xref: /linux/drivers/block/brd.c (revision cdd30ebb1b9f36159d66f088b61aee264e649d7a) 
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Ram backed block device driver.
4  *
5  * Copyright (C) 2007 Nick Piggin
6  * Copyright (C) 2007 Novell Inc.
7  *
8  * Parts derived from drivers/block/rd.c, and drivers/block/loop.c, copyright
9  * of their respective owners.
10  */
11 
12 #include <linux/init.h>
13 #include <linux/initrd.h>
14 #include <linux/module.h>
15 #include <linux/moduleparam.h>
16 #include <linux/major.h>
17 #include <linux/blkdev.h>
18 #include <linux/bio.h>
19 #include <linux/highmem.h>
20 #include <linux/mutex.h>
21 #include <linux/pagemap.h>
22 #include <linux/xarray.h>
23 #include <linux/fs.h>
24 #include <linux/slab.h>
25 #include <linux/backing-dev.h>
26 #include <linux/debugfs.h>
27 
28 #include <linux/uaccess.h>
29 
30 /*
31  * Each block ramdisk device has a xarray brd_pages of pages that stores
32  * the pages containing the block device's contents.
33  */
34 struct brd_device {
35 	int			brd_number;
36 	struct gendisk		*brd_disk;
37 	struct list_head	brd_list;
38 
39 	/*
40 	 * Backing store of pages. This is the contents of the block device.
41 	 */
42 	struct xarray	        brd_pages;
43 	u64			brd_nr_pages;
44 };
45 
46 /*
47  * Look up and return a brd's page for a given sector.
48  */
49 static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
50 {
51 	return xa_load(&brd->brd_pages, sector >> PAGE_SECTORS_SHIFT);
52 }
53 
54 /*
55  * Insert a new page for a given sector, if one does not already exist.
56  */
57 static int brd_insert_page(struct brd_device *brd, sector_t sector, gfp_t gfp)
58 {
59 	pgoff_t idx = sector >> PAGE_SECTORS_SHIFT;
60 	struct page *page;
61 	int ret = 0;
62 
63 	page = brd_lookup_page(brd, sector);
64 	if (page)
65 		return 0;
66 
67 	page = alloc_page(gfp | __GFP_ZERO | __GFP_HIGHMEM);
68 	if (!page)
69 		return -ENOMEM;
70 
71 	xa_lock(&brd->brd_pages);
72 	ret = __xa_insert(&brd->brd_pages, idx, page, gfp);
73 	if (!ret)
74 		brd->brd_nr_pages++;
75 	xa_unlock(&brd->brd_pages);
76 
77 	if (ret < 0) {
78 		__free_page(page);
79 		if (ret == -EBUSY)
80 			ret = 0;
81 	}
82 	return ret;
83 }
84 
85 /*
86  * Free all backing store pages and xarray. This must only be called when
87  * there are no other users of the device.
88  */
89 static void brd_free_pages(struct brd_device *brd)
90 {
91 	struct page *page;
92 	pgoff_t idx;
93 
94 	xa_for_each(&brd->brd_pages, idx, page) {
95 		__free_page(page);
96 		cond_resched();
97 	}
98 
99 	xa_destroy(&brd->brd_pages);
100 }
101 
102 /*
103  * copy_to_brd_setup must be called before copy_to_brd. It may sleep.
104  */
105 static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n,
106 			     gfp_t gfp)
107 {
108 	unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
109 	size_t copy;
110 	int ret;
111 
112 	copy = min_t(size_t, n, PAGE_SIZE - offset);
113 	ret = brd_insert_page(brd, sector, gfp);
114 	if (ret)
115 		return ret;
116 	if (copy < n) {
117 		sector += copy >> SECTOR_SHIFT;
118 		ret = brd_insert_page(brd, sector, gfp);
119 	}
120 	return ret;
121 }
122 
123 /*
124  * Copy n bytes from src to the brd starting at sector. Does not sleep.
