linux/drivers/block/brd.c
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   1/*
   2 * Ram backed block device driver.
   3 *
   4 * Copyright (C) 2007 Nick Piggin
   5 * Copyright (C) 2007 Novell Inc.
   6 *
   7 * Parts derived from drivers/block/rd.c, and drivers/block/loop.c, copyright
   8 * of their respective owners.
   9 */
  10
  11#include <linux/init.h>
  12#include <linux/module.h>
  13#include <linux/moduleparam.h>
  14#include <linux/major.h>
  15#include <linux/blkdev.h>
  16#include <linux/bio.h>
  17#include <linux/highmem.h>
  18#include <linux/gfp.h>
  19#include <linux/radix-tree.h>
  20#include <linux/buffer_head.h> /* invalidate_bh_lrus() */
  21
  22#include <asm/uaccess.h>
  23
  24#define SECTOR_SHIFT            9
  25#define PAGE_SECTORS_SHIFT      (PAGE_SHIFT - SECTOR_SHIFT)
  26#define PAGE_SECTORS            (1 << PAGE_SECTORS_SHIFT)
  27
  28/*
  29 * Each block ramdisk device has a radix_tree brd_pages of pages that stores
  30 * the pages containing the block device's contents. A brd page's ->index is
  31 * its offset in PAGE_SIZE units. This is similar to, but in no way connected
  32 * with, the kernel's pagecache or buffer cache (which sit above our block
  33 * device).
  34 */
  35struct brd_device {
  36        int             brd_number;
  37        int             brd_refcnt;
  38        loff_t          brd_offset;
  39        loff_t          brd_sizelimit;
  40        unsigned        brd_blocksize;
  41
  42        struct request_queue    *brd_queue;
  43        struct gendisk          *brd_disk;
  44        struct list_head        brd_list;
  45
  46        /*
  47         * Backing store of pages and lock to protect it. This is the contents
  48         * of the block device.
  49         */
  50        spinlock_t              brd_lock;
  51        struct radix_tree_root  brd_pages;
  52};
  53
  54/*
  55 * Look up and return a brd's page for a given sector.
  56 */
  57static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
  58{
  59        pgoff_t idx;
  60        struct page *page;
  61
  62        /*
  63         * The page lifetime is protected by the fact that we have opened the
  64         * device node -- brd pages will never be deleted under us, so we
  65         * don't need any further locking or refcounting.
  66         *
  67         * This is strictly true for the radix-tree nodes as well (ie. we
  68         * don't actually need the rcu_read_lock()), however that is not a
  69         * documented feature of the radix-tree API so it is better to be
  70         * safe here (we don't have total exclusion from radix tree updates
  71         * here, only deletes).
  72         */
  73        rcu_read_lock();
  74        idx = sector >> PAGE_SECTORS_SHIFT; /* sector to page index */
  75        page = radix_tree_lookup(&brd->brd_pages, idx);
  76        rcu_read_unlock();
  77
  78        BUG_ON(page && page->index != idx);
  79
  80        return page;
  81}
  82
  83/*
  84 * Look up and return a brd's page for a given sector.
  85 * If one does not exist, allocate an empty page, and insert that. Then
  86 * return it.
  87 */
  88static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
  89{
  90        pgoff_t idx;
  91        struct page *page;
  92        gfp_t gfp_flags;
  93
  94        page = brd_lookup_page(brd, sector);
  95        if (page)
  96                return page;
  97
  98        /*
  99         * Must use NOIO because we don't want to recurse back into the
 100         * block or filesystem layers from page reclaim.
 101         *
 102         * Cannot support XIP and highmem, because our ->direct_access
 103         * routine for XIP must return memory that is always addressable.
 104         * If XIP was reworked to use pfns and kmap throughout, this
 105         * restriction might be able to be lifted.
