_page(page);
        }
out:
        return ret;
fail:
        printk(KERN_ERR "loop: Failed to allocate temporary page for write.\n");
        ret = -ENOMEM;
        goto out;
}

struct lo_read_data {
        struct loop_device *lo;
        struct page *page;
        unsigned offset;
        int bsize;
};

static int
lo_read_actor(read_descriptor_t *desc, struct page *page,
              unsigned long offset, unsigned long size)
{
        unsigned long count = desc->count;
        struct lo_read_data *p = desc->arg.data;
        struct loop_device *lo = p->lo;
        sector_t IV;

        IV = ((sector_t) page->index << (PAGE_CACHE_SHIFT - 9))+(offset >> 9);

        if (size > count)
                size = count;

        if (lo_do_transfer(lo, READ, page, offset, p->page, p->offset, size, IV)) {
                size = 0;
                printk(KERN_ERR "loop: transfer error block %ld\n",
                       page->index);
                desc->error = -EINVAL;
        }

        flush_dcache_page(p->page);

        desc->count = count - size;
        desc->written += size;
        p->offset += size;
        return size;
}

static int
do_lo_receive(struct loop_device *lo,
              struct bio_vec *bvec, int bsize, loff_t pos)
{
        struct lo_read_data cookie;
        struct file *file;
        int retval;

        cookie.lo = lo;
        cookie.page = bvec->bv_page;
        cookie.offset = bvec->bv_offset;
        cookie.bsize = bsize;
        file = lo->lo_backing_file;
        retval = file->f_op->sendfile(file, &pos, bvec->bv_len,
                        lo_read_actor, &cookie);
        return (retval < 0)? retval: 0;
}

static int
lo_receive(struct loop_device *lo, struct bio *bio, int bsize, loff_t pos)
{
        struct bio_vec *bvec;
        int i, ret = 0;

        bio_for_each_segment(bvec, bio, i) {
                ret = do_lo_receive(lo, bvec, bsize, pos);
                if (ret < 0)
                        break;
                pos += bvec->bv_len;
        }
        return ret;
}

static int do_bio_filebacked(struct loop_device *lo, struct bio *bio)
{
        loff_t pos;
        int ret;

        pos = ((loff_t) bio->bi_sector << 9) + lo->lo_offset;
        if (bio_rw(bio) == WRITE)
                ret = lo_send(lo, bio, lo->lo_blocksize, pos);
        else
                ret = lo_receive(lo, bio, lo->lo_blocksize, pos);
        return ret;
}

/*
 * Add bio to back of pending list
 */
static void loop_add_bio(struct loop_device *lo, struct bio *bio)
{
        if (lo->lo_biotail) {
                lo->lo_biotail->bi_next = bio;
                lo->lo_biotail = bio;
        } else
                lo->lo_bio = lo->lo_biotail = bio;
}

/*
 * Grab first pending buffer
 */
static struct bio *loop_get_bio(struct loop_device *lo)
{
        struct bio *bio;

        if ((bio = lo->lo_bio)) {
                if (bio == lo->lo_biotail)
                        lo->lo_biotail = NULL;
                lo->lo_bio = bio->bi_next;
                bio->bi_next = NULL;
        }

        return bio;
}

static int loop_make_request(request_queue_t *q, struct bio *old_bio)
{
        struct loop_device *lo = q->queuedata;
        int rw = bio_rw(old_bio);

        if (rw == READA)
                rw = READ;

        BUG_ON(!lo || (rw != READ && rw != WRITE));

        spin_lock_irq(&lo->lo_lock);
        if (lo->lo_state != Lo_bound)
                goto out;
        if (unlikely(rw == WRITE && (lo->lo_flags & LO_FLAGS_READ_ONLY)))
                goto out;
        lo->lo_pending++;
        loop_add_bio(lo, old_bio);
        spin_unlock_irq(&lo->lo_lock);
        complete(&lo->lo_bh_done);
        return 0;

out:
        if (lo->lo_pending == 0)
                complete(&lo->lo_bh_done);
        spin_unlock_irq(&lo->lo_lock);
        bio_io_error(old_bio, old_bio->bi_size);
        return 0;
}

