brd.c

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/*
 * Ram backed block device driver.
 *
 * Copyright (C) 2007 Nick Piggin
 * Copyright (C) 2007 Novell Inc.
 *
 * Parts derived from drivers/block/rd.c, and drivers/block/loop.c, copyright
 * of their respective owners.
 */

#include <linux/init.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/major.h>
#include <linux/blkdev.h>
#include <linux/bio.h>
#include <linux/highmem.h>
#include <linux/mutex.h>
#include <linux/radix-tree.h>
#include <linux/fs.h>
#include <linux/slab.h>

#include <asm/uaccess.h>

#define SECTOR_SHIFT        9
#define PAGE_SECTORS_SHIFT  (PAGE_SHIFT - SECTOR_SHIFT)
#define PAGE_SECTORS        (1 << PAGE_SECTORS_SHIFT)

/*
 * Each block ramdisk device has a radix_tree brd_pages of pages that stores
 * the pages containing the block device's contents. A brd page's ->index is
 * its offset in PAGE_SIZE units. This is similar to, but in no way connected
 * with, the kernel's pagecache or buffer cache (which sit above our block
 * device).
 */
struct brd_device {
    int     brd_number;

    struct request_queue    *brd_queue;
    struct gendisk      *brd_disk;
    struct list_head    brd_list;

    /*
     * Backing store of pages and lock to protect it. This is the contents
     * of the block device.
     */
    spinlock_t      brd_lock;
    struct radix_tree_root  brd_pages;
};

/*
 * Look up and return a brd's page for a given sector.
 */
static DEFINE_MUTEX(brd_mutex);
static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
{
    pgoff_t idx;
    struct page *page;

    /*
     * The page lifetime is protected by the fact that we have opened the
     * device node -- brd pages will never be deleted under us, so we
     * don't need any further locking or refcounting.
     *
     * This is strictly true for the radix-tree nodes as well (ie. we
     * don't actually need the rcu_read_lock()), however that is not a
     * documented feature of the radix-tree API so it is better to be
     * safe here (we don't have total exclusion from radix tree updates
     * here, only deletes).
     */
    rcu_read_lock();
    idx = sector >> PAGE_SECTORS_SHIFT; /* sector to page index */
    page = radix_tree_lookup(&brd->brd_pages, idx);
    rcu_read_unlock();

    BUG_ON(page && page->index != idx);

    return page;
}

/*
 * Look up and return a brd's page for a given sector.
 * If one does not exist, allocate an empty page, and insert that. Then
 * return it.
 */
static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
{
    pgoff_t idx;
    struct page *page;
    gfp_t gfp_flags;

    page = brd_lookup_page(brd, sector);
    if (page)
        return page;

    /*
     * Must use NOIO because we don't want to recurse back into the
     * block or filesystem layers from page reclaim.
     *
     * Cannot support XIP and highmem, because our ->direct_access
     * routine for XIP must return memory that is always addressable.
     * If XIP was reworked to use pfns and kmap throughout, this
     * restriction might be able to be lifted.
     */
    gfp_flags = GFP_NOIO | __GFP_ZERO;
#ifndef CONFIG_BLK_DEV_XIP
    gfp_flags |= __GFP_HIGHMEM;
#endif
    page = alloc_page(gfp_flags);
    if (!page)
        return NULL;

    if (radix_tree_preload(GFP_NOIO)) {
        __free_page(page);
        return NULL;
    }

    spin_lock(&brd->brd_lock);
    idx = sector >> PAGE_SECTORS_SHIFT;
    if (radix_tree_insert(&brd->brd_pages, idx, page)) {
        __free_page(page);
        page = radix_tree_lookup(&brd->brd_pages, idx);
        BUG_ON(!page);
        BUG_ON(page->index != idx);
    } else
        page->index = idx;
    spin_unlock(&brd->brd_lock);

    radix_tree_preload_end();

    return page;
}

static void brd_free_page(struct brd_device *brd, sector_t sector)
{
    struct page *page;
    pgoff_t idx;

    spin_lock(&brd->brd_lock);
    idx = sector >> PAGE_SECTORS_SHIFT;
    page = radix_tree_delete(&brd->brd_pages, idx);
    spin_unlock(&brd->brd_lock);
    if (page)
        __free_page(page);
}

static void brd_zero_page(struct brd_device *brd, sector_t sector)
{
    struct page *page;

    page = brd_lookup_page(brd, sector);
    if (page)
        clear_highpage(page);
}

