FreeBSD/Linux Kernel Cross Reference
sys/kern/tty_outq.c
1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2008 Ed Schouten <ed@FreeBSD.org>
5 * All rights reserved.
6 *
7 * Portions of this software were developed under sponsorship from Snow
8 * B.V., the Netherlands.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 */
31
32 #include <sys/cdefs.h>
33 __FBSDID("$FreeBSD$");
34
35 #include <sys/param.h>
36 #include <sys/kernel.h>
37 #include <sys/lock.h>
38 #include <sys/queue.h>
39 #include <sys/systm.h>
40 #include <sys/tty.h>
41 #include <sys/uio.h>
42
43 #include <vm/uma.h>
44
45 /*
46 * TTY output queue buffering.
47 *
48 * The previous design of the TTY layer offered the so-called clists.
49 * These clists were used for both the input queues and the output
50 * queue. We don't use certain features on the output side, like quoting
51 * bits for parity marking and such. This mechanism is similar to the
52 * old clists, but only contains the features we need to buffer the
53 * output.
54 */
55
56 struct ttyoutq_block {
57 struct ttyoutq_block *tob_next;
58 char tob_data[TTYOUTQ_DATASIZE];
59 };
60
61 static uma_zone_t ttyoutq_zone;
62
63 #define TTYOUTQ_INSERT_TAIL(to, tob) do { \
64 if (to->to_end == 0) { \
65 tob->tob_next = to->to_firstblock; \
66 to->to_firstblock = tob; \
67 } else { \
68 tob->tob_next = to->to_lastblock->tob_next; \
69 to->to_lastblock->tob_next = tob; \
70 } \
71 to->to_nblocks++; \
72 } while (0)
73
74 #define TTYOUTQ_REMOVE_HEAD(to) do { \
75 to->to_firstblock = to->to_firstblock->tob_next; \
76 to->to_nblocks--; \
77 } while (0)
78
79 #define TTYOUTQ_RECYCLE(to, tob) do { \
80 if (to->to_quota <= to->to_nblocks) \
81 uma_zfree(ttyoutq_zone, tob); \
82 else \
83 TTYOUTQ_INSERT_TAIL(to, tob); \
84 } while (0)
85
86 void
87 ttyoutq_flush(struct ttyoutq *to)
88 {
89
90 to->to_begin = 0;
91 to->to_end = 0;
92 }
93
94 int
95 ttyoutq_setsize(struct ttyoutq *to, struct tty *tp, size_t size)
96 {
97 struct ttyoutq_block *tob;
98
99 to->to_quota = howmany(size, TTYOUTQ_DATASIZE);
100
101 while (to->to_quota > to->to_nblocks) {
102 /*
103 * List is getting bigger.
104 * Add new blocks to the tail of the list.
105 *
106 * We must unlock the TTY temporarily, because we need
107 * to allocate memory. This won't be a problem, because
108 * in the worst case, another thread ends up here, which
109 * may cause us to allocate too many blocks, but this
110 * will be caught by the loop below.
111 */
112 tty_unlock(tp);
113 tob = uma_zalloc(ttyoutq_zone, M_WAITOK);
114 tty_lock(tp);
115
116 if (tty_gone(tp)) {
117 uma_zfree(ttyoutq_zone, tob);
118 return (ENXIO);
119 }
120
121 TTYOUTQ_INSERT_TAIL(to, tob);
122 }
123 return (0);
124 }
125
126 void
127 ttyoutq_free(struct ttyoutq *to)
128 {
129 struct ttyoutq_block *tob;
130
131 ttyoutq_flush(to);
132 to->to_quota = 0;
133
134 while ((tob = to->to_firstblock) != NULL) {
135 TTYOUTQ_REMOVE_HEAD(to);
136 uma_zfree(ttyoutq_zone, tob);
137 }
138
139 MPASS(to->to_nblocks == 0);
140 }
141
142 size_t
143 ttyoutq_read(struct ttyoutq *to, void *buf, size_t len)
144 {
145 char *cbuf = buf;
146
147 while (len > 0) {
148 struct ttyoutq_block *tob;
149 size_t cbegin, cend, clen;
150
151 /* See if there still is data. */
152 if (to->to_begin == to->to_end)
153 break;
154 tob = to->to_firstblock;
155 if (tob == NULL)
156 break;
157
158 /*
159 * The end address should be the lowest of these three:
160 * - The write pointer
161 * - The blocksize - we can't read beyond the block
162 * - The end address if we could perform the full read
163 */
164 cbegin = to->to_begin;
165 cend = MIN(MIN(to->to_end, to->to_begin + len),
166 TTYOUTQ_DATASIZE);
167 clen = cend - cbegin;
168
169 /* Copy the data out of the buffers. */
170 memcpy(cbuf, tob->tob_data + cbegin, clen);
171 cbuf += clen;
172 len -= clen;
173
174 if (cend == to->to_end) {
175 /* Read the complete queue. */
176 to->to_begin = 0;
177 to->to_end = 0;
178 } else if (cend == TTYOUTQ_DATASIZE) {
179 /* Read the block until the end. */
180 TTYOUTQ_REMOVE_HEAD(to);
181 to->to_begin = 0;
182 to->to_end -= TTYOUTQ_DATASIZE;
183 TTYOUTQ_RECYCLE(to, tob);
184 } else {
185 /* Read the block partially. */
186 to->to_begin += clen;
187 }
188 }
189
190 return (cbuf - (char *)buf);
191 }
192
193 /*
194 * An optimized version of ttyoutq_read() which can be used in pseudo
195 * TTY drivers to directly copy data from the outq to userspace, instead
196 * of buffering it.