/*
 * kick off io on the underlying address space
 */
static void loop_unplug(request_queue_t *q)
{
        struct loop_device *lo = q->queuedata;

        clear_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags);
        blk_run_address_space(lo->lo_backing_file->f_mapping);
}

struct switch_request {
        struct file *file;
        struct completion wait;
};

static void do_loop_switch(struct loop_device *, struct switch_request *);

static inline void loop_handle_bio(struct loop_device *lo, struct bio *bio)
{
        if (unlikely(!bio->bi_bdev)) {
                do_loop_switch(lo, bio->bi_private);
                bio_put(bio);
        } else {
                int ret = do_bio_filebacked(lo, bio);
                bio_endio(bio, bio->bi_size, ret);
        }
}

/*
 * worker thread that handles reads/writes to file backed loop devices,
 * to avoid blocking in our make_request_fn. it also does loop decrypting
 * on reads for block backed loop, as that is too heavy to do from
 * b_end_io context where irqs may be disabled.
 */
static int loop_thread(void *data)
{
        struct loop_device *lo = data;
        struct bio *bio;

        daemonize("loop%d", lo->lo_number);

        /*
         * loop can be used in an encrypted device,
         * hence, it mustn't be stopped at all
         * because it could be indirectly used during suspension
         */
        current->flags |= PF_NOFREEZE;

        set_user_nice(current, -20);

        lo->lo_state = Lo_bound;
        lo->lo_pending = 1;

        /*
         * complete it, we are running
         */
        complete(&lo->lo_done);

        for (;;) {
                int pending;

                if (wait_for_completion_interruptible(&lo->lo_bh_done))
                        continue;

                spin_lock_irq(&lo->lo_lock);

                /*
                 * could be completed because of tear-down, not pending work
                 */
                if (unlikely(!lo->lo_pending)) {
                        spin_unlock_irq(&lo->lo_lock);
                        break;
                }

                bio = loop_get_bio(lo);
                lo->lo_pending--;
                pending = lo->lo_pending;
                spin_unlock_irq(&lo->lo_lock);

                BUG_ON(!bio);
                loop_handle_bio(lo, bio);

                /*
                 * upped both for pending work and tear-down, lo_pending
                 * will hit zero then
                 */
                if (unlikely(!pending))
                        break;
        }

        complete(&lo->lo_done);
        return 0;
}

/*
 * loop_switch performs the hard work of switching a backing store.
 * First it needs to flush existing IO, it does this by sending a magic
 * BIO down the pipe. The completion of this BIO does the actual switch.
 */
static int loop_switch(struct loop_device *lo, struct file *file)
{
        struct switch_request w;
        struct bio *bio = bio_alloc(GFP_KERNEL, 1);
        if (!bio)
                return -ENOMEM;
        init_completion(&w.wait);
        w.file = file;
        bio->bi_private = &w;
        bio->bi_bdev = NULL;
        loop_make_request(lo->lo_queue, bio);
        wait_for_completion(&w.wait);
        return 0;
}

/*
 * Do the actual switch; called from the BIO completion routine
 */
static void do_loop_switch(struct loop_device *lo, struct switch_request *p)
{
        struct file *file = p->file;
        struct file *old_file = lo->lo_backing_file;
        struct address_space *mapping = file->f_mapping;

        mapping_set_gfp_mask(old_file->f_mapping, lo->old_gfp_mask);
        lo->lo_backing_file = file;
        lo->lo_blocksize = mapping->host->i_blksize;
        lo->old_gfp_mask = mapping_gfp_mask(mapping);
        mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));
        complete(&p->wait);
}


/*
 * loop_change_fd switched the backing store of a loopback device to
 * a new file. This is useful for operating system installers to free up
 * the original file and in High Availability environments to switch to
 * an alternative location for the content in case of server meltdown.
 * This can only work if the loop device is used read-only, and if the
 * new backing store is the same size and type as the old backing store.
 */
static int loop_change_fd(struct loop_device *lo, struct file *lo_file,
                       struct block_device *bdev, unsigned int arg)
{
        struct file     *file, *old_file;
        struct inode    *inode;
        int             error;

        error = -ENXIO;
        if (lo->lo_state != Lo_bound)
                goto out;

