freeze_bdev: grab active reference to frozen superblocks

[mirror_ubuntu-zesty-kernel.git] / fs / block_dev.c

/*
 *  linux/fs/block_dev.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *  Copyright (C) 2001  Andrea Arcangeli <andrea@suse.de> SuSE
 */

#include <linux/init.h>
#include <linux/mm.h>
#include <linux/fcntl.h>
#include <linux/slab.h>
#include <linux/kmod.h>
#include <linux/major.h>
#include <linux/smp_lock.h>
#include <linux/device_cgroup.h>
#include <linux/highmem.h>
#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/blkpg.h>
#include <linux/buffer_head.h>
#include <linux/pagevec.h>
#include <linux/writeback.h>
#include <linux/mpage.h>
#include <linux/mount.h>
#include <linux/uio.h>
#include <linux/namei.h>
#include <linux/log2.h>
#include <linux/kmemleak.h>
#include <asm/uaccess.h>
#include "internal.h"

struct bdev_inode {
        struct block_device bdev;
        struct inode vfs_inode;
};

static const struct address_space_operations def_blk_aops;

static inline struct bdev_inode *BDEV_I(struct inode *inode)
{
        return container_of(inode, struct bdev_inode, vfs_inode);
}

inline struct block_device *I_BDEV(struct inode *inode)
{
        return &BDEV_I(inode)->bdev;
}

EXPORT_SYMBOL(I_BDEV);

static sector_t max_block(struct block_device *bdev)
{
        sector_t retval = ~((sector_t)0);
        loff_t sz = i_size_read(bdev->bd_inode);

        if (sz) {
                unsigned int size = block_size(bdev);
                unsigned int sizebits = blksize_bits(size);
                retval = (sz >> sizebits);
        }
        return retval;
}

/* Kill _all_ buffers and pagecache , dirty or not.. */
static void kill_bdev(struct block_device *bdev)
{
        if (bdev->bd_inode->i_mapping->nrpages == 0)
                return;
        invalidate_bh_lrus();
        truncate_inode_pages(bdev->bd_inode->i_mapping, 0);
}       

int set_blocksize(struct block_device *bdev, int size)
{
        /* Size must be a power of two, and between 512 and PAGE_SIZE */
        if (size > PAGE_SIZE || size < 512 || !is_power_of_2(size))
                return -EINVAL;

        /* Size cannot be smaller than the size supported by the device */
        if (size < bdev_logical_block_size(bdev))
                return -EINVAL;

        /* Don't change the size if it is same as current */
        if (bdev->bd_block_size != size) {
                sync_blockdev(bdev);
                bdev->bd_block_size = size;
                bdev->bd_inode->i_blkbits = blksize_bits(size);
                kill_bdev(bdev);
        }
        return 0;
}

EXPORT_SYMBOL(set_blocksize);

int sb_set_blocksize(struct super_block *sb, int size)
{
        if (set_blocksize(sb->s_bdev, size))
                return 0;
        /* If we get here, we know size is power of two
         * and it's value is between 512 and PAGE_SIZE */
        sb->s_blocksize = size;
        sb->s_blocksize_bits = blksize_bits(size);
        return sb->s_blocksize;
}

EXPORT_SYMBOL(sb_set_blocksize);

int sb_min_blocksize(struct super_block *sb, int size)
{
        int minsize = bdev_logical_block_size(sb->s_bdev);
        if (size < minsize)
                size = minsize;
        return sb_set_blocksize(sb, size);
}

EXPORT_SYMBOL(sb_min_blocksize);

static int
blkdev_get_block(struct inode *inode, sector_t iblock,
                struct buffer_head *bh, int create)
{
        if (iblock >= max_block(I_BDEV(inode))) {
                if (create)
                        return -EIO;

                /*
                 * for reads, we're just trying to fill a partial page.
                 * return a hole, they will have to call get_block again
                 * before they can fill it, and they will get -EIO at that
                 * time
                 */
                return 0;
        }
        bh->b_bdev = I_BDEV(inode);
        bh->b_blocknr = iblock;
        set_buffer_mapped(bh);
        return 0;
}

static int
blkdev_get_blocks(struct inode *inode, sector_t iblock,
                struct buffer_head *bh, int create)
{
        sector_t end_block = max_block(I_BDEV(inode));
        unsigned long max_blocks = bh->b_size >> inode->i_blkbits;

        if ((iblock + max_blocks) > end_block) {
                max_blocks = end_block - iblock;
                if ((long)max_blocks <= 0) {
                        if (create)
                                return -EIO;    /* write fully beyond EOF */
                        /*
                         * It is a read which is fully beyond EOF.  We return
                         * a !buffer_mapped buffer
                         */
                        max_blocks = 0;
                }
        }

        bh->b_bdev = I_BDEV(inode);
        bh->b_blocknr = iblock;
        bh->b_size = max_blocks << inode->i_blkbits;
        if (max_blocks)
                set_buffer_mapped(bh);
        return 0;
}

static ssize_t
blkdev_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
                        loff_t offset, unsigned long nr_segs)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file->f_mapping->host;

        return blockdev_direct_IO_no_locking(rw, iocb, inode, I_BDEV(inode),
                                iov, offset, nr_segs, blkdev_get_blocks, NULL);
}

int __sync_blockdev(struct block_device *bdev, int wait)
{
        if (!bdev)
                return 0;
        if (!wait)
                return filemap_flush(bdev->bd_inode->i_mapping);
        return filemap_write_and_wait(bdev->bd_inode->i_mapping);
}

/*
 * Write out and wait upon all the dirty data associated with a block
 * device via its mapping.  Does not take the superblock lock.
 */
int sync_blockdev(struct block_device *bdev)
{
        return __sync_blockdev(bdev, 1);
}
EXPORT_SYMBOL(sync_blockdev);

/*
 * Write out and wait upon all dirty data associated with this
 * device.   Filesystem data as well as the underlying block
 * device.  Takes the superblock lock.
 */
int fsync_bdev(struct block_device *bdev)
{
        struct super_block *sb = get_super(bdev);
        if (sb) {
                int res = sync_filesystem(sb);
                drop_super(sb);
                return res;
        }
        return sync_blockdev(bdev);
}
EXPORT_SYMBOL(fsync_bdev);