 106         */
 107        gfp_flags = GFP_NOIO | __GFP_ZERO;
 108#ifndef CONFIG_BLK_DEV_XIP
 109        gfp_flags |= __GFP_HIGHMEM;
 110#endif
 111        page = alloc_page(gfp_flags);
 112        if (!page)
 113                return NULL;
 114
 115        if (radix_tree_preload(GFP_NOIO)) {
 116                __free_page(page);
 117                return NULL;
 118        }
 119
 120        spin_lock(&brd->brd_lock);
 121        idx = sector >> PAGE_SECTORS_SHIFT;
 122        if (radix_tree_insert(&brd->brd_pages, idx, page)) {
 123                __free_page(page);
 124                page = radix_tree_lookup(&brd->brd_pages, idx);
 125                BUG_ON(!page);
 126                BUG_ON(page->index != idx);
 127        } else
 128                page->index = idx;
 129        spin_unlock(&brd->brd_lock);
 130
 131        radix_tree_preload_end();
 132
 133        return page;
 134}
 135
 136/*
 137 * Free all backing store pages and radix tree. This must only be called when
 138 * there are no other users of the device.
 139 */
 140#define FREE_BATCH 16
 141static void brd_free_pages(struct brd_device *brd)
 142{
 143        unsigned long pos = 0;
 144        struct page *pages[FREE_BATCH];
 145        int nr_pages;
 146
 147        do {
 148                int i;
 149
 150                nr_pages = radix_tree_gang_lookup(&brd->brd_pages,
 151                                (void **)pages, pos, FREE_BATCH);
 152
 153                for (i = 0; i < nr_pages; i++) {
 154                        void *ret;
 155
 156                        BUG_ON(pages[i]->index < pos);
 157                        pos = pages[i]->index;
 158                        ret = radix_tree_delete(&brd->brd_pages, pos);
 159                        BUG_ON(!ret || ret != pages[i]);
 160                        __free_page(pages[i]);
 161                }
 162
 163                pos++;
 164
 165                /*
 166                 * This assumes radix_tree_gang_lookup always returns as
 167                 * many pages as possible. If the radix-tree code changes,
 168                 * so will this have to.
 169                 */
 170        } while (nr_pages == FREE_BATCH);
 171}
 172
 173/*
 174 * copy_to_brd_setup must be called before copy_to_brd. It may sleep.
 175 */
 176static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n)
 177{
 178        unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
 179        size_t copy;
 180
 181        copy = min_t(size_t, n, PAGE_SIZE - offset);
 182        if (!brd_insert_page(brd, sector))
 183                return -ENOMEM;
 184        if (copy < n) {
 185                sector += copy >> SECTOR_SHIFT;
 186                if (!brd_insert_page(brd, sector))
 187                        return -ENOMEM;
 188        }
 189        return 0;
 190}
 191
 192/*
 193 * Copy n bytes from src to the brd starting at sector. Does not sleep.
 194 */
 195static void copy_to_brd(struct brd_device *brd, const void *src,
 196                        sector_t sector, size_t n)
 197{
 198        struct page *page;
 199        void *dst;
 200        unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
 201        size_t copy;
 202
 203        copy = min_t(size_t, n, PAGE_SIZE - offset);
 204        page = brd_lookup_page(brd, sector);
 205        BUG_ON(!page);
 206
 207        dst = kmap_atomic(page, KM_USER1);
 208        memcpy(dst + offset, src, copy);
 209        kunmap_atomic(dst, KM_USER1);
 210
 211        if (copy < n) {
 212                src += copy;
 213                sector += copy >> SECTOR_SHIFT;
 214                copy = n - copy;
 215                page = brd_lookup_page(brd, sector);
 216                BUG_ON(!page);
 217
 218                dst = kmap_atomic(page, KM_USER1);
 219                memcpy(dst, src, copy);
 220                kunmap_atomic(dst, KM_USER1);
 221        }
 222}
 223
 224/*
 225 * Copy n bytes to dst from the brd starting at sector. Does not sleep.
