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 retrieved 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 misalignment 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,enum req_op op,struct bio_vec * bv,struct bvec_iter * iter)64 static int __ebs_rw_bvec(struct ebs_c *ec, enum req_op op, struct bio_vec *bv,
65 struct bvec_iter *iter)
66 {
67 int r = 0;
68 unsigned char *ba, *pa;
69 unsigned int cur_len;
70 unsigned int bv_len = bv->bv_len;
71 unsigned int buf_off = to_bytes(__block_mod(iter->bi_sector, ec->u_bs));
72 sector_t block = __sector_to_block(ec, iter->bi_sector);
73 struct dm_buffer *b;
74
75 if (unlikely(!bv->bv_page || !bv_len))
76 return -EIO;
77
78 pa = bvec_virt(bv);
79
80 /* Handle overlapping page <-> blocks */
81 while (bv_len) {
82 cur_len = min(dm_bufio_get_block_size(ec->bufio) - buf_off, bv_len);
83
84 /* Avoid reading for writes in case bio vector's page overwrites block completely. */
85 if (op == REQ_OP_READ || buf_off || bv_len < dm_bufio_get_block_size(ec->bufio))
86 ba = dm_bufio_read(ec->bufio, block, &b);
87 else
88 ba = dm_bufio_new(ec->bufio, block, &b);
89
90 if (IS_ERR(ba)) {
91 /*
92 * Carry on with next buffer, if any, to issue all possible
93 * data but return error.
94 */
95 r = PTR_ERR(ba);
96 } else {
97 /* Copy data to/from bio to buffer if read/new was successful above. */
98 ba += buf_off;
99 if (op == REQ_OP_READ) {
100 memcpy(pa, ba, cur_len);
101 flush_dcache_page(bv->bv_page);
102 } else {
103 flush_dcache_page(bv->bv_page);
104 memcpy(ba, pa, cur_len);
105 dm_bufio_mark_partial_buffer_dirty(b, buf_off, buf_off + cur_len);
106 }
107
108 dm_bufio_release(b);
109 }
110
111 pa += cur_len;
112 bv_len -= cur_len;
113 buf_off = 0;
114 block++;
115 }
116
117 return r;
118 }
119
120 /* READ/WRITE: iterate bio vector's copying between (partial) pages and bufio blocks. */
__ebs_rw_bio(struct ebs_c * ec,enum req_op op,struct bio * bio)121 static int __ebs_rw_bio(struct ebs_c *ec, enum req_op op, struct bio *bio)
122 {
123 int r = 0, rr;
124 struct bio_vec bv;
125 struct bvec_iter iter;
126
127 bio_for_each_bvec(bv, bio, iter) {
128 rr = __ebs_rw_bvec(ec, op, &bv, &iter);
129 if (rr)
130 r = rr;
131 }
132
133 return r;
134 }
135
136 /*
137 * Discard bio's blocks, i.e. pass discards down.
138 *
139 * Avoid discarding partial blocks at beginning and end;
140 * return 0 in case no blocks can be discarded as a result.
141 */
__ebs_discard_bio(struct ebs_c * ec,struct bio * bio)142 static int __ebs_discard_bio(struct ebs_c *ec, struct bio *bio)
143 {
144 sector_t block, blocks, sector = bio->bi_iter.bi_sector;
145
146 block = __sector_to_block(ec, sector);
147 blocks = __nr_blocks(ec, bio);
148
149 /*
150 * Partial first underlying block (__nr_blocks() may have
151 * resulted in one block).