/**
 * freeze_bdev  --  lock a filesystem and force it into a consistent state
 * @bdev:       blockdevice to lock
 *
 * If a superblock is found on this device, we take the s_umount semaphore
 * on it to make sure nobody unmounts until the snapshot creation is done.
 * The reference counter (bd_fsfreeze_count) guarantees that only the last
 * unfreeze process can unfreeze the frozen filesystem actually when multiple
 * freeze requests arrive simultaneously. It counts up in freeze_bdev() and
 * count down in thaw_bdev(). When it becomes 0, thaw_bdev() will unfreeze
 * actually.
 */
struct super_block *freeze_bdev(struct block_device *bdev)
{
        struct super_block *sb;
        int error = 0;

        mutex_lock(&bdev->bd_fsfreeze_mutex);
        if (++bdev->bd_fsfreeze_count > 1) {
                /*
                 * We don't even need to grab a reference - the first call
                 * to freeze_bdev grab an active reference and only the last
                 * thaw_bdev drops it.
                 */
                sb = get_super(bdev);
                drop_super(sb);
                mutex_unlock(&bdev->bd_fsfreeze_mutex);
                return sb;
        }

        sb = get_active_super(bdev);
        if (!sb)
                goto out;
        if (sb->s_flags & MS_RDONLY) {
                deactivate_locked_super(sb);
                mutex_unlock(&bdev->bd_fsfreeze_mutex);
                return sb;
        }

        sb->s_frozen = SB_FREEZE_WRITE;
        smp_wmb();

        sync_filesystem(sb);

        sb->s_frozen = SB_FREEZE_TRANS;
        smp_wmb();

        sync_blockdev(sb->s_bdev);

        if (sb->s_op->freeze_fs) {
                error = sb->s_op->freeze_fs(sb);
                if (error) {
                        printk(KERN_ERR
                                "VFS:Filesystem freeze failed\n");
                        sb->s_frozen = SB_UNFROZEN;
                        deactivate_locked_super(sb);
                        bdev->bd_fsfreeze_count--;
                        mutex_unlock(&bdev->bd_fsfreeze_mutex);
                        return ERR_PTR(error);
                }
        }
        up_write(&sb->s_umount);

 out:
        sync_blockdev(bdev);
        mutex_unlock(&bdev->bd_fsfreeze_mutex);
        return sb;      /* thaw_bdev releases s->s_umount */
}
EXPORT_SYMBOL(freeze_bdev);

/**
 * thaw_bdev  -- unlock filesystem
 * @bdev:       blockdevice to unlock
 * @sb:         associated superblock
 *
 * Unlocks the filesystem and marks it writeable again after freeze_bdev().
 */
int thaw_bdev(struct block_device *bdev, struct super_block *sb)
{
        int error = -EINVAL;

        mutex_lock(&bdev->bd_fsfreeze_mutex);
        if (!bdev->bd_fsfreeze_count)
                goto out_unlock;

        error = 0;
        if (--bdev->bd_fsfreeze_count > 0)
                goto out_unlock;

        if (!sb)
                goto out_unlock;

        BUG_ON(sb->s_bdev != bdev);
        down_write(&sb->s_umount);
        if (sb->s_flags & MS_RDONLY)
                goto out_deactivate;

        if (sb->s_op->unfreeze_fs) {
                error = sb->s_op->unfreeze_fs(sb);
                if (error) {
                        printk(KERN_ERR
                                "VFS:Filesystem thaw failed\n");
                        sb->s_frozen = SB_FREEZE_TRANS;
                        bdev->bd_fsfreeze_count++;
                        mutex_unlock(&bdev->bd_fsfreeze_mutex);
                        return error;
                }
        }

        sb->s_frozen = SB_UNFROZEN;
        smp_wmb();
        wake_up(&sb->s_wait_unfrozen);

out_deactivate:
        if (sb)
                deactivate_locked_super(sb);
out_unlock:
        mutex_unlock(&bdev->bd_fsfreeze_mutex);
        return 0;
}
EXPORT_SYMBOL(thaw_bdev);

static int blkdev_writepage(struct page *page, struct writeback_control *wbc)
{
        return block_write_full_page(page, blkdev_get_block, wbc);
}

static int blkdev_readpage(struct file * file, struct page * page)
{
        return block_read_full_page(page, blkdev_get_block);
}

static int blkdev_write_begin(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned flags,
                        struct page **pagep, void **fsdata)
{
        *pagep = NULL;
        return block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
                                blkdev_get_block);
}

static int blkdev_write_end(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned copied,
                        struct page *page, void *fsdata)
{
        int ret;
        ret = block_write_end(file, mapping, pos, len, copied, page, fsdata);

        unlock_page(page);
        page_cache_release(page);

        return ret;
}

/*
 * private llseek:
 * for a block special file file->f_path.dentry->d_inode->i_size is zero
 * so we compute the size by hand (just as in block_read/write above)
 */
static loff_t block_llseek(struct file *file, loff_t offset, int origin)
{
        struct inode *bd_inode = file->f_mapping->host;
        loff_t size;
        loff_t retval;

        mutex_lock(&bd_inode->i_mutex);
        size = i_size_read(bd_inode);

        switch (origin) {
                case 2:
                        offset += size;
                        break;
                case 1:
                        offset += file->f_pos;
        }
        retval = -EINVAL;
        if (offset >= 0 && offset <= size) {
                if (offset != file->f_pos) {
                        file->f_pos = offset;
                }
                retval = offset;
        }
        mutex_unlock(&bd_inode->i_mutex);
        return retval;
}
        
/*
 *      Filp is never NULL; the only case when ->fsync() is called with
 *      NULL first argument is nfsd_sync_dir() and that's not a directory.
 */
 
static int block_fsync(struct file *filp, struct dentry *dentry, int datasync)
{
        return sync_blockdev(I_BDEV(filp->f_mapping->host));
}

