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
9#include "blk.h"
10
11/**
12 * blk_queue_ordered - does this queue support ordered writes
13 * @q: the request queue
14 * @ordered: one of QUEUE_ORDERED_*
15 * @prepare_flush_fn: rq setup helper for cache flush ordered writes
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              prepare_flush_fn *prepare_flush_fn)
26{
27    if (!prepare_flush_fn && (ordered & (QUEUE_ORDERED_DO_PREFLUSH |
28                         QUEUE_ORDERED_DO_POSTFLUSH))) {
29        printk(KERN_ERR "%s: prepare_flush_fn required\n", __func__);
30        return -EINVAL;
31    }
32
33    if (ordered != QUEUE_ORDERED_NONE &&
34        ordered != QUEUE_ORDERED_DRAIN &&
35        ordered != QUEUE_ORDERED_DRAIN_FLUSH &&
36        ordered != QUEUE_ORDERED_DRAIN_FUA &&
37        ordered != QUEUE_ORDERED_TAG &&
38        ordered != QUEUE_ORDERED_TAG_FLUSH &&
39        ordered != QUEUE_ORDERED_TAG_FUA) {
40        printk(KERN_ERR "blk_queue_ordered: bad value %d\n", ordered);
41        return -EINVAL;
42    }
43
44    q->ordered = ordered;
45    q->next_ordered = ordered;
46    q->prepare_flush_fn = prepare_flush_fn;
47
48    return 0;
49}
50EXPORT_SYMBOL(blk_queue_ordered);
51
52/*
53 * Cache flushing for ordered writes handling
54 */
55unsigned blk_ordered_cur_seq(struct request_queue *q)
56{
57    if (!q->ordseq)
58        return 0;
59    return 1 << ffz(q->ordseq);
60}
61
62unsigned blk_ordered_req_seq(struct request *rq)
63{
64    struct request_queue *q = rq->q;
65
66    BUG_ON(q->ordseq == 0);
67
68    if (rq == &q->pre_flush_rq)
69        return QUEUE_ORDSEQ_PREFLUSH;
70    if (rq == &q->bar_rq)
71        return QUEUE_ORDSEQ_BAR;
72    if (rq == &q->post_flush_rq)
73        return QUEUE_ORDSEQ_POSTFLUSH;
74
75    /*
76     * !fs requests don't need to follow barrier ordering. Always
77     * put them at the front. This fixes the following deadlock.
78     *
79     * http://thread.gmane.org/gmane.linux.kernel/537473
80     */
81    if (!blk_fs_request(rq))
82        return QUEUE_ORDSEQ_DRAIN;
83
84    if ((rq->cmd_flags & REQ_ORDERED_COLOR) ==
85        (q->orig_bar_rq->cmd_flags & REQ_ORDERED_COLOR))
86        return QUEUE_ORDSEQ_DRAIN;
87    else
88        return QUEUE_ORDSEQ_DONE;
89}
90
91bool blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
92{
93    struct request *rq;
94
95    if (error && !q->orderr)
96        q->orderr = error;
97
98    BUG_ON(q->ordseq & seq);
99    q->ordseq |= seq;
100
101    if (blk_ordered_cur_seq(q) != QUEUE_ORDSEQ_DONE)
102        return false;
103
104    /*
105     * Okay, sequence complete.
106     */
107    q->ordseq = 0;
108    rq = q->orig_bar_rq;
109    __blk_end_request_all(rq, q->orderr);
110    return true;
111}
112
113static void pre_flush_end_io(struct request *rq, int error)
114{
115    elv_completed_request(rq->q, rq);
116    blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_PREFLUSH, error);
117}
118
119static void bar_end_io(struct request *rq, int error)
120{
121    elv_completed_request(rq->q, rq);
122    blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_BAR, error);
123}
124
125static void post_flush_end_io(struct request *rq, int error)
126{
127    elv_completed_request(rq->q, rq);
128    blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_POSTFLUSH, error);
129}
130
131static void queue_flush(struct request_queue *q, unsigned which)
132{
133    struct request *rq;
134    rq_end_io_fn *end_io;
135
136    if (which == QUEUE_ORDERED_DO_PREFLUSH) {
137        rq = &q->pre_flush_rq;
138        end_io = pre_flush_end_io;
139    } else {
140        rq = &q->post_flush_rq;
141        end_io = post_flush_end_io;
142    }
143
144    blk_rq_init(q, rq);
145    rq->cmd_flags = REQ_HARDBARRIER;
146    rq->rq_disk = q->bar_rq.rq_disk;
147    rq->end_io = end_io;
148    q->prepare_flush_fn(q, rq);
149
150    elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
151}
152
153static inline bool start_ordered(struct request_queue *q, struct request **rqp)
154{
155    struct request *rq = *rqp;
156    unsigned skip = 0;
157
158    q->orderr = 0;
159    q->ordered = q->next_ordered;
160    q->ordseq |= QUEUE_ORDSEQ_STARTED;
161
162    /*
163     * For an empty barrier, there's no actual BAR request, which
164     * in turn makes POSTFLUSH unnecessary. Mask them off.
