loop: use BIO list management functions

[safe/jmp/linux-2.6] / 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 write_begin is 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/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/smp_lock.h>
#include <linux/swap.h>
#include <linux/slab.h>
#include <linux/loop.h>
#include <linux/compat.h>
#include <linux/suspend.h>
#include <linux/freezer.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 <linux/kthread.h>
#include <linux/splice.h>

#include <asm/uaccess.h>

static LIST_HEAD(loop_devices);
static DEFINE_MUTEX(loop_devices_mutex);

static int max_part;
static int part_shift;

/*
 * 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(lo->lo_disk, 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 write_begin and write_end.
 */
static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec,
                loff_t pos, struct page *unused)
{
        struct file *file = lo->lo_backing_file; /* kudos to NFsckingS */
        struct address_space *mapping = file->f_mapping;
        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, copied;
                int transfer_result;
                struct page *page;
                void *fsdata;

                IV = ((sector_t)index << (PAGE_CACHE_SHIFT - 9))+(offset >> 9);
                size = PAGE_CACHE_SIZE - offset;
                if (size > len)
                        size = len;

                ret = pagecache_write_begin(file, mapping, pos, size, 0,
                                                        &page, &fsdata);
                if (ret)
                        goto fail;

                transfer_result = lo_do_transfer(lo, WRITE, page, offset,
                                bvec->bv_page, bv_offs, size, IV);
                copied = size;
                if (unlikely(transfer_result))
                        copied = 0;

                ret = pagecache_write_end(file, mapping, pos, size, copied,
                                                        page, fsdata);
                if (ret < 0 || ret != copied)
                        goto fail;

                if (unlikely(transfer_result))
                        goto fail;

                bv_offs += copied;
                len -= copied;
                offset = 0;
                index++;
                pos += copied;
        }
        ret = 0;
out:
        mutex_unlock(&mapping->host->i_mutex);
        return ret;
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 *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 write_begin and write_end.
 * 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, loff_t pos, struct page *page)
{
        ssize_t bw = __do_lo_send_write(lo->lo_backing_file,
                        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 write_begin and write_end.  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,
                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,
                                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, loff_t pos)
{
        int (*do_lo_send)(struct loop_device *, struct bio_vec *, 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, 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_splice_actor(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
                struct splice_desc *sd)
{
        struct lo_read_data *p = sd->u.data;
        struct loop_device *lo = p->lo;
        struct page *page = buf->page;
        sector_t IV;
        int size, ret;

        ret = buf->ops->confirm(pipe, buf);
        if (unlikely(ret))
                return ret;

        IV = ((sector_t) page->index << (PAGE_CACHE_SHIFT - 9)) +
                                                        (buf->offset >> 9);
        size = sd->len;
        if (size > p->bsize)
                size = p->bsize;

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

        flush_dcache_page(p->page);

        if (size > 0)
                p->offset += size;

        return size;
}

static int
lo_direct_splice_actor(struct pipe_inode_info *pipe, struct splice_desc *sd)
{
        return __splice_from_pipe(pipe, sd, lo_splice_actor);
}

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

        cookie.lo = lo;
        cookie.page = bvec->bv_page;
        cookie.offset = bvec->bv_offset;
        cookie.bsize = bsize;

        sd.len = 0;
        sd.total_len = bvec->bv_len;
        sd.flags = 0;
        sd.pos = pos;
        sd.u.data = &cookie;

        file = lo->lo_backing_file;
        retval = splice_direct_to_actor(file, &sd, lo_direct_splice_actor);

        if (retval < 0)
                return retval;

        return 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) {
                int barrier = bio_barrier(bio);
                struct file *file = lo->lo_backing_file;

                if (barrier) {
                        if (unlikely(!file->f_op->fsync)) {
                                ret = -EOPNOTSUPP;
                                goto out;
                        }

                        ret = vfs_fsync(file, file->f_path.dentry, 0);
                        if (unlikely(ret)) {
                                ret = -EIO;
                                goto out;
                        }
                }

                ret = lo_send(lo, bio, pos);

                if (barrier && !ret) {
                        ret = vfs_fsync(file, file->f_path.dentry, 0);
                        if (unlikely(ret))
                                ret = -EIO;
                }
        } else
                ret = lo_receive(lo, bio, lo->lo_blocksize, pos);

out:
        return ret;
}

/*
 * Add bio to back of pending list
 */
static void loop_add_bio(struct loop_device *lo, struct bio *bio)
{
        bio_list_add(&lo->lo_bio_list, bio);
}