125  */
126 static void copy_to_brd(struct brd_device *brd, const void *src,
127 			sector_t sector, size_t n)
128 {
129 	struct page *page;
130 	void *dst;
131 	unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
132 	size_t copy;
133 
134 	copy = min_t(size_t, n, PAGE_SIZE - offset);
135 	page = brd_lookup_page(brd, sector);
136 	BUG_ON(!page);
137 
138 	dst = kmap_atomic(page);
139 	memcpy(dst + offset, src, copy);
140 	kunmap_atomic(dst);
141 
142 	if (copy < n) {
143 		src += copy;
144 		sector += copy >> SECTOR_SHIFT;
145 		copy = n - copy;
146 		page = brd_lookup_page(brd, sector);
147 		BUG_ON(!page);
148 
149 		dst = kmap_atomic(page);
150 		memcpy(dst, src, copy);
151 		kunmap_atomic(dst);
152 	}
153 }
154 
155 /*
156  * Copy n bytes to dst from the brd starting at sector. Does not sleep.
157  */
158 static void copy_from_brd(void *dst, struct brd_device *brd,
159 			sector_t sector, size_t n)
160 {
161 	struct page *page;
162 	void *src;
163 	unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
164 	size_t copy;
165 
166 	copy = min_t(size_t, n, PAGE_SIZE - offset);
167 	page = brd_lookup_page(brd, sector);
168 	if (page) {
169 		src = kmap_atomic(page);
170 		memcpy(dst, src + offset, copy);
171 		kunmap_atomic(src);
172 	} else
173 		memset(dst, 0, copy);
174 
175 	if (copy < n) {
176 		dst += copy;
177 		sector += copy >> SECTOR_SHIFT;
178 		copy = n - copy;
179 		page = brd_lookup_page(brd, sector);
180 		if (page) {
181 			src = kmap_atomic(page);
182 			memcpy(dst, src, copy);
183 			kunmap_atomic(src);
184 		} else
185 			memset(dst, 0, copy);
186 	}
187 }
188 
189 /*
190  * Process a single bvec of a bio.
191  */
192 static int brd_do_bvec(struct brd_device *brd, struct page *page,
193 			unsigned int len, unsigned int off, blk_opf_t opf,
194 			sector_t sector)
195 {
196 	void *mem;
197 	int err = 0;
198 
199 	if (op_is_write(opf)) {
200 		/*
201 		 * Must use NOIO because we don't want to recurse back into the
202 		 * block or filesystem layers from page reclaim.
203 		 */
204 		gfp_t gfp = opf & REQ_NOWAIT ? GFP_NOWAIT : GFP_NOIO;
205 
206 		err = copy_to_brd_setup(brd, sector, len, gfp);
207 		if (err)
208 			goto out;
209 	}
210 
211 	mem = kmap_atomic(page);
212 	if (!op_is_write(opf)) {
213 		copy_from_brd(mem + off, brd, sector, len);
214 		flush_dcache_page(page);
215 	} else {
216 		flush_dcache_page(page);
217 		copy_to_brd(brd, mem + off, sector, len);
218 	}
219 	kunmap_atomic(mem);
220 
221 out:
222 	return err;
223 }
224 
225 static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size)
226 {
227 	sector_t aligned_sector = (sector + PAGE_SECTORS) & ~PAGE_SECTORS;
228 	struct page *page;
229 
230 	size -= (aligned_sector - sector) * SECTOR_SIZE;
231 	xa_lock(&brd->brd_pages);
232 	while (size >= PAGE_SIZE && aligned_sector < rd_size * 2) {
233 		page = __xa_erase(&brd->brd_pages, aligned_sector >> PAGE_SECTORS_SHIFT);
234 		if (page) {
235 			__free_page(page);
236 			brd->brd_nr_pages--;
237 		}
238 		aligned_sector += PAGE_SECTORS;
239 		size -= PAGE_SIZE;
240 	}
241 	xa_unlock(&brd->brd_pages);
242 }
243 
244 static void brd_submit_bio(struct bio *bio)
245 {
246 	struct brd_device *brd = bio->bi_bdev->bd_disk->private_data;
247 	sector_t sector = bio->bi_iter.bi_sector;
248 	struct bio_vec bvec;
249 	struct bvec_iter iter;
250 
251 	if (unlikely(op_is_discard(bio->bi_opf))) {
252 		brd_do_discard(brd, sector, bio->bi_iter.bi_size);
253 		bio_endio(bio);
254 		return;
255 	}
256 
257 	bio_for_each_segment(bvec, bio, iter) {
258 		unsigned int len = bvec.bv_len;
259 		int err;
260 
261 		/* Don't support un-aligned buffer */
262 		WARN_ON_ONCE((bvec.bv_offset & (SECTOR_SIZE - 1)) ||
263 				(len & (SECTOR_SIZE - 1)));
264 
265 		err = brd_do_bvec(brd, bvec.bv_page, len, bvec.bv_offset,
266 				  bio->bi_opf, sector);
267 		if (err) {
268 			if (err == -ENOMEM && bio->bi_opf & REQ_NOWAIT) {
269 				bio_wouldblock_error(bio);
270 				return;
271 			}
272 			bio_io_error(bio);
273 			return;
274 		}
275 		sector += len >> SECTOR_SHIFT;
276 	}
277 
278 	bio_endio(bio);
279 }
280 
281 static const struct block_device_operations brd_fops = {
282 	.owner =		THIS_MODULE,
283 	.submit_bio =		brd_submit_bio,
284 };
285 
286 /*
287  * And now the modules code and kernel interface.