        /* the loop device has to be read-only */
        error = -EINVAL;
        if (!(lo->lo_flags & LO_FLAGS_READ_ONLY))
                goto out;

        error = -EBADF;
        file = fget(arg);
        if (!file)
                goto out;

        inode = file->f_mapping->host;
        old_file = lo->lo_backing_file;

        error = -EINVAL;

        if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode))
                goto out_putf;

        /* new backing store needs to support loop (eg sendfile) */
        if (!inode->i_fop->sendfile)
                goto out_putf;

        /* size of the new backing store needs to be the same */
        if (get_loop_size(lo, file) != get_loop_size(lo, old_file))
                goto out_putf;

        /* and ... switch */
        error = loop_switch(lo, file);
        if (error)
                goto out_putf;

        fput(old_file);
        return 0;

 out_putf:
        fput(file);
 out:
        return error;
}

static inline int is_loop_device(struct file *file)
{
        struct inode *i = file->f_mapping->host;

        return i && S_ISBLK(i->i_mode) && MAJOR(i->i_rdev) == LOOP_MAJOR;
}

static int loop_set_fd(struct loop_device *lo, struct file *lo_file,
                       struct block_device *bdev, unsigned int arg)
{
        struct file     *file, *f;
        struct inode    *inode;
        struct address_space *mapping;
        unsigned lo_blocksize;
        int             lo_flags = 0;
        int             error;
        loff_t          size;

        /* This is safe, since we have a reference from open(). */
        __module_get(THIS_MODULE);

        error = -EBADF;
        file = fget(arg);
        if (!file)
                goto out;

        error = -EBUSY;
        if (lo->lo_state != Lo_unbound)
                goto out_putf;

        /* Avoid recursion */
        f = file;
        while (is_loop_device(f)) {
                struct loop_device *l;

                if (f->f_mapping->host->i_rdev == lo_file->f_mapping->host->i_rdev)
                        goto out_putf;

                l = f->f_mapping->host->i_bdev->bd_disk->private_data;
                if (l->lo_state == Lo_unbound) {
                        error = -EINVAL;
                        goto out_putf;
                }
                f = l->lo_backing_file;
        }

        mapping = file->f_mapping;
        inode = mapping->host;

        if (!(file->f_mode & FMODE_WRITE))
                lo_flags |= LO_FLAGS_READ_ONLY;

        error = -EINVAL;
        if (S_ISREG(inode->i_mode) || S_ISBLK(inode->i_mode)) {
                struct address_space_operations *aops = mapping->a_ops;
                /*
                 * If we can't read - sorry. If we only can't write - well,
                 * it's going to be read-only.
                 */
                if (!file->f_op->sendfile)
                        goto out_putf;
                if (aops->prepare_write && aops->commit_write)
                        lo_flags |= LO_FLAGS_USE_AOPS;
                if (!(lo_flags & LO_FLAGS_USE_AOPS) && !file->f_op->write)
                        lo_flags |= LO_FLAGS_READ_ONLY;

                lo_blocksize = inode->i_blksize;
                error = 0;
        } else {
                goto out_putf;
        }

        size = get_loop_size(lo, file);

        if ((loff_t)(sector_t)size != size) {
                error = -EFBIG;
                goto out_putf;
        }

        if (!(lo_file->f_mode & FMODE_WRITE))
                lo_flags |= LO_FLAGS_READ_ONLY;

        set_device_ro(bdev, (lo_flags & LO_FLAGS_READ_ONLY) != 0);

        lo->lo_blocksize = lo_blocksize;
        lo->lo_device = bdev;
        lo->lo_flags = lo_flags;
        lo->lo_backing_file = file;
        lo->transfer = NULL;
        lo->ioctl = NULL;
        lo->lo_sizelimit = 0;
        lo->old_gfp_mask = mapping_gfp_mask(mapping);
        mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));

        lo->lo_bio = lo->lo_biotail = NULL;