/*
 * pseudo-fs
 */

static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(bdev_lock);
static struct kmem_cache * bdev_cachep __read_mostly;

static struct inode *bdev_alloc_inode(struct super_block *sb)
{
        struct bdev_inode *ei = kmem_cache_alloc(bdev_cachep, GFP_KERNEL);
        if (!ei)
                return NULL;
        return &ei->vfs_inode;
}

static void bdev_destroy_inode(struct inode *inode)
{
        struct bdev_inode *bdi = BDEV_I(inode);

        kmem_cache_free(bdev_cachep, bdi);
}

static void init_once(void *foo)
{
        struct bdev_inode *ei = (struct bdev_inode *) foo;
        struct block_device *bdev = &ei->bdev;

        memset(bdev, 0, sizeof(*bdev));
        mutex_init(&bdev->bd_mutex);
        INIT_LIST_HEAD(&bdev->bd_inodes);
        INIT_LIST_HEAD(&bdev->bd_list);
#ifdef CONFIG_SYSFS
        INIT_LIST_HEAD(&bdev->bd_holder_list);
#endif
        inode_init_once(&ei->vfs_inode);
        /* Initialize mutex for freeze. */
        mutex_init(&bdev->bd_fsfreeze_mutex);
}

static inline void __bd_forget(struct inode *inode)
{
        list_del_init(&inode->i_devices);
        inode->i_bdev = NULL;
        inode->i_mapping = &inode->i_data;
}

static void bdev_clear_inode(struct inode *inode)
{
        struct block_device *bdev = &BDEV_I(inode)->bdev;
        struct list_head *p;
        spin_lock(&bdev_lock);
        while ( (p = bdev->bd_inodes.next) != &bdev->bd_inodes ) {
                __bd_forget(list_entry(p, struct inode, i_devices));
        }
        list_del_init(&bdev->bd_list);
        spin_unlock(&bdev_lock);
}

static const struct super_operations bdev_sops = {
        .statfs = simple_statfs,
        .alloc_inode = bdev_alloc_inode,
        .destroy_inode = bdev_destroy_inode,
        .drop_inode = generic_delete_inode,
        .clear_inode = bdev_clear_inode,
};

static int bd_get_sb(struct file_system_type *fs_type,
        int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
        return get_sb_pseudo(fs_type, "bdev:", &bdev_sops, 0x62646576, mnt);
}

static struct file_system_type bd_type = {
        .name           = "bdev",
        .get_sb         = bd_get_sb,
        .kill_sb        = kill_anon_super,
};

struct super_block *blockdev_superblock __read_mostly;

void __init bdev_cache_init(void)
{
        int err;
        struct vfsmount *bd_mnt;

        bdev_cachep = kmem_cache_create("bdev_cache", sizeof(struct bdev_inode),
                        0, (SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT|
                                SLAB_MEM_SPREAD|SLAB_PANIC),
                        init_once);
        err = register_filesystem(&bd_type);
        if (err)
                panic("Cannot register bdev pseudo-fs");
        bd_mnt = kern_mount(&bd_type);
        if (IS_ERR(bd_mnt))
                panic("Cannot create bdev pseudo-fs");
        /*
         * This vfsmount structure is only used to obtain the
         * blockdev_superblock, so tell kmemleak not to report it.
         */
        kmemleak_not_leak(bd_mnt);
        blockdev_superblock = bd_mnt->mnt_sb;   /* For writeback */
}

/*
 * Most likely _very_ bad one - but then it's hardly critical for small
 * /dev and can be fixed when somebody will need really large one.
 * Keep in mind that it will be fed through icache hash function too.
 */
static inline unsigned long hash(dev_t dev)
{
        return MAJOR(dev)+MINOR(dev);
}

static int bdev_test(struct inode *inode, void *data)
{
        return BDEV_I(inode)->bdev.bd_dev == *(dev_t *)data;
}

static int bdev_set(struct inode *inode, void *data)
{
        BDEV_I(inode)->bdev.bd_dev = *(dev_t *)data;
        return 0;
}

static LIST_HEAD(all_bdevs);

struct block_device *bdget(dev_t dev)
{
        struct block_device *bdev;
        struct inode *inode;

        inode = iget5_locked(blockdev_superblock, hash(dev),
                        bdev_test, bdev_set, &dev);

        if (!inode)
                return NULL;

        bdev = &BDEV_I(inode)->bdev;

        if (inode->i_state & I_NEW) {
                bdev->bd_contains = NULL;
                bdev->bd_inode = inode;
                bdev->bd_block_size = (1 << inode->i_blkbits);
                bdev->bd_part_count = 0;
                bdev->bd_invalidated = 0;
                inode->i_mode = S_IFBLK;
                inode->i_rdev = dev;
                inode->i_bdev = bdev;
                inode->i_data.a_ops = &def_blk_aops;
                mapping_set_gfp_mask(&inode->i_data, GFP_USER);
                inode->i_data.backing_dev_info = &default_backing_dev_info;
                spin_lock(&bdev_lock);
                list_add(&bdev->bd_list, &all_bdevs);
                spin_unlock(&bdev_lock);
                unlock_new_inode(inode);
        }
        return bdev;
}

EXPORT_SYMBOL(bdget);

/**
 * bdgrab -- Grab a reference to an already referenced block device
 * @bdev:       Block device to grab a reference to.
 */
struct block_device *bdgrab(struct block_device *bdev)
{
        atomic_inc(&bdev->bd_inode->i_count);
        return bdev;
}

long nr_blockdev_pages(void)
{
        struct block_device *bdev;
        long ret = 0;
        spin_lock(&bdev_lock);
        list_for_each_entry(bdev, &all_bdevs, bd_list) {
                ret += bdev->bd_inode->i_mapping->nrpages;
        }
        spin_unlock(&bdev_lock);
        return ret;
}

void bdput(struct block_device *bdev)
{
        iput(bdev->bd_inode);
}

EXPORT_SYMBOL(bdput);
 
static struct block_device *bd_acquire(struct inode *inode)
{
        struct block_device *bdev;

        spin_lock(&bdev_lock);
        bdev = inode->i_bdev;
        if (bdev) {
                atomic_inc(&bdev->bd_inode->i_count);
                spin_unlock(&bdev_lock);
                return bdev;
        }
        spin_unlock(&bdev_lock);

        bdev = bdget(inode->i_rdev);
        if (bdev) {
                spin_lock(&bdev_lock);
                if (!inode->i_bdev) {
                        /*
                         * We take an additional bd_inode->i_count for inode,
                         * and it's released in clear_inode() of inode.
                         * So, we can access it via ->i_mapping always
                         * without igrab().
                         */
                        atomic_inc(&bdev->bd_inode->i_count);
                        inode->i_bdev = bdev;
                        inode->i_mapping = bdev->bd_inode->i_mapping;
                        list_add(&inode->i_devices, &bdev->bd_inodes);
                }
                spin_unlock(&bdev_lock);
        }
        return bdev;
}

