s390/kvm: REPLACE barrier fixup with READ_ONCE

[mirror_ubuntu-zesty-kernel.git] / block / genhd.c

/*
 *  gendisk handling
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/genhd.h>
#include <linux/kdev_t.h>
#include <linux/kernel.h>
#include <linux/blkdev.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/kmod.h>
#include <linux/kobj_map.h>
#include <linux/mutex.h>
#include <linux/idr.h>
#include <linux/log2.h>
#include <linux/pm_runtime.h>

#include "blk.h"

static DEFINE_MUTEX(block_class_lock);
struct kobject *block_depr;

/* for extended dynamic devt allocation, currently only one major is used */
#define NR_EXT_DEVT             (1 << MINORBITS)

/* For extended devt allocation.  ext_devt_lock prevents look up
 * results from going away underneath its user.
 */
static DEFINE_SPINLOCK(ext_devt_lock);
static DEFINE_IDR(ext_devt_idr);

static struct device_type disk_type;

static void disk_check_events(struct disk_events *ev,
                              unsigned int *clearing_ptr);
static void disk_alloc_events(struct gendisk *disk);
static void disk_add_events(struct gendisk *disk);
static void disk_del_events(struct gendisk *disk);
static void disk_release_events(struct gendisk *disk);

/**
 * disk_get_part - get partition
 * @disk: disk to look partition from
 * @partno: partition number
 *
 * Look for partition @partno from @disk.  If found, increment
 * reference count and return it.
 *
 * CONTEXT:
 * Don't care.
 *
 * RETURNS:
 * Pointer to the found partition on success, NULL if not found.
 */
struct hd_struct *disk_get_part(struct gendisk *disk, int partno)
{
        struct hd_struct *part = NULL;
        struct disk_part_tbl *ptbl;

        if (unlikely(partno < 0))
                return NULL;

        rcu_read_lock();

        ptbl = rcu_dereference(disk->part_tbl);
        if (likely(partno < ptbl->len)) {
                part = rcu_dereference(ptbl->part[partno]);
                if (part)
                        get_device(part_to_dev(part));
        }

        rcu_read_unlock();

        return part;
}
EXPORT_SYMBOL_GPL(disk_get_part);

/**
 * disk_part_iter_init - initialize partition iterator
 * @piter: iterator to initialize
 * @disk: disk to iterate over
 * @flags: DISK_PITER_* flags
 *
 * Initialize @piter so that it iterates over partitions of @disk.
 *
 * CONTEXT:
 * Don't care.
 */
void disk_part_iter_init(struct disk_part_iter *piter, struct gendisk *disk,
                          unsigned int flags)
{
        struct disk_part_tbl *ptbl;

        rcu_read_lock();
        ptbl = rcu_dereference(disk->part_tbl);

        piter->disk = disk;
        piter->part = NULL;

        if (flags & DISK_PITER_REVERSE)
                piter->idx = ptbl->len - 1;
        else if (flags & (DISK_PITER_INCL_PART0 | DISK_PITER_INCL_EMPTY_PART0))
                piter->idx = 0;
        else
                piter->idx = 1;

        piter->flags = flags;

        rcu_read_unlock();
}
EXPORT_SYMBOL_GPL(disk_part_iter_init);

/**
 * disk_part_iter_next - proceed iterator to the next partition and return it
 * @piter: iterator of interest
 *
 * Proceed @piter to the next partition and return it.
 *
 * CONTEXT:
 * Don't care.
 */
struct hd_struct *disk_part_iter_next(struct disk_part_iter *piter)
{
        struct disk_part_tbl *ptbl;
        int inc, end;

        /* put the last partition */
        disk_put_part(piter->part);
        piter->part = NULL;

        /* get part_tbl */
        rcu_read_lock();
        ptbl = rcu_dereference(piter->disk->part_tbl);

        /* determine iteration parameters */
        if (piter->flags & DISK_PITER_REVERSE) {
                inc = -1;
                if (piter->flags & (DISK_PITER_INCL_PART0 |
                                    DISK_PITER_INCL_EMPTY_PART0))
                        end = -1;
                else
                        end = 0;
        } else {
                inc = 1;
                end = ptbl->len;
        }

        /* iterate to the next partition */
        for (; piter->idx != end; piter->idx += inc) {
                struct hd_struct *part;

                part = rcu_dereference(ptbl->part[piter->idx]);
                if (!part)
                        continue;
                if (!part_nr_sects_read(part) &&
                    !(piter->flags & DISK_PITER_INCL_EMPTY) &&
                    !(piter->flags & DISK_PITER_INCL_EMPTY_PART0 &&
                      piter->idx == 0))
                        continue;

                get_device(part_to_dev(part));
                piter->part = part;
                piter->idx += inc;
                break;
        }

        rcu_read_unlock();

        return piter->part;
}
EXPORT_SYMBOL_GPL(disk_part_iter_next);

/**
 * disk_part_iter_exit - finish up partition iteration
 * @piter: iter of interest
 *
 * Called when iteration is over.  Cleans up @piter.
 *
 * CONTEXT:
 * Don't care.
 */
void disk_part_iter_exit(struct disk_part_iter *piter)
{
        disk_put_part(piter->part);
        piter->part = NULL;
}
EXPORT_SYMBOL_GPL(disk_part_iter_exit);

static inline int sector_in_part(struct hd_struct *part, sector_t sector)
{
        return part->start_sect <= sector &&
                sector < part->start_sect + part_nr_sects_read(part);
}

/**
 * disk_map_sector_rcu - map sector to partition
 * @disk: gendisk of interest
 * @sector: sector to map
 *
 * Find out which partition @sector maps to on @disk.  This is
 * primarily used for stats accounting.
 *
 * CONTEXT:
 * RCU read locked.  The returned partition pointer is valid only
 * while preemption is disabled.
 *
 * RETURNS:
 * Found partition on success, part0 is returned if no partition matches
 */
struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
{
        struct disk_part_tbl *ptbl;
        struct hd_struct *part;
        int i;

        ptbl = rcu_dereference(disk->part_tbl);

        part = rcu_dereference(ptbl->last_lookup);
        if (part && sector_in_part(part, sector))
                return part;

        for (i = 1; i < ptbl->len; i++) {
                part = rcu_dereference(ptbl->part[i]);

                if (part && sector_in_part(part, sector)) {
                        rcu_assign_pointer(ptbl->last_lookup, part);
                        return part;
                }
        }
        return &disk->part0;
}
EXPORT_SYMBOL_GPL(disk_map_sector_rcu);

/*
 * Can be deleted altogether. Later.
 *
 */
static struct blk_major_name {
        struct blk_major_name *next;
        int major;
        char name[16];
} *major_names[BLKDEV_MAJOR_HASH_SIZE];

/* index in the above - for now: assume no multimajor ranges */
static inline int major_to_index(unsigned major)
{
        return major % BLKDEV_MAJOR_HASH_SIZE;
}

