loop.c

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/*
 *  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 - [email protected] Mar 20, 1997
 *
 * Added devfs support - Richard Gooch <[email protected]> 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, [email protected]
 *
 * Maximum number of loop devices now dynamic via max_loop module parameter.
 * Russell Kroll <[email protected]> 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, <[email protected]>, 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 <[email protected]>, Nov 2000
 *
 * Support up to 256 loop devices
 * Heinz Mauelshagen <[email protected]>, 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/swap.h>
#include <linux/slab.h>
#include <linux/loop.h>
#include <linux/compat.h>
#include <linux/suspend.h>
#include <linux/freezer.h>
#include <linux/mutex.h>
#include <linux/writeback.h>
#include <linux/completion.h>
#include <linux/highmem.h>
#include <linux/kthread.h>
#include <linux/splice.h>
#include <linux/sysfs.h>
#include <linux/miscdevice.h>
#include <linux/falloc.h>

#include <asm/uaccess.h>

static DEFINE_IDR(loop_index_idr);
static DEFINE_MUTEX(loop_index_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) + raw_off;
    char *loop_buf = kmap_atomic(loop_page) + loop_off;

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

    kunmap_atomic(loop_buf);
    kunmap_atomic(raw_buf);
    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) + raw_off;
    char *loop_buf = kmap_atomic(loop_page) + 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(loop_buf);
    kunmap_atomic(raw_buf);
    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_size(loff_t offset, loff_t sizelimit, struct file *file)
{
    loff_t size, loopsize;

    /* Compute loopsize in bytes */
    size = i_size_read(file->f_mapping->host);
    loopsize = size - offset;
    /* offset is beyond i_size, wierd but possible */
    if (loopsize < 0)
        return 0;

    if (sizelimit > 0 && sizelimit < loopsize)
        loopsize = 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 loff_t get_loop_size(struct loop_device *lo, struct file *file)
{
    return get_size(lo->lo_offset, lo->lo_sizelimit, file);
}

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

    if (unlikely((loff_t)x != size))
        return -EFBIG;
    if (lo->lo_offset != offset)
        lo->lo_offset = offset;
    if (lo->lo_sizelimit != sizelimit)
        lo->lo_sizelimit = sizelimit;
    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);
}

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;
}

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;
}

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;

    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;
    } else {
        do_lo_send = do_lo_send_direct_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;

    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 ssize_t
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;
    ssize_t 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);

    return retval;
}

static int
lo_receive(struct loop_device *lo, struct bio *bio, int bsize, loff_t pos)
{
    struct bio_vec *bvec;
    ssize_t s;
    int i;

    bio_for_each_segment(bvec, bio, i) {
        s = do_lo_receive(lo, bvec, bsize, pos);
        if (s < 0)
            return s;

        if (s != bvec->bv_len) {
            zero_fill_bio(bio);
            break;
        }
        pos += bvec->bv_len;
    }
    return 0;
}

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) {
        struct file *file = lo->lo_backing_file;

        if (bio->bi_rw & REQ_FLUSH) {
            ret = vfs_fsync(file, 0);
            if (unlikely(ret && ret != -EINVAL)) {
                ret = -EIO;
                goto out;
            }
        }

        /*
         * We use punch hole to reclaim the free space used by the
         * image a.k.a. discard. However we do not support discard if
         * encryption is enabled, because it may give an attacker
         * useful information.
         */
        if (bio->bi_rw & REQ_DISCARD) {
            struct file *file = lo->lo_backing_file;
            int mode = FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE;

            if ((!file->f_op->fallocate) ||
                lo->lo_encrypt_key_size) {
                ret = -EOPNOTSUPP;
                goto out;
            }
            ret = file->f_op->fallocate(file, mode, pos,
                            bio->bi_size);
            if (unlikely(ret && ret != -EINVAL &&
                     ret != -EOPNOTSUPP))
                ret = -EIO;
            goto out;
        }

        ret = lo_send(lo, bio, pos);

        if ((bio->bi_rw & REQ_FUA) && !ret) {
            ret = vfs_fsync(file, 0);
            if (unlikely(ret && ret != -EINVAL))
                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 void 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;