/* Call when you free inode */

void bd_forget(struct inode *inode)
{
        struct block_device *bdev = NULL;

        spin_lock(&bdev_lock);
        if (inode->i_bdev) {
                if (!sb_is_blkdev_sb(inode->i_sb))
                        bdev = inode->i_bdev;
                __bd_forget(inode);
        }
        spin_unlock(&bdev_lock);

        if (bdev)
                iput(bdev->bd_inode);
}

int bd_claim(struct block_device *bdev, void *holder)
{
        int res;
        spin_lock(&bdev_lock);

        /* first decide result */
        if (bdev->bd_holder == holder)
                res = 0;         /* already a holder */
        else if (bdev->bd_holder != NULL)
                res = -EBUSY;    /* held by someone else */
        else if (bdev->bd_contains == bdev)
                res = 0;         /* is a whole device which isn't held */

        else if (bdev->bd_contains->bd_holder == bd_claim)
                res = 0;         /* is a partition of a device that is being partitioned */
        else if (bdev->bd_contains->bd_holder != NULL)
                res = -EBUSY;    /* is a partition of a held device */
        else
                res = 0;         /* is a partition of an un-held device */

        /* now impose change */
        if (res==0) {
                /* note that for a whole device bd_holders
                 * will be incremented twice, and bd_holder will
                 * be set to bd_claim before being set to holder
                 */
                bdev->bd_contains->bd_holders ++;
                bdev->bd_contains->bd_holder = bd_claim;
                bdev->bd_holders++;
                bdev->bd_holder = holder;
        }
        spin_unlock(&bdev_lock);
        return res;
}

EXPORT_SYMBOL(bd_claim);

void bd_release(struct block_device *bdev)
{
        spin_lock(&bdev_lock);
        if (!--bdev->bd_contains->bd_holders)
                bdev->bd_contains->bd_holder = NULL;
        if (!--bdev->bd_holders)
                bdev->bd_holder = NULL;
        spin_unlock(&bdev_lock);
}

EXPORT_SYMBOL(bd_release);

#ifdef CONFIG_SYSFS
/*
 * Functions for bd_claim_by_kobject / bd_release_from_kobject
 *
 *     If a kobject is passed to bd_claim_by_kobject()
 *     and the kobject has a parent directory,
 *     following symlinks are created:
 *        o from the kobject to the claimed bdev
 *        o from "holders" directory of the bdev to the parent of the kobject
 *     bd_release_from_kobject() removes these symlinks.
 *
 *     Example:
 *        If /dev/dm-0 maps to /dev/sda, kobject corresponding to
 *        /sys/block/dm-0/slaves is passed to bd_claim_by_kobject(), then:
 *           /sys/block/dm-0/slaves/sda --> /sys/block/sda
 *           /sys/block/sda/holders/dm-0 --> /sys/block/dm-0
 */

static int add_symlink(struct kobject *from, struct kobject *to)
{
        if (!from || !to)
                return 0;
        return sysfs_create_link(from, to, kobject_name(to));
}

static void del_symlink(struct kobject *from, struct kobject *to)
{
        if (!from || !to)
                return;
        sysfs_remove_link(from, kobject_name(to));
}

/*
 * 'struct bd_holder' contains pointers to kobjects symlinked by
 * bd_claim_by_kobject.
 * It's connected to bd_holder_list which is protected by bdev->bd_sem.
 */
struct bd_holder {
        struct list_head list;  /* chain of holders of the bdev */
        int count;              /* references from the holder */
        struct kobject *sdir;   /* holder object, e.g. "/block/dm-0/slaves" */
        struct kobject *hdev;   /* e.g. "/block/dm-0" */
        struct kobject *hdir;   /* e.g. "/block/sda/holders" */
        struct kobject *sdev;   /* e.g. "/block/sda" */
};

/*
 * Get references of related kobjects at once.
 * Returns 1 on success. 0 on failure.
 *
 * Should call bd_holder_release_dirs() after successful use.
 */
static int bd_holder_grab_dirs(struct block_device *bdev,
                        struct bd_holder *bo)
{
        if (!bdev || !bo)
                return 0;

        bo->sdir = kobject_get(bo->sdir);
        if (!bo->sdir)
                return 0;

        bo->hdev = kobject_get(bo->sdir->parent);
        if (!bo->hdev)
                goto fail_put_sdir;

        bo->sdev = kobject_get(&part_to_dev(bdev->bd_part)->kobj);
        if (!bo->sdev)
                goto fail_put_hdev;

        bo->hdir = kobject_get(bdev->bd_part->holder_dir);
        if (!bo->hdir)
                goto fail_put_sdev;

        return 1;

fail_put_sdev:
        kobject_put(bo->sdev);
fail_put_hdev:
        kobject_put(bo->hdev);
fail_put_sdir:
        kobject_put(bo->sdir);

        return 0;
}

/* Put references of related kobjects at once. */
static void bd_holder_release_dirs(struct bd_holder *bo)
{
        kobject_put(bo->hdir);
        kobject_put(bo->sdev);
        kobject_put(bo->hdev);
        kobject_put(bo->sdir);
}

static struct bd_holder *alloc_bd_holder(struct kobject *kobj)
{
        struct bd_holder *bo;

