drivers/base/node.c: reduce stack usage of node_read_meminfo()
[linux-2.6.git] / block / blk-barrier.c
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  * @prepare_flush_fn: rq setup helper for cache flush ordered writes
17  *
18  * Description:
19  *   For journalled file systems, doing ordered writes on a commit
20  *   block instead of explicitly doing wait_on_buffer (which is bad
21  *   for performance) can be a big win. Block drivers supporting this
22  *   feature should call this function and indicate so.
23  *
24  **/
25 int blk_queue_ordered(struct request_queue *q, unsigned ordered,
26                       prepare_flush_fn *prepare_flush_fn)
27 {
28         if (!prepare_flush_fn && (ordered & (QUEUE_ORDERED_DO_PREFLUSH |
29                                              QUEUE_ORDERED_DO_POSTFLUSH))) {
30                 printk(KERN_ERR "%s: prepare_flush_fn required\n", __func__);
31                 return -EINVAL;
32         }
33
34         if (ordered != QUEUE_ORDERED_NONE &&
35             ordered != QUEUE_ORDERED_DRAIN &&
36             ordered != QUEUE_ORDERED_DRAIN_FLUSH &&
37             ordered != QUEUE_ORDERED_DRAIN_FUA &&
38             ordered != QUEUE_ORDERED_TAG &&
39             ordered != QUEUE_ORDERED_TAG_FLUSH &&
40             ordered != QUEUE_ORDERED_TAG_FUA) {
41                 printk(KERN_ERR "blk_queue_ordered: bad value %d\n", ordered);
42                 return -EINVAL;
43         }
44
45         q->ordered = ordered;
46         q->next_ordered = ordered;
47         q->prepare_flush_fn = prepare_flush_fn;
48
49         return 0;
50 }
51 EXPORT_SYMBOL(blk_queue_ordered);
52
53 /*
54  * Cache flushing for ordered writes handling
55  */
56 unsigned blk_ordered_cur_seq(struct request_queue *q)
57 {
58         if (!q->ordseq)
59                 return 0;
60         return 1 << ffz(q->ordseq);
61 }
62
63 unsigned blk_ordered_req_seq(struct request *rq)
64 {
65         struct request_queue *q = rq->q;
66
67         BUG_ON(q->ordseq == 0);
68
69         if (rq == &q->pre_flush_rq)
70                 return QUEUE_ORDSEQ_PREFLUSH;
71         if (rq == &q->bar_rq)
72                 return QUEUE_ORDSEQ_BAR;
73         if (rq == &q->post_flush_rq)
74                 return QUEUE_ORDSEQ_POSTFLUSH;
75
76         /*
77          * !fs requests don't need to follow barrier ordering.  Always
78          * put them at the front.  This fixes the following deadlock.
79          *
80          * http://thread.gmane.org/gmane.linux.kernel/537473
81          */
82         if (!blk_fs_request(rq))
83                 return QUEUE_ORDSEQ_DRAIN;
84
85         if ((rq->cmd_flags & REQ_ORDERED_COLOR) ==
86             (q->orig_bar_rq->cmd_flags & REQ_ORDERED_COLOR))
87                 return QUEUE_ORDSEQ_DRAIN;
88         else
89                 return QUEUE_ORDSEQ_DONE;
90 }
91
92 bool blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
93 {
94         struct request *rq;
95
96         if (error && !q->orderr)
97                 q->orderr = error;
98
99         BUG_ON(q->ordseq & seq);
100         q->ordseq |= seq;
101
102         if (blk_ordered_cur_seq(q) != QUEUE_ORDSEQ_DONE)
103                 return false;
104
105         /*
106          * Okay, sequence complete.