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

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;

    /* 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 (lo->lo_flags & LO_FLAGS_PARTSCAN)
        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;
}

/* loop sysfs attributes */

static ssize_t loop_attr_show(struct device *dev, char *page,
                  ssize_t (*callback)(struct loop_device *, char *))
{
    struct gendisk *disk = dev_to_disk(dev);
    struct loop_device *lo = disk->private_data;

    return callback(lo, page);
}

#define LOOP_ATTR_RO(_name)                     \
static ssize_t loop_attr_##_name##_show(struct loop_device *, char *);  \
static ssize_t loop_attr_do_show_##_name(struct device *d,      \
                struct device_attribute *attr, char *b) \
{                                   \
    return loop_attr_show(d, b, loop_attr_##_name##_show);      \
}                                   \
static struct device_attribute loop_attr_##_name =          \
    __ATTR(_name, S_IRUGO, loop_attr_do_show_##_name, NULL);

static ssize_t loop_attr_backing_file_show(struct loop_device *lo, char *buf)
{
    ssize_t ret;
    char *p = NULL;

    spin_lock_irq(&lo->lo_lock);
    if (lo->lo_backing_file)
        p = d_path(&lo->lo_backing_file->f_path, buf, PAGE_SIZE - 1);
    spin_unlock_irq(&lo->lo_lock);

    if (IS_ERR_OR_NULL(p))
        ret = PTR_ERR(p);
    else {
        ret = strlen(p);
        memmove(buf, p, ret);
        buf[ret++] = '\n';
        buf[ret] = 0;
    }

    return ret;
}

static ssize_t loop_attr_offset_show(struct loop_device *lo, char *buf)
{
    return sprintf(buf, "%llu\n", (unsigned long long)lo->lo_offset);
}

static ssize_t loop_attr_sizelimit_show(struct loop_device *lo, char *buf)
{
    return sprintf(buf, "%llu\n", (unsigned long long)lo->lo_sizelimit);
}

static ssize_t loop_attr_autoclear_show(struct loop_device *lo, char *buf)
{
    int autoclear = (lo->lo_flags & LO_FLAGS_AUTOCLEAR);

    return sprintf(buf, "%s\n", autoclear ? "1" : "0");
}

static ssize_t loop_attr_partscan_show(struct loop_device *lo, char *buf)
{
    int partscan = (lo->lo_flags & LO_FLAGS_PARTSCAN);

    return sprintf(buf, "%s\n", partscan ? "1" : "0");
}

LOOP_ATTR_RO(backing_file);
LOOP_ATTR_RO(offset);
LOOP_ATTR_RO(sizelimit);
LOOP_ATTR_RO(autoclear);
LOOP_ATTR_RO(partscan);

static struct attribute *loop_attrs[] = {
    &loop_attr_backing_file.attr,
    &loop_attr_offset.attr,
    &loop_attr_sizelimit.attr,
    &loop_attr_autoclear.attr,
    &loop_attr_partscan.attr,
    NULL,
};

static struct attribute_group loop_attribute_group = {
    .name = "loop",
    .attrs= loop_attrs,
};

static int loop_sysfs_init(struct loop_device *lo)
{
    return sysfs_create_group(&disk_to_dev(lo->lo_disk)->kobj,
                  &loop_attribute_group);
}

static void loop_sysfs_exit(struct loop_device *lo)
{
    sysfs_remove_group(&disk_to_dev(lo->lo_disk)->kobj,
               &loop_attribute_group);
}

static void loop_config_discard(struct loop_device *lo)
{
    struct file *file = lo->lo_backing_file;
    struct inode *inode = file->f_mapping->host;
    struct request_queue *q = lo->lo_queue;