152 */
153 if (__block_mod(sector, ec->u_bs)) {
154 block++;
155 blocks--;
156 }
157
158 /* Partial last underlying block if any. */
159 if (blocks && __block_mod(bio_end_sector(bio), ec->u_bs))
160 blocks--;
161
162 return blocks ? dm_bufio_issue_discard(ec->bufio, block, blocks) : 0;
163 }
164
165 /* Release blocks them from the bufio cache. */
__ebs_forget_bio(struct ebs_c * ec,struct bio * bio)166 static void __ebs_forget_bio(struct ebs_c *ec, struct bio *bio)
167 {
168 sector_t blocks, sector = bio->bi_iter.bi_sector;
169
170 blocks = __nr_blocks(ec, bio);
171
172 dm_bufio_forget_buffers(ec->bufio, __sector_to_block(ec, sector), blocks);
173 }
174
175 /* Worker function to process incoming bios. */
__ebs_process_bios(struct work_struct * ws)176 static void __ebs_process_bios(struct work_struct *ws)
177 {
178 int r;
179 bool write = false;
180 sector_t block1, block2;
181 struct ebs_c *ec = container_of(ws, struct ebs_c, ws);
182 struct bio *bio;
183 struct bio_list bios;
184
185 bio_list_init(&bios);
186
187 spin_lock_irq(&ec->lock);
188 bios = ec->bios_in;
189 bio_list_init(&ec->bios_in);
190 spin_unlock_irq(&ec->lock);
191
192 /* Prefetch all read and any mis-aligned write buffers */
193 bio_list_for_each(bio, &bios) {
194 block1 = __sector_to_block(ec, bio->bi_iter.bi_sector);
195 if (bio_op(bio) == REQ_OP_READ)
196 dm_bufio_prefetch(ec->bufio, block1, __nr_blocks(ec, bio));
197 else if (bio_op(bio) == REQ_OP_WRITE && !(bio->bi_opf & REQ_PREFLUSH)) {
198 block2 = __sector_to_block(ec, bio_end_sector(bio));
199 if (__block_mod(bio->bi_iter.bi_sector, ec->u_bs))
200 dm_bufio_prefetch(ec->bufio, block1, 1);
201 if (__block_mod(bio_end_sector(bio), ec->u_bs) && block2 != block1)
202 dm_bufio_prefetch(ec->bufio, block2, 1);
203 }
204 }
205
206 bio_list_for_each(bio, &bios) {
207 r = -EIO;
208 if (bio_op(bio) == REQ_OP_READ)
209 r = __ebs_rw_bio(ec, REQ_OP_READ, bio);
210 else if (bio_op(bio) == REQ_OP_WRITE) {
211 write = true;
212 r = __ebs_rw_bio(ec, REQ_OP_WRITE, bio);
213 } else if (bio_op(bio) == REQ_OP_DISCARD) {
214 __ebs_forget_bio(ec, bio);
215 r = __ebs_discard_bio(ec, bio);
216 }
217
218 if (r < 0)
219 bio->bi_status = errno_to_blk_status(r);
220 }
221
222 /*
223 * We write dirty buffers after processing I/O on them
224 * but before we endio thus addressing REQ_FUA/REQ_SYNC.
225 */
226 r = write ? dm_bufio_write_dirty_buffers(ec->bufio) : 0;
227
228 while ((bio = bio_list_pop(&bios))) {
229 /* Any other request is endioed. */
230 if (unlikely(r && bio_op(bio) == REQ_OP_WRITE))
231 bio_io_error(bio);
232 else
233 bio_endio(bio);
234 }
235 }
236
237 /*
238 * Construct an emulated block size mapping: <dev_path> <offset> <ebs> [<ubs>]
239 *
240 * <dev_path>: path of the underlying device
241 * <offset>: offset in 512 bytes sectors into <dev_path>
242 * <ebs>: emulated block size in units of 512 bytes exposed to the upper layer
243 * [<ubs>]: underlying block size in units of 512 bytes imposed on the lower layer;
244 * optional, if not supplied, retrieve logical block size from underlying device
245 */
ebs_ctr(struct dm_target * ti,unsigned int argc,char ** argv)246 static int ebs_ctr(struct dm_target *ti, unsigned int argc, char **argv)
247 {
248 int r;
249 unsigned short tmp1;
250 unsigned long long tmp;