107          */
108         q->ordseq = 0;
109         rq = q->orig_bar_rq;
110         __blk_end_request_all(rq, q->orderr);
111         return true;
112 }
113
114 static void pre_flush_end_io(struct request *rq, int error)
115 {
116         elv_completed_request(rq->q, rq);
117         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_PREFLUSH, error);
118 }
119
120 static void bar_end_io(struct request *rq, int error)
121 {
122         elv_completed_request(rq->q, rq);
123         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_BAR, error);
124 }
125
126 static void post_flush_end_io(struct request *rq, int error)
127 {
128         elv_completed_request(rq->q, rq);
129         blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_POSTFLUSH, error);
130 }
131
132 static void queue_flush(struct request_queue *q, unsigned which)
133 {
134         struct request *rq;
135         rq_end_io_fn *end_io;
136
137         if (which == QUEUE_ORDERED_DO_PREFLUSH) {
138                 rq = &q->pre_flush_rq;
139                 end_io = pre_flush_end_io;
140         } else {
141                 rq = &q->post_flush_rq;
142                 end_io = post_flush_end_io;
143         }
144
145         blk_rq_init(q, rq);
146         rq->cmd_flags = REQ_HARDBARRIER;
147         rq->rq_disk = q->bar_rq.rq_disk;
148         rq->end_io = end_io;
149         q->prepare_flush_fn(q, rq);
150
151         elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
152 }
153
154 static inline bool start_ordered(struct request_queue *q, struct request **rqp)
155 {
156         struct request *rq = *rqp;
157         unsigned skip = 0;
158
159         q->orderr = 0;
160         q->ordered = q->next_ordered;
161         q->ordseq |= QUEUE_ORDSEQ_STARTED;
162
163         /*
164          * For an empty barrier, there's no actual BAR request, which
165          * in turn makes POSTFLUSH unnecessary.  Mask them off.
166          */
167         if (!blk_rq_sectors(rq)) {
168                 q->ordered &= ~(QUEUE_ORDERED_DO_BAR |
169                                 QUEUE_ORDERED_DO_POSTFLUSH);
170                 /*
171                  * Empty barrier on a write-through device w/ ordered
172                  * tag has no command to issue and without any command
173                  * to issue, ordering by tag can't be used.  Drain
174                  * instead.
175                  */
176                 if ((q->ordered & QUEUE_ORDERED_BY_TAG) &&
177                     !(q->ordered & QUEUE_ORDERED_DO_PREFLUSH)) {
178                         q->ordered &= ~QUEUE_ORDERED_BY_TAG;
179                         q->ordered |= QUEUE_ORDERED_BY_DRAIN;
180                 }
181         }
182
183         /* stash away the original request */
184         blk_dequeue_request(rq);
185         q->orig_bar_rq = rq;
186         rq = NULL;
187
188         /*
189          * Queue ordered sequence.  As we stack them at the head, we
190          * need to queue in reverse order.  Note that we rely on that
191          * no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
192          * request gets inbetween ordered sequence.
193          */
194         if (q->ordered & QUEUE_ORDERED_DO_POSTFLUSH) {
195                 queue_flush(q, QUEUE_ORDERED_DO_POSTFLUSH);
196                 rq = &q->post_flush_rq;
197         } else
198                 skip |= QUEUE_ORDSEQ_POSTFLUSH;
199
200         if (q->ordered & QUEUE_ORDERED_DO_BAR) {
201                 rq = &q->bar_rq;
202
203                 /* initialize proxy request and queue it */
204                 blk_rq_init(q, rq);
205                 if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
206                         rq->cmd_flags |= REQ_RW;
207                 if (q->ordered & QUEUE_ORDERED_DO_FUA)
208                         rq->cmd_flags |= REQ_FUA;
209                 init_request_from_bio(rq, q->orig_bar_rq->bio);
210                 rq->end_io = bar_end_io;
211
212                 elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
213         } else
214                 skip |= QUEUE_ORDSEQ_BAR;
215
216         if (q->ordered & QUEUE_ORDERED_DO_PREFLUSH) {
217                 queue_flush(q, QUEUE_ORDERED_DO_PREFLUSH);
218                 rq = &q->pre_flush_rq;
219         } else
220                 skip |= QUEUE_ORDSEQ_PREFLUSH;
221
222         if ((q->ordered & QUEUE_ORDERED_BY_DRAIN) && queue_in_flight(q))
223                 rq = NULL;
224         else
225                 skip |= QUEUE_ORDSEQ_DRAIN;
226
227         *rqp = rq;
228
229         /*
230          * Complete skipped sequences.  If whole sequence is complete,
231          * return false to tell elevator that this request is gone.
