Root/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 **/
25int 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}
51EXPORT_SYMBOL(blk_queue_ordered);
52
53/*
54 * Cache flushing for ordered writes handling
55 */
56unsigned blk_ordered_cur_seq(struct request_queue *q)
57{
58    if (!q->ordseq)
59        return 0;
60    return 1 << ffz(q->ordseq);
61}
62
63unsigned 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
92bool 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
114static 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
120static 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
126static 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
132static 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
154static 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
236bool 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
282static 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 */
307int 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}
349EXPORT_SYMBOL(blkdev_issue_flush);
350

Archive Download this file



interactive