251 char dummy;
252 struct ebs_c *ec;
253
254 if (argc < 3 || argc > 4) {
255 ti->error = "Invalid argument count";
256 return -EINVAL;
257 }
258
259 ec = ti->private = kzalloc(sizeof(*ec), GFP_KERNEL);
260 if (!ec) {
261 ti->error = "Cannot allocate ebs context";
262 return -ENOMEM;
263 }
264
265 r = -EINVAL;
266 if (sscanf(argv[1], "%llu%c", &tmp, &dummy) != 1 ||
267 tmp != (sector_t)tmp ||
268 (sector_t)tmp >= ti->len) {
269 ti->error = "Invalid device offset sector";
270 goto bad;
271 }
272 ec->start = tmp;
273
274 if (sscanf(argv[2], "%hu%c", &tmp1, &dummy) != 1 ||
275 !__ebs_check_bs(tmp1) ||
276 to_bytes(tmp1) > PAGE_SIZE) {
277 ti->error = "Invalid emulated block size";
278 goto bad;
279 }
280 ec->e_bs = tmp1;
281
282 if (argc > 3) {
283 if (sscanf(argv[3], "%hu%c", &tmp1, &dummy) != 1 || !__ebs_check_bs(tmp1)) {
284 ti->error = "Invalid underlying block size";
285 goto bad;
286 }
287 ec->u_bs = tmp1;
288 ec->u_bs_set = true;
289 } else
290 ec->u_bs_set = false;
291
292 r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &ec->dev);
293 if (r) {
294 ti->error = "Device lookup failed";
295 ec->dev = NULL;
296 goto bad;
297 }
298
299 r = -EINVAL;
300 if (!ec->u_bs_set) {
301 ec->u_bs = to_sector(bdev_logical_block_size(ec->dev->bdev));
302 if (!__ebs_check_bs(ec->u_bs)) {
303 ti->error = "Invalid retrieved underlying block size";
304 goto bad;
305 }
306 }
307
308 if (!ec->u_bs_set && ec->e_bs == ec->u_bs)
309 DMINFO("Emulation superfluous: emulated equal to underlying block size");
310
311 if (__block_mod(ec->start, ec->u_bs)) {
312 ti->error = "Device offset must be multiple of underlying block size";
313 goto bad;
314 }
315
316 ec->bufio = dm_bufio_client_create(ec->dev->bdev, to_bytes(ec->u_bs), 1,
317 0, NULL, NULL, 0);
318 if (IS_ERR(ec->bufio)) {
319 ti->error = "Cannot create dm bufio client";
320 r = PTR_ERR(ec->bufio);
321 ec->bufio = NULL;
322 goto bad;
323 }
324
325 ec->wq = alloc_ordered_workqueue("dm-" DM_MSG_PREFIX, WQ_MEM_RECLAIM);
326 if (!ec->wq) {
327 ti->error = "Cannot create dm-" DM_MSG_PREFIX " workqueue";
328 r = -ENOMEM;
329 goto bad;
330 }
331
332 ec->block_shift = __ffs(ec->u_bs);
333 INIT_WORK(&ec->ws, &__ebs_process_bios);
334 bio_list_init(&ec->bios_in);
335 spin_lock_init(&ec->lock);
336
337 ti->num_flush_bios = 1;
338 ti->num_discard_bios = 1;
339 ti->num_secure_erase_bios = 0;
340 ti->num_write_zeroes_bios = 0;
341 return 0;
342 bad:
343 ebs_dtr(ti);
344 return r;
345 }
346
ebs_dtr(struct dm_target * ti)347 static void ebs_dtr(struct dm_target *ti)
348 {
349 struct ebs_c *ec = ti->private;
350
351 if (ec->wq)
352 destroy_workqueue(ec->wq);
353 if (ec->bufio)
354 dm_bufio_client_destroy(ec->bufio);
355 if (ec->dev)
356 dm_put_device(ti, ec->dev);
357 kfree(ec);
358 }
359
ebs_map(struct dm_target * ti,struct bio * bio)360 static int ebs_map(struct dm_target *ti, struct bio *bio)
361 {
362 struct ebs_c *ec = ti->private;
363
364 bio_set_dev(bio, ec->dev->bdev);
365 bio->bi_iter.bi_sector = ec->start + dm_target_offset(ti, bio->bi_iter.bi_sector);
366
367 if (unlikely(bio_op(bio) == REQ_OP_FLUSH))
368 return DM_MAPIO_REMAPPED;
369 /*
370 * Only queue for bufio processing in case of partial or overlapping buffers
371 * -or-
372 * emulation with ebs == ubs aiming for tests of dm-bufio overhead.
