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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2020 Red Hat GmbH
4 *
5 * This file is released under the GPL.
6 *
7 * Device-mapper target to emulate smaller logical block
8 * size on backing devices exposing (natively) larger ones.
9 *
10 * E.g. 512 byte sector emulation on 4K native disks.
11 */
12
13#include "dm.h"
14#include <linux/module.h>
15#include <linux/workqueue.h>
16#include <linux/dm-bufio.h>
17
18#define DM_MSG_PREFIX "ebs"
19
20static void ebs_dtr(struct dm_target *ti);
21
22/* Emulated block size context. */
23struct ebs_c {
24 struct dm_dev *dev; /* Underlying device to emulate block size on. */
25 struct dm_bufio_client *bufio; /* Use dm-bufio for read and read-modify-write processing. */
26 struct workqueue_struct *wq; /* Workqueue for ^ processing of bios. */
27 struct work_struct ws; /* Work item used for ^. */
28 struct bio_list bios_in; /* Worker bios input list. */
29 spinlock_t lock; /* Guard bios input list above. */
30 sector_t start; /* <start> table line argument, see ebs_ctr below. */
31 unsigned int e_bs; /* Emulated block size in sectors exposed to upper layer. */
32 unsigned int u_bs; /* Underlying block size in sectors retrieved from/set on lower layer device. */
33 unsigned char block_shift; /* bitshift sectors -> blocks used in dm-bufio API. */
34 bool u_bs_set:1; /* Flag to indicate underlying block size is set on table line. */
35};
36
37static inline sector_t __sector_to_block(struct ebs_c *ec, sector_t sector)
38{
39 return sector >> ec->block_shift;
40}
41
42static inline sector_t __block_mod(sector_t sector, unsigned int bs)
43{
44 return sector & (bs - 1);
45}
46
47/* Return number of blocks for a bio, accounting for misalignment of start and end sectors. */
48static inline unsigned int __nr_blocks(struct ebs_c *ec, struct bio *bio)
49{
50 sector_t end_sector = __block_mod(bio->bi_iter.bi_sector, ec->u_bs) + bio_sectors(bio);
51
52 return __sector_to_block(ec, end_sector) + (__block_mod(end_sector, ec->u_bs) ? 1 : 0);
53}
54
55static inline bool __ebs_check_bs(unsigned int bs)
56{
57 return bs && is_power_of_2(bs);
58}
59
60/*
61 * READ/WRITE:
62 *
63 * copy blocks between bufio blocks and bio vector's (partial/overlapping) pages.
64 */
65static int __ebs_rw_bvec(struct ebs_c *ec, enum req_op op, struct bio_vec *bv,
66 struct bvec_iter *iter)
67{
68 int r = 0;
69 unsigned char *ba, *pa;
70 unsigned int cur_len;
71 unsigned int bv_len = bv->bv_len;
72 unsigned int buf_off = to_bytes(__block_mod(iter->bi_sector, ec->u_bs));
73 sector_t block = __sector_to_block(ec, iter->bi_sector);
74 struct dm_buffer *b;
75
76 if (unlikely(!bv->bv_page || !bv_len))
77 return -EIO;
78
79 pa = bvec_virt(bv);
80
81 /* Handle overlapping page <-> blocks */
82 while (bv_len) {
83 cur_len = min(dm_bufio_get_block_size(ec->bufio) - buf_off, bv_len);
84
85 /* Avoid reading for writes in case bio vector's page overwrites block completely. */
86 if (op == REQ_OP_READ || buf_off || bv_len < dm_bufio_get_block_size(ec->bufio))
87 ba = dm_bufio_read(ec->bufio, block, &b);
88 else
89 ba = dm_bufio_new(ec->bufio, block, &b);
90
91 if (IS_ERR(ba)) {
92 /*
93 * Carry on with next buffer, if any, to issue all possible
94 * data but return error.
