1/*
2 * Functions related to barrier IO handling
3 */
4#include <linux/kernel.h>
5#include <linux/module.h>
6#include <linux/bio.h>
7#include <linux/blkdev.h>
8#include <linux/gfp.h>
9
10#include "blk.h"
11
12/**
13 * blk_queue_ordered - does this queue support ordered writes
14 * @q:        the request queue
15 * @ordered:  one of QUEUE_ORDERED_*
16 *
17 * Description:
18 *   For journalled file systems, doing ordered writes on a commit
19 *   block instead of explicitly doing wait_on_buffer (which is bad
20 *   for performance) can be a big win. Block drivers supporting this
21 *   feature should call this function and indicate so.
22 *
23 **/
24int blk_queue_ordered(struct request_queue *q, unsigned ordered)
25{
26	if (ordered != QUEUE_ORDERED_NONE &&
27	    ordered != QUEUE_ORDERED_DRAIN &&
28	    ordered != QUEUE_ORDERED_DRAIN_FLUSH &&
29	    ordered != QUEUE_ORDERED_DRAIN_FUA &&
30	    ordered != QUEUE_ORDERED_TAG &&
31	    ordered != QUEUE_ORDERED_TAG_FLUSH &&
32	    ordered != QUEUE_ORDERED_TAG_FUA) {
33		printk(KERN_ERR "blk_queue_ordered: bad value %d\n", ordered);
34		return -EINVAL;
35	}
36
37	q->ordered = ordered;
38	q->next_ordered = ordered;
39
40	return 0;
41}
42EXPORT_SYMBOL(blk_queue_ordered);
43
44/*
45 * Cache flushing for ordered writes handling
46 */
47unsigned blk_ordered_cur_seq(struct request_queue *q)
48{
49	if (!q->ordseq)
50		return 0;
51	return 1 << ffz(q->ordseq);
52}
53
54unsigned blk_ordered_req_seq(struct request *rq)
55{
56	struct request_queue *q = rq->q;
57
58	BUG_ON(q->ordseq == 0);
59
60	if (rq == &q->pre_flush_rq)
61		return QUEUE_ORDSEQ_PREFLUSH;
62	if (rq == &q->bar_rq)
63		return QUEUE_ORDSEQ_BAR;
64	if (rq == &q->post_flush_rq)
65		return QUEUE_ORDSEQ_POSTFLUSH;
66
67	/*
68	 * !fs requests don't need to follow barrier ordering.  Always
69	 * put them at the front.  This fixes the following deadlock.
70	 *
71	 * http://thread.gmane.org/gmane.linux.kernel/537473
72	 */
73	if (rq->cmd_type != REQ_TYPE_FS)
74		return QUEUE_ORDSEQ_DRAIN;
75
76	if ((rq->cmd_flags & REQ_ORDERED_COLOR) ==
77	    (q->orig_bar_rq->cmd_flags & REQ_ORDERED_COLOR))
78		return QUEUE_ORDSEQ_DRAIN;
79	else
80		return QUEUE_ORDSEQ_DONE;
81}
82
83bool blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
84{
85	struct request *rq;
86
87	if (error && !q->orderr)
88		q->orderr = error;
89
90	BUG_ON(q->ordseq & seq);
91	q->ordseq |= seq;
92
93	if (blk_ordered_cur_seq(q) != QUEUE_ORDSEQ_DONE)
94		return false;
95
96	/*
97	 * Okay, sequence complete.