        /*
         * set queue make_request_fn, and add limits based on lower level
         * device
         */
        blk_queue_make_request(lo->lo_queue, loop_make_request);
        lo->lo_queue->queuedata = lo;
        lo->lo_queue->unplug_fn = loop_unplug;

        set_capacity(disks[lo->lo_number], size);
        bd_set_size(bdev, size << 9);

        set_blocksize(bdev, lo_blocksize);

        error = kernel_thread(loop_thread, lo, CLONE_KERNEL);
        if (error < 0)
                goto out_putf;
        wait_for_completion(&lo->lo_done);
        return 0;

 out_putf:
        fput(file);
 out:
        /* This is safe: open() is still holding a reference. */
        module_put(THIS_MODULE);
        return error;
}

static int
loop_release_xfer(struct loop_device *lo)
{
        int err = 0;
        struct loop_func_table *xfer = lo->lo_encryption;

        if (xfer) {
                if (xfer->release)
                        err = xfer->release(lo);
                lo->transfer = NULL;
                lo->lo_encryption = NULL;
                module_put(xfer->owner);
        }
        return err;
}

static int
loop_init_xfer(struct loop_device *lo, struct loop_func_table *xfer,
               const struct loop_info64 *i)
{
        int err = 0;

        if (xfer) {
                struct module *owner = xfer->owner;

                if (!try_module_get(owner))
                        return -EINVAL;
                if (xfer->init)
                        err = xfer->init(lo, i);
                if (err)
                        module_put(owner);
                else
                        lo->lo_encryption = xfer;
        }
        return err;
}

static int loop_clr_fd(struct loop_device *lo, struct block_device *bdev)
{
        struct file *filp = lo->lo_backing_file;
        gfp_t gfp = lo->old_gfp_mask;

        if (lo->lo_state != Lo_bound)
                return -ENXIO;

        if (lo->lo_refcnt > 1)  /* we needed one fd for the ioctl */
                return -EBUSY;

        if (filp == NULL)
                return -EINVAL;

        spin_lock_irq(&lo->lo_lock);
        lo->lo_state = Lo_rundown;
        lo->lo_pending--;
        if (!lo->lo_pending)
                complete(&lo->lo_bh_done);
        spin_unlock_irq(&lo->lo_lock);

        wait_for_completion(&lo->lo_done);

        lo->lo_backing_file = NULL;

        loop_release_xfer(lo);
        lo->transfer = NULL;
        lo->ioctl = NULL;
        lo->lo_device = NULL;
        lo->lo_encryption = NULL;
        lo->lo_offset = 0;
        lo->lo_sizelimit = 0;
        lo->lo_encrypt_key_size = 0;
        lo->lo_flags = 0;
        memset(lo->lo_encrypt_key, 0, LO_KEY_SIZE);
        memset(lo->lo_crypt_name, 0, LO_NAME_SIZE);
        memset(lo->lo_file_name, 0, LO_NAME_SIZE);
        invalidate_bdev(bdev, 0);
        set_capacity(disks[lo->lo_number], 0);
        bd_set_size(bdev, 0);
        mapping_set_gfp_mask(filp->f_mapping, gfp);
        lo->lo_state = Lo_unbound;
        fput(filp);
        /* This is safe: open() is still holding a reference. */
        module_put(THIS_MODULE);
        return 0;
}

static int
loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
{
        int err;
        struct loop_func_table *xfer;

        if (lo->lo_encrypt_key_size && lo->lo_key_owner != current->uid &&
            !capable(CAP_SYS_ADMIN))
                return -EPERM;
        if (lo->lo_state != Lo_bound)
                return -ENXIO;
        if ((unsigned int) info->lo_encrypt_key_size > LO_KEY_SIZE)
                return -EINVAL;

        err = loop_release_xfer(lo);
        if (err)
                return err;

        if (info->lo_encrypt_type) {
                unsigned int type = info->lo_encrypt_type;

                if (type >= MAX_LO_CRYPT)
                        return -EINVAL;
                xfer = xfer_funcs[type];
                if (xfer == NULL)
                        return -EINVAL;
        } else
                xfer = NULL;

        err = loop_init_xfer(lo, xfer, info);
        if (err)
                return err;

        if (lo->lo_offset != info->lo_offset ||
            lo->lo_sizelimit != info->lo_sizelimit) {
                lo->lo_offset = info->lo_offset;
                lo->lo_sizelimit = info->lo_sizelimit;
                if (figure_loop_size(lo))
                        return -EFBIG;
        }

        memcpy(lo->lo_file_name, info->lo_file_name, LO_NAME_SIZE);
        memcpy(lo->lo_crypt_name, info->lo_crypt_name, LO_NAME_SIZE);
        lo->lo_file_name[LO_NAME_SIZE-1] = 0;
        lo->lo_crypt_name[LO_NAME_SIZE-1] = 0;

