Root/drivers/block/brd.c

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/mutex.h>
19#include <linux/radix-tree.h>
20#include <linux/fs.h>
21#include <linux/slab.h>
22
23#include <asm/uaccess.h>
24
25#define SECTOR_SHIFT 9
26#define PAGE_SECTORS_SHIFT (PAGE_SHIFT - SECTOR_SHIFT)
27#define PAGE_SECTORS (1 << PAGE_SECTORS_SHIFT)
28
29/*
30 * Each block ramdisk device has a radix_tree brd_pages of pages that stores
31 * the pages containing the block device's contents. A brd page's ->index is
32 * its offset in PAGE_SIZE units. This is similar to, but in no way connected
33 * with, the kernel's pagecache or buffer cache (which sit above our block
34 * device).
35 */
36struct brd_device {
37    int brd_number;
38
39    struct request_queue *brd_queue;
40    struct gendisk *brd_disk;
41    struct list_head brd_list;
42
43    /*
44     * Backing store of pages and lock to protect it. This is the contents
45     * of the block device.
46     */
47    spinlock_t brd_lock;
48    struct radix_tree_root brd_pages;
49};
50
51/*
52 * Look up and return a brd's page for a given sector.
53 */
54static DEFINE_MUTEX(brd_mutex);
55static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
56{
57    pgoff_t idx;
58    struct page *page;
59
60    /*
61     * The page lifetime is protected by the fact that we have opened the
62     * device node -- brd pages will never be deleted under us, so we
63     * don't need any further locking or refcounting.
64     *
65     * This is strictly true for the radix-tree nodes as well (ie. we
66     * don't actually need the rcu_read_lock()), however that is not a
67     * documented feature of the radix-tree API so it is better to be
68     * safe here (we don't have total exclusion from radix tree updates
69     * here, only deletes).
70     */
71    rcu_read_lock();
72    idx = sector >> PAGE_SECTORS_SHIFT; /* sector to page index */
73    page = radix_tree_lookup(&brd->brd_pages, idx);
74    rcu_read_unlock();
75
76    BUG_ON(page && page->index != idx);
77
78    return page;
79}
80
81/*
82 * Look up and return a brd's page for a given sector.
83 * If one does not exist, allocate an empty page, and insert that. Then
84 * return it.
85 */
86static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
87{
88    pgoff_t idx;
89    struct page *page;
90    gfp_t gfp_flags;
91
92    page = brd_lookup_page(brd, sector);
93    if (page)
94        return page;
95
96    /*
97     * Must use NOIO because we don't want to recurse back into the
98     * block or filesystem layers from page reclaim.
99     *
100     * Cannot support XIP and highmem, because our ->direct_access
101     * routine for XIP must return memory that is always addressable.
102     * If XIP was reworked to use pfns and kmap throughout, this
103     * restriction might be able to be lifted.
104     */
105    gfp_flags = GFP_NOIO | __GFP_ZERO;
106#ifndef CONFIG_BLK_DEV_XIP
107    gfp_flags |= __GFP_HIGHMEM;
108#endif
109    page = alloc_page(gfp_flags);
110    if (!page)
111        return NULL;
112
113    if (radix_tree_preload(GFP_NOIO)) {
114        __free_page(page);
115        return NULL;
116    }
117
118    spin_lock(&brd->brd_lock);
119    idx = sector >> PAGE_SECTORS_SHIFT;
120    if (radix_tree_insert(&brd->brd_pages, idx, page)) {
121        __free_page(page);
122        page = radix_tree_lookup(&brd->brd_pages, idx);
123        BUG_ON(!page);
124        BUG_ON(page->index != idx);
125    } else
126        page->index = idx;
127    spin_unlock(&brd->brd_lock);
128
129    radix_tree_preload_end();
130
131    return page;
132}
133
134static void brd_free_page(struct brd_device *brd, sector_t sector)
135{
136    struct page *page;
137    pgoff_t idx;
138
139    spin_lock(&brd->brd_lock);
140    idx = sector >> PAGE_SECTORS_SHIFT;
141    page = radix_tree_delete(&brd->brd_pages, idx);
142    spin_unlock(&brd->brd_lock);
143    if (page)
144        __free_page(page);
145}
146
147static void brd_zero_page(struct brd_device *brd, sector_t sector)
148{
149    struct page *page;
150
151    page = brd_lookup_page(brd, sector);
152    if (page)
153        clear_highpage(page);
154}
155
156/*
157 * Free all backing store pages and radix tree. This must only be called when
158 * there are no other users of the device.
