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: releng/8.0/sys/kern/tty_outq.c 189061 2009-02-26 10:28:32Z ed $");
32
33 #include <sys/param.h>
34 #include <sys/kernel.h>
35 #include <sys/lock.h>
36 #include <sys/queue.h>
37 #include <sys/sysctl.h>
38 #include <sys/systm.h>
39 #include <sys/tty.h>
40 #include <sys/uio.h>
41
42 #include <vm/uma.h>
43
44 /*
45 * TTY output queue buffering.
46 *
47 * The previous design of the TTY layer offered the so-called clists.
48 * These clists were used for both the input queues and the output
49 * queue. We don't use certain features on the output side, like quoting
50 * bits for parity marking and such. This mechanism is similar to the
51 * old clists, but only contains the features we need to buffer the
52 * output.
53 */
54
55 /* Statistics. */
56 static unsigned long ttyoutq_nfast = 0;
57 SYSCTL_ULONG(_kern, OID_AUTO, tty_outq_nfast, CTLFLAG_RD,
58 &ttyoutq_nfast, 0, "Unbuffered reads to userspace on output");
59 static unsigned long ttyoutq_nslow = 0;
60 SYSCTL_ULONG(_kern, OID_AUTO, tty_outq_nslow, CTLFLAG_RD,
61 &ttyoutq_nslow, 0, "Buffered reads to userspace on output");
62
63 struct ttyoutq_block {
64 struct ttyoutq_block *tob_next;
65 char tob_data[TTYOUTQ_DATASIZE];
66 };
67
68 static uma_zone_t ttyoutq_zone;
69
70 #define TTYOUTQ_INSERT_TAIL(to, tob) do { \
71 if (to->to_end == 0) { \
72 tob->tob_next = to->to_firstblock; \
73 to->to_firstblock = tob; \
74 } else { \
75 tob->tob_next = to->to_lastblock->tob_next; \
76 to->to_lastblock->tob_next = tob; \
77 } \
78 to->to_nblocks++; \
79 } while (0)
80
81 #define TTYOUTQ_REMOVE_HEAD(to) do { \
82 to->to_firstblock = to->to_firstblock->tob_next; \
83 to->to_nblocks--; \
84 } while (0)
85
86 #define TTYOUTQ_RECYCLE(to, tob) do { \
87 if (to->to_quota <= to->to_nblocks) \
88 uma_zfree(ttyoutq_zone, tob); \
89 else \
90 TTYOUTQ_INSERT_TAIL(to, tob); \
91 } while(0)
92
93 void
94 ttyoutq_flush(struct ttyoutq *to)
95 {
96
97 to->to_begin = 0;
98 to->to_end = 0;
99 }
100
101 void
102 ttyoutq_setsize(struct ttyoutq *to, struct tty *tp, size_t size)
103 {
104 struct ttyoutq_block *tob;
105
106 to->to_quota = howmany(size, TTYOUTQ_DATASIZE);
107
108 while (to->to_quota > to->to_nblocks) {
109 /*
110 * List is getting bigger.
111 * Add new blocks to the tail of the list.
112 *
113 * We must unlock the TTY temporarily, because we need
114 * to allocate memory. This won't be a problem, because
115 * in the worst case, another thread ends up here, which
116 * may cause us to allocate too many blocks, but this
117 * will be caught by the loop below.
118 */
119 tty_unlock(tp);
120 tob = uma_zalloc(ttyoutq_zone, M_WAITOK);
121 tty_lock(tp);
122
123 TTYOUTQ_INSERT_TAIL(to, tob);
124 }
125 }
126
127 void
128 ttyoutq_free(struct ttyoutq *to)
129 {
130 struct ttyoutq_block *tob;
131
132 ttyoutq_flush(to);
133 to->to_quota = 0;
134
135 while ((tob = to->to_firstblock) != NULL) {
136 TTYOUTQ_REMOVE_HEAD(to);
137 uma_zfree(ttyoutq_zone, tob);
138 }
139
140 MPASS(to->to_nblocks == 0);
141 }
142
143 size_t
144 ttyoutq_read(struct ttyoutq *to, void *buf, size_t len)
145 {
146 char *cbuf = buf;
147
148 while (len > 0) {
149 struct ttyoutq_block *tob;
150 size_t cbegin, cend, clen;
151
152 /* See if there still is data. */
153 if (to->to_begin == to->to_end)
154 break;
155 tob = to->to_firstblock;
156 if (tob == NULL)
157 break;
158
159 /*
160 * The end address should be the lowest of these three:
161 * - The write pointer
162 * - The blocksize - we can't read beyond the block
163 * - The end address if we could perform the full read
164 */
165 cbegin = to->to_begin;
166 cend = MIN(MIN(to->to_end, to->to_begin + len),
167 TTYOUTQ_DATASIZE);
168 clen = cend - cbegin;
169
170 /* Copy the data out of the buffers. */
171 memcpy(cbuf, tob->tob_data + cbegin, clen);
172 cbuf += clen;
173 len -= clen;
174
175 if (cend == to->to_end) {
176 /* Read the complete queue. */
177 to->to_begin = 0;
178 to->to_end = 0;
179 } else if (cend == TTYOUTQ_DATASIZE) {
180 /* Read the block until the end. */
181 TTYOUTQ_REMOVE_HEAD(to);
182 to->to_begin = 0;
183 to->to_end -= TTYOUTQ_DATASIZE;
184 TTYOUTQ_RECYCLE(to, tob);
185 } else {
186 /* Read the block partially. */
187 to->to_begin += clen;
188 }
189 }
190
191 return (cbuf - (char *)buf);
192 }
193
194 /*
195 * An optimized version of ttyoutq_read() which can be used in pseudo
196 * TTY drivers to directly copy data from the outq to userspace, instead
197 * of buffering it.