        if (!xfer)
                xfer = &none_funcs;
        lo->transfer = xfer->transfer;
        lo->ioctl = xfer->ioctl;

        lo->lo_encrypt_key_size = info->lo_encrypt_key_size;
        lo->lo_init[0] = info->lo_init[0];
        lo->lo_init[1] = info->lo_init[1];
        if (info->lo_encrypt_key_size) {
                memcpy(lo->lo_encrypt_key, info->lo_encrypt_key,
                       info->lo_encrypt_key_size);
                lo->lo_key_owner = current->uid;
        }       

        return 0;
}

static int
loop_get_status(struct loop_device *lo, struct loop_info64 *info)
{
        struct file *file = lo->lo_backing_file;
        struct kstat stat;
        int error;

        if (lo->lo_state != Lo_bound)
                return -ENXIO;
        error = vfs_getattr(file->f_vfsmnt, file->f_dentry, &stat);
        if (error)
                return error;
        memset(info, 0, sizeof(*info));
        info->lo_number = lo->lo_number;
        info->lo_device = huge_encode_dev(stat.dev);
        info->lo_inode = stat.ino;
        info->lo_rdevice = huge_encode_dev(lo->lo_device ? stat.rdev : stat.dev);
        info->lo_offset = lo->lo_offset;
        info->lo_sizelimit = lo->lo_sizelimit;
        info->lo_flags = lo->lo_flags;
        memcpy(info->lo_file_name, lo->lo_file_name, LO_NAME_SIZE);
        memcpy(info->lo_crypt_name, lo->lo_crypt_name, LO_NAME_SIZE);
        info->lo_encrypt_type =
                lo->lo_encryption ? lo->lo_encryption->number : 0;
        if (lo->lo_encrypt_key_size && capable(CAP_SYS_ADMIN)) {
                info->lo_encrypt_key_size = lo->lo_encrypt_key_size;
                memcpy(info->lo_encrypt_key, lo->lo_encrypt_key,
                       lo->lo_encrypt_key_size);
        }
        return 0;
}

static void
loop_info64_from_old(const struct loop_info *info, struct loop_info64 *info64)
{
        memset(info64, 0, sizeof(*info64));
        info64->lo_number = info->lo_number;
        info64->lo_device = info->lo_device;
        info64->lo_inode = info->lo_inode;
        info64->lo_rdevice = info->lo_rdevice;
        info64->lo_offset = info->lo_offset;
        info64->lo_sizelimit = 0;
        info64->lo_encrypt_type = info->lo_encrypt_type;
        info64->lo_encrypt_key_size = info->lo_encrypt_key_size;
        info64->lo_flags = info->lo_flags;
        info64->lo_init[0] = info->lo_init[0];
        info64->lo_init[1] = info->lo_init[1];
        if (info->lo_encrypt_type == LO_CRYPT_CRYPTOAPI)
                memcpy(info64->lo_crypt_name, info->lo_name, LO_NAME_SIZE);
        else
                memcpy(info64->lo_file_name, info->lo_name, LO_NAME_SIZE);
        memcpy(info64->lo_encrypt_key, info->lo_encrypt_key, LO_KEY_SIZE);
}

static int
loop_info64_to_old(const struct loop_info64 *info64, struct loop_info *info)
{
        memset(info, 0, sizeof(*info));
        info->lo_number = info64->lo_number;
        info->lo_device = info64->lo_device;
        info->lo_inode = info64->lo_inode;
        info->lo_rdevice = info64->lo_rdevice;
        info->lo_offset = info64->lo_offset;
        info->lo_encrypt_type = info64->lo_encrypt_type;
        info->lo_encrypt_key_size = info64->lo_encrypt_key_size;
        info->lo_flags = info64->lo_flags;
        info->lo_init[0] = info64->lo_init[0];
        info->lo_init[1] = info64->lo_init[1];
        if (info->lo_encrypt_type == LO_CRYPT_CRYPTOAPI)
                memcpy(info->lo_name, info64->lo_crypt_name, LO_NAME_SIZE);
        else
                memcpy(info->lo_name, info64->lo_file_name, LO_NAME_SIZE);
        memcpy(info->lo_encrypt_key, info64->lo_encrypt_key, LO_KEY_SIZE);