#ifdef CONFIG_PROC_FS
void blkdev_show(struct seq_file *seqf, off_t offset)
{
        struct blk_major_name *dp;

        if (offset < BLKDEV_MAJOR_HASH_SIZE) {
                mutex_lock(&block_class_lock);
                for (dp = major_names[offset]; dp; dp = dp->next)
                        seq_printf(seqf, "%3d %s\n", dp->major, dp->name);
                mutex_unlock(&block_class_lock);
        }
}
#endif /* CONFIG_PROC_FS */

/**
 * register_blkdev - register a new block device
 *
 * @major: the requested major device number [1..255]. If @major=0, try to
 *         allocate any unused major number.
 * @name: the name of the new block device as a zero terminated string
 *
 * The @name must be unique within the system.
 *
 * The return value depends on the @major input parameter.
 *  - if a major device number was requested in range [1..255] then the
 *    function returns zero on success, or a negative error code
 *  - if any unused major number was requested with @major=0 parameter
 *    then the return value is the allocated major number in range
 *    [1..255] or a negative error code otherwise
 */
int register_blkdev(unsigned int major, const char *name)
{
        struct blk_major_name **n, *p;
        int index, ret = 0;

        mutex_lock(&block_class_lock);

        /* temporary */
        if (major == 0) {
                for (index = ARRAY_SIZE(major_names)-1; index > 0; index--) {
                        if (major_names[index] == NULL)
                                break;
                }

                if (index == 0) {
                        printk("register_blkdev: failed to get major for %s\n",
                               name);
                        ret = -EBUSY;
                        goto out;
                }
                major = index;
                ret = major;
        }

        p = kmalloc(sizeof(struct blk_major_name), GFP_KERNEL);
        if (p == NULL) {
                ret = -ENOMEM;
                goto out;
        }

        p->major = major;
        strlcpy(p->name, name, sizeof(p->name));
        p->next = NULL;
        index = major_to_index(major);

        for (n = &major_names[index]; *n; n = &(*n)->next) {
                if ((*n)->major == major)
                        break;
        }
        if (!*n)
                *n = p;
        else
                ret = -EBUSY;

        if (ret < 0) {
                printk("register_blkdev: cannot get major %d for %s\n",
                       major, name);
                kfree(p);
        }
out:
        mutex_unlock(&block_class_lock);
        return ret;
}

EXPORT_SYMBOL(register_blkdev);

void unregister_blkdev(unsigned int major, const char *name)
{
        struct blk_major_name **n;
        struct blk_major_name *p = NULL;
        int index = major_to_index(major);

        mutex_lock(&block_class_lock);
        for (n = &major_names[index]; *n; n = &(*n)->next)
                if ((*n)->major == major)
                        break;
        if (!*n || strcmp((*n)->name, name)) {
                WARN_ON(1);
        } else {
                p = *n;
                *n = p->next;
        }
        mutex_unlock(&block_class_lock);
        kfree(p);
}

EXPORT_SYMBOL(unregister_blkdev);

static struct kobj_map *bdev_map;

/**
 * blk_mangle_minor - scatter minor numbers apart
 * @minor: minor number to mangle
 *
 * Scatter consecutively allocated @minor number apart if MANGLE_DEVT
 * is enabled.  Mangling twice gives the original value.
 *
 * RETURNS:
 * Mangled value.
 *
 * CONTEXT:
 * Don't care.
 */
static int blk_mangle_minor(int minor)
{
#ifdef CONFIG_DEBUG_BLOCK_EXT_DEVT
        int i;

        for (i = 0; i < MINORBITS / 2; i++) {
                int low = minor & (1 << i);
                int high = minor & (1 << (MINORBITS - 1 - i));
                int distance = MINORBITS - 1 - 2 * i;

                minor ^= low | high;    /* clear both bits */
                low <<= distance;       /* swap the positions */
                high >>= distance;
                minor |= low | high;    /* and set */
        }
#endif
        return minor;
}

/**
 * blk_alloc_devt - allocate a dev_t for a partition
 * @part: partition to allocate dev_t for
 * @devt: out parameter for resulting dev_t
 *
 * Allocate a dev_t for block device.
 *
 * RETURNS:
 * 0 on success, allocated dev_t is returned in *@devt.  -errno on
 * failure.
 *
 * CONTEXT:
 * Might sleep.
 */
int blk_alloc_devt(struct hd_struct *part, dev_t *devt)
{
        struct gendisk *disk = part_to_disk(part);
        int idx;

        /* in consecutive minor range? */
        if (part->partno < disk->minors) {
                *devt = MKDEV(disk->major, disk->first_minor + part->partno);
                return 0;
        }

        /* allocate ext devt */
        idr_preload(GFP_KERNEL);

        spin_lock(&ext_devt_lock);
        idx = idr_alloc(&ext_devt_idr, part, 0, NR_EXT_DEVT, GFP_NOWAIT);
        spin_unlock(&ext_devt_lock);

        idr_preload_end();
        if (idx < 0)
                return idx == -ENOSPC ? -EBUSY : idx;

        *devt = MKDEV(BLOCK_EXT_MAJOR, blk_mangle_minor(idx));
        return 0;
}

/**
 * blk_free_devt - free a dev_t
 * @devt: dev_t to free
 *
 * Free @devt which was allocated using blk_alloc_devt().
 *
 * CONTEXT:
 * Might sleep.
 */
void blk_free_devt(dev_t devt)
{
        if (devt == MKDEV(0, 0))
                return;

        if (MAJOR(devt) == BLOCK_EXT_MAJOR) {
                spin_lock(&ext_devt_lock);
                idr_remove(&ext_devt_idr, blk_mangle_minor(MINOR(devt)));
                spin_unlock(&ext_devt_lock);
        }
}

static char *bdevt_str(dev_t devt, char *buf)
{
        if (MAJOR(devt) <= 0xff && MINOR(devt) <= 0xff) {
                char tbuf[BDEVT_SIZE];
                snprintf(tbuf, BDEVT_SIZE, "%02x%02x", MAJOR(devt), MINOR(devt));
                snprintf(buf, BDEVT_SIZE, "%-9s", tbuf);
        } else
                snprintf(buf, BDEVT_SIZE, "%03x:%05x", MAJOR(devt), MINOR(devt));

        return buf;
}

/*
 * Register device numbers dev..(dev+range-1)
 * range must be nonzero
 * The hash chain is sorted on range, so that subranges can override.
 */
void blk_register_region(dev_t devt, unsigned long range, struct module *module,
                         struct kobject *(*probe)(dev_t, int *, void *),
                         int (*lock)(dev_t, void *), void *data)
{
        kobj_map(bdev_map, devt, range, module, probe, lock, data);
}

EXPORT_SYMBOL(blk_register_region);

void blk_unregister_region(dev_t devt, unsigned long range)
{
        kobj_unmap(bdev_map, devt, range);
}