288  */
289 static int rd_nr = CONFIG_BLK_DEV_RAM_COUNT;
290 module_param(rd_nr, int, 0444);
291 MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices");
292 
293 unsigned long rd_size = CONFIG_BLK_DEV_RAM_SIZE;
294 module_param(rd_size, ulong, 0444);
295 MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");
296 
297 static int max_part = 1;
298 module_param(max_part, int, 0444);
299 MODULE_PARM_DESC(max_part, "Num Minors to reserve between devices");
300 
301 MODULE_DESCRIPTION("Ram backed block device driver");
302 MODULE_LICENSE("GPL");
303 MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR);
304 MODULE_ALIAS("rd");
305 
306 #ifndef MODULE
307 /* Legacy boot options - nonmodular */
308 static int __init ramdisk_size(char *str)
309 {
310 	rd_size = simple_strtol(str, NULL, 0);
311 	return 1;
312 }
313 __setup("ramdisk_size=", ramdisk_size);
314 #endif
315 
316 /*
317  * The device scheme is derived from loop.c. Keep them in synch where possible
318  * (should share code eventually).
319  */
320 static LIST_HEAD(brd_devices);
321 static DEFINE_MUTEX(brd_devices_mutex);
322 static struct dentry *brd_debugfs_dir;
323 
324 static struct brd_device *brd_find_or_alloc_device(int i)
325 {
326 	struct brd_device *brd;
327 
328 	mutex_lock(&brd_devices_mutex);
329 	list_for_each_entry(brd, &brd_devices, brd_list) {
330 		if (brd->brd_number == i) {
331 			mutex_unlock(&brd_devices_mutex);
332 			return ERR_PTR(-EEXIST);
333 		}
334 	}
335 
336 	brd = kzalloc(sizeof(*brd), GFP_KERNEL);
337 	if (!brd) {
338 		mutex_unlock(&brd_devices_mutex);
339 		return ERR_PTR(-ENOMEM);
340 	}
341 	brd->brd_number	= i;
342 	list_add_tail(&brd->brd_list, &brd_devices);
343 	mutex_unlock(&brd_devices_mutex);
344 	return brd;
345 }
346 
347 static void brd_free_device(struct brd_device *brd)
348 {
349 	mutex_lock(&brd_devices_mutex);
350 	list_del(&brd->brd_list);
351 	mutex_unlock(&brd_devices_mutex);
352 	kfree(brd);
353 }
354 
355 static int brd_alloc(int i)
356 {
357 	struct brd_device *brd;
358 	struct gendisk *disk;
359 	char buf[DISK_NAME_LEN];
360 	int err = -ENOMEM;
361 	struct queue_limits lim = {
362 		/*
363 		 * This is so fdisk will align partitions on 4k, because of
364 		 * direct_access API needing 4k alignment, returning a PFN
365 		 * (This is only a problem on very small devices <= 4M,
366 		 *  otherwise fdisk will align on 1M. Regardless this call
367 		 *  is harmless)
368 		 */
369 		.physical_block_size	= PAGE_SIZE,
370 		.max_hw_discard_sectors	= UINT_MAX,
371 		.max_discard_segments	= 1,
372 		.discard_granularity	= PAGE_SIZE,
373 		.features		= BLK_FEAT_SYNCHRONOUS |
374 					  BLK_FEAT_NOWAIT,
375 	};
376 
377 	brd = brd_find_or_alloc_device(i);
378 	if (IS_ERR(brd))
379 		return PTR_ERR(brd);
380 
381 	xa_init(&brd->brd_pages);
382 
383 	snprintf(buf, DISK_NAME_LEN, "ram%d", i);
384 	if (!IS_ERR_OR_NULL(brd_debugfs_dir))
385 		debugfs_create_u64(buf, 0444, brd_debugfs_dir,
386 				&brd->brd_nr_pages);
387 
388 	disk = brd->brd_disk = blk_alloc_disk(&lim, NUMA_NO_NODE);