165     */
166    if (!blk_rq_sectors(rq)) {
167        q->ordered &= ~(QUEUE_ORDERED_DO_BAR |
168                QUEUE_ORDERED_DO_POSTFLUSH);
169        /*
170         * Empty barrier on a write-through device w/ ordered
171         * tag has no command to issue and without any command
172         * to issue, ordering by tag can't be used. Drain
173         * instead.
174         */
175        if ((q->ordered & QUEUE_ORDERED_BY_TAG) &&
176            !(q->ordered & QUEUE_ORDERED_DO_PREFLUSH)) {
177            q->ordered &= ~QUEUE_ORDERED_BY_TAG;
178            q->ordered |= QUEUE_ORDERED_BY_DRAIN;
179        }
180    }
181
182    /* stash away the original request */
183    blk_dequeue_request(rq);
184    q->orig_bar_rq = rq;
185    rq = NULL;
186
187    /*
188     * Queue ordered sequence. As we stack them at the head, we
189     * need to queue in reverse order. Note that we rely on that
190     * no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
191     * request gets inbetween ordered sequence.
192     */
193    if (q->ordered & QUEUE_ORDERED_DO_POSTFLUSH) {
194        queue_flush(q, QUEUE_ORDERED_DO_POSTFLUSH);
195        rq = &q->post_flush_rq;
196    } else
197        skip |= QUEUE_ORDSEQ_POSTFLUSH;
198
199    if (q->ordered & QUEUE_ORDERED_DO_BAR) {
200        rq = &q->bar_rq;
201
202        /* initialize proxy request and queue it */
203        blk_rq_init(q, rq);
204        if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
205            rq->cmd_flags |= REQ_RW;
206        if (q->ordered & QUEUE_ORDERED_DO_FUA)
207            rq->cmd_flags |= REQ_FUA;
208        init_request_from_bio(rq, q->orig_bar_rq->bio);
209        rq->end_io = bar_end_io;
210
211        elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
212    } else
213        skip |= QUEUE_ORDSEQ_BAR;
214
215    if (q->ordered & QUEUE_ORDERED_DO_PREFLUSH) {
216        queue_flush(q, QUEUE_ORDERED_DO_PREFLUSH);
217        rq = &q->pre_flush_rq;
218    } else
219        skip |= QUEUE_ORDSEQ_PREFLUSH;
220
221    if ((q->ordered & QUEUE_ORDERED_BY_DRAIN) && queue_in_flight(q))
222        rq = NULL;
223    else
224        skip |= QUEUE_ORDSEQ_DRAIN;
225
226    *rqp = rq;
227
228    /*
229     * Complete skipped sequences. If whole sequence is complete,
230     * return false to tell elevator that this request is gone.
231     */
232    return !blk_ordered_complete_seq(q, skip, 0);
233}
234
235bool blk_do_ordered(struct request_queue *q, struct request **rqp)
236{
237    struct request *rq = *rqp;
238    const int is_barrier = blk_fs_request(rq) && blk_barrier_rq(rq);
239
240    if (!q->ordseq) {
241        if (!is_barrier)
242            return true;
243
244        if (q->next_ordered != QUEUE_ORDERED_NONE)
245            return start_ordered(q, rqp);
246        else {
247            /*
248             * Queue ordering not supported. Terminate
249             * with prejudice.
250             */
251            blk_dequeue_request(rq);
252            __blk_end_request_all(rq, -EOPNOTSUPP);
253            *rqp = NULL;
254            return false;
255        }
256    }
257
258    /*
259     * Ordered sequence in progress
260     */
261
262    /* Special requests are not subject to ordering rules. */
263    if (!blk_fs_request(rq) &&
264        rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
265        return true;
266
267    if (q->ordered & QUEUE_ORDERED_BY_TAG) {
268        /* Ordered by tag. Blocking the next barrier is enough. */
269        if (is_barrier && rq != &q->bar_rq)
270            *rqp = NULL;
271    } else {
272        /* Ordered by draining. Wait for turn. */
273        WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
274        if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
275            *rqp = NULL;
276    }
277
278    return true;
279}
280
281static void bio_end_empty_barrier(struct bio *bio, int err)
282{
283    if (err) {
284        if (err == -EOPNOTSUPP)
285            set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
286        clear_bit(BIO_UPTODATE, &bio->bi_flags);
287    }
288
289    complete(bio->bi_private);
290}
291
292/**
293 * blkdev_issue_flush - queue a flush
294 * @bdev: blockdev to issue flush for
295 * @error_sector: error sector
296 *
297 * Description:
298 * Issue a flush for the block device in question. Caller can supply
299 * room for storing the error offset in case of a flush error, if they
300 * wish to.