EXPORT_SYMBOL(blk_unregister_region);

static struct kobject *exact_match(dev_t devt, int *partno, void *data)
{
        struct gendisk *p = data;

        return &disk_to_dev(p)->kobj;
}

static int exact_lock(dev_t devt, void *data)
{
        struct gendisk *p = data;

        if (!get_disk(p))
                return -1;
        return 0;
}

static void register_disk(struct gendisk *disk)
{
        struct device *ddev = disk_to_dev(disk);
        struct block_device *bdev;
        struct disk_part_iter piter;
        struct hd_struct *part;
        int err;

        ddev->parent = disk->driverfs_dev;

        dev_set_name(ddev, "%s", disk->disk_name);

        /* delay uevents, until we scanned partition table */
        dev_set_uevent_suppress(ddev, 1);

        if (device_add(ddev))
                return;
        if (!sysfs_deprecated) {
                err = sysfs_create_link(block_depr, &ddev->kobj,
                                        kobject_name(&ddev->kobj));
                if (err) {
                        device_del(ddev);
                        return;
                }
        }

        /*
         * avoid probable deadlock caused by allocating memory with
         * GFP_KERNEL in runtime_resume callback of its all ancestor
         * devices
         */
        pm_runtime_set_memalloc_noio(ddev, true);

        disk->part0.holder_dir = kobject_create_and_add("holders", &ddev->kobj);
        disk->slave_dir = kobject_create_and_add("slaves", &ddev->kobj);

        /* No minors to use for partitions */
        if (!disk_part_scan_enabled(disk))
                goto exit;

        /* No such device (e.g., media were just removed) */
        if (!get_capacity(disk))
                goto exit;

        bdev = bdget_disk(disk, 0);
        if (!bdev)
                goto exit;

        bdev->bd_invalidated = 1;
        err = blkdev_get(bdev, FMODE_READ, NULL);
        if (err < 0)
                goto exit;
        blkdev_put(bdev, FMODE_READ);

exit:
        /* announce disk after possible partitions are created */
        dev_set_uevent_suppress(ddev, 0);
        kobject_uevent(&ddev->kobj, KOBJ_ADD);

        /* announce possible partitions */
        disk_part_iter_init(&piter, disk, 0);
        while ((part = disk_part_iter_next(&piter)))
                kobject_uevent(&part_to_dev(part)->kobj, KOBJ_ADD);
        disk_part_iter_exit(&piter);
}

/**
 * add_disk - add partitioning information to kernel list
 * @disk: per-device partitioning information
 *
 * This function registers the partitioning information in @disk
 * with the kernel.
 *
 * FIXME: error handling
 */
void add_disk(struct gendisk *disk)
{
        struct backing_dev_info *bdi;
        dev_t devt;
        int retval;

        /* minors == 0 indicates to use ext devt from part0 and should
         * be accompanied with EXT_DEVT flag.  Make sure all
         * parameters make sense.
         */
        WARN_ON(disk->minors && !(disk->major || disk->first_minor));
        WARN_ON(!disk->minors && !(disk->flags & GENHD_FL_EXT_DEVT));

        disk->flags |= GENHD_FL_UP;

        retval = blk_alloc_devt(&disk->part0, &devt);
        if (retval) {
                WARN_ON(1);
                return;
        }
        disk_to_dev(disk)->devt = devt;

        /* ->major and ->first_minor aren't supposed to be
         * dereferenced from here on, but set them just in case.
         */
        disk->major = MAJOR(devt);
        disk->first_minor = MINOR(devt);

        disk_alloc_events(disk);

        /* Register BDI before referencing it from bdev */
        bdi = &disk->queue->backing_dev_info;
        bdi_register_dev(bdi, disk_devt(disk));

        blk_register_region(disk_devt(disk), disk->minors, NULL,
                            exact_match, exact_lock, disk);
        register_disk(disk);
        blk_register_queue(disk);

        /*
         * Take an extra ref on queue which will be put on disk_release()
         * so that it sticks around as long as @disk is there.
         */
        WARN_ON_ONCE(!blk_get_queue(disk->queue));

        retval = sysfs_create_link(&disk_to_dev(disk)->kobj, &bdi->dev->kobj,
                                   "bdi");
        WARN_ON(retval);

        disk_add_events(disk);
}
EXPORT_SYMBOL(add_disk);

void del_gendisk(struct gendisk *disk)
{
        struct disk_part_iter piter;
        struct hd_struct *part;

        disk_del_events(disk);

        /* invalidate stuff */
        disk_part_iter_init(&piter, disk,
                             DISK_PITER_INCL_EMPTY | DISK_PITER_REVERSE);
        while ((part = disk_part_iter_next(&piter))) {
                invalidate_partition(disk, part->partno);
                delete_partition(disk, part->partno);
        }
        disk_part_iter_exit(&piter);

        invalidate_partition(disk, 0);
        set_capacity(disk, 0);
        disk->flags &= ~GENHD_FL_UP;

        sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi");
        bdi_unregister(&disk->queue->backing_dev_info);
        blk_unregister_queue(disk);
        blk_unregister_region(disk_devt(disk), disk->minors);

        part_stat_set_all(&disk->part0, 0);
        disk->part0.stamp = 0;

        kobject_put(disk->part0.holder_dir);
        kobject_put(disk->slave_dir);
        disk->driverfs_dev = NULL;
        if (!sysfs_deprecated)
                sysfs_remove_link(block_depr, dev_name(disk_to_dev(disk)));
        pm_runtime_set_memalloc_noio(disk_to_dev(disk), false);
        device_del(disk_to_dev(disk));
}
EXPORT_SYMBOL(del_gendisk);

/**
 * get_gendisk - get partitioning information for a given device
 * @devt: device to get partitioning information for
 * @partno: returned partition index
 *
 * This function gets the structure containing partitioning
 * information for the given device @devt.
 */
struct gendisk *get_gendisk(dev_t devt, int *partno)
{
        struct gendisk *disk = NULL;

        if (MAJOR(devt) != BLOCK_EXT_MAJOR) {
                struct kobject *kobj;

                kobj = kobj_lookup(bdev_map, devt, partno);
                if (kobj)
                        disk = dev_to_disk(kobj_to_dev(kobj));
        } else {
                struct hd_struct *part;

                spin_lock(&ext_devt_lock);
                part = idr_find(&ext_devt_idr, blk_mangle_minor(MINOR(devt)));
                if (part && get_disk(part_to_disk(part))) {
                        *partno = part->partno;
                        disk = part_to_disk(part);
                }
                spin_unlock(&ext_devt_lock);
        }

        return disk;
}
EXPORT_SYMBOL(get_gendisk);