/*
 * Free all backing store pages and radix tree. This must only be called when
 * there are no other users of the device.
 */
#define FREE_BATCH 16
static void brd_free_pages(struct brd_device *brd)
{
    unsigned long pos = 0;
    struct page *pages[FREE_BATCH];
    int nr_pages;

    do {
        int i;

        nr_pages = radix_tree_gang_lookup(&brd->brd_pages,
                (void **)pages, pos, FREE_BATCH);

        for (i = 0; i < nr_pages; i++) {
            void *ret;

            BUG_ON(pages[i]->index < pos);
            pos = pages[i]->index;
            ret = radix_tree_delete(&brd->brd_pages, pos);
            BUG_ON(!ret || ret != pages[i]);
            __free_page(pages[i]);
        }

        pos++;

        /*
         * This assumes radix_tree_gang_lookup always returns as
         * many pages as possible. If the radix-tree code changes,
         * so will this have to.
         */
    } while (nr_pages == FREE_BATCH);
}

/*
 * copy_to_brd_setup must be called before copy_to_brd. It may sleep.
 */
static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n)
{
    unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
    size_t copy;

    copy = min_t(size_t, n, PAGE_SIZE - offset);
    if (!brd_insert_page(brd, sector))
        return -ENOMEM;
    if (copy < n) {
        sector += copy >> SECTOR_SHIFT;
        if (!brd_insert_page(brd, sector))
            return -ENOMEM;
    }
    return 0;
}

static void discard_from_brd(struct brd_device *brd,
            sector_t sector, size_t n)
{
    while (n >= PAGE_SIZE) {
        /*
         * Don't want to actually discard pages here because
         * re-allocating the pages can result in writeback
         * deadlocks under heavy load.
         */
        if (0)
            brd_free_page(brd, sector);
        else
            brd_zero_page(brd, sector);
        sector += PAGE_SIZE >> SECTOR_SHIFT;
        n -= PAGE_SIZE;
    }
}

/*
 * Copy n bytes from src to the brd starting at sector. Does not sleep.
 */
static void copy_to_brd(struct brd_device *brd, const void *src,
            sector_t sector, size_t n)
{
    struct page *page;
    void *dst;
    unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
    size_t copy;

    copy = min_t(size_t, n, PAGE_SIZE - offset);
    page = brd_lookup_page(brd, sector);
    BUG_ON(!page);

    dst = kmap_atomic(page);
    memcpy(dst + offset, src, copy);
    kunmap_atomic(dst);

    if (copy < n) {
        src += copy;
        sector += copy >> SECTOR_SHIFT;
        copy = n - copy;
        page = brd_lookup_page(brd, sector);
        BUG_ON(!page);

        dst = kmap_atomic(page);
        memcpy(dst, src, copy);
        kunmap_atomic(dst);
    }
}

/*
 * Copy n bytes to dst from the brd starting at sector. Does not sleep.
 */
static void copy_from_brd(void *dst, struct brd_device *brd,
            sector_t sector, size_t n)
{
    struct page *page;
    void *src;
    unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
    size_t copy;

    copy = min_t(size_t, n, PAGE_SIZE - offset);
    page = brd_lookup_page(brd, sector);
    if (page) {
        src = kmap_atomic(page);
        memcpy(dst, src + offset, copy);
        kunmap_atomic(src);
    } else
        memset(dst, 0, copy);

    if (copy < n) {
        dst += copy;
        sector += copy >> SECTOR_SHIFT;
        copy = n - copy;
        page = brd_lookup_page(brd, sector);
        if (page) {
            src = kmap_atomic(page);
            memcpy(dst, src, copy);
            kunmap_atomic(src);
        } else
            memset(dst, 0, copy);
    }
}

/*
 * Process a single bvec of a bio.
 */
static int brd_do_bvec(struct brd_device *brd, struct page *page,
            unsigned int len, unsigned int off, int rw,
            sector_t sector)
{
    void *mem;
    int err = 0;

    if (rw != READ) {
        err = copy_to_brd_setup(brd, sector, len);
        if (err)
            goto out;
    }

    mem = kmap_atomic(page);
    if (rw == READ) {
        copy_from_brd(mem + off, brd, sector, len);
        flush_dcache_page(page);
    } else {
        flush_dcache_page(page);
        copy_to_brd(brd, mem + off, sector, len);
    }
    kunmap_atomic(mem);