 226 */
 227static void copy_from_brd(void *dst, struct brd_device *brd,
 228                        sector_t sector, size_t n)
 229{
 230        struct page *page;
 231        void *src;
 232        unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
 233        size_t copy;
 234
 235        copy = min_t(size_t, n, PAGE_SIZE - offset);
 236        page = brd_lookup_page(brd, sector);
 237        if (page) {
 238                src = kmap_atomic(page, KM_USER1);
 239                memcpy(dst, src + offset, copy);
 240                kunmap_atomic(src, KM_USER1);
 241        } else
 242                memset(dst, 0, copy);
 243
 244        if (copy < n) {
 245                dst += copy;
 246                sector += copy >> SECTOR_SHIFT;
 247                copy = n - copy;
 248                page = brd_lookup_page(brd, sector);
 249                if (page) {
 250                        src = kmap_atomic(page, KM_USER1);
 251                        memcpy(dst, src, copy);
 252                        kunmap_atomic(src, KM_USER1);
 253                } else
 254                        memset(dst, 0, copy);
 255        }
 256}
 257
 258/*
 259 * Process a single bvec of a bio.
 260 */
 261static int brd_do_bvec(struct brd_device *brd, struct page *page,
 262                        unsigned int len, unsigned int off, int rw,
 263                        sector_t sector)
 264{
 265        void *mem;
 266        int err = 0;
 267
 268        if (rw != READ) {
 269                err = copy_to_brd_setup(brd, sector, len);
 270                if (err)
 271                        goto out;
 272        }
 273
 274        mem = kmap_atomic(page, KM_USER0);
 275        if (rw == READ) {
 276                copy_from_brd(mem + off, brd, sector, len);
 277                flush_dcache_page(page);
 278        } else
 279                copy_to_brd(brd, mem + off, sector, len);
 280        kunmap_atomic(mem, KM_USER0);
 281
 282out:
 283        return err;
 284}
 285
 286static int brd_make_request(struct request_queue *q, struct bio *bio)
 287{
 288        struct block_device *bdev = bio->bi_bdev;
 289        struct brd_device *brd = bdev->bd_disk->private_data;
 290        int rw;
 291        struct bio_vec *bvec;
 292        sector_t sector;
 293        int i;
 294        int err = -EIO;
 295
 296        sector = bio->bi_sector;
 297        if (sector + (bio->bi_size >> SECTOR_SHIFT) >
 298                                                get_capacity(bdev->bd_disk))
 299                goto out;
 300
 301        rw = bio_rw(bio);
 302        if (rw == READA)
 303                rw = READ;
 304
 305        bio_for_each_segment(bvec, bio, i) {
 306                unsigned int len = bvec->bv_len;
 307                err = brd_do_bvec(brd, bvec->bv_page, len,
 308                                        bvec->bv_offset, rw, sector);
 309                if (err)
 310                        break;
 311                sector += len >> SECTOR_SHIFT;
 312        }
 313
 314out:
 315        bio_endio(bio, err);
 316
 317        return 0;
 318}
 319
 320#ifdef CONFIG_BLK_DEV_XIP
 321static int brd_direct_access (struct block_device *bdev, sector_t sector,
 322                        void **kaddr, unsigned long *pfn)
 323{
 324        struct brd_device *brd = bdev->bd_disk->private_data;
 325        struct page *page;
 326
 327        if (!brd)
 328                return -ENODEV;
 329        if (sector & (PAGE_SECTORS-1))
 330                return -EINVAL;
 331        if (sector + PAGE_SECTORS > get_capacity(bdev->bd_disk))
 332                return -ERANGE;
 333        page = brd_insert_page(brd, sector);
 334        if (!page)
 335                return -ENOMEM;
 336        *kaddr = page_address(page);
 337        *pfn = page_to_pfn(page);
 338
 339        return 0;
 340}
 341#endif
 342
 343static int brd_ioctl(struct inode *inode, struct file *file,
 344                        unsigned int cmd, unsigned long arg)
 345{
 346        int error;
 347        struct block_device *bdev = inode->i_bdev;
 348        struct brd_device *brd = bdev->bd_disk->private_data;
 349
 350        if (cmd != BLKFLSBUF)
 351                return -ENOTTY;
 352
 353        /*
 354         * ram device BLKFLSBUF has special semantics, we want to actually
 355         * release and destroy the ramdisk data.