/**
 * bdget_disk - do bdget() by gendisk and partition number
 * @disk: gendisk of interest
 * @partno: partition number
 *
 * Find partition @partno from @disk, do bdget() on it.
 *
 * CONTEXT:
 * Don't care.
 *
 * RETURNS:
 * Resulting block_device on success, NULL on failure.
 */
struct block_device *bdget_disk(struct gendisk *disk, int partno)
{
        struct hd_struct *part;
        struct block_device *bdev = NULL;

        part = disk_get_part(disk, partno);
        if (part)
                bdev = bdget(part_devt(part));
        disk_put_part(part);

        return bdev;
}
EXPORT_SYMBOL(bdget_disk);

/*
 * print a full list of all partitions - intended for places where the root
 * filesystem can't be mounted and thus to give the victim some idea of what
 * went wrong
 */
void __init printk_all_partitions(void)
{
        struct class_dev_iter iter;
        struct device *dev;

        class_dev_iter_init(&iter, &block_class, NULL, &disk_type);
        while ((dev = class_dev_iter_next(&iter))) {
                struct gendisk *disk = dev_to_disk(dev);
                struct disk_part_iter piter;
                struct hd_struct *part;
                char name_buf[BDEVNAME_SIZE];
                char devt_buf[BDEVT_SIZE];

                /*
                 * Don't show empty devices or things that have been
                 * suppressed
                 */
                if (get_capacity(disk) == 0 ||
                    (disk->flags & GENHD_FL_SUPPRESS_PARTITION_INFO))
                        continue;

                /*
                 * Note, unlike /proc/partitions, I am showing the
                 * numbers in hex - the same format as the root=
                 * option takes.
                 */
                disk_part_iter_init(&piter, disk, DISK_PITER_INCL_PART0);
                while ((part = disk_part_iter_next(&piter))) {
                        bool is_part0 = part == &disk->part0;

                        printk("%s%s %10llu %s %s", is_part0 ? "" : "  ",
                               bdevt_str(part_devt(part), devt_buf),
                               (unsigned long long)part_nr_sects_read(part) >> 1
                               , disk_name(disk, part->partno, name_buf),
                               part->info ? part->info->uuid : "");
                        if (is_part0) {
                                if (disk->driverfs_dev != NULL &&
                                    disk->driverfs_dev->driver != NULL)
                                        printk(" driver: %s\n",
                                              disk->driverfs_dev->driver->name);
                                else
                                        printk(" (driver?)\n");
                        } else
                                printk("\n");
                }
                disk_part_iter_exit(&piter);
        }
        class_dev_iter_exit(&iter);
}

#ifdef CONFIG_PROC_FS
/* iterator */
static void *disk_seqf_start(struct seq_file *seqf, loff_t *pos)
{
        loff_t skip = *pos;
        struct class_dev_iter *iter;
        struct device *dev;

        iter = kmalloc(sizeof(*iter), GFP_KERNEL);
        if (!iter)
                return ERR_PTR(-ENOMEM);

        seqf->private = iter;
        class_dev_iter_init(iter, &block_class, NULL, &disk_type);
        do {
                dev = class_dev_iter_next(iter);
                if (!dev)
                        return NULL;
        } while (skip--);

        return dev_to_disk(dev);
}

static void *disk_seqf_next(struct seq_file *seqf, void *v, loff_t *pos)
{
        struct device *dev;

        (*pos)++;
        dev = class_dev_iter_next(seqf->private);
        if (dev)
                return dev_to_disk(dev);

        return NULL;
}

static void disk_seqf_stop(struct seq_file *seqf, void *v)
{
        struct class_dev_iter *iter = seqf->private;

        /* stop is called even after start failed :-( */
        if (iter) {
                class_dev_iter_exit(iter);
                kfree(iter);
        }
}

static void *show_partition_start(struct seq_file *seqf, loff_t *pos)
{
        void *p;

        p = disk_seqf_start(seqf, pos);
        if (!IS_ERR_OR_NULL(p) && !*pos)
                seq_puts(seqf, "major minor  #blocks  name\n\n");
        return p;
}

static int show_partition(struct seq_file *seqf, void *v)
{
        struct gendisk *sgp = v;
        struct disk_part_iter piter;
        struct hd_struct *part;
        char buf[BDEVNAME_SIZE];

        /* Don't show non-partitionable removeable devices or empty devices */
        if (!get_capacity(sgp) || (!disk_max_parts(sgp) &&
                                   (sgp->flags & GENHD_FL_REMOVABLE)))
                return 0;
        if (sgp->flags & GENHD_FL_SUPPRESS_PARTITION_INFO)
                return 0;

        /* show the full disk and all non-0 size partitions of it */
        disk_part_iter_init(&piter, sgp, DISK_PITER_INCL_PART0);
        while ((part = disk_part_iter_next(&piter)))
                seq_printf(seqf, "%4d  %7d %10llu %s\n",
                           MAJOR(part_devt(part)), MINOR(part_devt(part)),
                           (unsigned long long)part_nr_sects_read(part) >> 1,
                           disk_name(sgp, part->partno, buf));
        disk_part_iter_exit(&piter);

        return 0;
}

static const struct seq_operations partitions_op = {
        .start  = show_partition_start,
        .next   = disk_seqf_next,
        .stop   = disk_seqf_stop,
        .show   = show_partition
};

static int partitions_open(struct inode *inode, struct file *file)
{
        return seq_open(file, &partitions_op);
}

static const struct file_operations proc_partitions_operations = {
        .open           = partitions_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release,
};
#endif


static struct kobject *base_probe(dev_t devt, int *partno, void *data)
{
        if (request_module("block-major-%d-%d", MAJOR(devt), MINOR(devt)) > 0)
                /* Make old-style 2.4 aliases work */
                request_module("block-major-%d", MAJOR(devt));
        return NULL;
}

static int __init genhd_device_init(void)
{
        int error;

        block_class.dev_kobj = sysfs_dev_block_kobj;
        error = class_register(&block_class);
        if (unlikely(error))
                return error;
        bdev_map = kobj_map_init(base_probe, &block_class_lock);
        blk_dev_init();

        register_blkdev(BLOCK_EXT_MAJOR, "blkext");