159 */
160#define FREE_BATCH 16
161static void brd_free_pages(struct brd_device *brd)
162{
163    unsigned long pos = 0;
164    struct page *pages[FREE_BATCH];
165    int nr_pages;
166
167    do {
168        int i;
169
170        nr_pages = radix_tree_gang_lookup(&brd->brd_pages,
171                (void **)pages, pos, FREE_BATCH);
172
173        for (i = 0; i < nr_pages; i++) {
174            void *ret;
175
176            BUG_ON(pages[i]->index < pos);
177            pos = pages[i]->index;
178            ret = radix_tree_delete(&brd->brd_pages, pos);
179            BUG_ON(!ret || ret != pages[i]);
180            __free_page(pages[i]);
181        }
182
183        pos++;
184
185        /*
186         * This assumes radix_tree_gang_lookup always returns as
187         * many pages as possible. If the radix-tree code changes,
188         * so will this have to.
189         */
190    } while (nr_pages == FREE_BATCH);
191}
192
193/*
194 * copy_to_brd_setup must be called before copy_to_brd. It may sleep.
195 */
196static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n)
197{
198    unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
199    size_t copy;
200
201    copy = min_t(size_t, n, PAGE_SIZE - offset);
202    if (!brd_insert_page(brd, sector))
203        return -ENOMEM;
204    if (copy < n) {
205        sector += copy >> SECTOR_SHIFT;
206        if (!brd_insert_page(brd, sector))
207            return -ENOMEM;
208    }
209    return 0;
210}
211
212static void discard_from_brd(struct brd_device *brd,
213            sector_t sector, size_t n)
214{
215    while (n >= PAGE_SIZE) {
216        /*
217         * Don't want to actually discard pages here because
218         * re-allocating the pages can result in writeback
219         * deadlocks under heavy load.
220         */
221        if (0)
222            brd_free_page(brd, sector);
223        else
224            brd_zero_page(brd, sector);
225        sector += PAGE_SIZE >> SECTOR_SHIFT;
226        n -= PAGE_SIZE;
227    }
228}
229
230/*
231 * Copy n bytes from src to the brd starting at sector. Does not sleep.
232 */
233static void copy_to_brd(struct brd_device *brd, const void *src,
234            sector_t sector, size_t n)
235{
236    struct page *page;
237    void *dst;
238    unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
239    size_t copy;
240
241    copy = min_t(size_t, n, PAGE_SIZE - offset);
242    page = brd_lookup_page(brd, sector);
243    BUG_ON(!page);
244
245    dst = kmap_atomic(page);
246    memcpy(dst + offset, src, copy);
247    kunmap_atomic(dst);
248
249    if (copy < n) {
250        src += copy;
251        sector += copy >> SECTOR_SHIFT;
252        copy = n - copy;
253        page = brd_lookup_page(brd, sector);
254        BUG_ON(!page);
255
256        dst = kmap_atomic(page);
257        memcpy(dst, src, copy);
258        kunmap_atomic(dst);
259    }
260}
261
262/*
263 * Copy n bytes to dst from the brd starting at sector. Does not sleep.