/*
 * Grab first pending buffer
 */
static struct bio *loop_get_bio(struct loop_device *lo)
{
        return bio_list_pop(&lo->lo_bio_list);
}

static int loop_make_request(struct request_queue *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;
        loop_add_bio(lo, old_bio);
        wake_up(&lo->lo_event);
        spin_unlock_irq(&lo->lo_lock);
        return 0;

out:
        spin_unlock_irq(&lo->lo_lock);
        bio_io_error(old_bio);
        return 0;
}

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

        queue_flag_clear_unlocked(QUEUE_FLAG_PLUGGED, q);
        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, 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.
 *
 * Loop explanation:  loop_clr_fd() sets lo_state to Lo_rundown before
 * calling kthread_stop().  Therefore once kthread_should_stop() is
 * true, make_request will not place any more requests.  Therefore
 * once kthread_should_stop() is true and lo_bio is NULL, we are
 * done with the loop.
 */
static int loop_thread(void *data)
{
        struct loop_device *lo = data;
        struct bio *bio;

        set_user_nice(current, -20);

        while (!kthread_should_stop() || !bio_list_empty(&lo->lo_bio_list)) {

                wait_event_interruptible(lo->lo_event,
                                !bio_list_empty(&lo->lo_bio_list) ||
                                kthread_should_stop());

                if (bio_list_empty(&lo->lo_bio_list))
                        continue;
                spin_lock_irq(&lo->lo_lock);
                bio = loop_get_bio(lo);
                spin_unlock_irq(&lo->lo_lock);

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

        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, 0);
        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;
}

/*
 * Helper to flush the IOs in loop, but keeping loop thread running
 */
static int loop_flush(struct loop_device *lo)
{
        /* loop not yet configured, no running thread, nothing to flush */
        if (!lo->lo_thread)
                return 0;

        return loop_switch(lo, NULL);
}

/*
 * 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;

        /* if no new file, only flush of queued bios requested */
        if (!file)
                goto out;

        mapping = file->f_mapping;
        mapping_set_gfp_mask(old_file->f_mapping, lo->old_gfp_mask);
        lo->lo_backing_file = file;
        lo->lo_blocksize = S_ISBLK(mapping->host->i_mode) ?
                mapping->host->i_bdev->bd_block_size : PAGE_SIZE;
        lo->old_gfp_mask = mapping_gfp_mask(mapping);
        mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));
out:
        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 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 splice_read) */
        if (!inode->i_fop->splice_read)
                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);
        if (max_part > 0)
                ioctl_by_bdev(bdev, BLKRRPART, 0);
        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, fmode_t mode,
                       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_bdev == bdev)
                        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)) {
                const 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->splice_read)
                        goto out_putf;
                if (aops->write_begin)
                        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 = S_ISBLK(inode->i_mode) ?
                        inode->i_bdev->bd_block_size : PAGE_SIZE;

                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 (!(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 = transfer_none;
        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));

        bio_list_init(&lo->lo_bio_list);

        /*
         * 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;

        if (!(lo_flags & LO_FLAGS_READ_ONLY) && file->f_op->fsync)
                blk_queue_ordered(lo->lo_queue, QUEUE_ORDERED_DRAIN, NULL);

        set_capacity(lo->lo_disk, size);
        bd_set_size(bdev, size << 9);

        set_blocksize(bdev, lo_blocksize);

        lo->lo_thread = kthread_create(loop_thread, lo, "loop%d",
                                                lo->lo_number);
        if (IS_ERR(lo->lo_thread)) {
                error = PTR_ERR(lo->lo_thread);
                goto out_clr;
        }
        lo->lo_state = Lo_bound;
        wake_up_process(lo->lo_thread);
        if (max_part > 0)
                ioctl_by_bdev(bdev, BLKRRPART, 0);
        return 0;

