FreeBSD/Linux Kernel Cross Reference
sys/kern/tty_outq.c
1 /*-
2 * Copyright (c) 2008 Ed Schouten <ed@FreeBSD.org>
3 * All rights reserved.
4 *
5 * Portions of this software were developed under sponsorship from Snow
6 * B.V., the Netherlands.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 */
29
30 #include <sys/cdefs.h>
31 __FBSDID("$FreeBSD$");
32
33 #include <sys/param.h>
34 #include <sys/kernel.h>
35 #include <sys/lock.h>
36 #include <sys/queue.h>
37 #include <sys/systm.h>
38 #include <sys/tty.h>
39 #include <sys/uio.h>
40
41 #include <vm/uma.h>
42
43 /*
44 * TTY output queue buffering.
45 *
46 * The previous design of the TTY layer offered the so-called clists.
47 * These clists were used for both the input queues and the output
48 * queue. We don't use certain features on the output side, like quoting
49 * bits for parity marking and such. This mechanism is similar to the
50 * old clists, but only contains the features we need to buffer the
51 * output.
52 */
53
54 struct ttyoutq_block {
55 struct ttyoutq_block *tob_next;
56 char tob_data[TTYOUTQ_DATASIZE];
57 };
58
59 static uma_zone_t ttyoutq_zone;
60
61 #define TTYOUTQ_INSERT_TAIL(to, tob) do { \
62 if (to->to_end == 0) { \
63 tob->tob_next = to->to_firstblock; \
64 to->to_firstblock = tob; \
65 } else { \
66 tob->tob_next = to->to_lastblock->tob_next; \
67 to->to_lastblock->tob_next = tob; \
68 } \
69 to->to_nblocks++; \
70 } while (0)
71
72 #define TTYOUTQ_REMOVE_HEAD(to) do { \
73 to->to_firstblock = to->to_firstblock->tob_next; \
74 to->to_nblocks--; \
75 } while (0)
76
77 #define TTYOUTQ_RECYCLE(to, tob) do { \
78 if (to->to_quota <= to->to_nblocks) \
79 uma_zfree(ttyoutq_zone, tob); \
80 else \
81 TTYOUTQ_INSERT_TAIL(to, tob); \
82 } while(0)
83
84 void
85 ttyoutq_flush(struct ttyoutq *to)
86 {
87
88 to->to_begin = 0;
89 to->to_end = 0;
90 }
91
92 int
93 ttyoutq_setsize(struct ttyoutq *to, struct tty *tp, size_t size)
94 {
95 struct ttyoutq_block *tob;
96
97 to->to_quota = howmany(size, TTYOUTQ_DATASIZE);
98
99 while (to->to_quota > to->to_nblocks) {
100 /*
101 * List is getting bigger.
102 * Add new blocks to the tail of the list.
103 *
104 * We must unlock the TTY temporarily, because we need
105 * to allocate memory. This won't be a problem, because
106 * in the worst case, another thread ends up here, which
107 * may cause us to allocate too many blocks, but this
108 * will be caught by the loop below.
109 */
110 tty_unlock(tp);
111 tob = uma_zalloc(ttyoutq_zone, M_WAITOK);
112 tty_lock(tp);
113
114 if (tty_gone(tp)) {
115 uma_zfree(ttyoutq_zone, tob);
116 return (ENXIO);
117 }
118
119 TTYOUTQ_INSERT_TAIL(to, tob);
120 }
121 return (0);
122 }
123
124 void
125 ttyoutq_free(struct ttyoutq *to)
126 {
127 struct ttyoutq_block *tob;
128
129 ttyoutq_flush(to);
130 to->to_quota = 0;
131
132 while ((tob = to->to_firstblock) != NULL) {
133 TTYOUTQ_REMOVE_HEAD(to);
134 uma_zfree(ttyoutq_zone, tob);
135 }
136
137 MPASS(to->to_nblocks == 0);
138 }
139
140 size_t
141 ttyoutq_read(struct ttyoutq *to, void *buf, size_t len)
142 {
143 char *cbuf = buf;
144
145 while (len > 0) {
146 struct ttyoutq_block *tob;
147 size_t cbegin, cend, clen;
148
149 /* See if there still is data. */
150 if (to->to_begin == to->to_end)
151 break;
152 tob = to->to_firstblock;
153 if (tob == NULL)
154 break;
155
156 /*
157 * The end address should be the lowest of these three:
158 * - The write pointer
159 * - The blocksize - we can't read beyond the block
160 * - The end address if we could perform the full read
161 */
162 cbegin = to->to_begin;
163 cend = MIN(MIN(to->to_end, to->to_begin + len),
164 TTYOUTQ_DATASIZE);
165 clen = cend - cbegin;
166
167 /* Copy the data out of the buffers. */
168 memcpy(cbuf, tob->tob_data + cbegin, clen);
169 cbuf += clen;
170 len -= clen;
171
172 if (cend == to->to_end) {
173 /* Read the complete queue. */
174 to->to_begin = 0;
175 to->to_end = 0;
176 } else if (cend == TTYOUTQ_DATASIZE) {
177 /* Read the block until the end. */
178 TTYOUTQ_REMOVE_HEAD(to);
179 to->to_begin = 0;
180 to->to_end -= TTYOUTQ_DATASIZE;
181 TTYOUTQ_RECYCLE(to, tob);
182 } else {
183 /* Read the block partially. */
184 to->to_begin += clen;
185 }
186 }
187
188 return (cbuf - (char *)buf);
189 }
190
191 /*
192 * An optimized version of ttyoutq_read() which can be used in pseudo
193 * TTY drivers to directly copy data from the outq to userspace, instead
194 * of buffering it.