264 */
265static void copy_from_brd(void *dst, struct brd_device *brd,
266            sector_t sector, size_t n)
267{
268    struct page *page;
269    void *src;
270    unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
271    size_t copy;
272
273    copy = min_t(size_t, n, PAGE_SIZE - offset);
274    page = brd_lookup_page(brd, sector);
275    if (page) {
276        src = kmap_atomic(page);
277        memcpy(dst, src + offset, copy);
278        kunmap_atomic(src);
279    } else
280        memset(dst, 0, copy);
281
282    if (copy < n) {
283        dst += copy;
284        sector += copy >> SECTOR_SHIFT;
285        copy = n - copy;
286        page = brd_lookup_page(brd, sector);
287        if (page) {
288            src = kmap_atomic(page);
289            memcpy(dst, src, copy);
290            kunmap_atomic(src);
291        } else
292            memset(dst, 0, copy);
293    }
294}
295
296/*
297 * Process a single bvec of a bio.
298 */
299static int brd_do_bvec(struct brd_device *brd, struct page *page,
300            unsigned int len, unsigned int off, int rw,
301            sector_t sector)
302{
303    void *mem;
304    int err = 0;
305
306    if (rw != READ) {
307        err = copy_to_brd_setup(brd, sector, len);
308        if (err)
309            goto out;
310    }
311
312    mem = kmap_atomic(page);
313    if (rw == READ) {
314        copy_from_brd(mem + off, brd, sector, len);
315        flush_dcache_page(page);
316    } else {
317        flush_dcache_page(page);
318        copy_to_brd(brd, mem + off, sector, len);
319    }
320    kunmap_atomic(mem);
321
322out:
323    return err;
324}
325
326static void brd_make_request(struct request_queue *q, struct bio *bio)
327{
328    struct block_device *bdev = bio->bi_bdev;
329    struct brd_device *brd = bdev->bd_disk->private_data;
330    int rw;
331    struct bio_vec *bvec;
332    sector_t sector;
333    int i;
334    int err = -EIO;
335
336    sector = bio->bi_sector;
337    if (sector + (bio->bi_size >> SECTOR_SHIFT) >
338                        get_capacity(bdev->bd_disk))
339        goto out;
340
341    if (unlikely(bio->bi_rw & REQ_DISCARD)) {
342        err = 0;
343        discard_from_brd(brd, sector, bio->bi_size);
344        goto out;
345    }
346
347    rw = bio_rw(bio);
348    if (rw == READA)
349        rw = READ;
350
351    bio_for_each_segment(bvec, bio, i) {
352        unsigned int len = bvec->bv_len;
353        err = brd_do_bvec(brd, bvec->bv_page, len,
354                    bvec->bv_offset, rw, sector);
355        if (err)
356            break;
357        sector += len >> SECTOR_SHIFT;
358    }
359
360out:
361    bio_endio(bio, err);
362}
363
364#ifdef CONFIG_BLK_DEV_XIP
365static int brd_direct_access(struct block_device *bdev, sector_t sector,
366            void **kaddr, unsigned long *pfn)
367{
368    struct brd_device *brd = bdev->bd_disk->private_data;
369    struct page *page;
370
371    if (!brd)
372        return -ENODEV;
373    if (sector & (PAGE_SECTORS-1))
374        return -EINVAL;
375    if (sector + PAGE_SECTORS > get_capacity(bdev->bd_disk))
376        return -ERANGE;
377    page = brd_insert_page(brd, sector);
378    if (!page)
379        return -ENOMEM;
380    *kaddr = page_address(page);
381    *pfn = page_to_pfn(page);
382
383    return 0;
384}
385#endif
386
387static int brd_ioctl(struct block_device *bdev, fmode_t mode,
388            unsigned int cmd, unsigned long arg)
389{
390    int error;
391    struct brd_device *brd = bdev->bd_disk->private_data;
392
393    if (cmd != BLKFLSBUF)
394        return -ENOTTY;
395
396    /*
397     * ram device BLKFLSBUF has special semantics, we want to actually
398     * release and destroy the ramdisk data.
399     */
400    mutex_lock(&brd_mutex);
401    mutex_lock(&bdev->bd_mutex);
402    error = -EBUSY;
403    if (bdev->bd_openers <= 1) {
404        /*
405         * Kill the cache first, so it isn't written back to the
406         * device.