out_clr:
        lo->lo_thread = NULL;
        lo->lo_device = NULL;
        lo->lo_backing_file = NULL;
        lo->lo_flags = 0;
        set_capacity(lo->lo_disk, 0);
        invalidate_bdev(bdev);
        bd_set_size(bdev, 0);
        mapping_set_gfp_mask(mapping, lo->old_gfp_mask);
        lo->lo_state = Lo_unbound;
 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;
        spin_unlock_irq(&lo->lo_lock);

        kthread_stop(lo->lo_thread);

        lo->lo_queue->unplug_fn = NULL;
        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;
        lo->lo_thread = NULL;
        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);
        if (bdev)
                invalidate_bdev(bdev);
        set_capacity(lo->lo_disk, 0);
        if (bdev)
                bd_set_size(bdev, 0);
        mapping_set_gfp_mask(filp->f_mapping, gfp);
        lo->lo_state = Lo_unbound;
        /* This is safe: open() is still holding a reference. */
        module_put(THIS_MODULE);
        if (max_part > 0)
                ioctl_by_bdev(bdev, BLKRRPART, 0);
        mutex_unlock(&lo->lo_ctl_mutex);
        /*
         * Need not hold lo_ctl_mutex to fput backing file.
         * Calling fput holding lo_ctl_mutex triggers a circular
         * lock dependency possibility warning as fput can take
         * bd_mutex which is usually taken before lo_ctl_mutex.
         */
        fput(filp);
        return 0;
}

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

        if (lo->lo_encrypt_key_size &&
            lo->lo_key_owner != 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;

        if ((lo->lo_flags & LO_FLAGS_AUTOCLEAR) !=
             (info->lo_flags & LO_FLAGS_AUTOCLEAR))
                lo->lo_flags ^= LO_FLAGS_AUTOCLEAR;

        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 = 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_path.mnt, file->f_path.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 loop_set_capacity(struct loop_device *lo, struct block_device *bdev)
{
        int err;
        sector_t sec;
        loff_t sz;

        err = -ENXIO;
        if (unlikely(lo->lo_state != Lo_bound))
                goto out;
        err = figure_loop_size(lo);
        if (unlikely(err))
                goto out;
        sec = get_capacity(lo->lo_disk);
        /* the width of sector_t may be narrow for bit-shift */
        sz = sec;
        sz <<= 9;
        mutex_lock(&bdev->bd_mutex);
        bd_set_size(bdev, sz);
        mutex_unlock(&bdev->bd_mutex);

 out:
        return err;
}

static int lo_ioctl(struct block_device *bdev, fmode_t mode,
        unsigned int cmd, unsigned long arg)
{
        struct loop_device *lo = bdev->bd_disk->private_data;
        int err;

        mutex_lock_nested(&lo->lo_ctl_mutex, 1);
        switch (cmd) {
        case LOOP_SET_FD:
                err = loop_set_fd(lo, mode, bdev, arg);
                break;
        case LOOP_CHANGE_FD:
                err = loop_change_fd(lo, bdev, arg);
                break;
        case LOOP_CLR_FD:
                /* loop_clr_fd would have unlocked lo_ctl_mutex on success */
                err = loop_clr_fd(lo, bdev);
                if (!err)
                        goto out_unlocked;
                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;
        case LOOP_SET_CAPACITY:
                err = -EPERM;
                if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN))
                        err = loop_set_capacity(lo, bdev);
                break;
        default:
                err = lo->ioctl ? lo->ioctl(lo, cmd, arg) : -EINVAL;
        }
        mutex_unlock(&lo->lo_ctl_mutex);

out_unlocked:
        return err;
}

#ifdef CONFIG_COMPAT
struct compat_loop_info {
        compat_int_t    lo_number;      /* ioctl r/o */
        compat_dev_t    lo_device;      /* ioctl r/o */
        compat_ulong_t  lo_inode;       /* ioctl r/o */
        compat_dev_t    lo_rdevice;     /* ioctl r/o */
        compat_int_t    lo_offset;
        compat_int_t    lo_encrypt_type;
        compat_int_t    lo_encrypt_key_size;    /* ioctl w/o */
        compat_int_t    lo_flags;       /* ioctl r/o */
        char            lo_name[LO_NAME_SIZE];
        unsigned char   lo_encrypt_key[LO_KEY_SIZE]; /* ioctl w/o */
        compat_ulong_t  lo_init[2];
        char            reserved[4];
};