        /* create top-level block dir */
        if (!sysfs_deprecated)
                block_depr = kobject_create_and_add("block", NULL);
        return 0;
}

subsys_initcall(genhd_device_init);

static ssize_t disk_range_show(struct device *dev,
                               struct device_attribute *attr, char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);

        return sprintf(buf, "%d\n", disk->minors);
}

static ssize_t disk_ext_range_show(struct device *dev,
                                   struct device_attribute *attr, char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);

        return sprintf(buf, "%d\n", disk_max_parts(disk));
}

static ssize_t disk_removable_show(struct device *dev,
                                   struct device_attribute *attr, char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);

        return sprintf(buf, "%d\n",
                       (disk->flags & GENHD_FL_REMOVABLE ? 1 : 0));
}

static ssize_t disk_ro_show(struct device *dev,
                                   struct device_attribute *attr, char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);

        return sprintf(buf, "%d\n", get_disk_ro(disk) ? 1 : 0);
}

static ssize_t disk_capability_show(struct device *dev,
                                    struct device_attribute *attr, char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);

        return sprintf(buf, "%x\n", disk->flags);
}

static ssize_t disk_alignment_offset_show(struct device *dev,
                                          struct device_attribute *attr,
                                          char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);

        return sprintf(buf, "%d\n", queue_alignment_offset(disk->queue));
}

static ssize_t disk_discard_alignment_show(struct device *dev,
                                           struct device_attribute *attr,
                                           char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);

        return sprintf(buf, "%d\n", queue_discard_alignment(disk->queue));
}

static DEVICE_ATTR(range, S_IRUGO, disk_range_show, NULL);
static DEVICE_ATTR(ext_range, S_IRUGO, disk_ext_range_show, NULL);
static DEVICE_ATTR(removable, S_IRUGO, disk_removable_show, NULL);
static DEVICE_ATTR(ro, S_IRUGO, disk_ro_show, NULL);
static DEVICE_ATTR(size, S_IRUGO, part_size_show, NULL);
static DEVICE_ATTR(alignment_offset, S_IRUGO, disk_alignment_offset_show, NULL);
static DEVICE_ATTR(discard_alignment, S_IRUGO, disk_discard_alignment_show,
                   NULL);
static DEVICE_ATTR(capability, S_IRUGO, disk_capability_show, NULL);
static DEVICE_ATTR(stat, S_IRUGO, part_stat_show, NULL);
static DEVICE_ATTR(inflight, S_IRUGO, part_inflight_show, NULL);
#ifdef CONFIG_FAIL_MAKE_REQUEST
static struct device_attribute dev_attr_fail =
        __ATTR(make-it-fail, S_IRUGO|S_IWUSR, part_fail_show, part_fail_store);
#endif
#ifdef CONFIG_FAIL_IO_TIMEOUT
static struct device_attribute dev_attr_fail_timeout =
        __ATTR(io-timeout-fail,  S_IRUGO|S_IWUSR, part_timeout_show,
                part_timeout_store);
#endif

static struct attribute *disk_attrs[] = {
        &dev_attr_range.attr,
        &dev_attr_ext_range.attr,
        &dev_attr_removable.attr,
        &dev_attr_ro.attr,
        &dev_attr_size.attr,
        &dev_attr_alignment_offset.attr,
        &dev_attr_discard_alignment.attr,
        &dev_attr_capability.attr,
        &dev_attr_stat.attr,
        &dev_attr_inflight.attr,
#ifdef CONFIG_FAIL_MAKE_REQUEST
        &dev_attr_fail.attr,
#endif
#ifdef CONFIG_FAIL_IO_TIMEOUT
        &dev_attr_fail_timeout.attr,
#endif
        NULL
};

static struct attribute_group disk_attr_group = {
        .attrs = disk_attrs,
};

static const struct attribute_group *disk_attr_groups[] = {
        &disk_attr_group,
        NULL
};

/**
 * disk_replace_part_tbl - replace disk->part_tbl in RCU-safe way
 * @disk: disk to replace part_tbl for
 * @new_ptbl: new part_tbl to install
 *
 * Replace disk->part_tbl with @new_ptbl in RCU-safe way.  The
 * original ptbl is freed using RCU callback.
 *
 * LOCKING:
 * Matching bd_mutx locked.
 */
static void disk_replace_part_tbl(struct gendisk *disk,
                                  struct disk_part_tbl *new_ptbl)
{
        struct disk_part_tbl *old_ptbl = disk->part_tbl;

        rcu_assign_pointer(disk->part_tbl, new_ptbl);

        if (old_ptbl) {
                rcu_assign_pointer(old_ptbl->last_lookup, NULL);
                kfree_rcu(old_ptbl, rcu_head);
        }
}

/**
 * disk_expand_part_tbl - expand disk->part_tbl
 * @disk: disk to expand part_tbl for
 * @partno: expand such that this partno can fit in
 *
 * Expand disk->part_tbl such that @partno can fit in.  disk->part_tbl
 * uses RCU to allow unlocked dereferencing for stats and other stuff.
 *
 * LOCKING:
 * Matching bd_mutex locked, might sleep.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
int disk_expand_part_tbl(struct gendisk *disk, int partno)
{
        struct disk_part_tbl *old_ptbl = disk->part_tbl;
        struct disk_part_tbl *new_ptbl;
        int len = old_ptbl ? old_ptbl->len : 0;
        int target = partno + 1;
        size_t size;
        int i;

        /* disk_max_parts() is zero during initialization, ignore if so */
        if (disk_max_parts(disk) && target > disk_max_parts(disk))
                return -EINVAL;

        if (target <= len)
                return 0;

        size = sizeof(*new_ptbl) + target * sizeof(new_ptbl->part[0]);
        new_ptbl = kzalloc_node(size, GFP_KERNEL, disk->node_id);
        if (!new_ptbl)
                return -ENOMEM;

        new_ptbl->len = target;

        for (i = 0; i < len; i++)
                rcu_assign_pointer(new_ptbl->part[i], old_ptbl->part[i]);

        disk_replace_part_tbl(disk, new_ptbl);
        return 0;
}

static void disk_release(struct device *dev)
{
        struct gendisk *disk = dev_to_disk(dev);

        blk_free_devt(dev->devt);
        disk_release_events(disk);
        kfree(disk->random);
        disk_replace_part_tbl(disk, NULL);
        free_part_stats(&disk->part0);
        free_part_info(&disk->part0);
        if (disk->queue)
                blk_put_queue(disk->queue);
        kfree(disk);
}
struct class block_class = {
        .name           = "block",
};

static char *block_devnode(struct device *dev, umode_t *mode,
                           kuid_t *uid, kgid_t *gid)
{
        struct gendisk *disk = dev_to_disk(dev);

        if (disk->devnode)
                return disk->devnode(disk, mode);
        return NULL;
}

static struct device_type disk_type = {
        .name           = "disk",
        .groups         = disk_attr_groups,
        .release        = disk_release,
        .devnode        = block_devnode,
};

#ifdef CONFIG_PROC_FS
/*
 * aggregate disk stat collector.  Uses the same stats that the sysfs
 * entries do, above, but makes them available through one seq_file.
 *
 * The output looks suspiciously like /proc/partitions with a bunch of
 * extra fields.
 */
static int diskstats_show(struct seq_file *seqf, void *v)
{
        struct gendisk *gp = v;
        struct disk_part_iter piter;
        struct hd_struct *hd;
        char buf[BDEVNAME_SIZE];
        int cpu;