232          */
233         return !blk_ordered_complete_seq(q, skip, 0);
234 }
235
236 bool blk_do_ordered(struct request_queue *q, struct request **rqp)
237 {
238         struct request *rq = *rqp;
239         const int is_barrier = blk_fs_request(rq) && blk_barrier_rq(rq);
240
241         if (!q->ordseq) {
242                 if (!is_barrier)
243                         return true;
244
245                 if (q->next_ordered != QUEUE_ORDERED_NONE)
246                         return start_ordered(q, rqp);
247                 else {
248                         /*
249                          * Queue ordering not supported.  Terminate
250                          * with prejudice.
251                          */
252                         blk_dequeue_request(rq);
253                         __blk_end_request_all(rq, -EOPNOTSUPP);
254                         *rqp = NULL;
255                         return false;
256                 }
257         }
258
259         /*
260          * Ordered sequence in progress
261          */
262
263         /* Special requests are not subject to ordering rules. */
264         if (!blk_fs_request(rq) &&
265             rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
266                 return true;
267
268         if (q->ordered & QUEUE_ORDERED_BY_TAG) {
269                 /* Ordered by tag.  Blocking the next barrier is enough. */
270                 if (is_barrier && rq != &q->bar_rq)
271                         *rqp = NULL;
272         } else {
273                 /* Ordered by draining.  Wait for turn. */
274                 WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
275                 if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
276                         *rqp = NULL;
277         }
278
279         return true;
280 }
281
282 static void bio_end_empty_barrier(struct bio *bio, int err)
283 {
284         if (err) {
285                 if (err == -EOPNOTSUPP)
286                         set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
287                 clear_bit(BIO_UPTODATE, &bio->bi_flags);
288         }
289         if (bio->bi_private)
290                 complete(bio->bi_private);
291         bio_put(bio);
292 }
293
294 /**
295  * blkdev_issue_flush - queue a flush
296  * @bdev:       blockdev to issue flush for
297  * @gfp_mask:   memory allocation flags (for bio_alloc)
298  * @error_sector:       error sector
299  * @flags:      BLKDEV_IFL_* flags to control behaviour
300  *
301  * Description:
302  *    Issue a flush for the block device in question. Caller can supply
303  *    room for storing the error offset in case of a flush error, if they
304  *    wish to. If WAIT flag is not passed then caller may check only what
305  *    request was pushed in some internal queue for later handling.
306  */
307 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
308                 sector_t *error_sector, unsigned long flags)
309 {
310         DECLARE_COMPLETION_ONSTACK(wait);
311         struct request_queue *q;
312         struct bio *bio;
313         int ret = 0;
314
315         if (bdev->bd_disk == NULL)
316                 return -ENXIO;
317
318         q = bdev_get_queue(bdev);
319         if (!q)
320                 return -ENXIO;
321
322         bio = bio_alloc(gfp_mask, 0);
323         bio->bi_end_io = bio_end_empty_barrier;
324         bio->bi_bdev = bdev;
325         if (test_bit(BLKDEV_WAIT, &flags))
326                 bio->bi_private = &wait;
327
328         bio_get(bio);
329         submit_bio(WRITE_BARRIER, bio);
330         if (test_bit(BLKDEV_WAIT, &flags)) {
331                 wait_for_completion(&wait);
332                 /*
333                  * The driver must store the error location in ->bi_sector, if
334                  * it supports it. For non-stacked drivers, this should be
335                  * copied from blk_rq_pos(rq).
336                  */
337                 if (error_sector)
338                         *error_sector = bio->bi_sector;
339         }
340
341         if (bio_flagged(bio, BIO_EOPNOTSUPP))
342                 ret = -EOPNOTSUPP;
343         else if (!bio_flagged(bio, BIO_UPTODATE))
344                 ret = -EIO;
345
346         bio_put(bio);
347         return ret;
348 }
349 EXPORT_SYMBOL(blkdev_issue_flush);