        bo = kzalloc(sizeof(*bo), GFP_KERNEL);
        if (!bo)
                return NULL;

        bo->count = 1;
        bo->sdir = kobj;

        return bo;
}

static void free_bd_holder(struct bd_holder *bo)
{
        kfree(bo);
}

/**
 * find_bd_holder - find matching struct bd_holder from the block device
 *
 * @bdev:       struct block device to be searched
 * @bo:         target struct bd_holder
 *
 * Returns matching entry with @bo in @bdev->bd_holder_list.
 * If found, increment the reference count and return the pointer.
 * If not found, returns NULL.
 */
static struct bd_holder *find_bd_holder(struct block_device *bdev,
                                        struct bd_holder *bo)
{
        struct bd_holder *tmp;

        list_for_each_entry(tmp, &bdev->bd_holder_list, list)
                if (tmp->sdir == bo->sdir) {
                        tmp->count++;
                        return tmp;
                }

        return NULL;
}

/**
 * add_bd_holder - create sysfs symlinks for bd_claim() relationship
 *
 * @bdev:       block device to be bd_claimed
 * @bo:         preallocated and initialized by alloc_bd_holder()
 *
 * Add @bo to @bdev->bd_holder_list, create symlinks.
 *
 * Returns 0 if symlinks are created.
 * Returns -ve if something fails.
 */
static int add_bd_holder(struct block_device *bdev, struct bd_holder *bo)
{
        int err;

        if (!bo)
                return -EINVAL;

        if (!bd_holder_grab_dirs(bdev, bo))
                return -EBUSY;

        err = add_symlink(bo->sdir, bo->sdev);
        if (err)
                return err;

        err = add_symlink(bo->hdir, bo->hdev);
        if (err) {
                del_symlink(bo->sdir, bo->sdev);
                return err;
        }

        list_add_tail(&bo->list, &bdev->bd_holder_list);
        return 0;
}

/**
 * del_bd_holder - delete sysfs symlinks for bd_claim() relationship
 *
 * @bdev:       block device to be bd_claimed
 * @kobj:       holder's kobject
 *
 * If there is matching entry with @kobj in @bdev->bd_holder_list
 * and no other bd_claim() from the same kobject,
 * remove the struct bd_holder from the list, delete symlinks for it.
 *
 * Returns a pointer to the struct bd_holder when it's removed from the list
 * and ready to be freed.
 * Returns NULL if matching claim isn't found or there is other bd_claim()
 * by the same kobject.
 */
static struct bd_holder *del_bd_holder(struct block_device *bdev,
                                        struct kobject *kobj)
{
        struct bd_holder *bo;

        list_for_each_entry(bo, &bdev->bd_holder_list, list) {
                if (bo->sdir == kobj) {
                        bo->count--;
                        BUG_ON(bo->count < 0);
                        if (!bo->count) {
                                list_del(&bo->list);
                                del_symlink(bo->sdir, bo->sdev);
                                del_symlink(bo->hdir, bo->hdev);
                                bd_holder_release_dirs(bo);
                                return bo;
                        }
                        break;
                }
        }

        return NULL;
}

/**
 * bd_claim_by_kobject - bd_claim() with additional kobject signature
 *
 * @bdev:       block device to be claimed
 * @holder:     holder's signature
 * @kobj:       holder's kobject
 *
 * Do bd_claim() and if it succeeds, create sysfs symlinks between
 * the bdev and the holder's kobject.
 * Use bd_release_from_kobject() when relesing the claimed bdev.
 *
 * Returns 0 on success. (same as bd_claim())
 * Returns errno on failure.
 */
static int bd_claim_by_kobject(struct block_device *bdev, void *holder,
                                struct kobject *kobj)
{
        int err;
        struct bd_holder *bo, *found;

        if (!kobj)
                return -EINVAL;

        bo = alloc_bd_holder(kobj);
        if (!bo)
                return -ENOMEM;

        mutex_lock(&bdev->bd_mutex);

        err = bd_claim(bdev, holder);
        if (err)
                goto fail;

        found = find_bd_holder(bdev, bo);
        if (found)
                goto fail;

        err = add_bd_holder(bdev, bo);
        if (err)
                bd_release(bdev);
        else
                bo = NULL;
fail:
        mutex_unlock(&bdev->bd_mutex);
        free_bd_holder(bo);
        return err;
}

/**
 * bd_release_from_kobject - bd_release() with additional kobject signature
 *
 * @bdev:       block device to be released
 * @kobj:       holder's kobject
 *
 * Do bd_release() and remove sysfs symlinks created by bd_claim_by_kobject().
 */
static void bd_release_from_kobject(struct block_device *bdev,
                                        struct kobject *kobj)
{
        if (!kobj)
                return;

        mutex_lock(&bdev->bd_mutex);
        bd_release(bdev);
        free_bd_holder(del_bd_holder(bdev, kobj));
        mutex_unlock(&bdev->bd_mutex);
}

/**
 * bd_claim_by_disk - wrapper function for bd_claim_by_kobject()
 *
 * @bdev:       block device to be claimed
 * @holder:     holder's signature
 * @disk:       holder's gendisk
 *
 * Call bd_claim_by_kobject() with getting @disk->slave_dir.
 */
int bd_claim_by_disk(struct block_device *bdev, void *holder,
                        struct gendisk *disk)
{
        return bd_claim_by_kobject(bdev, holder, kobject_get(disk->slave_dir));
}
EXPORT_SYMBOL_GPL(bd_claim_by_disk);

/**
 * bd_release_from_disk - wrapper function for bd_release_from_kobject()
 *
 * @bdev:       block device to be claimed
 * @disk:       holder's gendisk
 *
 * Call bd_release_from_kobject() and put @disk->slave_dir.
 */
void bd_release_from_disk(struct block_device *bdev, struct gendisk *disk)
{
        bd_release_from_kobject(bdev, disk->slave_dir);
        kobject_put(disk->slave_dir);
}
EXPORT_SYMBOL_GPL(bd_release_from_disk);
#endif