98	 */
99	q->ordseq = 0;
100	rq = q->orig_bar_rq;
101	__blk_end_request_all(rq, q->orderr);
102	return true;
103}
104
105static void pre_flush_end_io(struct request *rq, int error)
106{
107	elv_completed_request(rq->q, rq);
108	blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_PREFLUSH, error);
109}
110
111static void bar_end_io(struct request *rq, int error)
112{
113	elv_completed_request(rq->q, rq);
114	blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_BAR, error);
115}
116
117static void post_flush_end_io(struct request *rq, int error)
118{
119	elv_completed_request(rq->q, rq);
120	blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_POSTFLUSH, error);
121}
122
123static void queue_flush(struct request_queue *q, unsigned which)
124{
125	struct request *rq;
126	rq_end_io_fn *end_io;
127
128	if (which == QUEUE_ORDERED_DO_PREFLUSH) {
129		rq = &q->pre_flush_rq;
130		end_io = pre_flush_end_io;
131	} else {
132		rq = &q->post_flush_rq;
133		end_io = post_flush_end_io;
134	}
135
136	blk_rq_init(q, rq);
137	rq->cmd_type = REQ_TYPE_FS;
138	rq->cmd_flags = REQ_HARDBARRIER | REQ_FLUSH;
139	rq->rq_disk = q->orig_bar_rq->rq_disk;
140	rq->end_io = end_io;
141
142	elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
143}
144
145static inline bool start_ordered(struct request_queue *q, struct request **rqp)
146{
147	struct request *rq = *rqp;
148	unsigned skip = 0;
149
150	q->orderr = 0;
151	q->ordered = q->next_ordered;
152	q->ordseq |= QUEUE_ORDSEQ_STARTED;
153
154	/*
155	 * For an empty barrier, there's no actual BAR request, which
156	 * in turn makes POSTFLUSH unnecessary.  Mask them off.
157	 */
158	if (!blk_rq_sectors(rq)) {
159		q->ordered &= ~(QUEUE_ORDERED_DO_BAR |
160				QUEUE_ORDERED_DO_POSTFLUSH);
161		/*
162		 * Empty barrier on a write-through device w/ ordered
163		 * tag has no command to issue and without any command
164		 * to issue, ordering by tag can't be used.  Drain
165		 * instead.
166		 */
167		if ((q->ordered & QUEUE_ORDERED_BY_TAG) &&
168		    !(q->ordered & QUEUE_ORDERED_DO_PREFLUSH)) {
169			q->ordered &= ~QUEUE_ORDERED_BY_TAG;
170			q->ordered |= QUEUE_ORDERED_BY_DRAIN;
171		}
172	}
173
174	/* stash away the original request */
175	blk_dequeue_request(rq);
176	q->orig_bar_rq = rq;
177	rq = NULL;
178
179	/*
180	 * Queue ordered sequence.  As we stack them at the head, we
181	 * need to queue in reverse order.  Note that we rely on that
182	 * no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
183	 * request gets inbetween ordered sequence.
184	 */
185	if (q->ordered & QUEUE_ORDERED_DO_POSTFLUSH) {
186		queue_flush(q, QUEUE_ORDERED_DO_POSTFLUSH);
187		rq = &q->post_flush_rq;
188	} else
189		skip |= QUEUE_ORDSEQ_POSTFLUSH;
190
191	if (q->ordered & QUEUE_ORDERED_DO_BAR) {
192		rq = &q->bar_rq;
193
194		/* initialize proxy request and queue it */
195		blk_rq_init(q, rq);
196		if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
197			rq->cmd_flags |= REQ_WRITE;
198		if (q->ordered & QUEUE_ORDERED_DO_FUA)
199			rq->cmd_flags |= REQ_FUA;
200		init_request_from_bio(rq, q->orig_bar_rq->bio);
201		rq->end_io = bar_end_io;
202
203		elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
204	} else
205		skip |= QUEUE_ORDSEQ_BAR;
206
207	if (q->ordered & QUEUE_ORDERED_DO_PREFLUSH) {
208		queue_flush(q, QUEUE_ORDERED_DO_PREFLUSH);
209		rq = &q->pre_flush_rq;
210	} else
211		skip |= QUEUE_ORDSEQ_PREFLUSH;
212
213	if ((q->ordered & QUEUE_ORDERED_BY_DRAIN) && queue_in_flight(q))
214		rq = NULL;
215	else
216		skip |= QUEUE_ORDSEQ_DRAIN;
217
218	*rqp = rq;
219
220	/*
221	 * Complete skipped sequences.  If whole sequence is complete,
222	 * return false to tell elevator that this request is gone.