197 *
198 * We can only copy data directly if we need to read the entire block
199 * back to the user, because we temporarily remove the block from the
200 * queue. Otherwise we need to copy it to a temporary buffer first, to
201 * make sure data remains in the correct order.
202 */
203 int
204 ttyoutq_read_uio(struct ttyoutq *to, struct tty *tp, struct uio *uio)
205 {
206
207 while (uio->uio_resid > 0) {
208 int error;
209 struct ttyoutq_block *tob;
210 size_t cbegin, cend, clen;
211
212 /* See if there still is data. */
213 if (to->to_begin == to->to_end)
214 return (0);
215 tob = to->to_firstblock;
216 if (tob == NULL)
217 return (0);
218
219 /*
220 * The end address should be the lowest of these three:
221 * - The write pointer
222 * - The blocksize - we can't read beyond the block
223 * - The end address if we could perform the full read
224 */
225 cbegin = to->to_begin;
226 cend = MIN(MIN(to->to_end, to->to_begin + uio->uio_resid),
227 TTYOUTQ_DATASIZE);
228 clen = cend - cbegin;
229
230 /*
231 * We can prevent buffering in some cases:
232 * - We need to read the block until the end.
233 * - We don't need to read the block until the end, but
234 * there is no data beyond it, which allows us to move
235 * the write pointer to a new block.
236 */
237 if (cend == TTYOUTQ_DATASIZE || cend == to->to_end) {
238 /*
239 * Fast path: zero copy. Remove the first block,
240 * so we can unlock the TTY temporarily.
241 */
242 TTYOUTQ_REMOVE_HEAD(to);
243 to->to_begin = 0;
244 if (to->to_end <= TTYOUTQ_DATASIZE)
245 to->to_end = 0;
246 else
247 to->to_end -= TTYOUTQ_DATASIZE;
248
249 /* Temporary unlock and copy the data to userspace. */
250 tty_unlock(tp);
251 error = uiomove(tob->tob_data + cbegin, clen, uio);
252 tty_lock(tp);
253
254 /* Block can now be readded to the list. */
255 TTYOUTQ_RECYCLE(to, tob);
256 } else {
257 char ob[TTYOUTQ_DATASIZE - 1];
258
259 /*
260 * Slow path: store data in a temporary buffer.
261 */
262 memcpy(ob, tob->tob_data + cbegin, clen);
263 to->to_begin += clen;
264 MPASS(to->to_begin < TTYOUTQ_DATASIZE);
265
266 /* Temporary unlock and copy the data to userspace. */
267 tty_unlock(tp);
268 error = uiomove(ob, clen, uio);
269 tty_lock(tp);
270 }
271
272 if (error != 0)
273 return (error);
274 }
275
276 return (0);
277 }
278
279 size_t
280 ttyoutq_write(struct ttyoutq *to, const void *buf, size_t nbytes)
281 {
282 const char *cbuf = buf;
283 struct ttyoutq_block *tob;
284 unsigned int boff;
285 size_t l;
286
287 while (nbytes > 0) {
288 boff = to->to_end % TTYOUTQ_DATASIZE;
289
290 if (to->to_end == 0) {
291 /* First time we're being used or drained. */
292 MPASS(to->to_begin == 0);
293 tob = to->to_firstblock;
294 if (tob == NULL) {
295 /* Queue has no blocks. */
296 break;
297 }
298 to->to_lastblock = tob;
299 } else if (boff == 0) {
300 /* We reached the end of this block on last write. */
301 tob = to->to_lastblock->tob_next;
302 if (tob == NULL) {
303 /* We've reached the watermark. */
304 break;
305 }
306 to->to_lastblock = tob;
307 } else {
308 tob = to->to_lastblock;
309 }
310
311 /* Don't copy more than was requested. */
312 l = MIN(nbytes, TTYOUTQ_DATASIZE - boff);
313 MPASS(l > 0);
314 memcpy(tob->tob_data + boff, cbuf, l);
315
316 cbuf += l;
317 nbytes -= l;
318 to->to_end += l;
319 }
320
321 return (cbuf - (const char *)buf);
322 }
323
324 int
325 ttyoutq_write_nofrag(struct ttyoutq *to, const void *buf, size_t nbytes)
326 {
327 size_t ret __unused;
328
329 if (ttyoutq_bytesleft(to) < nbytes)
330 return (-1);
331
332 /* We should always be able to write it back. */
333 ret = ttyoutq_write(to, buf, nbytes);
334 MPASS(ret == nbytes);
335
336 return (0);
337 }
338
339 static void
340 ttyoutq_startup(void *dummy)
341 {
342
343 ttyoutq_zone = uma_zcreate("ttyoutq", sizeof(struct ttyoutq_block),
344 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
345 }
346
347 SYSINIT(ttyoutq, SI_SUB_DRIVERS, SI_ORDER_FIRST, ttyoutq_startup, NULL);
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