out:
    return err;
}

static void brd_make_request(struct request_queue *q, struct bio *bio)
{
    struct block_device *bdev = bio->bi_bdev;
    struct brd_device *brd = bdev->bd_disk->private_data;
    int rw;
    struct bio_vec *bvec;
    sector_t sector;
    int i;
    int err = -EIO;

    sector = bio->bi_sector;
    if (sector + (bio->bi_size >> SECTOR_SHIFT) >
                        get_capacity(bdev->bd_disk))
        goto out;

    if (unlikely(bio->bi_rw & REQ_DISCARD)) {
        err = 0;
        discard_from_brd(brd, sector, bio->bi_size);
        goto out;
    }

    rw = bio_rw(bio);
    if (rw == READA)
        rw = READ;

    bio_for_each_segment(bvec, bio, i) {
        unsigned int len = bvec->bv_len;
        err = brd_do_bvec(brd, bvec->bv_page, len,
                    bvec->bv_offset, rw, sector);
        if (err)
            break;
        sector += len >> SECTOR_SHIFT;
    }

out:
    bio_endio(bio, err);
}

#ifdef CONFIG_BLK_DEV_XIP
static int brd_direct_access(struct block_device *bdev, sector_t sector,
            void **kaddr, unsigned long *pfn)
{
    struct brd_device *brd = bdev->bd_disk->private_data;
    struct page *page;

    if (!brd)
        return -ENODEV;
    if (sector & (PAGE_SECTORS-1))
        return -EINVAL;
    if (sector + PAGE_SECTORS > get_capacity(bdev->bd_disk))
        return -ERANGE;
    page = brd_insert_page(brd, sector);
    if (!page)
        return -ENOMEM;
    *kaddr = page_address(page);
    *pfn = page_to_pfn(page);

    return 0;
}
#endif

static int brd_ioctl(struct block_device *bdev, fmode_t mode,
            unsigned int cmd, unsigned long arg)
{
    int error;
    struct brd_device *brd = bdev->bd_disk->private_data;

    if (cmd != BLKFLSBUF)
        return -ENOTTY;

    /*
     * ram device BLKFLSBUF has special semantics, we want to actually
     * release and destroy the ramdisk data.
     */
    mutex_lock(&brd_mutex);
    mutex_lock(&bdev->bd_mutex);
    error = -EBUSY;
    if (bdev->bd_openers <= 1) {
        /*
         * Kill the cache first, so it isn't written back to the
         * device.
         *
         * Another thread might instantiate more buffercache here,
         * but there is not much we can do to close that race.
         */
        kill_bdev(bdev);
        brd_free_pages(brd);
        error = 0;
    }
    mutex_unlock(&bdev->bd_mutex);
    mutex_unlock(&brd_mutex);

    return error;
}

static const struct block_device_operations brd_fops = {
    .owner =        THIS_MODULE,
    .ioctl =        brd_ioctl,
#ifdef CONFIG_BLK_DEV_XIP
    .direct_access =    brd_direct_access,
#endif
};

/*
 * And now the modules code and kernel interface.
 */
static int rd_nr;
int rd_size = CONFIG_BLK_DEV_RAM_SIZE;
static int max_part;
static int part_shift;
module_param(rd_nr, int, S_IRUGO);
MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices");
module_param(rd_size, int, S_IRUGO);
MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");
module_param(max_part, int, S_IRUGO);
MODULE_PARM_DESC(max_part, "Maximum number of partitions per RAM disk");
MODULE_LICENSE("GPL");
MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR);
MODULE_ALIAS("rd");

#ifndef MODULE
/* Legacy boot options - nonmodular */
static int __init ramdisk_size(char *str)
{
    rd_size = simple_strtol(str, NULL, 0);
    return 1;
}
__setup("ramdisk_size=", ramdisk_size);
#endif

/*
 * The device scheme is derived from loop.c. Keep them in synch where possible
 * (should share code eventually).
 */
static LIST_HEAD(brd_devices);
static DEFINE_MUTEX(brd_devices_mutex);

static struct brd_device *brd_alloc(int i)
{
    struct brd_device *brd;
    struct gendisk *disk;

    brd = kzalloc(sizeof(*brd), GFP_KERNEL);
    if (!brd)
        goto out;
    brd->brd_number     = i;
    spin_lock_init(&brd->brd_lock);
    INIT_RADIX_TREE(&brd->brd_pages, GFP_ATOMIC);

    brd->brd_queue = blk_alloc_queue(GFP_KERNEL);
    if (!brd->brd_queue)
        goto out_free_dev;
    blk_queue_make_request(brd->brd_queue, brd_make_request);
    blk_queue_max_hw_sectors(brd->brd_queue, 1024);
    blk_queue_bounce_limit(brd->brd_queue, BLK_BOUNCE_ANY);