/*
 * Tries to open block device by device number.  Use it ONLY if you
 * really do not have anything better - i.e. when you are behind a
 * truly sucky interface and all you are given is a device number.  _Never_
 * to be used for internal purposes.  If you ever need it - reconsider
 * your API.
 */
struct block_device *open_by_devnum(dev_t dev, fmode_t mode)
{
        struct block_device *bdev = bdget(dev);
        int err = -ENOMEM;
        if (bdev)
                err = blkdev_get(bdev, mode);
        return err ? ERR_PTR(err) : bdev;
}

EXPORT_SYMBOL(open_by_devnum);

/**
 * flush_disk - invalidates all buffer-cache entries on a disk
 *
 * @bdev:      struct block device to be flushed
 *
 * Invalidates all buffer-cache entries on a disk. It should be called
 * when a disk has been changed -- either by a media change or online
 * resize.
 */
static void flush_disk(struct block_device *bdev)
{
        if (__invalidate_device(bdev)) {
                char name[BDEVNAME_SIZE] = "";

                if (bdev->bd_disk)
                        disk_name(bdev->bd_disk, 0, name);
                printk(KERN_WARNING "VFS: busy inodes on changed media or "
                       "resized disk %s\n", name);
        }

        if (!bdev->bd_disk)
                return;
        if (disk_partitionable(bdev->bd_disk))
                bdev->bd_invalidated = 1;
}

/**
 * check_disk_size_change - checks for disk size change and adjusts bdev size.
 * @disk: struct gendisk to check
 * @bdev: struct bdev to adjust.
 *
 * This routine checks to see if the bdev size does not match the disk size
 * and adjusts it if it differs.
 */
void check_disk_size_change(struct gendisk *disk, struct block_device *bdev)
{
        loff_t disk_size, bdev_size;

        disk_size = (loff_t)get_capacity(disk) << 9;
        bdev_size = i_size_read(bdev->bd_inode);
        if (disk_size != bdev_size) {
                char name[BDEVNAME_SIZE];

                disk_name(disk, 0, name);
                printk(KERN_INFO
                       "%s: detected capacity change from %lld to %lld\n",
                       name, bdev_size, disk_size);
                i_size_write(bdev->bd_inode, disk_size);
                flush_disk(bdev);
        }
}
EXPORT_SYMBOL(check_disk_size_change);

/**
 * revalidate_disk - wrapper for lower-level driver's revalidate_disk call-back
 * @disk: struct gendisk to be revalidated
 *
 * This routine is a wrapper for lower-level driver's revalidate_disk
 * call-backs.  It is used to do common pre and post operations needed
 * for all revalidate_disk operations.
 */
int revalidate_disk(struct gendisk *disk)
{
        struct block_device *bdev;
        int ret = 0;

        if (disk->fops->revalidate_disk)
                ret = disk->fops->revalidate_disk(disk);

        bdev = bdget_disk(disk, 0);
        if (!bdev)
                return ret;

        mutex_lock(&bdev->bd_mutex);
        check_disk_size_change(disk, bdev);
        mutex_unlock(&bdev->bd_mutex);
        bdput(bdev);
        return ret;
}
EXPORT_SYMBOL(revalidate_disk);

/*
 * This routine checks whether a removable media has been changed,
 * and invalidates all buffer-cache-entries in that case. This
 * is a relatively slow routine, so we have to try to minimize using
 * it. Thus it is called only upon a 'mount' or 'open'. This
 * is the best way of combining speed and utility, I think.
 * People changing diskettes in the middle of an operation deserve
 * to lose :-)
 */
int check_disk_change(struct block_device *bdev)
{
        struct gendisk *disk = bdev->bd_disk;
        const struct block_device_operations *bdops = disk->fops;

        if (!bdops->media_changed)
                return 0;
        if (!bdops->media_changed(bdev->bd_disk))
                return 0;

        flush_disk(bdev);
        if (bdops->revalidate_disk)
                bdops->revalidate_disk(bdev->bd_disk);
        return 1;
}

EXPORT_SYMBOL(check_disk_change);

void bd_set_size(struct block_device *bdev, loff_t size)
{
        unsigned bsize = bdev_logical_block_size(bdev);

        bdev->bd_inode->i_size = size;
        while (bsize < PAGE_CACHE_SIZE) {
                if (size & bsize)
                        break;
                bsize <<= 1;
        }
        bdev->bd_block_size = bsize;
        bdev->bd_inode->i_blkbits = blksize_bits(bsize);
}
EXPORT_SYMBOL(bd_set_size);

static int __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part);

/*
 * bd_mutex locking:
 *
 *  mutex_lock(part->bd_mutex)
 *    mutex_lock_nested(whole->bd_mutex, 1)
 */

static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
{
        struct gendisk *disk;
        int ret;
        int partno;
        int perm = 0;

        if (mode & FMODE_READ)
                perm |= MAY_READ;
        if (mode & FMODE_WRITE)
                perm |= MAY_WRITE;
        /*
         * hooks: /n/, see "layering violations".
         */
        ret = devcgroup_inode_permission(bdev->bd_inode, perm);
        if (ret != 0) {
                bdput(bdev);
                return ret;
        }

        lock_kernel();
 restart:

        ret = -ENXIO;
        disk = get_gendisk(bdev->bd_dev, &partno);
        if (!disk)
                goto out_unlock_kernel;

        mutex_lock_nested(&bdev->bd_mutex, for_part);
        if (!bdev->bd_openers) {
                bdev->bd_disk = disk;
                bdev->bd_contains = bdev;
                if (!partno) {
                        struct backing_dev_info *bdi;

                        ret = -ENXIO;
                        bdev->bd_part = disk_get_part(disk, partno);
                        if (!bdev->bd_part)
                                goto out_clear;

