1 /*
2 * Copyright (C) 2020 Red Hat GmbH
3 *
4 * This file is released under the GPL.
5 *
6 * Device-mapper target to emulate smaller logical block
7 * size on backing devices exposing (natively) larger ones.
8 *
9 * E.g. 512 byte sector emulation on 4K native disks.
10 */
11
12 #include "dm.h"
13 #include <linux/module.h>
14 #include <linux/workqueue.h>
15 #include <linux/dm-bufio.h>
16
17 #define DM_MSG_PREFIX "ebs"
18
19 static void ebs_dtr(struct dm_target *ti);
20
21 /* Emulated block size context. */
22 struct ebs_c {
23 struct dm_dev *dev; /* Underlying device to emulate block size on. */
24 struct dm_bufio_client *bufio; /* Use dm-bufio for read and read-modify-write processing. */
25 struct workqueue_struct *wq; /* Workqueue for ^ processing of bios. */
26 struct work_struct ws; /* Work item used for ^. */
27 struct bio_list bios_in; /* Worker bios input list. */
28 spinlock_t lock; /* Guard bios input list above. */
29 sector_t start; /* <start> table line argument, see ebs_ctr below. */
30 unsigned int e_bs; /* Emulated block size in sectors exposed to upper layer. */
31 unsigned int u_bs; /* Underlying block size in sectors retrievd from/set on lower layer device. */
32 unsigned char block_shift; /* bitshift sectors -> blocks used in dm-bufio API. */
33 bool u_bs_set:1; /* Flag to indicate underlying block size is set on table line. */
34 };
35
__sector_to_block(struct ebs_c * ec,sector_t sector)36 static inline sector_t __sector_to_block(struct ebs_c *ec, sector_t sector)
37 {
38 return sector >> ec->block_shift;
39 }
40
__block_mod(sector_t sector,unsigned int bs)41 static inline sector_t __block_mod(sector_t sector, unsigned int bs)
42 {
43 return sector & (bs - 1);
44 }
45
46 /* Return number of blocks for a bio, accounting for misalignement of start and end sectors. */
__nr_blocks(struct ebs_c * ec,struct bio * bio)47 static inline unsigned int __nr_blocks(struct ebs_c *ec, struct bio *bio)
48 {
49 sector_t end_sector = __block_mod(bio->bi_iter.bi_sector, ec->u_bs) + bio_sectors(bio);
50
51 return __sector_to_block(ec, end_sector) + (__block_mod(end_sector, ec->u_bs) ? 1 : 0);
52 }
53
__ebs_check_bs(unsigned int bs)54 static inline bool __ebs_check_bs(unsigned int bs)
55 {
56 return bs && is_power_of_2(bs);
57 }
58
59 /*
60 * READ/WRITE:
61 *
62 * copy blocks between bufio blocks and bio vector's (partial/overlapping) pages.
63 */
__ebs_rw_bvec(struct ebs_c * ec,int rw,struct bio_vec * bv,struct bvec_iter * iter)64 static int __ebs_rw_bvec(struct ebs_c *ec, int rw, struct bio_vec *bv, struct bvec_iter *iter)
65 {
66 int r = 0;
67 unsigned char *ba, *pa;
68 unsigned int cur_len;
69 unsigned int bv_len = bv->bv_len;
70 unsigned int buf_off = to_bytes(__block_mod(iter->bi_sector, ec->u_bs));
71 sector_t block = __sector_to_block(ec, iter->bi_sector);
72 struct dm_buffer *b;
73
74 if (unlikely(!bv->bv_page || !bv_len))
75 return -EIO;
76
77 pa = page_address(bv->bv_page) + bv->bv_offset;
78
79 /* Handle overlapping page <-> blocks */
80 while (bv_len) {
81 cur_len = min(dm_bufio_get_block_size(ec->bufio) - buf_off, bv_len);
82
83 /* Avoid reading for writes in case bio vector's page overwrites block completely. */
84 if (rw == READ || buf_off || bv_len < dm_bufio_get_block_size(ec->bufio))
85 ba = dm_bufio_read(ec->bufio, block, &b);
86 else
87 ba = dm_bufio_new(ec->bufio, block, &b);
88
89 if (unlikely(IS_ERR(ba))) {
90 /*
91 * Carry on with next buffer, if any, to issue all possible
92 * data but return error.
