Root/block/blk-flush.c

1/*
2 * Functions to sequence FLUSH and FUA writes.
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/* FLUSH/FUA sequences */
13enum {
14    QUEUE_FSEQ_STARTED = (1 << 0), /* flushing in progress */
15    QUEUE_FSEQ_PREFLUSH = (1 << 1), /* pre-flushing in progress */
16    QUEUE_FSEQ_DATA = (1 << 2), /* data write in progress */
17    QUEUE_FSEQ_POSTFLUSH = (1 << 3), /* post-flushing in progress */
18    QUEUE_FSEQ_DONE = (1 << 4),
19};
20
21static struct request *queue_next_fseq(struct request_queue *q);
22
23unsigned blk_flush_cur_seq(struct request_queue *q)
24{
25    if (!q->flush_seq)
26        return 0;
27    return 1 << ffz(q->flush_seq);
28}
29
30static struct request *blk_flush_complete_seq(struct request_queue *q,
31                          unsigned seq, int error)
32{
33    struct request *next_rq = NULL;
34
35    if (error && !q->flush_err)
36        q->flush_err = error;
37
38    BUG_ON(q->flush_seq & seq);
39    q->flush_seq |= seq;
40
41    if (blk_flush_cur_seq(q) != QUEUE_FSEQ_DONE) {
42        /* not complete yet, queue the next flush sequence */
43        next_rq = queue_next_fseq(q);
44    } else {
45        /* complete this flush request */
46        __blk_end_request_all(q->orig_flush_rq, q->flush_err);
47        q->orig_flush_rq = NULL;
48        q->flush_seq = 0;
49
50        /* dispatch the next flush if there's one */
51        if (!list_empty(&q->pending_flushes)) {
52            next_rq = list_entry_rq(q->pending_flushes.next);
53            list_move(&next_rq->queuelist, &q->queue_head);
54        }
55    }
56    return next_rq;
57}
58
59static void blk_flush_complete_seq_end_io(struct request_queue *q,
60                      unsigned seq, int error)
61{
62    bool was_empty = elv_queue_empty(q);
63    struct request *next_rq;
64
65    next_rq = blk_flush_complete_seq(q, seq, error);
66
67    /*
68     * Moving a request silently to empty queue_head may stall the
69     * queue. Kick the queue in those cases.
70     */
71    if (was_empty && next_rq)
72        __blk_run_queue(q);
73}
74
75static void pre_flush_end_io(struct request *rq, int error)
76{
77    elv_completed_request(rq->q, rq);
78    blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_PREFLUSH, error);
79}
80
81static void flush_data_end_io(struct request *rq, int error)
82{
83    elv_completed_request(rq->q, rq);
84    blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_DATA, error);
85}
86
87static void post_flush_end_io(struct request *rq, int error)
88{
89    elv_completed_request(rq->q, rq);
90    blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_POSTFLUSH, error);
91}
92
93static void init_flush_request(struct request *rq, struct gendisk *disk)
94{
95    rq->cmd_type = REQ_TYPE_FS;
96    rq->cmd_flags = WRITE_FLUSH;
97    rq->rq_disk = disk;
98}
99
100static struct request *queue_next_fseq(struct request_queue *q)
101{
102    struct request *orig_rq = q->orig_flush_rq;
103    struct request *rq = &q->flush_rq;
104
105    blk_rq_init(q, rq);
106
107    switch (blk_flush_cur_seq(q)) {
108    case QUEUE_FSEQ_PREFLUSH:
109        init_flush_request(rq, orig_rq->rq_disk);
110        rq->end_io = pre_flush_end_io;
111        break;
112    case QUEUE_FSEQ_DATA:
113        init_request_from_bio(rq, orig_rq->bio);
114        /*
115         * orig_rq->rq_disk may be different from
116         * bio->bi_bdev->bd_disk if orig_rq got here through
117         * remapping drivers. Make sure rq->rq_disk points
118         * to the same one as orig_rq.