301 */
302int blkdev_issue_flush(struct block_device *bdev, sector_t *error_sector)
303{
304    DECLARE_COMPLETION_ONSTACK(wait);
305    struct request_queue *q;
306    struct bio *bio;
307    int ret;
308
309    if (bdev->bd_disk == NULL)
310        return -ENXIO;
311
312    q = bdev_get_queue(bdev);
313    if (!q)
314        return -ENXIO;
315
316    bio = bio_alloc(GFP_KERNEL, 0);
317    bio->bi_end_io = bio_end_empty_barrier;
318    bio->bi_private = &wait;
319    bio->bi_bdev = bdev;
320    submit_bio(WRITE_BARRIER, bio);
321
322    wait_for_completion(&wait);
323
324    /*
325     * The driver must store the error location in ->bi_sector, if
326     * it supports it. For non-stacked drivers, this should be copied
327     * from blk_rq_pos(rq).
328     */
329    if (error_sector)
330        *error_sector = bio->bi_sector;
331
332    ret = 0;
333    if (bio_flagged(bio, BIO_EOPNOTSUPP))
334        ret = -EOPNOTSUPP;
335    else if (!bio_flagged(bio, BIO_UPTODATE))
336        ret = -EIO;
337
338    bio_put(bio);
339    return ret;
340}
341EXPORT_SYMBOL(blkdev_issue_flush);
342
343static void blkdev_discard_end_io(struct bio *bio, int err)
344{
345    if (err) {
346        if (err == -EOPNOTSUPP)
347            set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
348        clear_bit(BIO_UPTODATE, &bio->bi_flags);
349    }
350
351    if (bio->bi_private)
352        complete(bio->bi_private);
353    __free_page(bio_page(bio));
354
355    bio_put(bio);
356}
357
358/**
359 * blkdev_issue_discard - queue a discard
360 * @bdev: blockdev to issue discard for
361 * @sector: start sector
362 * @nr_sects: number of sectors to discard
363 * @gfp_mask: memory allocation flags (for bio_alloc)
364 * @flags: DISCARD_FL_* flags to control behaviour
365 *
366 * Description:
367 * Issue a discard request for the sectors in question.
368 */
369int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
370        sector_t nr_sects, gfp_t gfp_mask, int flags)
371{
372    DECLARE_COMPLETION_ONSTACK(wait);
373    struct request_queue *q = bdev_get_queue(bdev);
374    int type = flags & DISCARD_FL_BARRIER ?
375        DISCARD_BARRIER : DISCARD_NOBARRIER;
376    struct bio *bio;
377    struct page *page;
378    int ret = 0;
379
380    if (!q)
381        return -ENXIO;
382
383    if (!blk_queue_discard(q))
384        return -EOPNOTSUPP;
385
386    while (nr_sects && !ret) {
387        unsigned int sector_size = q->limits.logical_block_size;
388        unsigned int max_discard_sectors =
389            min(q->limits.max_discard_sectors, UINT_MAX >> 9);
390
391        bio = bio_alloc(gfp_mask, 1);
392        if (!bio)
393            goto out;
394        bio->bi_sector = sector;
395        bio->bi_end_io = blkdev_discard_end_io;
396        bio->bi_bdev = bdev;
397        if (flags & DISCARD_FL_WAIT)
398            bio->bi_private = &wait;
399
400        /*
401         * Add a zeroed one-sector payload as that's what
402         * our current implementations need. If we'll ever need
403         * more the interface will need revisiting.
404         */
405        page = alloc_page(GFP_KERNEL | __GFP_ZERO);
406        if (!page)
407            goto out_free_bio;
408        if (bio_add_pc_page(q, bio, page, sector_size, 0) < sector_size)
409            goto out_free_page;
410
411        /*
412         * And override the bio size - the way discard works we
413         * touch many more blocks on disk than the actual payload
414         * length.
415         */
416        if (nr_sects > max_discard_sectors) {
417            bio->bi_size = max_discard_sectors << 9;
418            nr_sects -= max_discard_sectors;
419            sector += max_discard_sectors;
420        } else {
421            bio->bi_size = nr_sects << 9;
422            nr_sects = 0;
423        }
424
425        bio_get(bio);
426        submit_bio(type, bio);
427
428        if (flags & DISCARD_FL_WAIT)
429            wait_for_completion(&wait);
430
431        if (bio_flagged(bio, BIO_EOPNOTSUPP))
432            ret = -EOPNOTSUPP;
433        else if (!bio_flagged(bio, BIO_UPTODATE))
434            ret = -EIO;
435        bio_put(bio);
436    }
437    return ret;
438out_free_page:
439    __free_page(page);
440out_free_bio:
441    bio_put(bio);
442out:
443    return -ENOMEM;
444}
445EXPORT_SYMBOL(blkdev_issue_discard);
446

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