93 */
94 r = PTR_ERR(ba);
95 } else {
96 /* Copy data to/from bio to buffer if read/new was successful above. */
97 ba += buf_off;
98 if (rw == READ) {
99 memcpy(pa, ba, cur_len);
100 flush_dcache_page(bv->bv_page);
101 } else {
102 flush_dcache_page(bv->bv_page);
103 memcpy(ba, pa, cur_len);
104 dm_bufio_mark_partial_buffer_dirty(b, buf_off, buf_off + cur_len);
105 }
106
107 dm_bufio_release(b);
108 }
109
110 pa += cur_len;
111 bv_len -= cur_len;
112 buf_off = 0;
113 block++;
114 }
115
116 return r;
117 }
118
119 /* READ/WRITE: iterate bio vector's copying between (partial) pages and bufio blocks. */
__ebs_rw_bio(struct ebs_c * ec,int rw,struct bio * bio)120 static int __ebs_rw_bio(struct ebs_c *ec, int rw, struct bio *bio)
121 {
122 int r = 0, rr;
123 struct bio_vec bv;
124 struct bvec_iter iter;
125
126 bio_for_each_bvec(bv, bio, iter) {
127 rr = __ebs_rw_bvec(ec, rw, &bv, &iter);
128 if (rr)
129 r = rr;
130 }
131
132 return r;
133 }
134
135 /*
136 * Discard bio's blocks, i.e. pass discards down.
137 *
138 * Avoid discarding partial blocks at beginning and end;
139 * return 0 in case no blocks can be discarded as a result.
140 */
__ebs_discard_bio(struct ebs_c * ec,struct bio * bio)141 static int __ebs_discard_bio(struct ebs_c *ec, struct bio *bio)
142 {
143 sector_t block, blocks, sector = bio->bi_iter.bi_sector;
144
145 block = __sector_to_block(ec, sector);
146 blocks = __nr_blocks(ec, bio);
147
148 /*
149 * Partial first underlying block (__nr_blocks() may have
150 * resulted in one block).
151 */
152 if (__block_mod(sector, ec->u_bs)) {
153 block++;
154 blocks--;
155 }
156
157 /* Partial last underlying block if any. */
158 if (blocks && __block_mod(bio_end_sector(bio), ec->u_bs))
159 blocks--;
160
161 return blocks ? dm_bufio_issue_discard(ec->bufio, block, blocks) : 0;
162 }
163
164 /* Release blocks them from the bufio cache. */
__ebs_forget_bio(struct ebs_c * ec,struct bio * bio)165 static void __ebs_forget_bio(struct ebs_c *ec, struct bio *bio)
166 {
167 sector_t blocks, sector = bio->bi_iter.bi_sector;
168
169 blocks = __nr_blocks(ec, bio);
170
171 dm_bufio_forget_buffers(ec->bufio, __sector_to_block(ec, sector), blocks);
172 }
173
174 /* Worker funtion to process incoming bios. */
__ebs_process_bios(struct work_struct * ws)175 static void __ebs_process_bios(struct work_struct *ws)
176 {
177 int r;
178 bool write = false;
179 sector_t block1, block2;
180 struct ebs_c *ec = container_of(ws, struct ebs_c, ws);
181 struct bio *bio;
182 struct bio_list bios;
183
184 bio_list_init(&bios);
185
186 spin_lock_irq(&ec->lock);
187 bios = ec->bios_in;
188 bio_list_init(&ec->bios_in);
189 spin_unlock_irq(&ec->lock);
190