/*
 * Transfer 32-bit compatibility structure in userspace to 64-bit loop info
 * - noinlined to reduce stack space usage in main part of driver
 */
static noinline int
loop_info64_from_compat(const struct compat_loop_info __user *arg,
                        struct loop_info64 *info64)
{
        struct compat_loop_info info;

        if (copy_from_user(&info, arg, sizeof(info)))
                return -EFAULT;

        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);
        return 0;
}

/*
 * Transfer 64-bit loop info to 32-bit compatibility structure in userspace
 * - noinlined to reduce stack space usage in main part of driver
 */
static noinline int
loop_info64_to_compat(const struct loop_info64 *info64,
                      struct compat_loop_info __user *arg)
{
        struct compat_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 ||
            info.lo_init[0] != info64->lo_init[0] ||
            info.lo_init[1] != info64->lo_init[1])
                return -EOVERFLOW;

        if (copy_to_user(arg, &info, sizeof(info)))
                return -EFAULT;
        return 0;
}

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

        ret = loop_info64_from_compat(arg, &info64);
        if (ret < 0)
                return ret;
        return loop_set_status(lo, &info64);
}

static int
loop_get_status_compat(struct loop_device *lo,
                       struct compat_loop_info __user *arg)
{
        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_compat(&info64, arg);
        return err;
}

static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
                           unsigned int cmd, unsigned long arg)
{
        struct loop_device *lo = bdev->bd_disk->private_data;
        int err;

        switch(cmd) {
        case LOOP_SET_STATUS:
                mutex_lock(&lo->lo_ctl_mutex);
                err = loop_set_status_compat(
                        lo, (const struct compat_loop_info __user *) arg);
                mutex_unlock(&lo->lo_ctl_mutex);
                break;
        case LOOP_GET_STATUS:
                mutex_lock(&lo->lo_ctl_mutex);
                err = loop_get_status_compat(
                        lo, (struct compat_loop_info __user *) arg);
                mutex_unlock(&lo->lo_ctl_mutex);
                break;
        case LOOP_SET_CAPACITY:
        case LOOP_CLR_FD:
        case LOOP_GET_STATUS64:
        case LOOP_SET_STATUS64:
                arg = (unsigned long) compat_ptr(arg);
        case LOOP_SET_FD:
        case LOOP_CHANGE_FD:
                err = lo_ioctl(bdev, mode, cmd, arg);
                break;
        default:
                err = -ENOIOCTLCMD;
                break;
        }
        return err;
}
#endif

static int lo_open(struct block_device *bdev, fmode_t mode)
{
        struct loop_device *lo = 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 gendisk *disk, fmode_t mode)
{
        struct loop_device *lo = disk->private_data;
        int err;

        mutex_lock(&lo->lo_ctl_mutex);

        if (--lo->lo_refcnt)
                goto out;

        if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) {
                /*
                 * In autoclear mode, stop the loop thread
                 * and remove configuration after last close.
                 */
                err = loop_clr_fd(lo, NULL);
                if (!err)
                        goto out_unlocked;
        } else {
                /*
                 * Otherwise keep thread (if running) and config,
                 * but flush possible ongoing bios in thread.
                 */
                loop_flush(lo);
        }

out:
        mutex_unlock(&lo->lo_ctl_mutex);
out_unlocked:
        return 0;
}

static struct block_device_operations lo_fops = {
        .owner =        THIS_MODULE,
        .open =         lo_open,
        .release =      lo_release,
        .ioctl =        lo_ioctl,
#ifdef CONFIG_COMPAT
        .compat_ioctl = lo_compat_ioctl,
#endif
};

/*
 * And now the modules code and kernel interface.
 */
static int max_loop;
module_param(max_loop, int, 0);
MODULE_PARM_DESC(max_loop, "Maximum number of loop devices");
module_param(max_part, int, 0);
MODULE_PARM_DESC(max_part, "Maximum number of partitions per loop device");
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;

        list_for_each_entry(lo, &loop_devices, lo_list) {
                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 struct loop_device *loop_alloc(int i)
{
        struct loop_device *lo;
        struct gendisk *disk;

        lo = kzalloc(sizeof(*lo), GFP_KERNEL);
        if (!lo)
                goto out;

        lo->lo_queue = blk_alloc_queue(GFP_KERNEL);
        if (!lo->lo_queue)
                goto out_free_dev;