 356         */
 357        mutex_lock(&bdev->bd_mutex);
 358        error = -EBUSY;
 359        if (bdev->bd_openers <= 1) {
 360                /*
 361                 * Invalidate the cache first, so it isn't written
 362                 * back to the device.
 363                 *
 364                 * Another thread might instantiate more buffercache here,
 365                 * but there is not much we can do to close that race.
 366                 */
 367                invalidate_bh_lrus();
 368                truncate_inode_pages(bdev->bd_inode->i_mapping, 0);
 369                brd_free_pages(brd);
 370                error = 0;
 371        }
 372        mutex_unlock(&bdev->bd_mutex);
 373
 374        return error;
 375}
 376
 377static struct block_device_operations brd_fops = {
 378        .owner =                THIS_MODULE,
 379        .ioctl =                brd_ioctl,
 380#ifdef CONFIG_BLK_DEV_XIP
 381        .direct_access =        brd_direct_access,
 382#endif
 383};
 384
 385/*
 386 * And now the modules code and kernel interface.
 387 */
 388static int rd_nr;
 389int rd_size = CONFIG_BLK_DEV_RAM_SIZE;
 390static int max_part;
 391static int part_shift;
 392module_param(rd_nr, int, 0);
 393MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices");
 394module_param(rd_size, int, 0);
 395MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");
 396module_param(max_part, int, 0);
 397MODULE_PARM_DESC(max_part, "Maximum number of partitions per RAM disk");
 398MODULE_LICENSE("GPL");
 399MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR);
 400MODULE_ALIAS("rd");
 401
 402#ifndef MODULE
 403/* Legacy boot options - nonmodular */
 404static int __init ramdisk_size(char *str)
 405{
 406        rd_size = simple_strtol(str, NULL, 0);
 407        return 1;
 408}
 409static int __init ramdisk_size2(char *str)
 410{
 411        return ramdisk_size(str);
 412}
 413__setup("ramdisk=", ramdisk_size);
 414__setup("ramdisk_size=", ramdisk_size2);
 415#endif
 416
 417/*
 418 * The device scheme is derived from loop.c. Keep them in synch where possible
 419 * (should share code eventually).
 420 */
 421static LIST_HEAD(brd_devices);
 422static DEFINE_MUTEX(brd_devices_mutex);
 423
 424static struct brd_device *brd_alloc(int i)
 425{
 426        struct brd_device *brd;
 427        struct gendisk *disk;
 428
 429        brd = kzalloc(sizeof(*brd), GFP_KERNEL);
 430        if (!brd)
 431                goto out;
 432        brd->brd_number         = i;
 433        spin_lock_init(&brd->brd_lock);
 434        INIT_RADIX_TREE(&brd->brd_pages, GFP_ATOMIC);
 435
 436        brd->brd_queue = blk_alloc_queue(GFP_KERNEL);
 437        if (!brd->brd_queue)
 438                goto out_free_dev;
 439        blk_queue_make_request(brd->brd_queue, brd_make_request);
 440        blk_queue_max_sectors(brd->brd_queue, 1024);
 441        blk_queue_bounce_limit(brd->brd_queue, BLK_BOUNCE_ANY);
 442
 443        disk = brd->brd_disk = alloc_disk(1 << part_shift);
 444        if (!disk)
 445                goto out_free_queue;
 446        disk->major             = RAMDISK_MAJOR;
 447        disk->first_minor       = i << part_shift;
 448        disk->fops              = &brd_fops;
 449        disk->private_data      = brd;
 450        disk->queue             = brd->brd_queue;
 451        disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
 452        sprintf(disk->disk_name, "ram%d", i);
 453        set_capacity(disk, rd_size * 2);
 454
 455        return brd;
 456
 457out_free_queue:
 458        blk_cleanup_queue(brd->brd_queue);
 459out_free_dev:
 460        kfree(brd);
 461out:
 462        return NULL;
 463}
 464
 465static void brd_free(struct brd_device *brd)
 466{
 467        put_disk(brd->brd_disk);
 468        blk_cleanup_queue(brd->brd_queue);
 469        brd_free_pages(brd);
 470        kfree(brd);
 471}
 472
 473static struct brd_device *brd_init_one(int i)
 474{