407         *
408         * Another thread might instantiate more buffercache here,
409         * but there is not much we can do to close that race.
410         */
411        kill_bdev(bdev);
412        brd_free_pages(brd);
413        error = 0;
414    }
415    mutex_unlock(&bdev->bd_mutex);
416    mutex_unlock(&brd_mutex);
417
418    return error;
419}
420
421static const struct block_device_operations brd_fops = {
422    .owner = THIS_MODULE,
423    .ioctl = brd_ioctl,
424#ifdef CONFIG_BLK_DEV_XIP
425    .direct_access = brd_direct_access,
426#endif
427};
428
429/*
430 * And now the modules code and kernel interface.
431 */
432static int rd_nr;
433int rd_size = CONFIG_BLK_DEV_RAM_SIZE;
434static int max_part;
435static int part_shift;
436module_param(rd_nr, int, S_IRUGO);
437MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices");
438module_param(rd_size, int, S_IRUGO);
439MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");
440module_param(max_part, int, S_IRUGO);
441MODULE_PARM_DESC(max_part, "Maximum number of partitions per RAM disk");
442MODULE_LICENSE("GPL");
443MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR);
444MODULE_ALIAS("rd");
445
446#ifndef MODULE
447/* Legacy boot options - nonmodular */
448static int __init ramdisk_size(char *str)
449{
450    rd_size = simple_strtol(str, NULL, 0);
451    return 1;
452}
453__setup("ramdisk_size=", ramdisk_size);
454#endif
455
456/*
457 * The device scheme is derived from loop.c. Keep them in synch where possible
458 * (should share code eventually).
459 */
460static LIST_HEAD(brd_devices);
461static DEFINE_MUTEX(brd_devices_mutex);
462
463static struct brd_device *brd_alloc(int i)
464{
465    struct brd_device *brd;
466    struct gendisk *disk;
467
468    brd = kzalloc(sizeof(*brd), GFP_KERNEL);
469    if (!brd)
470        goto out;
471    brd->brd_number = i;
472    spin_lock_init(&brd->brd_lock);
473    INIT_RADIX_TREE(&brd->brd_pages, GFP_ATOMIC);
474
475    brd->brd_queue = blk_alloc_queue(GFP_KERNEL);
476    if (!brd->brd_queue)
477        goto out_free_dev;
478    blk_queue_make_request(brd->brd_queue, brd_make_request);
479    blk_queue_max_hw_sectors(brd->brd_queue, 1024);
480    blk_queue_bounce_limit(brd->brd_queue, BLK_BOUNCE_ANY);
481
482    brd->brd_queue->limits.discard_granularity = PAGE_SIZE;
483    brd->brd_queue->limits.max_discard_sectors = UINT_MAX;
484    brd->brd_queue->limits.discard_zeroes_data = 1;
485    queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, brd->brd_queue);
486
487    disk = brd->brd_disk = alloc_disk(1 << part_shift);
488    if (!disk)
489        goto out_free_queue;
490    disk->major = RAMDISK_MAJOR;
491    disk->first_minor = i << part_shift;
492    disk->fops = &brd_fops;
493    disk->private_data = brd;
494    disk->queue = brd->brd_queue;
495    disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
496    sprintf(disk->disk_name, "ram%d", i);
497    set_capacity(disk, rd_size * 2);
498
499    return brd;
500
501out_free_queue:
502    blk_cleanup_queue(brd->brd_queue);
503out_free_dev:
504    kfree(brd);
505out:
506    return NULL;
507}
508
509static void brd_free(struct brd_device *brd)
510{
511    put_disk(brd->brd_disk);
512    blk_cleanup_queue(brd->brd_queue);
513    brd_free_pages(brd);
514    kfree(brd);
515}
516
517static struct brd_device *brd_init_one(int i)
518{
519    struct brd_device *brd;
520
521    list_for_each_entry(brd, &brd_devices, brd_list) {
522        if (brd->brd_number == i)
523            goto out;
524    }
525
526    brd = brd_alloc(i);
527    if (brd) {
528        add_disk(brd->brd_disk);
529        list_add_tail(&brd->brd_list, &brd_devices);
530    }
531out:
532    return brd;
533}
534
535static void brd_del_one(struct brd_device *brd)
536{
537    list_del(&brd->brd_list);
538    del_gendisk(brd->brd_disk);
539    brd_free(brd);
540}
541
542static struct kobject *brd_probe(dev_t dev, int *part, void *data)
543{
544    struct brd_device *brd;
545    struct kobject *kobj;
546
547    mutex_lock(&brd_devices_mutex);
548    brd = brd_init_one(MINOR(dev) >> part_shift);
549    kobj = brd ? get_disk(brd->brd_disk) : ERR_PTR(-ENOMEM);
550    mutex_unlock(&brd_devices_mutex);
551
552    *part = 0;
553    return kobj;
554}
555
556static int __init brd_init(void)
557{
558    int i, nr;
559    unsigned long range;
560    struct brd_device *brd, *next;
561
562    /*
563     * brd module now has a feature to instantiate underlying device
564     * structure on-demand, provided that there is an access dev node.