    /*
     * We use punch hole to reclaim the free space used by the
     * image a.k.a. discard. However we do support discard if
     * encryption is enabled, because it may give an attacker
     * useful information.
     */
    if ((!file->f_op->fallocate) ||
        lo->lo_encrypt_key_size) {
        q->limits.discard_granularity = 0;
        q->limits.discard_alignment = 0;
        q->limits.max_discard_sectors = 0;
        q->limits.discard_zeroes_data = 0;
        queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, q);
        return;
    }

    q->limits.discard_granularity = inode->i_sb->s_blocksize;
    q->limits.discard_alignment = 0;
    q->limits.max_discard_sectors = UINT_MAX >> 9;
    q->limits.discard_zeroes_data = 1;
    queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
}

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;

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

    if (!(file->f_mode & FMODE_WRITE) || !(mode & FMODE_WRITE) ||
        !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 = -EFBIG;
    size = get_loop_size(lo, file);
    if ((loff_t)(sector_t)size != size)
        goto out_putf;

    error = 0;

    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;

    if (!(lo_flags & LO_FLAGS_READ_ONLY) && file->f_op->fsync)
        blk_queue_flush(lo->lo_queue, REQ_FLUSH);

    set_capacity(lo->lo_disk, size);
    bd_set_size(bdev, size << 9);
    loop_sysfs_init(lo);
    /* let user-space know about the new size */
    kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);

    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 (part_shift)
        lo->lo_flags |= LO_FLAGS_PARTSCAN;
    if (lo->lo_flags & LO_FLAGS_PARTSCAN)
        ioctl_by_bdev(bdev, BLKRRPART, 0);
    return 0;

out_clr:
    loop_sysfs_exit(lo);
    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);
    kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
    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 file *filp = lo->lo_backing_file;
    gfp_t gfp = lo->old_gfp_mask;
    struct block_device *bdev = lo->lo_device;

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

    /*
     * If we've explicitly asked to tear down the loop device,
     * and it has an elevated reference count, set it for auto-teardown when
     * the last reference goes away. This stops $!~#$@ udev from
     * preventing teardown because it decided that it needs to run blkid on
     * the loopback device whenever they appear. xfstests is notorious for
     * failing tests because blkid via udev races with a losetup
     * <dev>/do something like mkfs/losetup -d <dev> causing the losetup -d
     * command to fail with EBUSY.
     */
    if (lo->lo_refcnt > 1) {
        lo->lo_flags |= LO_FLAGS_AUTOCLEAR;
        mutex_unlock(&lo->lo_ctl_mutex);
        return 0;
    }

    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);

    spin_lock_irq(&lo->lo_lock);
    lo->lo_backing_file = NULL;
    spin_unlock_irq(&lo->lo_lock);

    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_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);
    loop_sysfs_exit(lo);
    if (bdev) {
        bd_set_size(bdev, 0);
        /* let user-space know about this change */
        kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
    }
    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 (lo->lo_flags & LO_FLAGS_PARTSCAN && bdev)
        ioctl_by_bdev(bdev, BLKRRPART, 0);
    lo->lo_flags = 0;
    if (!part_shift)
        lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
    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;
    kuid_t uid = current_uid();

    if (lo->lo_encrypt_key_size &&
        !uid_eq(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) {
        if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit))
            return -EFBIG;
    }
    loop_config_discard(lo);

    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;

    if ((info->lo_flags & LO_FLAGS_PARTSCAN) &&
         !(lo->lo_flags & LO_FLAGS_PARTSCAN)) {
        lo->lo_flags |= LO_FLAGS_PARTSCAN;
        lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN;
        ioctl_by_bdev(lo->lo_device, BLKRRPART, 0);
    }

    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, lo->lo_offset, lo->lo_sizelimit);
    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);
    /* let user-space know about the new size */
    kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
    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);
        if (!err)
            goto out_unlocked;
        break;
    case LOOP_SET_STATUS:
        err = -EPERM;
        if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN))
            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 = -EPERM;
        if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN))
            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;
    int err = 0;

    mutex_lock(&loop_index_mutex);
    lo = bdev->bd_disk->private_data;
    if (!lo) {
        err = -ENXIO;
        goto out;
    }

    mutex_lock(&lo->lo_ctl_mutex);
    lo->lo_refcnt++;
    mutex_unlock(&lo->lo_ctl_mutex);
out:
    mutex_unlock(&loop_index_mutex);
    return err;
}