        /*
        if (&disk_to_dev(gp)->kobj.entry == block_class.devices.next)
                seq_puts(seqf,  "major minor name"
                                "     rio rmerge rsect ruse wio wmerge "
                                "wsect wuse running use aveq"
                                "\n\n");
        */

        disk_part_iter_init(&piter, gp, DISK_PITER_INCL_EMPTY_PART0);
        while ((hd = disk_part_iter_next(&piter))) {
                cpu = part_stat_lock();
                part_round_stats(cpu, hd);
                part_stat_unlock();
                seq_printf(seqf, "%4d %7d %s %lu %lu %lu "
                           "%u %lu %lu %lu %u %u %u %u\n",
                           MAJOR(part_devt(hd)), MINOR(part_devt(hd)),
                           disk_name(gp, hd->partno, buf),
                           part_stat_read(hd, ios[READ]),
                           part_stat_read(hd, merges[READ]),
                           part_stat_read(hd, sectors[READ]),
                           jiffies_to_msecs(part_stat_read(hd, ticks[READ])),
                           part_stat_read(hd, ios[WRITE]),
                           part_stat_read(hd, merges[WRITE]),
                           part_stat_read(hd, sectors[WRITE]),
                           jiffies_to_msecs(part_stat_read(hd, ticks[WRITE])),
                           part_in_flight(hd),
                           jiffies_to_msecs(part_stat_read(hd, io_ticks)),
                           jiffies_to_msecs(part_stat_read(hd, time_in_queue))
                        );
        }
        disk_part_iter_exit(&piter);

        return 0;
}

static const struct seq_operations diskstats_op = {
        .start  = disk_seqf_start,
        .next   = disk_seqf_next,
        .stop   = disk_seqf_stop,
        .show   = diskstats_show
};

static int diskstats_open(struct inode *inode, struct file *file)
{
        return seq_open(file, &diskstats_op);
}

static const struct file_operations proc_diskstats_operations = {
        .open           = diskstats_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release,
};

static int __init proc_genhd_init(void)
{
        proc_create("diskstats", 0, NULL, &proc_diskstats_operations);
        proc_create("partitions", 0, NULL, &proc_partitions_operations);
        return 0;
}
module_init(proc_genhd_init);
#endif /* CONFIG_PROC_FS */

dev_t blk_lookup_devt(const char *name, int partno)
{
        dev_t devt = MKDEV(0, 0);
        struct class_dev_iter iter;
        struct device *dev;

        class_dev_iter_init(&iter, &block_class, NULL, &disk_type);
        while ((dev = class_dev_iter_next(&iter))) {
                struct gendisk *disk = dev_to_disk(dev);
                struct hd_struct *part;

                if (strcmp(dev_name(dev), name))
                        continue;

                if (partno < disk->minors) {
                        /* We need to return the right devno, even
                         * if the partition doesn't exist yet.
                         */
                        devt = MKDEV(MAJOR(dev->devt),
                                     MINOR(dev->devt) + partno);
                        break;
                }
                part = disk_get_part(disk, partno);
                if (part) {
                        devt = part_devt(part);
                        disk_put_part(part);
                        break;
                }
                disk_put_part(part);
        }
        class_dev_iter_exit(&iter);
        return devt;
}
EXPORT_SYMBOL(blk_lookup_devt);

struct gendisk *alloc_disk(int minors)
{
        return alloc_disk_node(minors, NUMA_NO_NODE);
}
EXPORT_SYMBOL(alloc_disk);

struct gendisk *alloc_disk_node(int minors, int node_id)
{
        struct gendisk *disk;

        disk = kzalloc_node(sizeof(struct gendisk), GFP_KERNEL, node_id);
        if (disk) {
                if (!init_part_stats(&disk->part0)) {
                        kfree(disk);
                        return NULL;
                }
                disk->node_id = node_id;
                if (disk_expand_part_tbl(disk, 0)) {
                        free_part_stats(&disk->part0);
                        kfree(disk);
                        return NULL;
                }
                disk->part_tbl->part[0] = &disk->part0;

                /*
                 * set_capacity() and get_capacity() currently don't use
                 * seqcounter to read/update the part0->nr_sects. Still init
                 * the counter as we can read the sectors in IO submission
                 * patch using seqence counters.
                 *
                 * TODO: Ideally set_capacity() and get_capacity() should be
                 * converted to make use of bd_mutex and sequence counters.
                 */
                seqcount_init(&disk->part0.nr_sects_seq);
                hd_ref_init(&disk->part0);

                disk->minors = minors;
                rand_initialize_disk(disk);
                disk_to_dev(disk)->class = &block_class;
                disk_to_dev(disk)->type = &disk_type;
                device_initialize(disk_to_dev(disk));
        }
        return disk;
}
EXPORT_SYMBOL(alloc_disk_node);

struct kobject *get_disk(struct gendisk *disk)
{
        struct module *owner;
        struct kobject *kobj;

        if (!disk->fops)
                return NULL;
        owner = disk->fops->owner;
        if (owner && !try_module_get(owner))
                return NULL;
        kobj = kobject_get(&disk_to_dev(disk)->kobj);
        if (kobj == NULL) {
                module_put(owner);
                return NULL;
        }
        return kobj;

}

EXPORT_SYMBOL(get_disk);

void put_disk(struct gendisk *disk)
{
        if (disk)
                kobject_put(&disk_to_dev(disk)->kobj);
}

EXPORT_SYMBOL(put_disk);

static void set_disk_ro_uevent(struct gendisk *gd, int ro)
{
        char event[] = "DISK_RO=1";
        char *envp[] = { event, NULL };

        if (!ro)
                event[8] = '0';
        kobject_uevent_env(&disk_to_dev(gd)->kobj, KOBJ_CHANGE, envp);
}

void set_device_ro(struct block_device *bdev, int flag)
{
        bdev->bd_part->policy = flag;
}

EXPORT_SYMBOL(set_device_ro);

void set_disk_ro(struct gendisk *disk, int flag)
{
        struct disk_part_iter piter;
        struct hd_struct *part;

        if (disk->part0.policy != flag) {
                set_disk_ro_uevent(disk, flag);
                disk->part0.policy = flag;
        }

        disk_part_iter_init(&piter, disk, DISK_PITER_INCL_EMPTY);
        while ((part = disk_part_iter_next(&piter)))
                part->policy = flag;
        disk_part_iter_exit(&piter);
}

EXPORT_SYMBOL(set_disk_ro);

int bdev_read_only(struct block_device *bdev)
{
        if (!bdev)
                return 0;
        return bdev->bd_part->policy;
}

EXPORT_SYMBOL(bdev_read_only);

int invalidate_partition(struct gendisk *disk, int partno)
{
        int res = 0;
        struct block_device *bdev = bdget_disk(disk, partno);
        if (bdev) {
                fsync_bdev(bdev);
                res = __invalidate_device(bdev, true);
                bdput(bdev);
        }
        return res;
}

EXPORT_SYMBOL(invalidate_partition);