95 */
96 r = PTR_ERR(ba);
97 } else {
98 /* Copy data to/from bio to buffer if read/new was successful above. */
99 ba += buf_off;
100 if (op == REQ_OP_READ) {
101 memcpy(pa, ba, cur_len);
102 flush_dcache_page(bv->bv_page);
103 } else {
104 flush_dcache_page(bv->bv_page);
105 memcpy(ba, pa, cur_len);
106 dm_bufio_mark_buffer_dirty(b);
107 }
108
109 dm_bufio_release(b);
110 }
111
112 pa += cur_len;
113 bv_len -= cur_len;
114 buf_off = 0;
115 block++;
116 }
117
118 return r;
119}
120
121/* READ/WRITE: iterate bio vector's copying between (partial) pages and bufio blocks. */
122static int __ebs_rw_bio(struct ebs_c *ec, enum req_op op, struct bio *bio)
123{
124 int r = 0, rr;
125 struct bio_vec bv;
126 struct bvec_iter iter;
127
128 bio_for_each_bvec(bv, bio, iter) {
129 rr = __ebs_rw_bvec(ec, op, &bv, &iter);
130 if (rr)
131 r = rr;
132 }
133
134 return r;
135}
136
137/*
138 * Discard bio's blocks, i.e. pass discards down.
139 *
140 * Avoid discarding partial blocks at beginning and end;
141 * return 0 in case no blocks can be discarded as a result.
142 */
143static int __ebs_discard_bio(struct ebs_c *ec, struct bio *bio)
144{
145 sector_t block, blocks, sector = bio->bi_iter.bi_sector;
146
147 block = __sector_to_block(ec, sector);
148 blocks = __nr_blocks(ec, bio);
149
150 /*
151 * Partial first underlying block (__nr_blocks() may have
152 * resulted in one block).
153 */
154 if (__block_mod(sector, ec->u_bs)) {
155 block++;
156 blocks--;
157 }
158
159 /* Partial last underlying block if any. */
160 if (blocks && __block_mod(bio_end_sector(bio), ec->u_bs))
161 blocks--;
162
163 return blocks ? dm_bufio_issue_discard(ec->bufio, block, blocks) : 0;
164}
165
166/* Release blocks them from the bufio cache. */
167static void __ebs_forget_bio(struct ebs_c *ec, struct bio *bio)
168{
169 sector_t blocks, sector = bio->bi_iter.bi_sector;
170
171 blocks = __nr_blocks(ec, bio);
172
173 dm_bufio_forget_buffers(ec->bufio, __sector_to_block(ec, sector), blocks);
174}
175
176/* Worker function to process incoming bios. */
177static void __ebs_process_bios(struct work_struct *ws)
178{
179 int r;
180 bool write = false;
181 sector_t block1, block2;
182 struct ebs_c *ec = container_of(ws, struct ebs_c, ws);
183 struct bio *bio;
184 struct bio_list bios;
185
186 bio_list_init(&bios);
187
188 spin_lock_irq(&ec->lock);
189 bios = ec->bios_in;
190 bio_list_init(&ec->bios_in);
191 spin_unlock_irq(&ec->lock);
192
193 /* Prefetch all read and any mis-aligned write buffers */
194 bio_list_for_each(bio, &bios) {
195 block1 = __sector_to_block(ec, bio->bi_iter.bi_sector);
196 if (bio_op(bio) == REQ_OP_READ)
197 dm_bufio_prefetch(ec->bufio, block1, __nr_blocks(ec, bio));
198 else if (bio_op(bio) == REQ_OP_WRITE && !(bio->bi_opf & REQ_PREFLUSH)) {
199 block2 = __sector_to_block(ec, bio_end_sector(bio));
200 if (__block_mod(bio->bi_iter.bi_sector, ec->u_bs))
201 dm_bufio_prefetch(ec->bufio, block1, 1);
202 if (__block_mod(bio_end_sector(bio), ec->u_bs) && block2 != block1)
203 dm_bufio_prefetch(ec->bufio, block2, 1);
204 }
205 }
206
207 bio_list_for_each(bio, &bios) {
208 r = -EIO;
209 if (bio_op(bio) == REQ_OP_READ)
210 r = __ebs_rw_bio(ec, REQ_OP_READ, bio);
211 else if (bio_op(bio) == REQ_OP_WRITE) {
212 write = true;
213 r = __ebs_rw_bio(ec, REQ_OP_WRITE, bio);
214 } else if (bio_op(bio) == REQ_OP_DISCARD) {
215 __ebs_forget_bio(ec, bio);
216 r = __ebs_discard_bio(ec, bio);
217 }
218
219 if (r < 0)
220 bio->bi_status = errno_to_blk_status(r);
221 }
222
223 /*
224 * We write dirty buffers after processing I/O on them
225 * but before we endio thus addressing REQ_FUA/REQ_SYNC.