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);
        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 const 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, S_IRUGO);
MODULE_PARM_DESC(max_loop, "Maximum number of loop devices");
module_param(max_part, int, S_IRUGO);
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;
}

static int unregister_transfer_cb(int id, void *ptr, void *data)
{
    struct loop_device *lo = ptr;
    struct loop_func_table *xfer = data;

    mutex_lock(&lo->lo_ctl_mutex);
    if (lo->lo_encryption == xfer)
        loop_release_xfer(lo);
    mutex_unlock(&lo->lo_ctl_mutex);
    return 0;
}

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

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

    xfer_funcs[n] = NULL;
    idr_for_each(&loop_index_idr, &unregister_transfer_cb, xfer);
    return 0;
}

EXPORT_SYMBOL(loop_register_transfer);
EXPORT_SYMBOL(loop_unregister_transfer);

static int loop_add(struct loop_device **l, int i)
{
    struct loop_device *lo;
    struct gendisk *disk;
    int err;

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

    if (!idr_pre_get(&loop_index_idr, GFP_KERNEL))
        goto out_free_dev;

    if (i >= 0) {
        int m;

        /* create specific i in the index */
        err = idr_get_new_above(&loop_index_idr, lo, i, &m);
        if (err >= 0 && i != m) {
            idr_remove(&loop_index_idr, m);
            err = -EEXIST;
        }
    } else if (i == -1) {
        int m;

        /* get next free nr */
        err = idr_get_new(&loop_index_idr, lo, &m);
        if (err >= 0)
            i = m;
    } else {
        err = -EINVAL;
    }
    if (err < 0)
        goto out_free_dev;

    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;

    /*
     * Disable partition scanning by default. The in-kernel partition
     * scanning can be requested individually per-device during its
     * setup. Userspace can always add and remove partitions from all
     * devices. The needed partition minors are allocated from the
     * extended minor space, the main loop device numbers will continue
     * to match the loop minors, regardless of the number of partitions
     * used.
     *
     * If max_part is given, partition scanning is globally enabled for
     * all loop devices. The minors for the main loop devices will be
     * multiples of max_part.
     *
     * Note: Global-for-all-devices, set-only-at-init, read-only module
     * parameteters like 'max_loop' and 'max_part' make things needlessly
     * complicated, are too static, inflexible and may surprise
     * userspace tools. Parameters like this in general should be avoided.
     */
    if (!part_shift)
        disk->flags |= GENHD_FL_NO_PART_SCAN;
    disk->flags |= GENHD_FL_EXT_DEVT;
    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);
    add_disk(disk);
    *l = lo;
    return lo->lo_number;

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

static void loop_remove(struct loop_device *lo)
{
    del_gendisk(lo->lo_disk);
    blk_cleanup_queue(lo->lo_queue);
    put_disk(lo->lo_disk);
    kfree(lo);
}

static int find_free_cb(int id, void *ptr, void *data)
{
    struct loop_device *lo = ptr;
    struct loop_device **l = data;

    if (lo->lo_state == Lo_unbound) {
        *l = lo;
        return 1;
    }
    return 0;
}

static int loop_lookup(struct loop_device **l, int i)
{
    struct loop_device *lo;
    int ret = -ENODEV;

    if (i < 0) {
        int err;

        err = idr_for_each(&loop_index_idr, &find_free_cb, &lo);
        if (err == 1) {
            *l = lo;
            ret = lo->lo_number;
        }
        goto out;
    }

    /* lookup and return a specific i */
    lo = idr_find(&loop_index_idr, i);
    if (lo) {
        *l = lo;
        ret = lo->lo_number;
    }
out:
    return ret;
}