 475        struct brd_device *brd;
 476
 477        list_for_each_entry(brd, &brd_devices, brd_list) {
 478                if (brd->brd_number == i)
 479                        goto out;
 480        }
 481
 482        brd = brd_alloc(i);
 483        if (brd) {
 484                add_disk(brd->brd_disk);
 485                list_add_tail(&brd->brd_list, &brd_devices);
 486        }
 487out:
 488        return brd;
 489}
 490
 491static void brd_del_one(struct brd_device *brd)
 492{
 493        list_del(&brd->brd_list);
 494        del_gendisk(brd->brd_disk);
 495        brd_free(brd);
 496}
 497
 498static struct kobject *brd_probe(dev_t dev, int *part, void *data)
 499{
 500        struct brd_device *brd;
 501        struct kobject *kobj;
 502
 503        mutex_lock(&brd_devices_mutex);
 504        brd = brd_init_one(dev & MINORMASK);
 505        kobj = brd ? get_disk(brd->brd_disk) : ERR_PTR(-ENOMEM);
 506        mutex_unlock(&brd_devices_mutex);
 507
 508        *part = 0;
 509        return kobj;
 510}
 511
 512static int __init brd_init(void)
 513{
 514        int i, nr;
 515        unsigned long range;
 516        struct brd_device *brd, *next;
 517
 518        /*
 519         * brd module now has a feature to instantiate underlying device
 520         * structure on-demand, provided that there is an access dev node.
 521         * However, this will not work well with user space tool that doesn't
 522         * know about such "feature".  In order to not break any existing
 523         * tool, we do the following:
 524         *
 525         * (1) if rd_nr is specified, create that many upfront, and this
 526         *     also becomes a hard limit.
 527         * (2) if rd_nr is not specified, create 1 rd device on module
 528         *     load, user can further extend brd device by create dev node
 529         *     themselves and have kernel automatically instantiate actual
 530         *     device on-demand.
 531         */
 532
 533        part_shift = 0;
 534        if (max_part > 0)
 535                part_shift = fls(max_part);
 536
 537        if (rd_nr > 1UL << (MINORBITS - part_shift))
 538                return -EINVAL;
 539
 540        if (rd_nr) {
 541                nr = rd_nr;
 542                range = rd_nr;
 543        } else {
 544                nr = CONFIG_BLK_DEV_RAM_COUNT;
 545                range = 1UL << (MINORBITS - part_shift);
 546        }
 547
 548        if (register_blkdev(RAMDISK_MAJOR, "ramdisk"))
 549                return -EIO;
 550
 551        for (i = 0; i < nr; i++) {
 552                brd = brd_alloc(i);
 553                if (!brd)
 554                        goto out_free;
 555                list_add_tail(&brd->brd_list, &brd_devices);
 556        }
 557
 558        /* point of no return */
 559
 560        list_for_each_entry(brd, &brd_devices, brd_list)
 561                add_disk(brd->brd_disk);
 562
 563        blk_register_region(MKDEV(RAMDISK_MAJOR, 0), range,
 564                                  THIS_MODULE, brd_probe, NULL, NULL);
 565
 566        printk(KERN_INFO "brd: module loaded\n");
 567        return 0;
 568
 569out_free:
 570        list_for_each_entry_safe(brd, next, &brd_devices, brd_list) {
 571                list_del(&brd->brd_list);
 572                brd_free(brd);
 573        }
 574        unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
 575
 576        return -ENOMEM;
 577}
 578
 579static void __exit brd_exit(void)
 580{
 581        unsigned long range;
 582        struct brd_device *brd, *next;
 583
 584        range = rd_nr ? rd_nr :  1UL << (MINORBITS - part_shift);
 585
 586        list_for_each_entry_safe(brd, next, &brd_devices, brd_list)
 587                brd_del_one(brd);
 588
 589        blk_unregister_region(MKDEV(RAMDISK_MAJOR, 0), range);
 590        unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
 591}
 592
 593module_init(brd_init);
 594module_exit(brd_exit);
 595
 596