/*
 * Disk events - monitor disk events like media change and eject request.
 */
struct disk_events {
        struct list_head        node;           /* all disk_event's */
        struct gendisk          *disk;          /* the associated disk */
        spinlock_t              lock;

        struct mutex            block_mutex;    /* protects blocking */
        int                     block;          /* event blocking depth */
        unsigned int            pending;        /* events already sent out */
        unsigned int            clearing;       /* events being cleared */

        long                    poll_msecs;     /* interval, -1 for default */
        struct delayed_work     dwork;
};

static const char *disk_events_strs[] = {
        [ilog2(DISK_EVENT_MEDIA_CHANGE)]        = "media_change",
        [ilog2(DISK_EVENT_EJECT_REQUEST)]       = "eject_request",
};

static char *disk_uevents[] = {
        [ilog2(DISK_EVENT_MEDIA_CHANGE)]        = "DISK_MEDIA_CHANGE=1",
        [ilog2(DISK_EVENT_EJECT_REQUEST)]       = "DISK_EJECT_REQUEST=1",
};

/* list of all disk_events */
static DEFINE_MUTEX(disk_events_mutex);
static LIST_HEAD(disk_events);

/* disable in-kernel polling by default */
static unsigned long disk_events_dfl_poll_msecs = 0;

static unsigned long disk_events_poll_jiffies(struct gendisk *disk)
{
        struct disk_events *ev = disk->ev;
        long intv_msecs = 0;

        /*
         * If device-specific poll interval is set, always use it.  If
         * the default is being used, poll iff there are events which
         * can't be monitored asynchronously.
         */
        if (ev->poll_msecs >= 0)
                intv_msecs = ev->poll_msecs;
        else if (disk->events & ~disk->async_events)
                intv_msecs = disk_events_dfl_poll_msecs;

        return msecs_to_jiffies(intv_msecs);
}

/**
 * disk_block_events - block and flush disk event checking
 * @disk: disk to block events for
 *
 * On return from this function, it is guaranteed that event checking
 * isn't in progress and won't happen until unblocked by
 * disk_unblock_events().  Events blocking is counted and the actual
 * unblocking happens after the matching number of unblocks are done.
 *
 * Note that this intentionally does not block event checking from
 * disk_clear_events().
 *
 * CONTEXT:
 * Might sleep.
 */
void disk_block_events(struct gendisk *disk)
{
        struct disk_events *ev = disk->ev;
        unsigned long flags;
        bool cancel;

        if (!ev)
                return;

        /*
         * Outer mutex ensures that the first blocker completes canceling
         * the event work before further blockers are allowed to finish.
         */
        mutex_lock(&ev->block_mutex);

        spin_lock_irqsave(&ev->lock, flags);
        cancel = !ev->block++;
        spin_unlock_irqrestore(&ev->lock, flags);

        if (cancel)
                cancel_delayed_work_sync(&disk->ev->dwork);

        mutex_unlock(&ev->block_mutex);
}

static void __disk_unblock_events(struct gendisk *disk, bool check_now)
{
        struct disk_events *ev = disk->ev;
        unsigned long intv;
        unsigned long flags;

        spin_lock_irqsave(&ev->lock, flags);

        if (WARN_ON_ONCE(ev->block <= 0))
                goto out_unlock;

        if (--ev->block)
                goto out_unlock;

        /*
         * Not exactly a latency critical operation, set poll timer
         * slack to 25% and kick event check.
         */
        intv = disk_events_poll_jiffies(disk);
        set_timer_slack(&ev->dwork.timer, intv / 4);
        if (check_now)
                queue_delayed_work(system_freezable_power_efficient_wq,
                                &ev->dwork, 0);
        else if (intv)
                queue_delayed_work(system_freezable_power_efficient_wq,
                                &ev->dwork, intv);
out_unlock:
        spin_unlock_irqrestore(&ev->lock, flags);
}

/**
 * disk_unblock_events - unblock disk event checking
 * @disk: disk to unblock events for
 *
 * Undo disk_block_events().  When the block count reaches zero, it
 * starts events polling if configured.
 *
 * CONTEXT:
 * Don't care.  Safe to call from irq context.
 */
void disk_unblock_events(struct gendisk *disk)
{
        if (disk->ev)
                __disk_unblock_events(disk, false);
}

/**
 * disk_flush_events - schedule immediate event checking and flushing
 * @disk: disk to check and flush events for
 * @mask: events to flush
 *
 * Schedule immediate event checking on @disk if not blocked.  Events in
 * @mask are scheduled to be cleared from the driver.  Note that this
 * doesn't clear the events from @disk->ev.
 *
 * CONTEXT:
 * If @mask is non-zero must be called with bdev->bd_mutex held.
 */
void disk_flush_events(struct gendisk *disk, unsigned int mask)
{
        struct disk_events *ev = disk->ev;

        if (!ev)
                return;

        spin_lock_irq(&ev->lock);
        ev->clearing |= mask;
        if (!ev->block)
                mod_delayed_work(system_freezable_power_efficient_wq,
                                &ev->dwork, 0);
        spin_unlock_irq(&ev->lock);
}

/**
 * disk_clear_events - synchronously check, clear and return pending events
 * @disk: disk to fetch and clear events from
 * @mask: mask of events to be fetched and cleared
 *
 * Disk events are synchronously checked and pending events in @mask
 * are cleared and returned.  This ignores the block count.
 *
 * CONTEXT:
 * Might sleep.
 */
unsigned int disk_clear_events(struct gendisk *disk, unsigned int mask)
{
        const struct block_device_operations *bdops = disk->fops;
        struct disk_events *ev = disk->ev;
        unsigned int pending;
        unsigned int clearing = mask;

        if (!ev) {
                /* for drivers still using the old ->media_changed method */
                if ((mask & DISK_EVENT_MEDIA_CHANGE) &&
                    bdops->media_changed && bdops->media_changed(disk))
                        return DISK_EVENT_MEDIA_CHANGE;
                return 0;
        }

        disk_block_events(disk);

        /*
         * store the union of mask and ev->clearing on the stack so that the
         * race with disk_flush_events does not cause ambiguity (ev->clearing
         * can still be modified even if events are blocked).
         */
        spin_lock_irq(&ev->lock);
        clearing |= ev->clearing;
        ev->clearing = 0;
        spin_unlock_irq(&ev->lock);

        disk_check_events(ev, &clearing);
        /*
         * if ev->clearing is not 0, the disk_flush_events got called in the
         * middle of this function, so we want to run the workfn without delay.
         */
        __disk_unblock_events(disk, ev->clearing ? true : false);

        /* then, fetch and clear pending events */
        spin_lock_irq(&ev->lock);
        pending = ev->pending & mask;
        ev->pending &= ~mask;
        spin_unlock_irq(&ev->lock);
        WARN_ON_ONCE(clearing & mask);

        return pending;
}

/*
 * Separate this part out so that a different pointer for clearing_ptr can be
 * passed in for disk_clear_events.
 */
static void disk_events_workfn(struct work_struct *work)
{
        struct delayed_work *dwork = to_delayed_work(work);
        struct disk_events *ev = container_of(dwork, struct disk_events, dwork);

        disk_check_events(ev, &ev->clearing);
}

static void disk_check_events(struct disk_events *ev,
                              unsigned int *clearing_ptr)
{
        struct gendisk *disk = ev->disk;
        char *envp[ARRAY_SIZE(disk_uevents) + 1] = { };
        unsigned int clearing = *clearing_ptr;
        unsigned int events;
        unsigned long intv;
        int nr_events = 0, i;