        disk = lo->lo_disk = alloc_disk(1 << part_shift);
        if (!disk)
                goto out_free_queue;

        mutex_init(&lo->lo_ctl_mutex);
        lo->lo_number           = i;
        lo->lo_thread           = NULL;
        init_waitqueue_head(&lo->lo_event);
        spin_lock_init(&lo->lo_lock);
        disk->major             = LOOP_MAJOR;
        disk->first_minor       = i << part_shift;
        disk->fops              = &lo_fops;
        disk->private_data      = lo;
        disk->queue             = lo->lo_queue;
        sprintf(disk->disk_name, "loop%d", i);
        return lo;

out_free_queue:
        blk_cleanup_queue(lo->lo_queue);
out_free_dev:
        kfree(lo);
out:
        return NULL;
}

static void loop_free(struct loop_device *lo)
{
        blk_cleanup_queue(lo->lo_queue);
        put_disk(lo->lo_disk);
        list_del(&lo->lo_list);
        kfree(lo);
}

static struct loop_device *loop_init_one(int i)
{
        struct loop_device *lo;

        list_for_each_entry(lo, &loop_devices, lo_list) {
                if (lo->lo_number == i)
                        return lo;
        }

        lo = loop_alloc(i);
        if (lo) {
                add_disk(lo->lo_disk);
                list_add_tail(&lo->lo_list, &loop_devices);
        }
        return lo;
}

static void loop_del_one(struct loop_device *lo)
{
        del_gendisk(lo->lo_disk);
        loop_free(lo);
}

static struct kobject *loop_probe(dev_t dev, int *part, void *data)
{
        struct loop_device *lo;
        struct kobject *kobj;

        mutex_lock(&loop_devices_mutex);
        lo = loop_init_one(dev & MINORMASK);
        kobj = lo ? get_disk(lo->lo_disk) : ERR_PTR(-ENOMEM);
        mutex_unlock(&loop_devices_mutex);

        *part = 0;
        return kobj;
}

static int __init loop_init(void)
{
        int i, nr;
        unsigned long range;
        struct loop_device *lo, *next;

        /*
         * loop module now has a feature to instantiate underlying device
         * structure on-demand, provided that there is an access dev node.
         * However, this will not work well with user space tool that doesn't
         * know about such "feature".  In order to not break any existing
         * tool, we do the following:
         *
         * (1) if max_loop is specified, create that many upfront, and this
         *     also becomes a hard limit.
         * (2) if max_loop is not specified, create 8 loop device on module
         *     load, user can further extend loop device by create dev node
         *     themselves and have kernel automatically instantiate actual
         *     device on-demand.
         */

        part_shift = 0;
        if (max_part > 0)
                part_shift = fls(max_part);

        if (max_loop > 1UL << (MINORBITS - part_shift))
                return -EINVAL;

        if (max_loop) {
                nr = max_loop;
                range = max_loop;
        } else {
                nr = 8;
                range = 1UL << (MINORBITS - part_shift);
        }

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

        for (i = 0; i < nr; i++) {
                lo = loop_alloc(i);
                if (!lo)
                        goto Enomem;
                list_add_tail(&lo->lo_list, &loop_devices);
        }

        /* point of no return */

        list_for_each_entry(lo, &loop_devices, lo_list)
                add_disk(lo->lo_disk);

        blk_register_region(MKDEV(LOOP_MAJOR, 0), range,
                                  THIS_MODULE, loop_probe, NULL, NULL);

        printk(KERN_INFO "loop: module loaded\n");
        return 0;

Enomem:
        printk(KERN_INFO "loop: out of memory\n");

        list_for_each_entry_safe(lo, next, &loop_devices, lo_list)
                loop_free(lo);

        unregister_blkdev(LOOP_MAJOR, "loop");
        return -ENOMEM;
}

static void __exit loop_exit(void)
{
        unsigned long range;
        struct loop_device *lo, *next;

        range = max_loop ? max_loop :  1UL << (MINORBITS - part_shift);

        list_for_each_entry_safe(lo, next, &loop_devices, lo_list)
                loop_del_one(lo);

        blk_unregister_region(MKDEV(LOOP_MAJOR, 0), range);
        unregister_blkdev(LOOP_MAJOR, "loop");
}

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