        /* error in case values were truncated */
        if (info->lo_device != info64->lo_device ||
            info->lo_rdevice != info64->lo_rdevice ||
            info->lo_inode != info64->lo_inode ||
            info->lo_offset != info64->lo_offset)
                return -EOVERFLOW;

        return 0;
}

static int
loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg)
{
        struct loop_info info;
        struct loop_info64 info64;

        if (copy_from_user(&info, arg, sizeof (struct loop_info)))
                return -EFAULT;
        loop_info64_from_old(&info, &info64);
        return loop_set_status(lo, &info64);
}

static int
loop_set_status64(struct loop_device *lo, const struct loop_info64 __user *arg)
{
        struct loop_info64 info64;

        if (copy_from_user(&info64, arg, sizeof (struct loop_info64)))
                return -EFAULT;
        return loop_set_status(lo, &info64);
}

static int
loop_get_status_old(struct loop_device *lo, struct loop_info __user *arg) {
        struct loop_info info;
        struct loop_info64 info64;
        int err = 0;

        if (!arg)
                err = -EINVAL;
        if (!err)
                err = loop_get_status(lo, &info64);
        if (!err)
                err = loop_info64_to_old(&info64, &info);
        if (!err && copy_to_user(arg, &info, sizeof(info)))
                err = -EFAULT;

        return err;
}

static int
loop_get_status64(struct loop_device *lo, struct loop_info64 __user *arg) {
        struct loop_info64 info64;
        int err = 0;

        if (!arg)
                err = -EINVAL;
        if (!err)
                err = loop_get_status(lo, &info64);
        if (!err && copy_to_user(arg, &info64, sizeof(info64)))
                err = -EFAULT;

        return err;
}

static int lo_ioctl(struct inode * inode, struct file * file,
        unsigned int cmd, unsigned long arg)
{
        struct loop_device *lo = inode->i_bdev->bd_disk->private_data;
        int err;

        mutex_lock(&lo->lo_ctl_mutex);
        switch (cmd) {
        case LOOP_SET_FD:
                err = loop_set_fd(lo, file, inode->i_bdev, arg);
                break;
        case LOOP_CHANGE_FD:
                err = loop_change_fd(lo, file, inode->i_bdev, arg);
                break;
        case LOOP_CLR_FD:
                err = loop_clr_fd(lo, inode->i_bdev);
                break;
        case LOOP_SET_STATUS:
                err = loop_set_status_old(lo, (struct loop_info __user *) arg);
                break;
        case LOOP_GET_STATUS:
                err = loop_get_status_old(lo, (struct loop_info __user *) arg);
                break;
        case LOOP_SET_STATUS64:
                err = loop_set_status64(lo, (struct loop_info64 __user *) arg);
                break;
        case LOOP_GET_STATUS64:
                err = loop_get_status64(lo, (struct loop_info64 __user *) arg);
                break;
        default:
                err = lo->ioctl ? lo->ioctl(lo, cmd, arg) : -EINVAL;
        }
        mutex_unlock(&lo->lo_ctl_mutex);
        return err;
}

static int lo_open(struct inode *inode, struct file *file)
{
        struct loop_device *lo = inode->i_bdev->bd_disk->private_data;

        mutex_lock(&lo->lo_ctl_mutex);
        lo->lo_refcnt++;
        mutex_unlock(&lo->lo_ctl_mutex);

        return 0;
}

static int lo_release(struct inode *inode, struct file *file)
{
        struct loop_device *lo = inode->i_bdev->bd_disk->private_data;

        mutex_lock(&lo->lo_ctl_mutex);
        --lo->lo_refcnt;
        mutex_unlock(&lo->lo_ctl_mutex);

        return 0;
}

static struct block_device_operations lo_fops = {
        .owner =        THIS_MODULE,
        .open =         lo_open,
        .release =      lo_release,
        .ioctl =        lo_ioctl,
};