                        if (disk->fops->open) {
                                ret = disk->fops->open(bdev, mode);
                                if (ret == -ERESTARTSYS) {
                                        /* Lost a race with 'disk' being
                                         * deleted, try again.
                                         * See md.c
                                         */
                                        disk_put_part(bdev->bd_part);
                                        bdev->bd_part = NULL;
                                        module_put(disk->fops->owner);
                                        put_disk(disk);
                                        bdev->bd_disk = NULL;
                                        mutex_unlock(&bdev->bd_mutex);
                                        goto restart;
                                }
                                if (ret)
                                        goto out_clear;
                        }
                        if (!bdev->bd_openers) {
                                bd_set_size(bdev,(loff_t)get_capacity(disk)<<9);
                                bdi = blk_get_backing_dev_info(bdev);
                                if (bdi == NULL)
                                        bdi = &default_backing_dev_info;
                                bdev->bd_inode->i_data.backing_dev_info = bdi;
                        }
                        if (bdev->bd_invalidated)
                                rescan_partitions(disk, bdev);
                } else {
                        struct block_device *whole;
                        whole = bdget_disk(disk, 0);
                        ret = -ENOMEM;
                        if (!whole)
                                goto out_clear;
                        BUG_ON(for_part);
                        ret = __blkdev_get(whole, mode, 1);
                        if (ret)
                                goto out_clear;
                        bdev->bd_contains = whole;
                        bdev->bd_inode->i_data.backing_dev_info =
                           whole->bd_inode->i_data.backing_dev_info;
                        bdev->bd_part = disk_get_part(disk, partno);
                        if (!(disk->flags & GENHD_FL_UP) ||
                            !bdev->bd_part || !bdev->bd_part->nr_sects) {
                                ret = -ENXIO;
                                goto out_clear;
                        }
                        bd_set_size(bdev, (loff_t)bdev->bd_part->nr_sects << 9);
                }
        } else {
                put_disk(disk);
                module_put(disk->fops->owner);
                disk = NULL;
                if (bdev->bd_contains == bdev) {
                        if (bdev->bd_disk->fops->open) {
                                ret = bdev->bd_disk->fops->open(bdev, mode);
                                if (ret)
                                        goto out_unlock_bdev;
                        }
                        if (bdev->bd_invalidated)
                                rescan_partitions(bdev->bd_disk, bdev);
                }
        }
        bdev->bd_openers++;
        if (for_part)
                bdev->bd_part_count++;
        mutex_unlock(&bdev->bd_mutex);
        unlock_kernel();
        return 0;

 out_clear:
        disk_put_part(bdev->bd_part);
        bdev->bd_disk = NULL;
        bdev->bd_part = NULL;
        bdev->bd_inode->i_data.backing_dev_info = &default_backing_dev_info;
        if (bdev != bdev->bd_contains)
                __blkdev_put(bdev->bd_contains, mode, 1);
        bdev->bd_contains = NULL;
 out_unlock_bdev:
        mutex_unlock(&bdev->bd_mutex);
 out_unlock_kernel:
        unlock_kernel();

        if (disk)
                module_put(disk->fops->owner);
        put_disk(disk);
        bdput(bdev);

        return ret;
}

int blkdev_get(struct block_device *bdev, fmode_t mode)
{
        return __blkdev_get(bdev, mode, 0);
}
EXPORT_SYMBOL(blkdev_get);

static int blkdev_open(struct inode * inode, struct file * filp)
{
        struct block_device *bdev;
        int res;

        /*
         * Preserve backwards compatibility and allow large file access
         * even if userspace doesn't ask for it explicitly. Some mkfs
         * binary needs it. We might want to drop this workaround
         * during an unstable branch.
         */
        filp->f_flags |= O_LARGEFILE;

        if (filp->f_flags & O_NDELAY)
                filp->f_mode |= FMODE_NDELAY;
        if (filp->f_flags & O_EXCL)
                filp->f_mode |= FMODE_EXCL;
        if ((filp->f_flags & O_ACCMODE) == 3)
                filp->f_mode |= FMODE_WRITE_IOCTL;

        bdev = bd_acquire(inode);
        if (bdev == NULL)
                return -ENOMEM;

        filp->f_mapping = bdev->bd_inode->i_mapping;

        res = blkdev_get(bdev, filp->f_mode);
        if (res)
                return res;

        if (filp->f_mode & FMODE_EXCL) {
                res = bd_claim(bdev, filp);
                if (res)
                        goto out_blkdev_put;
        }

        return 0;

 out_blkdev_put:
        blkdev_put(bdev, filp->f_mode);
        return res;
}

static int __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
{
        int ret = 0;
        struct gendisk *disk = bdev->bd_disk;
        struct block_device *victim = NULL;

        mutex_lock_nested(&bdev->bd_mutex, for_part);
        lock_kernel();
        if (for_part)
                bdev->bd_part_count--;

        if (!--bdev->bd_openers) {
                sync_blockdev(bdev);
                kill_bdev(bdev);
        }
        if (bdev->bd_contains == bdev) {
                if (disk->fops->release)
                        ret = disk->fops->release(disk, mode);
        }
        if (!bdev->bd_openers) {
                struct module *owner = disk->fops->owner;

                put_disk(disk);
                module_put(owner);
                disk_put_part(bdev->bd_part);
                bdev->bd_part = NULL;
                bdev->bd_disk = NULL;
                bdev->bd_inode->i_data.backing_dev_info = &default_backing_dev_info;
                if (bdev != bdev->bd_contains)
                        victim = bdev->bd_contains;
                bdev->bd_contains = NULL;
        }
        unlock_kernel();
        mutex_unlock(&bdev->bd_mutex);
        bdput(bdev);
        if (victim)
                __blkdev_put(victim, mode, 1);
        return ret;
}

int blkdev_put(struct block_device *bdev, fmode_t mode)
{
        return __blkdev_put(bdev, mode, 0);
}
EXPORT_SYMBOL(blkdev_put);

static int blkdev_close(struct inode * inode, struct file * filp)
{
        struct block_device *bdev = I_BDEV(filp->f_mapping->host);
        if (bdev->bd_holder == filp)
                bd_release(bdev);
        return blkdev_put(bdev, filp->f_mode);
}

static long block_ioctl(struct file *file, unsigned cmd, unsigned long arg)
{
        struct block_device *bdev = I_BDEV(file->f_mapping->host);
        fmode_t mode = file->f_mode;