389 	if (IS_ERR(disk)) {
390 		err = PTR_ERR(disk);
391 		goto out_free_dev;
392 	}
393 	disk->major		= RAMDISK_MAJOR;
394 	disk->first_minor	= i * max_part;
395 	disk->minors		= max_part;
396 	disk->fops		= &brd_fops;
397 	disk->private_data	= brd;
398 	strscpy(disk->disk_name, buf, DISK_NAME_LEN);
399 	set_capacity(disk, rd_size * 2);
400 
401 	err = add_disk(disk);
402 	if (err)
403 		goto out_cleanup_disk;
404 
405 	return 0;
406 
407 out_cleanup_disk:
408 	put_disk(disk);
409 out_free_dev:
410 	brd_free_device(brd);
411 	return err;
412 }
413 
414 static void brd_probe(dev_t dev)
415 {
416 	brd_alloc(MINOR(dev) / max_part);
417 }
418 
419 static void brd_cleanup(void)
420 {
421 	struct brd_device *brd, *next;
422 
423 	debugfs_remove_recursive(brd_debugfs_dir);
424 
425 	list_for_each_entry_safe(brd, next, &brd_devices, brd_list) {
426 		del_gendisk(brd->brd_disk);
427 		put_disk(brd->brd_disk);
428 		brd_free_pages(brd);
429 		brd_free_device(brd);
430 	}
431 }
432 
433 static inline void brd_check_and_reset_par(void)
434 {
435 	if (unlikely(!max_part))
436 		max_part = 1;
437 
438 	/*
439 	 * make sure 'max_part' can be divided exactly by (1U << MINORBITS),
440 	 * otherwise, it is possiable to get same dev_t when adding partitions.
441 	 */
442 	if ((1U << MINORBITS) % max_part != 0)
443 		max_part = 1UL << fls(max_part);
444 
445 	if (max_part > DISK_MAX_PARTS) {
446 		pr_info("brd: max_part can't be larger than %d, reset max_part = %d.\n",
447 			DISK_MAX_PARTS, DISK_MAX_PARTS);
448 		max_part = DISK_MAX_PARTS;
449 	}
450 }
451 
452 static int __init brd_init(void)
453 {
454 	int err, i;
455 
456 	/*
457 	 * brd module now has a feature to instantiate underlying device
458 	 * structure on-demand, provided that there is an access dev node.
459 	 *
460 	 * (1) if rd_nr is specified, create that many upfront. else
461 	 *     it defaults to CONFIG_BLK_DEV_RAM_COUNT
462 	 * (2) User can further extend brd devices by create dev node themselves
463 	 *     and have kernel automatically instantiate actual device
464 	 *     on-demand. Example:
465 	 *		mknod /path/devnod_name b 1 X	# 1 is the rd major
466 	 *		fdisk -l /path/devnod_name
467 	 *	If (X / max_part) was not already created it will be created
468 	 *	dynamically.
469 	 */
470 
471 	brd_check_and_reset_par();
472 
473 	brd_debugfs_dir = debugfs_create_dir("ramdisk_pages", NULL);
474 
475 	if (__register_blkdev(RAMDISK_MAJOR, "ramdisk", brd_probe)) {
476 		err = -EIO;
477 		goto out_free;
478 	}
479 
480 	for (i = 0; i < rd_nr; i++)
481 		brd_alloc(i);
482 
483 	pr_info("brd: module loaded\n");
484 	return 0;
485 
486 out_free:
487 	brd_cleanup();
488 
489 	pr_info("brd: module NOT loaded !!!\n");
490 	return err;
491 }
492 
493 static void __exit brd_exit(void)
494 {
495 
496 	unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
497 	brd_cleanup();
498 
499 	pr_info("brd: module unloaded\n");
500 }
501 
502 module_init(brd_init);
503 module_exit(brd_exit);
504 
505