226 */
227 r = write ? dm_bufio_write_dirty_buffers(ec->bufio) : 0;
228
229 while ((bio = bio_list_pop(&bios))) {
230 /* Any other request is endioed. */
231 if (unlikely(r && bio_op(bio) == REQ_OP_WRITE))
232 bio_io_error(bio);
233 else
234 bio_endio(bio);
235 }
236}
237
238/*
239 * Construct an emulated block size mapping: <dev_path> <offset> <ebs> [<ubs>]
240 *
241 * <dev_path>: path of the underlying device
242 * <offset>: offset in 512 bytes sectors into <dev_path>
243 * <ebs>: emulated block size in units of 512 bytes exposed to the upper layer
244 * [<ubs>]: underlying block size in units of 512 bytes imposed on the lower layer;
245 * optional, if not supplied, retrieve logical block size from underlying device
246 */
247static int ebs_ctr(struct dm_target *ti, unsigned int argc, char **argv)
248{
249 int r;
250 unsigned short tmp1;
251 unsigned long long tmp;
252 char dummy;
253 struct ebs_c *ec;
254
255 if (argc < 3 || argc > 4) {
256 ti->error = "Invalid argument count";
257 return -EINVAL;
258 }
259
260 ec = ti->private = kzalloc_obj(*ec);
261 if (!ec) {
262 ti->error = "Cannot allocate ebs context";
263 return -ENOMEM;
264 }
265
266 r = -EINVAL;
267 if (sscanf(argv[1], "%llu%c", &tmp, &dummy) != 1 ||
268 tmp != (sector_t)tmp) {
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;
342bad:
343 ebs_dtr(ti);
344 return r;
345}
346
347static 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
360static 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
392static void ebs_postsuspend(struct dm_target *ti)
393{
394 struct ebs_c *ec = ti->private;
395 dm_bufio_client_reset(ec->bufio);
396}
397
398static void ebs_status(struct dm_target *ti, status_type_t type,
399 unsigned int status_flags, char *result, unsigned int maxlen)
400{
401 struct ebs_c *ec = ti->private;
402
403 switch (type) {
404 case STATUSTYPE_INFO:
405 *result = '\0';
406 break;
407 case STATUSTYPE_TABLE:
408 snprintf(result, maxlen, ec->u_bs_set ? "%s %llu %u %u" : "%s %llu %u",
409 ec->dev->name, (unsigned long long) ec->start, ec->e_bs, ec->u_bs);
410 break;
411 case STATUSTYPE_IMA:
412 *result = '\0';
413 break;
414 }
415}
416
417static int ebs_prepare_ioctl(struct dm_target *ti, struct block_device **bdev,
418 unsigned int cmd, unsigned long arg, bool *forward)
419{
420 struct ebs_c *ec = ti->private;
421 struct dm_dev *dev = ec->dev;
422
423 /*
424 * Only pass ioctls through if the device sizes match exactly.
425 */
426 *bdev = dev->bdev;
427 return !!(ec->start || ti->len != bdev_nr_sectors(dev->bdev));
428}
429
430static void ebs_io_hints(struct dm_target *ti, struct queue_limits *limits)
431{
432 struct ebs_c *ec = ti->private;
433
434 limits->logical_block_size = to_bytes(ec->e_bs);
435 limits->physical_block_size = to_bytes(ec->u_bs);
436 limits->alignment_offset = limits->physical_block_size;
437 limits->io_min = limits->logical_block_size;
438}
439
440static int ebs_iterate_devices(struct dm_target *ti,
441 iterate_devices_callout_fn fn, void *data)
442{
443 struct ebs_c *ec = ti->private;
444
445 return fn(ti, ec->dev, ec->start, ti->len, data);
446}
447
448static struct target_type ebs_target = {
449 .name = "ebs",
450 .version = {1, 0, 1},
451 .features = 0,
452 .module = THIS_MODULE,
453 .ctr = ebs_ctr,
454 .dtr = ebs_dtr,
455 .map = ebs_map,
456 .postsuspend = ebs_postsuspend,
457 .status = ebs_status,
458 .io_hints = ebs_io_hints,
459 .prepare_ioctl = ebs_prepare_ioctl,
460 .iterate_devices = ebs_iterate_devices,
461};
462module_dm(ebs);
463
464MODULE_AUTHOR("Heinz Mauelshagen <[email protected]>");
465MODULE_DESCRIPTION(DM_NAME " emulated block size target");
466MODULE_LICENSE("GPL");