        /* check events */
        events = disk->fops->check_events(disk, clearing);

        /* accumulate pending events and schedule next poll if necessary */
        spin_lock_irq(&ev->lock);

        events &= ~ev->pending;
        ev->pending |= events;
        *clearing_ptr &= ~clearing;

        intv = disk_events_poll_jiffies(disk);
        if (!ev->block && intv)
                queue_delayed_work(system_freezable_power_efficient_wq,
                                &ev->dwork, intv);

        spin_unlock_irq(&ev->lock);

        /*
         * Tell userland about new events.  Only the events listed in
         * @disk->events are reported.  Unlisted events are processed the
         * same internally but never get reported to userland.
         */
        for (i = 0; i < ARRAY_SIZE(disk_uevents); i++)
                if (events & disk->events & (1 << i))
                        envp[nr_events++] = disk_uevents[i];

        if (nr_events)
                kobject_uevent_env(&disk_to_dev(disk)->kobj, KOBJ_CHANGE, envp);
}

/*
 * A disk events enabled device has the following sysfs nodes under
 * its /sys/block/X/ directory.
 *
 * events               : list of all supported events
 * events_async         : list of events which can be detected w/o polling
 * events_poll_msecs    : polling interval, 0: disable, -1: system default
 */
static ssize_t __disk_events_show(unsigned int events, char *buf)
{
        const char *delim = "";
        ssize_t pos = 0;
        int i;

        for (i = 0; i < ARRAY_SIZE(disk_events_strs); i++)
                if (events & (1 << i)) {
                        pos += sprintf(buf + pos, "%s%s",
                                       delim, disk_events_strs[i]);
                        delim = " ";
                }
        if (pos)
                pos += sprintf(buf + pos, "\n");
        return pos;
}

static ssize_t disk_events_show(struct device *dev,
                                struct device_attribute *attr, char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);

        return __disk_events_show(disk->events, buf);
}

static ssize_t disk_events_async_show(struct device *dev,
                                      struct device_attribute *attr, char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);

        return __disk_events_show(disk->async_events, buf);
}

static ssize_t disk_events_poll_msecs_show(struct device *dev,
                                           struct device_attribute *attr,
                                           char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);

        return sprintf(buf, "%ld\n", disk->ev->poll_msecs);
}

static ssize_t disk_events_poll_msecs_store(struct device *dev,
                                            struct device_attribute *attr,
                                            const char *buf, size_t count)
{
        struct gendisk *disk = dev_to_disk(dev);
        long intv;

        if (!count || !sscanf(buf, "%ld", &intv))
                return -EINVAL;

        if (intv < 0 && intv != -1)
                return -EINVAL;

        disk_block_events(disk);
        disk->ev->poll_msecs = intv;
        __disk_unblock_events(disk, true);

        return count;
}

static const DEVICE_ATTR(events, S_IRUGO, disk_events_show, NULL);
static const DEVICE_ATTR(events_async, S_IRUGO, disk_events_async_show, NULL);
static const DEVICE_ATTR(events_poll_msecs, S_IRUGO|S_IWUSR,
                         disk_events_poll_msecs_show,
                         disk_events_poll_msecs_store);

static const struct attribute *disk_events_attrs[] = {
        &dev_attr_events.attr,
        &dev_attr_events_async.attr,
        &dev_attr_events_poll_msecs.attr,
        NULL,
};

/*
 * The default polling interval can be specified by the kernel
 * parameter block.events_dfl_poll_msecs which defaults to 0
 * (disable).  This can also be modified runtime by writing to
 * /sys/module/block/events_dfl_poll_msecs.
 */
static int disk_events_set_dfl_poll_msecs(const char *val,
                                          const struct kernel_param *kp)
{
        struct disk_events *ev;
        int ret;

        ret = param_set_ulong(val, kp);
        if (ret < 0)
                return ret;

        mutex_lock(&disk_events_mutex);

        list_for_each_entry(ev, &disk_events, node)
                disk_flush_events(ev->disk, 0);

        mutex_unlock(&disk_events_mutex);

        return 0;
}

static const struct kernel_param_ops disk_events_dfl_poll_msecs_param_ops = {
        .set    = disk_events_set_dfl_poll_msecs,
        .get    = param_get_ulong,
};

#undef MODULE_PARAM_PREFIX
#define MODULE_PARAM_PREFIX     "block."

module_param_cb(events_dfl_poll_msecs, &disk_events_dfl_poll_msecs_param_ops,
                &disk_events_dfl_poll_msecs, 0644);

/*
 * disk_{alloc|add|del|release}_events - initialize and destroy disk_events.
 */
static void disk_alloc_events(struct gendisk *disk)
{
        struct disk_events *ev;

        if (!disk->fops->check_events)
                return;

        ev = kzalloc(sizeof(*ev), GFP_KERNEL);
        if (!ev) {
                pr_warn("%s: failed to initialize events\n", disk->disk_name);
                return;
        }

        INIT_LIST_HEAD(&ev->node);
        ev->disk = disk;
        spin_lock_init(&ev->lock);
        mutex_init(&ev->block_mutex);
        ev->block = 1;
        ev->poll_msecs = -1;
        INIT_DELAYED_WORK(&ev->dwork, disk_events_workfn);

        disk->ev = ev;
}

static void disk_add_events(struct gendisk *disk)
{
        if (!disk->ev)
                return;

        /* FIXME: error handling */
        if (sysfs_create_files(&disk_to_dev(disk)->kobj, disk_events_attrs) < 0)
                pr_warn("%s: failed to create sysfs files for events\n",
                        disk->disk_name);

        mutex_lock(&disk_events_mutex);
        list_add_tail(&disk->ev->node, &disk_events);
        mutex_unlock(&disk_events_mutex);

        /*
         * Block count is initialized to 1 and the following initial
         * unblock kicks it into action.
         */
        __disk_unblock_events(disk, true);
}

static void disk_del_events(struct gendisk *disk)
{
        if (!disk->ev)
                return;

        disk_block_events(disk);

        mutex_lock(&disk_events_mutex);
        list_del_init(&disk->ev->node);
        mutex_unlock(&disk_events_mutex);

        sysfs_remove_files(&disk_to_dev(disk)->kobj, disk_events_attrs);
}

static void disk_release_events(struct gendisk *disk)
{
        /* the block count should be 1 from disk_del_events() */
        WARN_ON_ONCE(disk->ev && disk->ev->block != 1);
        kfree(disk->ev);
}