        /*
         * O_NDELAY can be altered using fcntl(.., F_SETFL, ..), so we have
         * to updated it before every ioctl.
         */
        if (file->f_flags & O_NDELAY)
                mode |= FMODE_NDELAY;
        else
                mode &= ~FMODE_NDELAY;

        return blkdev_ioctl(bdev, mode, cmd, arg);
}

/*
 * Write data to the block device.  Only intended for the block device itself
 * and the raw driver which basically is a fake block device.
 *
 * Does not take i_mutex for the write and thus is not for general purpose
 * use.
 */
ssize_t blkdev_aio_write(struct kiocb *iocb, const struct iovec *iov,
                         unsigned long nr_segs, loff_t pos)
{
        struct file *file = iocb->ki_filp;
        ssize_t ret;

        BUG_ON(iocb->ki_pos != pos);

        ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
        if (ret > 0 || ret == -EIOCBQUEUED) {
                ssize_t err;

                err = generic_write_sync(file, pos, ret);
                if (err < 0 && ret > 0)
                        ret = err;
        }
        return ret;
}
EXPORT_SYMBOL_GPL(blkdev_aio_write);

/*
 * Try to release a page associated with block device when the system
 * is under memory pressure.
 */
static int blkdev_releasepage(struct page *page, gfp_t wait)
{
        struct super_block *super = BDEV_I(page->mapping->host)->bdev.bd_super;

        if (super && super->s_op->bdev_try_to_free_page)
                return super->s_op->bdev_try_to_free_page(super, page, wait);

        return try_to_free_buffers(page);
}

static const struct address_space_operations def_blk_aops = {
        .readpage       = blkdev_readpage,
        .writepage      = blkdev_writepage,
        .sync_page      = block_sync_page,
        .write_begin    = blkdev_write_begin,
        .write_end      = blkdev_write_end,
        .writepages     = generic_writepages,
        .releasepage    = blkdev_releasepage,
        .direct_IO      = blkdev_direct_IO,
};

const struct file_operations def_blk_fops = {
        .open           = blkdev_open,
        .release        = blkdev_close,
        .llseek         = block_llseek,
        .read           = do_sync_read,
        .write          = do_sync_write,
        .aio_read       = generic_file_aio_read,
        .aio_write      = blkdev_aio_write,
        .mmap           = generic_file_mmap,
        .fsync          = block_fsync,
        .unlocked_ioctl = block_ioctl,
#ifdef CONFIG_COMPAT
        .compat_ioctl   = compat_blkdev_ioctl,
#endif
        .splice_read    = generic_file_splice_read,
        .splice_write   = generic_file_splice_write,
};

int ioctl_by_bdev(struct block_device *bdev, unsigned cmd, unsigned long arg)
{
        int res;
        mm_segment_t old_fs = get_fs();
        set_fs(KERNEL_DS);
        res = blkdev_ioctl(bdev, 0, cmd, arg);
        set_fs(old_fs);
        return res;
}

EXPORT_SYMBOL(ioctl_by_bdev);

/**
 * lookup_bdev  - lookup a struct block_device by name
 * @pathname:   special file representing the block device
 *
 * Get a reference to the blockdevice at @pathname in the current
 * namespace if possible and return it.  Return ERR_PTR(error)
 * otherwise.
 */
struct block_device *lookup_bdev(const char *pathname)
{
        struct block_device *bdev;
        struct inode *inode;
        struct path path;
        int error;

        if (!pathname || !*pathname)
                return ERR_PTR(-EINVAL);

        error = kern_path(pathname, LOOKUP_FOLLOW, &path);
        if (error)
                return ERR_PTR(error);

        inode = path.dentry->d_inode;
        error = -ENOTBLK;
        if (!S_ISBLK(inode->i_mode))
                goto fail;
        error = -EACCES;
        if (path.mnt->mnt_flags & MNT_NODEV)
                goto fail;
        error = -ENOMEM;
        bdev = bd_acquire(inode);
        if (!bdev)
                goto fail;
out:
        path_put(&path);
        return bdev;
fail:
        bdev = ERR_PTR(error);
        goto out;
}
EXPORT_SYMBOL(lookup_bdev);

/**
 * open_bdev_exclusive  -  open a block device by name and set it up for use
 *
 * @path:       special file representing the block device
 * @mode:       FMODE_... combination to pass be used
 * @holder:     owner for exclusion
 *
 * Open the blockdevice described by the special file at @path, claim it
 * for the @holder.
 */
struct block_device *open_bdev_exclusive(const char *path, fmode_t mode, void *holder)
{
        struct block_device *bdev;
        int error = 0;

        bdev = lookup_bdev(path);
        if (IS_ERR(bdev))
                return bdev;

        error = blkdev_get(bdev, mode);
        if (error)
                return ERR_PTR(error);
        error = -EACCES;
        if ((mode & FMODE_WRITE) && bdev_read_only(bdev))
                goto blkdev_put;
        error = bd_claim(bdev, holder);
        if (error)
                goto blkdev_put;

        return bdev;
        
blkdev_put:
        blkdev_put(bdev, mode);
        return ERR_PTR(error);
}

EXPORT_SYMBOL(open_bdev_exclusive);

/**
 * close_bdev_exclusive  -  close a blockdevice opened by open_bdev_exclusive()
 *
 * @bdev:       blockdevice to close
 * @mode:       mode, must match that used to open.
 *
 * This is the counterpart to open_bdev_exclusive().
 */
void close_bdev_exclusive(struct block_device *bdev, fmode_t mode)
{
        bd_release(bdev);
        blkdev_put(bdev, mode);
}

EXPORT_SYMBOL(close_bdev_exclusive);

int __invalidate_device(struct block_device *bdev)
{
        struct super_block *sb = get_super(bdev);
        int res = 0;

        if (sb) {
                /*
                 * no need to lock the super, get_super holds the
                 * read mutex so the filesystem cannot go away
                 * under us (->put_super runs with the write lock
                 * hold).
                 */
                shrink_dcache_sb(sb);
                res = invalidate_inodes(sb);
                drop_super(sb);
        }
        invalidate_bdev(bdev);
        return res;
}
EXPORT_SYMBOL(__invalidate_device);