373 */
374 if (likely(__block_mod(bio->bi_iter.bi_sector, ec->u_bs) ||
375 __block_mod(bio_end_sector(bio), ec->u_bs) ||
376 ec->e_bs == ec->u_bs)) {
377 spin_lock_irq(&ec->lock);
378 bio_list_add(&ec->bios_in, bio);
379 spin_unlock_irq(&ec->lock);
380
381 queue_work(ec->wq, &ec->ws);
382
383 return DM_MAPIO_SUBMITTED;
384 }
385
386 /* Forget any buffer content relative to this direct backing device I/O. */
387 __ebs_forget_bio(ec, bio);
388
389 return DM_MAPIO_REMAPPED;
390 }
391
ebs_status(struct dm_target * ti,status_type_t type,unsigned status_flags,char * result,unsigned maxlen)392 static void ebs_status(struct dm_target *ti, status_type_t type,
393 unsigned status_flags, char *result, unsigned maxlen)
394 {
395 struct ebs_c *ec = ti->private;
396
397 switch (type) {
398 case STATUSTYPE_INFO:
399 *result = '\0';
400 break;
401 case STATUSTYPE_TABLE:
402 snprintf(result, maxlen, ec->u_bs_set ? "%s %llu %u %u" : "%s %llu %u",
403 ec->dev->name, (unsigned long long) ec->start, ec->e_bs, ec->u_bs);
404 break;
405 case STATUSTYPE_IMA:
406 *result = '\0';
407 break;
408 }
409 }
410
ebs_prepare_ioctl(struct dm_target * ti,struct block_device ** bdev)411 static int ebs_prepare_ioctl(struct dm_target *ti, struct block_device **bdev)
412 {
413 struct ebs_c *ec = ti->private;
414 struct dm_dev *dev = ec->dev;
415
416 /*
417 * Only pass ioctls through if the device sizes match exactly.
418 */
419 *bdev = dev->bdev;
420 return !!(ec->start || ti->len != bdev_nr_sectors(dev->bdev));
421 }
422
ebs_io_hints(struct dm_target * ti,struct queue_limits * limits)423 static void ebs_io_hints(struct dm_target *ti, struct queue_limits *limits)
424 {
425 struct ebs_c *ec = ti->private;
426
427 limits->logical_block_size = to_bytes(ec->e_bs);
428 limits->physical_block_size = to_bytes(ec->u_bs);
429 limits->alignment_offset = limits->physical_block_size;
430 blk_limits_io_min(limits, limits->logical_block_size);
431 }
432
ebs_iterate_devices(struct dm_target * ti,iterate_devices_callout_fn fn,void * data)433 static int ebs_iterate_devices(struct dm_target *ti,
434 iterate_devices_callout_fn fn, void *data)
435 {
436 struct ebs_c *ec = ti->private;
437
438 return fn(ti, ec->dev, ec->start, ti->len, data);
439 }
440
441 static struct target_type ebs_target = {
442 .name = "ebs",
443 .version = {1, 0, 1},
444 .features = DM_TARGET_PASSES_INTEGRITY,
445 .module = THIS_MODULE,
446 .ctr = ebs_ctr,
447 .dtr = ebs_dtr,
448 .map = ebs_map,
449 .status = ebs_status,
450 .io_hints = ebs_io_hints,
451 .prepare_ioctl = ebs_prepare_ioctl,
452 .iterate_devices = ebs_iterate_devices,
453 };
454
dm_ebs_init(void)455 static int __init dm_ebs_init(void)
456 {
457 int r = dm_register_target(&ebs_target);
458
459 if (r < 0)
460 DMERR("register failed %d", r);
461
462 return r;
463 }
464
dm_ebs_exit(void)465 static void dm_ebs_exit(void)
466 {
467 dm_unregister_target(&ebs_target);
468 }
469
470 module_init(dm_ebs_init);
471 module_exit(dm_ebs_exit);
472
473 MODULE_AUTHOR("Heinz Mauelshagen <dm-devel@redhat.com>");
474 MODULE_DESCRIPTION(DM_NAME " emulated block size target");
475 MODULE_LICENSE("GPL");
476
