FreeBSD/Linux Kernel Cross Reference
sys/kern/subr_disk.c
1 /*-
2 * ----------------------------------------------------------------------------
3 * "THE BEER-WARE LICENSE" (Revision 42):
4 * <phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you
5 * can do whatever you want with this stuff. If we meet some day, and you think
6 * this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
7 * ----------------------------------------------------------------------------
8 *
9 * The bioq_disksort() (and the specification of the bioq API)
10 * have been written by Luigi Rizzo and Fabio Checconi under the same
11 * license as above.
12 */
13
14 #include <sys/cdefs.h>
15 __FBSDID("$FreeBSD$");
16
17 #include "opt_geom.h"
18
19 #include <sys/param.h>
20 #include <sys/systm.h>
21 #include <sys/bio.h>
22 #include <sys/conf.h>
23 #include <sys/disk.h>
24 #include <geom/geom_disk.h>
25
26 /*-
27 * Disk error is the preface to plaintive error messages
28 * about failing disk transfers. It prints messages of the form
29 * "hp0g: BLABLABLA cmd=read fsbn 12345 of 12344-12347"
30 * blkdone should be -1 if the position of the error is unknown.
31 * The message is printed with printf.
32 */
33 void
34 disk_err(struct bio *bp, const char *what, int blkdone, int nl)
35 {
36 daddr_t sn;
37
38 if (bp->bio_dev != NULL)
39 printf("%s: %s ", devtoname(bp->bio_dev), what);
40 else if (bp->bio_disk != NULL)
41 printf("%s%d: %s ",
42 bp->bio_disk->d_name, bp->bio_disk->d_unit, what);
43 else
44 printf("disk??: %s ", what);
45 switch(bp->bio_cmd) {
46 case BIO_READ: printf("cmd=read "); break;
47 case BIO_WRITE: printf("cmd=write "); break;
48 case BIO_DELETE: printf("cmd=delete "); break;
49 case BIO_GETATTR: printf("cmd=getattr "); break;
50 case BIO_FLUSH: printf("cmd=flush "); break;
51 default: printf("cmd=%x ", bp->bio_cmd); break;
52 }
53 sn = bp->bio_pblkno;
54 if (bp->bio_bcount <= DEV_BSIZE) {
55 printf("fsbn %jd%s", (intmax_t)sn, nl ? "\n" : "");
56 return;
57 }
58 if (blkdone >= 0) {
59 sn += blkdone;
60 printf("fsbn %jd of ", (intmax_t)sn);
61 }
62 printf("%jd-%jd", (intmax_t)bp->bio_pblkno,
63 (intmax_t)(bp->bio_pblkno + (bp->bio_bcount - 1) / DEV_BSIZE));
64 if (nl)
65 printf("\n");
66 }
67
68 /*
69 * BIO queue implementation
70 *
71 * Please read carefully the description below before making any change
72 * to the code, or you might change the behaviour of the data structure
73 * in undesirable ways.
74 *
75 * A bioq stores disk I/O request (bio), normally sorted according to
76 * the distance of the requested position (bio->bio_offset) from the
77 * current head position (bioq->last_offset) in the scan direction, i.e.
78 *
79 * (uoff_t)(bio_offset - last_offset)
80 *
81 * Note that the cast to unsigned (uoff_t) is fundamental to insure
82 * that the distance is computed in the scan direction.
83 *
84 * The main methods for manipulating the bioq are:
85 *
86 * bioq_disksort() performs an ordered insertion;
87 *
88 * bioq_first() return the head of the queue, without removing;
89 *
90 * bioq_takefirst() return and remove the head of the queue,
91 * updating the 'current head position' as
92 * bioq->last_offset = bio->bio_offset + bio->bio_length;
93 *
94 * When updating the 'current head position', we assume that the result of
95 * bioq_takefirst() is dispatched to the device, so bioq->last_offset
96 * represents the head position once the request is complete.
97 *
98 * If the bioq is manipulated using only the above calls, it starts
99 * with a sorted sequence of requests with bio_offset >= last_offset,
100 * possibly followed by another sorted sequence of requests with
101 * 0 <= bio_offset < bioq->last_offset
102 *
103 * NOTE: historical behaviour was to ignore bio->bio_length in the
104 * update, but its use tracks the head position in a better way.
105 * Historical behaviour was also to update the head position when
106 * the request under service is complete, rather than when the
107 * request is extracted from the queue. However, the current API
108 * has no method to update the head position; secondly, once
109 * a request has been submitted to the disk, we have no idea of
110 * the actual head position, so the final one is our best guess.