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

    mutex_lock(&loop_index_mutex);
    err = loop_lookup(&lo, MINOR(dev) >> part_shift);
    if (err < 0)
        err = loop_add(&lo, MINOR(dev) >> part_shift);
    if (err < 0)
        kobj = ERR_PTR(err);
    else
        kobj = get_disk(lo->lo_disk);
    mutex_unlock(&loop_index_mutex);

    *part = 0;
    return kobj;
}

static long loop_control_ioctl(struct file *file, unsigned int cmd,
                   unsigned long parm)
{
    struct loop_device *lo;
    int ret = -ENOSYS;

    mutex_lock(&loop_index_mutex);
    switch (cmd) {
    case LOOP_CTL_ADD:
        ret = loop_lookup(&lo, parm);
        if (ret >= 0) {
            ret = -EEXIST;
            break;
        }
        ret = loop_add(&lo, parm);
        break;
    case LOOP_CTL_REMOVE:
        ret = loop_lookup(&lo, parm);
        if (ret < 0)
            break;
        mutex_lock(&lo->lo_ctl_mutex);
        if (lo->lo_state != Lo_unbound) {
            ret = -EBUSY;
            mutex_unlock(&lo->lo_ctl_mutex);
            break;
        }
        if (lo->lo_refcnt > 0) {
            ret = -EBUSY;
            mutex_unlock(&lo->lo_ctl_mutex);
            break;
        }
        lo->lo_disk->private_data = NULL;
        mutex_unlock(&lo->lo_ctl_mutex);
        idr_remove(&loop_index_idr, lo->lo_number);
        loop_remove(lo);
        break;
    case LOOP_CTL_GET_FREE:
        ret = loop_lookup(&lo, -1);
        if (ret >= 0)
            break;
        ret = loop_add(&lo, -1);
    }
    mutex_unlock(&loop_index_mutex);

    return ret;
}

static const struct file_operations loop_ctl_fops = {
    .open       = nonseekable_open,
    .unlocked_ioctl = loop_control_ioctl,
    .compat_ioctl   = loop_control_ioctl,
    .owner      = THIS_MODULE,
    .llseek     = noop_llseek,
};

static struct miscdevice loop_misc = {
    .minor      = LOOP_CTRL_MINOR,
    .name       = "loop-control",
    .fops       = &loop_ctl_fops,
};

MODULE_ALIAS_MISCDEV(LOOP_CTRL_MINOR);
MODULE_ALIAS("devname:loop-control");

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

    err = misc_register(&loop_misc);
    if (err < 0)
        return err;

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

        /*
         * Adjust max_part according to part_shift as it is exported
         * to user space so that user can decide correct minor number
         * if [s]he want to create more devices.
         *
         * Note that -1 is required because partition 0 is reserved
         * for the whole disk.
         */
        max_part = (1UL << part_shift) - 1;
    }

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

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

    /*
     * If max_loop is specified, create that many devices upfront.
     * This also becomes a hard limit. If max_loop is not specified,
     * create CONFIG_BLK_DEV_LOOP_MIN_COUNT loop devices at module
     * init time. Loop devices can be requested on-demand with the
     * /dev/loop-control interface, or be instantiated by accessing
     * a 'dead' device node.
     */
    if (max_loop) {
        nr = max_loop;
        range = max_loop << part_shift;
    } else {
        nr = CONFIG_BLK_DEV_LOOP_MIN_COUNT;
        range = 1UL << MINORBITS;
    }

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

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

    /* pre-create number of devices given by config or max_loop */
    mutex_lock(&loop_index_mutex);
    for (i = 0; i < nr; i++)
        loop_add(&lo, i);
    mutex_unlock(&loop_index_mutex);

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

static int loop_exit_cb(int id, void *ptr, void *data)
{
    struct loop_device *lo = ptr;

    loop_remove(lo);
    return 0;
}

static void __exit loop_exit(void)
{
    unsigned long range;

    range = max_loop ? max_loop << part_shift : 1UL << MINORBITS;

    idr_for_each(&loop_index_idr, &loop_exit_cb, NULL);
    idr_remove_all(&loop_index_idr);
    idr_destroy(&loop_index_idr);

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

    misc_deregister(&loop_misc);
}

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