/*
 * And now the modules code and kernel interface.
 */
module_param(max_loop, int, 0);
MODULE_PARM_DESC(max_loop, "Maximum number of loop devices (1-256)");
MODULE_LICENSE("GPL");
MODULE_ALIAS_BLOCKDEV_MAJOR(LOOP_MAJOR);

int loop_register_transfer(struct loop_func_table *funcs)
{
        unsigned int n = funcs->number;

        if (n >= MAX_LO_CRYPT || xfer_funcs[n])
                return -EINVAL;
        xfer_funcs[n] = funcs;
        return 0;
}

int loop_unregister_transfer(int number)
{
        unsigned int n = number;
        struct loop_device *lo;
        struct loop_func_table *xfer;

        if (n == 0 || n >= MAX_LO_CRYPT || (xfer = xfer_funcs[n]) == NULL)
                return -EINVAL;

        xfer_funcs[n] = NULL;

        for (lo = &loop_dev[0]; lo < &loop_dev[max_loop]; lo++) {
                mutex_lock(&lo->lo_ctl_mutex);

                if (lo->lo_encryption == xfer)
                        loop_release_xfer(lo);

                mutex_unlock(&lo->lo_ctl_mutex);
        }

        return 0;
}

EXPORT_SYMBOL(loop_register_transfer);
EXPORT_SYMBOL(loop_unregister_transfer);

static int __init loop_init(void)
{
        int     i;

        if (max_loop < 1 || max_loop > 256) {
                printk(KERN_WARNING "loop: invalid max_loop (must be between"
                                    " 1 and 256), using default (8)\n");
                max_loop = 8;
        }

        if (register_blkdev(LOOP_MAJOR, "loop"))
                return -EIO;

        loop_dev = kmalloc(max_loop * sizeof(struct loop_device), GFP_KERNEL);
        if (!loop_dev)
                goto out_mem1;
        memset(loop_dev, 0, max_loop * sizeof(struct loop_device));

        disks = kmalloc(max_loop * sizeof(struct gendisk *), GFP_KERNEL);
        if (!disks)
                goto out_mem2;

        for (i = 0; i < max_loop; i++) {
                disks[i] = alloc_disk(1);
                if (!disks[i])
                        goto out_mem3;
        }

        devfs_mk_dir("loop");

        for (i = 0; i < max_loop; i++) {
                struct loop_device *lo = &loop_dev[i];
                struct gendisk *disk = disks[i];

                memset(lo, 0, sizeof(*lo));
                lo->lo_queue = blk_alloc_queue(GFP_KERNEL);
                if (!lo->lo_queue)
                        goto out_mem4;
                mutex_init(&lo->lo_ctl_mutex);
                init_completion(&lo->lo_done);
                init_completion(&lo->lo_bh_done);
                lo->lo_number = i;
                spin_lock_init(&lo->lo_lock);
                disk->major = LOOP_MAJOR;
                disk->first_minor = i;
                disk->fops = &lo_fops;
                sprintf(disk->disk_name, "loop%d", i);
                sprintf(disk->devfs_name, "loop/%d", i);
                disk->private_data = lo;
                disk->queue = lo->lo_queue;
        }

        /* We cannot fail after we call this, so another loop!*/
        for (i = 0; i < max_loop; i++)
                add_disk(disks[i]);
        printk(KERN_INFO "loop: loaded (max %d devices)\n", max_loop);
        return 0;

out_mem4:
        while (i--)
                blk_cleanup_queue(loop_dev[i].lo_queue);
        devfs_remove("loop");
        i = max_loop;
out_mem3:
        while (i--)
                put_disk(disks[i]);
        kfree(disks);
out_mem2:
        kfree(loop_dev);
out_mem1:
        unregister_blkdev(LOOP_MAJOR, "loop");
        printk(KERN_ERR "loop: ran out of memory\n");
        return -ENOMEM;
}

static void loop_exit(void)
{
        int i;

        for (i = 0; i < max_loop; i++) {
                del_gendisk(disks[i]);
                blk_cleanup_queue(loop_dev[i].lo_queue);
                put_disk(disks[i]);
        }
        devfs_remove("loop");
        if (unregister_blkdev(LOOP_MAJOR, "loop"))
                printk(KERN_WARNING "loop: cannot unregister blkdev\n");

        kfree(disks);
        kfree(loop_dev);
}

module_init(loop_init);
module_exit(loop_exit);

#ifndef MODULE
static int __init max_loop_setup(char *str)
{
        max_loop = simple_strtol(str, NULL, 0);
        return 1;
}

__setup("max_loop=", max_loop_setup);
#endif