191 /* Prefetch all read and any mis-aligned write buffers */
192 bio_list_for_each(bio, &bios) {
193 block1 = __sector_to_block(ec, bio->bi_iter.bi_sector);
194 if (bio_op(bio) == REQ_OP_READ)
195 dm_bufio_prefetch(ec->bufio, block1, __nr_blocks(ec, bio));
196 else if (bio_op(bio) == REQ_OP_WRITE && !(bio->bi_opf & REQ_PREFLUSH)) {
197 block2 = __sector_to_block(ec, bio_end_sector(bio));
198 if (__block_mod(bio->bi_iter.bi_sector, ec->u_bs))
199 dm_bufio_prefetch(ec->bufio, block1, 1);
200 if (__block_mod(bio_end_sector(bio), ec->u_bs) && block2 != block1)
201 dm_bufio_prefetch(ec->bufio, block2, 1);
202 }
203 }
204
205 bio_list_for_each(bio, &bios) {
206 r = -EIO;
207 if (bio_op(bio) == REQ_OP_READ)
208 r = __ebs_rw_bio(ec, READ, bio);
209 else if (bio_op(bio) == REQ_OP_WRITE) {
210 write = true;
211 r = __ebs_rw_bio(ec, WRITE, bio);
212 } else if (bio_op(bio) == REQ_OP_DISCARD) {
213 __ebs_forget_bio(ec, bio);
214 r = __ebs_discard_bio(ec, bio);
215 }
216
217 if (r < 0)
218 bio->bi_status = errno_to_blk_status(r);
219 }
220
221 /*
222 * We write dirty buffers after processing I/O on them
223 * but before we endio thus addressing REQ_FUA/REQ_SYNC.
224 */
225 r = write ? dm_bufio_write_dirty_buffers(ec->bufio) : 0;
226
227 while ((bio = bio_list_pop(&bios))) {
228 /* Any other request is endioed. */
229 if (unlikely(r && bio_op(bio) == REQ_OP_WRITE))
230 bio_io_error(bio);
231 else
232 bio_endio(bio);
233 }
234 }
235
236 /*
237 * Construct an emulated block size mapping: <dev_path> <offset> <ebs> [<ubs>]
238 *
239 * <dev_path>: path of the underlying device
240 * <offset>: offset in 512 bytes sectors into <dev_path>
241 * <ebs>: emulated block size in units of 512 bytes exposed to the upper layer
242 * [<ubs>]: underlying block size in units of 512 bytes imposed on the lower layer;
243 * optional, if not supplied, retrieve logical block size from underlying device
244 */
ebs_ctr(struct dm_target * ti,unsigned int argc,char ** argv)245 static int ebs_ctr(struct dm_target *ti, unsigned int argc, char **argv)
246 {
247 int r;
248 unsigned short tmp1;
249 unsigned long long tmp;
250 char dummy;
251 struct ebs_c *ec;
252
253 if (argc < 3 || argc > 4) {
254 ti->error = "Invalid argument count";
255 return -EINVAL;
256 }
257
258 ec = ti->private = kzalloc(sizeof(*ec), GFP_KERNEL);
259 if (!ec) {
260 ti->error = "Cannot allocate ebs context";
261 return -ENOMEM;
262 }
263
264 r = -EINVAL;
265 if (sscanf(argv[1], "%llu%c", &tmp, &dummy) != 1 ||
266 tmp != (sector_t)tmp ||
267 (sector_t)tmp >= ti->len) {
268 ti->error = "Invalid device offset sector";
269 goto bad;
270 }
271 ec->start = tmp;
272
273 if (sscanf(argv[2], "%hu%c", &tmp1, &dummy) != 1 ||
274 !__ebs_check_bs(tmp1) ||