    brd->brd_queue->limits.discard_granularity = PAGE_SIZE;
    brd->brd_queue->limits.max_discard_sectors = UINT_MAX;
    brd->brd_queue->limits.discard_zeroes_data = 1;
    queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, brd->brd_queue);

    disk = brd->brd_disk = alloc_disk(1 << part_shift);
    if (!disk)
        goto out_free_queue;
    disk->major     = RAMDISK_MAJOR;
    disk->first_minor   = i << part_shift;
    disk->fops      = &brd_fops;
    disk->private_data  = brd;
    disk->queue     = brd->brd_queue;
    disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
    sprintf(disk->disk_name, "ram%d", i);
    set_capacity(disk, rd_size * 2);

    return brd;

out_free_queue:
    blk_cleanup_queue(brd->brd_queue);
out_free_dev:
    kfree(brd);
out:
    return NULL;
}

static void brd_free(struct brd_device *brd)
{
    put_disk(brd->brd_disk);
    blk_cleanup_queue(brd->brd_queue);
    brd_free_pages(brd);
    kfree(brd);
}

static struct brd_device *brd_init_one(int i)
{
    struct brd_device *brd;

    list_for_each_entry(brd, &brd_devices, brd_list) {
        if (brd->brd_number == i)
            goto out;
    }

    brd = brd_alloc(i);
    if (brd) {
        add_disk(brd->brd_disk);
        list_add_tail(&brd->brd_list, &brd_devices);
    }
out:
    return brd;
}

static void brd_del_one(struct brd_device *brd)
{
    list_del(&brd->brd_list);
    del_gendisk(brd->brd_disk);
    brd_free(brd);
}

static struct kobject *brd_probe(dev_t dev, int *part, void *data)
{
    struct brd_device *brd;
    struct kobject *kobj;

    mutex_lock(&brd_devices_mutex);
    brd = brd_init_one(MINOR(dev) >> part_shift);
    kobj = brd ? get_disk(brd->brd_disk) : ERR_PTR(-ENOMEM);
    mutex_unlock(&brd_devices_mutex);

    *part = 0;
    return kobj;
}

static int __init brd_init(void)
{
    int i, nr;
    unsigned long range;
    struct brd_device *brd, *next;

    /*
     * brd module now has a feature to instantiate underlying device
     * structure on-demand, provided that there is an access dev node.
     * However, this will not work well with user space tool that doesn't
     * know about such "feature".  In order to not break any existing
     * tool, we do the following:
     *
     * (1) if rd_nr is specified, create that many upfront, and this
     *     also becomes a hard limit.
     * (2) if rd_nr is not specified, create CONFIG_BLK_DEV_RAM_COUNT
     *     (default 16) rd device on module load, user can further
     *     extend brd device by create dev node themselves and have
     *     kernel automatically instantiate actual device on-demand.
     */

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

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

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

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

    if (rd_nr) {
        nr = rd_nr;
        range = rd_nr << part_shift;
    } else {
        nr = CONFIG_BLK_DEV_RAM_COUNT;
        range = 1UL << MINORBITS;
    }

    if (register_blkdev(RAMDISK_MAJOR, "ramdisk"))
        return -EIO;

    for (i = 0; i < nr; i++) {
        brd = brd_alloc(i);
        if (!brd)
            goto out_free;
        list_add_tail(&brd->brd_list, &brd_devices);
    }

    /* point of no return */

    list_for_each_entry(brd, &brd_devices, brd_list)
        add_disk(brd->brd_disk);

    blk_register_region(MKDEV(RAMDISK_MAJOR, 0), range,
                  THIS_MODULE, brd_probe, NULL, NULL);

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

out_free:
    list_for_each_entry_safe(brd, next, &brd_devices, brd_list) {
        list_del(&brd->brd_list);
        brd_free(brd);
    }
    unregister_blkdev(RAMDISK_MAJOR, "ramdisk");

    return -ENOMEM;
}

static void __exit brd_exit(void)
{
    unsigned long range;
    struct brd_device *brd, *next;

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

    list_for_each_entry_safe(brd, next, &brd_devices, brd_list)
        brd_del_one(brd);

    blk_unregister_region(MKDEV(RAMDISK_MAJOR, 0), range);
    unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
}

module_init(brd_init);
module_exit(brd_exit);