198 *
199 * We can only copy data directly if we need to read the entire block
200 * back to the user, because we temporarily remove the block from the
201 * queue. Otherwise we need to copy it to a temporary buffer first, to
202 * make sure data remains in the correct order.
203 */
204 int
205 ttyoutq_read_uio(struct ttyoutq *to, struct tty *tp, struct uio *uio)
206 {
207
208 while (uio->uio_resid > 0) {
209 int error;
210 struct ttyoutq_block *tob;
211 size_t cbegin, cend, clen;
212
213 /* See if there still is data. */
214 if (to->to_begin == to->to_end)
215 return (0);
216 tob = to->to_firstblock;
217 if (tob == NULL)
218 return (0);
219
220 /*
221 * The end address should be the lowest of these three:
222 * - The write pointer
223 * - The blocksize - we can't read beyond the block
224 * - The end address if we could perform the full read
225 */
226 cbegin = to->to_begin;
227 cend = MIN(MIN(to->to_end, to->to_begin + uio->uio_resid),
228 TTYOUTQ_DATASIZE);
229 clen = cend - cbegin;
230
231 /*
232 * We can prevent buffering in some cases:
233 * - We need to read the block until the end.
234 * - We don't need to read the block until the end, but
235 * there is no data beyond it, which allows us to move
236 * the write pointer to a new block.
237 */
238 if (cend == TTYOUTQ_DATASIZE || cend == to->to_end) {
239 atomic_add_long(&ttyoutq_nfast, 1);
240
241 /*
242 * Fast path: zero copy. Remove the first block,
243 * so we can unlock the TTY temporarily.
244 */
245 TTYOUTQ_REMOVE_HEAD(to);
246 to->to_begin = 0;
247 if (to->to_end <= TTYOUTQ_DATASIZE)
248 to->to_end = 0;
249 else
250 to->to_end -= TTYOUTQ_DATASIZE;
251
252 /* Temporary unlock and copy the data to userspace. */
253 tty_unlock(tp);
254 error = uiomove(tob->tob_data + cbegin, clen, uio);
255 tty_lock(tp);
256
257 /* Block can now be readded to the list. */
258 TTYOUTQ_RECYCLE(to, tob);
259 } else {
260 char ob[TTYOUTQ_DATASIZE - 1];
261 atomic_add_long(&ttyoutq_nslow, 1);
262
263 /*
264 * Slow path: store data in a temporary buffer.
265 */
266 memcpy(ob, tob->tob_data + cbegin, clen);
267 to->to_begin += clen;
268 MPASS(to->to_begin < TTYOUTQ_DATASIZE);
269
270 /* Temporary unlock and copy the data to userspace. */
271 tty_unlock(tp);
272 error = uiomove(ob, clen, uio);
273 tty_lock(tp);
274 }
275
276 if (error != 0)
277 return (error);
278 }
279
280 return (0);
281 }
282
283 size_t
284 ttyoutq_write(struct ttyoutq *to, const void *buf, size_t nbytes)
285 {
286 const char *cbuf = buf;
287 struct ttyoutq_block *tob;
288 unsigned int boff;
289 size_t l;
290
291 while (nbytes > 0) {
292 boff = to->to_end % TTYOUTQ_DATASIZE;
293
294 if (to->to_end == 0) {
295 /* First time we're being used or drained. */
296 MPASS(to->to_begin == 0);
297 tob = to->to_firstblock;
298 if (tob == NULL) {
299 /* Queue has no blocks. */
300 break;
301 }
302 to->to_lastblock = tob;
303 } else if (boff == 0) {
304 /* We reached the end of this block on last write. */
305 tob = to->to_lastblock->tob_next;
306 if (tob == NULL) {
307 /* We've reached the watermark. */
308 break;
309 }
310 to->to_lastblock = tob;
311 } else {
312 tob = to->to_lastblock;
313 }
314
315 /* Don't copy more than was requested. */
316 l = MIN(nbytes, TTYOUTQ_DATASIZE - boff);
317 MPASS(l > 0);
318 memcpy(tob->tob_data + boff, cbuf, l);
319
320 cbuf += l;
321 nbytes -= l;
322 to->to_end += l;
323 }
324
325 return (cbuf - (const char *)buf);
326 }
327
328 int
329 ttyoutq_write_nofrag(struct ttyoutq *to, const void *buf, size_t nbytes)
330 {
331 size_t ret;
332
333 if (ttyoutq_bytesleft(to) < nbytes)
334 return (-1);
335
336 /* We should always be able to write it back. */
337 ret = ttyoutq_write(to, buf, nbytes);
338 MPASS(ret == nbytes);
339
340 return (0);
341 }
342
343 static void
344 ttyoutq_startup(void *dummy)
345 {
346
347 ttyoutq_zone = uma_zcreate("ttyoutq", sizeof(struct ttyoutq_block),
348 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
349 }
350
351 SYSINIT(ttyoutq, SI_SUB_DRIVERS, SI_ORDER_FIRST, ttyoutq_startup, NULL);
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