275 to_bytes(tmp1) > PAGE_SIZE) {
276 ti->error = "Invalid emulated block size";
277 goto bad;
278 }
279 ec->e_bs = tmp1;
280
281 if (argc > 3) {
282 if (sscanf(argv[3], "%hu%c", &tmp1, &dummy) != 1 || !__ebs_check_bs(tmp1)) {
283 ti->error = "Invalid underlying block size";
284 goto bad;
285 }
286 ec->u_bs = tmp1;
287 ec->u_bs_set = true;
288 } else
289 ec->u_bs_set = false;
290
291 r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &ec->dev);
292 if (r) {
293 ti->error = "Device lookup failed";
294 ec->dev = NULL;
295 goto bad;
296 }
297
298 r = -EINVAL;
299 if (!ec->u_bs_set) {
300 ec->u_bs = to_sector(bdev_logical_block_size(ec->dev->bdev));
301 if (!__ebs_check_bs(ec->u_bs)) {
302 ti->error = "Invalid retrieved underlying block size";
303 goto bad;
304 }
305 }
306
307 if (!ec->u_bs_set && ec->e_bs == ec->u_bs)
308 DMINFO("Emulation superfluous: emulated equal to underlying block size");
309
310 if (__block_mod(ec->start, ec->u_bs)) {
311 ti->error = "Device offset must be multiple of underlying block size";
312 goto bad;
313 }
314
315 ec->bufio = dm_bufio_client_create(ec->dev->bdev, to_bytes(ec->u_bs), 1, 0, NULL, NULL);
316 if (IS_ERR(ec->bufio)) {
317 ti->error = "Cannot create dm bufio client";
318 r = PTR_ERR(ec->bufio);
319 ec->bufio = NULL;
320 goto bad;
321 }
322
323 ec->wq = alloc_ordered_workqueue("dm-" DM_MSG_PREFIX, WQ_MEM_RECLAIM);
324 if (!ec->wq) {
325 ti->error = "Cannot create dm-" DM_MSG_PREFIX " workqueue";
326 r = -ENOMEM;
327 goto bad;
328 }
329
330 ec->block_shift = __ffs(ec->u_bs);
331 INIT_WORK(&ec->ws, &__ebs_process_bios);
332 bio_list_init(&ec->bios_in);
333 spin_lock_init(&ec->lock);
334
335 ti->num_flush_bios = 1;
336 ti->num_discard_bios = 1;
337 ti->num_secure_erase_bios = 0;
338 ti->num_write_same_bios = 0;
339 ti->num_write_zeroes_bios = 0;
340 return 0;
341 bad:
342 ebs_dtr(ti);
343 return r;
344 }
345
ebs_dtr(struct dm_target * ti)346 static void ebs_dtr(struct dm_target *ti)
347 {
348 struct ebs_c *ec = ti->private;
349
350 if (ec->wq)
351 destroy_workqueue(ec->wq);
352 if (ec->bufio)
353 dm_bufio_client_destroy(ec->bufio);
354 if (ec->dev)
355 dm_put_device(ti, ec->dev);
356 kfree(ec);
357 }
358
ebs_map(struct dm_target * ti,struct bio * bio)359 static int ebs_map(struct dm_target *ti, struct bio *bio)
360 {
361 struct ebs_c *ec = ti->private;
362
363 bio_set_dev(bio, ec->dev->bdev);
364 bio->bi_iter.bi_sector = ec->start + dm_target_offset(ti, bio->bi_iter.bi_sector);
365
366 if (unlikely(bio_op(bio) == REQ_OP_FLUSH))
367 return DM_MAPIO_REMAPPED;
368 /*
369 * Only queue for bufio processing in case of partial or overlapping buffers
370 * -or-
371 * emulation with ebs == ubs aiming for tests of dm-bufio overhead.