119         */
120        rq->rq_disk = orig_rq->rq_disk;
121        rq->cmd_flags &= ~(REQ_FLUSH | REQ_FUA);
122        rq->cmd_flags |= orig_rq->cmd_flags & (REQ_FLUSH | REQ_FUA);
123        rq->end_io = flush_data_end_io;
124        break;
125    case QUEUE_FSEQ_POSTFLUSH:
126        init_flush_request(rq, orig_rq->rq_disk);
127        rq->end_io = post_flush_end_io;
128        break;
129    default:
130        BUG();
131    }
132
133    elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
134    return rq;
135}
136
137struct request *blk_do_flush(struct request_queue *q, struct request *rq)
138{
139    unsigned int fflags = q->flush_flags; /* may change, cache it */
140    bool has_flush = fflags & REQ_FLUSH, has_fua = fflags & REQ_FUA;
141    bool do_preflush = has_flush && (rq->cmd_flags & REQ_FLUSH);
142    bool do_postflush = has_flush && !has_fua && (rq->cmd_flags & REQ_FUA);
143    unsigned skip = 0;
144
145    /*
146     * Special case. If there's data but flush is not necessary,
147     * the request can be issued directly.
148     *
149     * Flush w/o data should be able to be issued directly too but
150     * currently some drivers assume that rq->bio contains
151     * non-zero data if it isn't NULL and empty FLUSH requests
152     * getting here usually have bio's without data.
153     */
154    if (blk_rq_sectors(rq) && !do_preflush && !do_postflush) {
155        rq->cmd_flags &= ~REQ_FLUSH;
156        if (!has_fua)
157            rq->cmd_flags &= ~REQ_FUA;
158        return rq;
159    }
160
161    /*
162     * Sequenced flushes can't be processed in parallel. If
163     * another one is already in progress, queue for later
164     * processing.
165     */
166    if (q->flush_seq) {
167        list_move_tail(&rq->queuelist, &q->pending_flushes);
168        return NULL;
169    }
170
171    /*
172     * Start a new flush sequence
173     */
174    q->flush_err = 0;
175    q->flush_seq |= QUEUE_FSEQ_STARTED;
176
177    /* adjust FLUSH/FUA of the original request and stash it away */
178    rq->cmd_flags &= ~REQ_FLUSH;
179    if (!has_fua)
180        rq->cmd_flags &= ~REQ_FUA;
181    blk_dequeue_request(rq);
182    q->orig_flush_rq = rq;
183
184    /* skip unneded sequences and return the first one */
185    if (!do_preflush)
186        skip |= QUEUE_FSEQ_PREFLUSH;
187    if (!blk_rq_sectors(rq))
188        skip |= QUEUE_FSEQ_DATA;
189    if (!do_postflush)
190        skip |= QUEUE_FSEQ_POSTFLUSH;
191    return blk_flush_complete_seq(q, skip, 0);
192}
193
194static void bio_end_flush(struct bio *bio, int err)
195{
196    if (err)
197        clear_bit(BIO_UPTODATE, &bio->bi_flags);
198    if (bio->bi_private)
199        complete(bio->bi_private);
200    bio_put(bio);
201}
202
203/**
204 * blkdev_issue_flush - queue a flush
205 * @bdev: blockdev to issue flush for
206 * @gfp_mask: memory allocation flags (for bio_alloc)
207 * @error_sector: error sector
208 *
209 * Description:
210 * Issue a flush for the block device in question. Caller can supply
211 * room for storing the error offset in case of a flush error, if they
212 * wish to. If WAIT flag is not passed then caller may check only what
213 * request was pushed in some internal queue for later handling.
214 */
215int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
216        sector_t *error_sector)
217{
218    DECLARE_COMPLETION_ONSTACK(wait);
219    struct request_queue *q;
220    struct bio *bio;
221    int ret = 0;
222
223    if (bdev->bd_disk == NULL)
224        return -ENXIO;
225
226    q = bdev_get_queue(bdev);
227    if (!q)
228        return -ENXIO;
229
230    /*
231     * some block devices may not have their queue correctly set up here
232     * (e.g. loop device without a backing file) and so issuing a flush
233     * here will panic. Ensure there is a request function before issuing
234     * the flush.
235     */
236    if (!q->make_request_fn)
237        return -ENXIO;
238
239    bio = bio_alloc(gfp_mask, 0);
240    bio->bi_end_io = bio_end_flush;
241    bio->bi_bdev = bdev;
242    bio->bi_private = &wait;
243
244    bio_get(bio);
245    submit_bio(WRITE_FLUSH, bio);
246    wait_for_completion(&wait);
247
248    /*
249     * The driver must store the error location in ->bi_sector, if
250     * it supports it. For non-stacked drivers, this should be
251     * copied from blk_rq_pos(rq).
252     */
253    if (error_sector)
254               *error_sector = bio->bi_sector;
255
256    if (!bio_flagged(bio, BIO_UPTODATE))
257        ret = -EIO;
258
259    bio_put(bio);
260    return ret;
261}
262EXPORT_SYMBOL(blkdev_issue_flush);
263

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