565     * However, this will not work well with user space tool that doesn't
566     * know about such "feature". In order to not break any existing
567     * tool, we do the following:
568     *
569     * (1) if rd_nr is specified, create that many upfront, and this
570     * also becomes a hard limit.
571     * (2) if rd_nr is not specified, create CONFIG_BLK_DEV_RAM_COUNT
572     * (default 16) rd device on module load, user can further
573     * extend brd device by create dev node themselves and have
574     * kernel automatically instantiate actual device on-demand.
575     */
576
577    part_shift = 0;
578    if (max_part > 0) {
579        part_shift = fls(max_part);
580
581        /*
582         * Adjust max_part according to part_shift as it is exported
583         * to user space so that user can decide correct minor number
584         * if [s]he want to create more devices.
585         *
586         * Note that -1 is required because partition 0 is reserved
587         * for the whole disk.
588         */
589        max_part = (1UL << part_shift) - 1;
590    }
591
592    if ((1UL << part_shift) > DISK_MAX_PARTS)
593        return -EINVAL;
594
595    if (rd_nr > 1UL << (MINORBITS - part_shift))
596        return -EINVAL;
597
598    if (rd_nr) {
599        nr = rd_nr;
600        range = rd_nr << part_shift;
601    } else {
602        nr = CONFIG_BLK_DEV_RAM_COUNT;
603        range = 1UL << MINORBITS;
604    }
605
606    if (register_blkdev(RAMDISK_MAJOR, "ramdisk"))
607        return -EIO;
608
609    for (i = 0; i < nr; i++) {
610        brd = brd_alloc(i);
611        if (!brd)
612            goto out_free;
613        list_add_tail(&brd->brd_list, &brd_devices);
614    }
615
616    /* point of no return */
617
618    list_for_each_entry(brd, &brd_devices, brd_list)
619        add_disk(brd->brd_disk);
620
621    blk_register_region(MKDEV(RAMDISK_MAJOR, 0), range,
622                  THIS_MODULE, brd_probe, NULL, NULL);
623
624    printk(KERN_INFO "brd: module loaded\n");
625    return 0;
626
627out_free:
628    list_for_each_entry_safe(brd, next, &brd_devices, brd_list) {
629        list_del(&brd->brd_list);
630        brd_free(brd);
631    }
632    unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
633
634    return -ENOMEM;
635}
636
637static void __exit brd_exit(void)
638{
639    unsigned long range;
640    struct brd_device *brd, *next;
641
642    range = rd_nr ? rd_nr << part_shift : 1UL << MINORBITS;
643
644    list_for_each_entry_safe(brd, next, &brd_devices, brd_list)
645        brd_del_one(brd);
646
647    blk_unregister_region(MKDEV(RAMDISK_MAJOR, 0), range);
648    unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
649}
650
651module_init(brd_init);
652module_exit(brd_exit);
653
654

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jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master

Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9



interactive