195 *
196 * We can only copy data directly if we need to read the entire block
197 * back to the user, because we temporarily remove the block from the
198 * queue. Otherwise we need to copy it to a temporary buffer first, to
199 * make sure data remains in the correct order.
200 */
201 int
202 ttyoutq_read_uio(struct ttyoutq *to, struct tty *tp, struct uio *uio)
203 {
204
205 while (uio->uio_resid > 0) {
206 int error;
207 struct ttyoutq_block *tob;
208 size_t cbegin, cend, clen;
209
210 /* See if there still is data. */
211 if (to->to_begin == to->to_end)
212 return (0);
213 tob = to->to_firstblock;
214 if (tob == NULL)
215 return (0);
216
217 /*
218 * The end address should be the lowest of these three:
219 * - The write pointer
220 * - The blocksize - we can't read beyond the block
221 * - The end address if we could perform the full read
222 */
223 cbegin = to->to_begin;
224 cend = MIN(MIN(to->to_end, to->to_begin + uio->uio_resid),
225 TTYOUTQ_DATASIZE);
226 clen = cend - cbegin;
227
228 /*
229 * We can prevent buffering in some cases:
230 * - We need to read the block until the end.
231 * - We don't need to read the block until the end, but
232 * there is no data beyond it, which allows us to move
233 * the write pointer to a new block.
234 */
235 if (cend == TTYOUTQ_DATASIZE || cend == to->to_end) {
236 /*
237 * Fast path: zero copy. Remove the first block,
238 * so we can unlock the TTY temporarily.
239 */
240 TTYOUTQ_REMOVE_HEAD(to);
241 to->to_begin = 0;
242 if (to->to_end <= TTYOUTQ_DATASIZE)
243 to->to_end = 0;
244 else
245 to->to_end -= TTYOUTQ_DATASIZE;
246
247 /* Temporary unlock and copy the data to userspace. */
248 tty_unlock(tp);
249 error = uiomove(tob->tob_data + cbegin, clen, uio);
250 tty_lock(tp);
251
252 /* Block can now be readded to the list. */
253 TTYOUTQ_RECYCLE(to, tob);
254 } else {
255 char ob[TTYOUTQ_DATASIZE - 1];
256
257 /*
258 * Slow path: store data in a temporary buffer.
259 */
260 memcpy(ob, tob->tob_data + cbegin, clen);
261 to->to_begin += clen;
262 MPASS(to->to_begin < TTYOUTQ_DATASIZE);
263
264 /* Temporary unlock and copy the data to userspace. */
265 tty_unlock(tp);
266 error = uiomove(ob, clen, uio);
267 tty_lock(tp);
268 }
269
270 if (error != 0)
271 return (error);
272 }
273
274 return (0);
275 }
276
277 size_t
278 ttyoutq_write(struct ttyoutq *to, const void *buf, size_t nbytes)
279 {
280 const char *cbuf = buf;
281 struct ttyoutq_block *tob;
282 unsigned int boff;
283 size_t l;
284
285 while (nbytes > 0) {
286 boff = to->to_end % TTYOUTQ_DATASIZE;
287
288 if (to->to_end == 0) {
289 /* First time we're being used or drained. */
290 MPASS(to->to_begin == 0);
291 tob = to->to_firstblock;
292 if (tob == NULL) {
293 /* Queue has no blocks. */
294 break;
295 }
296 to->to_lastblock = tob;
297 } else if (boff == 0) {
298 /* We reached the end of this block on last write. */
299 tob = to->to_lastblock->tob_next;
300 if (tob == NULL) {
301 /* We've reached the watermark. */
302 break;
303 }
304 to->to_lastblock = tob;
305 } else {
306 tob = to->to_lastblock;
307 }
308
309 /* Don't copy more than was requested. */
310 l = MIN(nbytes, TTYOUTQ_DATASIZE - boff);
311 MPASS(l > 0);
312 memcpy(tob->tob_data + boff, cbuf, l);
313
314 cbuf += l;
315 nbytes -= l;
316 to->to_end += l;
317 }
318
319 return (cbuf - (const char *)buf);
320 }
321
322 int
323 ttyoutq_write_nofrag(struct ttyoutq *to, const void *buf, size_t nbytes)
324 {
325 size_t ret;
326
327 if (ttyoutq_bytesleft(to) < nbytes)
328 return (-1);
329
330 /* We should always be able to write it back. */
331 ret = ttyoutq_write(to, buf, nbytes);
332 MPASS(ret == nbytes);
333
334 return (0);
335 }
336
337 static void
338 ttyoutq_startup(void *dummy)
339 {
340
341 ttyoutq_zone = uma_zcreate("ttyoutq", sizeof(struct ttyoutq_block),
342 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
343 }
344
345 SYSINIT(ttyoutq, SI_SUB_DRIVERS, SI_ORDER_FIRST, ttyoutq_startup, NULL);
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