372 */
373 if (likely(__block_mod(bio->bi_iter.bi_sector, ec->u_bs) ||
374 __block_mod(bio_end_sector(bio), ec->u_bs) ||
375 ec->e_bs == ec->u_bs)) {
376 spin_lock_irq(&ec->lock);
377 bio_list_add(&ec->bios_in, bio);
378 spin_unlock_irq(&ec->lock);
379
380 queue_work(ec->wq, &ec->ws);
381
382 return DM_MAPIO_SUBMITTED;
383 }
384
385 /* Forget any buffer content relative to this direct backing device I/O. */
386 __ebs_forget_bio(ec, bio);
387
388 return DM_MAPIO_REMAPPED;
389 }
390
ebs_status(struct dm_target * ti,status_type_t type,unsigned status_flags,char * result,unsigned maxlen)391 static void ebs_status(struct dm_target *ti, status_type_t type,
392 unsigned status_flags, char *result, unsigned maxlen)
393 {
394 struct ebs_c *ec = ti->private;
395
396 switch (type) {
397 case STATUSTYPE_INFO:
398 *result = '\0';
399 break;
400 case STATUSTYPE_TABLE:
401 snprintf(result, maxlen, ec->u_bs_set ? "%s %llu %u %u" : "%s %llu %u",
402 ec->dev->name, (unsigned long long) ec->start, ec->e_bs, ec->u_bs);
403 break;
404 }
405 }
406
ebs_prepare_ioctl(struct dm_target * ti,struct block_device ** bdev)407 static int ebs_prepare_ioctl(struct dm_target *ti, struct block_device **bdev)
408 {
409 struct ebs_c *ec = ti->private;
410 struct dm_dev *dev = ec->dev;
411
412 /*
413 * Only pass ioctls through if the device sizes match exactly.
414 */
415 *bdev = dev->bdev;
416 return !!(ec->start || ti->len != i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT);
417 }
418
ebs_io_hints(struct dm_target * ti,struct queue_limits * limits)419 static void ebs_io_hints(struct dm_target *ti, struct queue_limits *limits)
420 {
421 struct ebs_c *ec = ti->private;
422
423 limits->logical_block_size = to_bytes(ec->e_bs);
424 limits->physical_block_size = to_bytes(ec->u_bs);
425 limits->alignment_offset = limits->physical_block_size;
426 blk_limits_io_min(limits, limits->logical_block_size);
427 }
428
ebs_iterate_devices(struct dm_target * ti,iterate_devices_callout_fn fn,void * data)429 static int ebs_iterate_devices(struct dm_target *ti,
430 iterate_devices_callout_fn fn, void *data)
431 {
432 struct ebs_c *ec = ti->private;
433
434 return fn(ti, ec->dev, ec->start, ti->len, data);
435 }
436
437 static struct target_type ebs_target = {
438 .name = "ebs",
439 .version = {1, 0, 1},
440 .features = DM_TARGET_PASSES_INTEGRITY,
441 .module = THIS_MODULE,
442 .ctr = ebs_ctr,
443 .dtr = ebs_dtr,
444 .map = ebs_map,
445 .status = ebs_status,
446 .io_hints = ebs_io_hints,
447 .prepare_ioctl = ebs_prepare_ioctl,
448 .iterate_devices = ebs_iterate_devices,
449 };
450
dm_ebs_init(void)451 static int __init dm_ebs_init(void)
452 {
453 int r = dm_register_target(&ebs_target);
454
455 if (r < 0)
456 DMERR("register failed %d", r);
457
458 return r;
459 }
460
dm_ebs_exit(void)461 static void dm_ebs_exit(void)
462 {
463 dm_unregister_target(&ebs_target);
464 }
465
466 module_init(dm_ebs_init);
467 module_exit(dm_ebs_exit);
468
469 MODULE_AUTHOR("Heinz Mauelshagen <dm-devel@redhat.com>");
470 MODULE_DESCRIPTION(DM_NAME " emulated block size target");
471 MODULE_LICENSE("GPL");
472