223	 */
224	return !blk_ordered_complete_seq(q, skip, 0);
225}
226
227bool blk_do_ordered(struct request_queue *q, struct request **rqp)
228{
229	struct request *rq = *rqp;
230	const int is_barrier = rq->cmd_type == REQ_TYPE_FS &&
231				(rq->cmd_flags & REQ_HARDBARRIER);
232
233	if (!q->ordseq) {
234		if (!is_barrier)
235			return true;
236
237		if (q->next_ordered != QUEUE_ORDERED_NONE)
238			return start_ordered(q, rqp);
239		else {
240			/*
241			 * Queue ordering not supported.  Terminate
242			 * with prejudice.
243			 */
244			blk_dequeue_request(rq);
245			__blk_end_request_all(rq, -EOPNOTSUPP);
246			*rqp = NULL;
247			return false;
248		}
249	}
250
251	/*
252	 * Ordered sequence in progress
253	 */
254
255	/* Special requests are not subject to ordering rules. */
256	if (rq->cmd_type != REQ_TYPE_FS &&
257	    rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
258		return true;
259
260	if (q->ordered & QUEUE_ORDERED_BY_TAG) {
261		/* Ordered by tag.  Blocking the next barrier is enough. */
262		if (is_barrier && rq != &q->bar_rq)
263			*rqp = NULL;
264	} else {
265		/* Ordered by draining.  Wait for turn. */
266		WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
267		if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
268			*rqp = NULL;
269	}
270
271	return true;
272}
273
274static void bio_end_empty_barrier(struct bio *bio, int err)
275{
276	if (err) {
277		if (err == -EOPNOTSUPP)
278			set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
279		clear_bit(BIO_UPTODATE, &bio->bi_flags);
280	}
281	if (bio->bi_private)
282		complete(bio->bi_private);
283	bio_put(bio);
284}
285
286/**
287 * blkdev_issue_flush - queue a flush
288 * @bdev:	blockdev to issue flush for
289 * @gfp_mask:	memory allocation flags (for bio_alloc)
290 * @error_sector:	error sector
291 * @flags:	BLKDEV_IFL_* flags to control behaviour
292 *
293 * Description:
294 *    Issue a flush for the block device in question. Caller can supply
295 *    room for storing the error offset in case of a flush error, if they
296 *    wish to. If WAIT flag is not passed then caller may check only what
297 *    request was pushed in some internal queue for later handling.
298 */
299int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
300		sector_t *error_sector, unsigned long flags)
301{
302	DECLARE_COMPLETION_ONSTACK(wait);
303	struct request_queue *q;
304	struct bio *bio;
305	int ret = 0;
306
307	if (bdev->bd_disk == NULL)
308		return -ENXIO;
309
310	q = bdev_get_queue(bdev);
311	if (!q)
312		return -ENXIO;
313
314	/*
315	 * some block devices may not have their queue correctly set up here
316	 * (e.g. loop device without a backing file) and so issuing a flush
317	 * here will panic. Ensure there is a request function before issuing
318	 * the barrier.
319	 */
320	if (!q->make_request_fn)
321		return -ENXIO;
322
323	bio = bio_alloc(gfp_mask, 0);
324	bio->bi_end_io = bio_end_empty_barrier;
325	bio->bi_bdev = bdev;
326	if (test_bit(BLKDEV_WAIT, &flags))
327		bio->bi_private = &wait;
328
329	bio_get(bio);
330	submit_bio(WRITE_BARRIER, bio);
331	if (test_bit(BLKDEV_WAIT, &flags)) {
332		wait_for_completion(&wait);
333		/*
334		 * The driver must store the error location in ->bi_sector, if
335		 * it supports it. For non-stacked drivers, this should be
336		 * copied from blk_rq_pos(rq).
337		 */
338		if (error_sector)
339			*error_sector = bio->bi_sector;
340	}
341
342	if (bio_flagged(bio, BIO_EOPNOTSUPP))
343		ret = -EOPNOTSUPP;
344	else if (!bio_flagged(bio, BIO_UPTODATE))
345		ret = -EIO;
346
347	bio_put(bio);
348	return ret;
349}
350EXPORT_SYMBOL(blkdev_issue_flush);
351