111 *
112 * --- Direct queue manipulation ---
113 *
114 * A bioq uses an underlying TAILQ to store requests, so we also
115 * export methods to manipulate the TAILQ, in particular:
116 *
117 * bioq_insert_tail() insert an entry at the end.
118 * It also creates a 'barrier' so all subsequent
119 * insertions through bioq_disksort() will end up
120 * after this entry;
121 *
122 * bioq_insert_head() insert an entry at the head, update
123 * bioq->last_offset = bio->bio_offset so that
124 * all subsequent insertions through bioq_disksort()
125 * will end up after this entry;
126 *
127 * bioq_remove() remove a generic element from the queue, act as
128 * bioq_takefirst() if invoked on the head of the queue.
129 *
130 * The semantic of these methods is the same of the operations
131 * on the underlying TAILQ, but with additional guarantees on
132 * subsequent bioq_disksort() calls. E.g. bioq_insert_tail()
133 * can be useful for making sure that all previous ops are flushed
134 * to disk before continuing.
135 *
136 * Updating bioq->last_offset on a bioq_insert_head() guarantees
137 * that the bio inserted with the last bioq_insert_head() will stay
138 * at the head of the queue even after subsequent bioq_disksort().
139 *
140 * Note that when the direct queue manipulation functions are used,
141 * the queue may contain multiple inversion points (i.e. more than
142 * two sorted sequences of requests).
143 *
144 */
145
146 void
147 bioq_init(struct bio_queue_head *head)
148 {
149
150 TAILQ_INIT(&head->queue);
151 head->last_offset = 0;
152 head->insert_point = NULL;
153 }
154
155 void
156 bioq_remove(struct bio_queue_head *head, struct bio *bp)
157 {
158
159 if (bp == TAILQ_FIRST(&head->queue))
160 head->last_offset = bp->bio_offset + bp->bio_length;
161
162 if (bp == head->insert_point)
163 head->insert_point = NULL;
164
165 TAILQ_REMOVE(&head->queue, bp, bio_queue);
166 }
167
168 void
169 bioq_flush(struct bio_queue_head *head, struct devstat *stp, int error)
170 {
171 struct bio *bp;
172
173 while ((bp = bioq_takefirst(head)) != NULL)
174 biofinish(bp, stp, error);
175 }
176
177 void
178 bioq_insert_head(struct bio_queue_head *head, struct bio *bp)
179 {
180
181 head->last_offset = bp->bio_offset;
182 TAILQ_INSERT_HEAD(&head->queue, bp, bio_queue);
183 }
184
185 void
186 bioq_insert_tail(struct bio_queue_head *head, struct bio *bp)
187 {
188
189 TAILQ_INSERT_TAIL(&head->queue, bp, bio_queue);
190 head->insert_point = bp;
191 }
192
193 struct bio *
194 bioq_first(struct bio_queue_head *head)
195 {
196
197 return (TAILQ_FIRST(&head->queue));
198 }
199
200 struct bio *
201 bioq_takefirst(struct bio_queue_head *head)
202 {
203 struct bio *bp;
204
205 bp = TAILQ_FIRST(&head->queue);
206 if (bp != NULL)
207 bioq_remove(head, bp);
208 return (bp);
209 }
210
211 /*
212 * Compute the sorting key. The cast to unsigned is
213 * fundamental for correctness, see the description
214 * near the beginning of the file.
215 */
216 static inline uoff_t
217 bioq_bio_key(struct bio_queue_head *head, struct bio *bp)
218 {
219
220 return ((uoff_t)(bp->bio_offset - head->last_offset));
221 }
222
223 /*
224 * Seek sort for disks.
225 *
226 * Sort all requests in a single queue while keeping
227 * track of the current position of the disk with last_offset.
228 * See above for details.
229 */
230 void
231 bioq_disksort(struct bio_queue_head *head, struct bio *bp)
232 {
233 struct bio *cur, *prev = NULL;
234 uoff_t key = bioq_bio_key(head, bp);
235
236 cur = TAILQ_FIRST(&head->queue);
237
238 if (head->insert_point)
239 cur = head->insert_point;
240
241 while (cur != NULL && key >= bioq_bio_key(head, cur)) {
242 prev = cur;
243 cur = TAILQ_NEXT(cur, bio_queue);
244 }
245
246 if (prev == NULL)
247 TAILQ_INSERT_HEAD(&head->queue, bp, bio_queue);
248 else
249 TAILQ_INSERT_AFTER(&head->queue, prev, bp, bio_queue);
250 }
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