xref: /openbmc/linux/arch/um/os-Linux/sigio.c (revision c3d5f267)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Copyright (C) 2002 - 2008 Jeff Dike (jdike@{addtoit,linux.intel}.com)
4  */
5 
6 #include <unistd.h>
7 #include <errno.h>
8 #include <fcntl.h>
9 #include <poll.h>
10 #include <pty.h>
11 #include <sched.h>
12 #include <signal.h>
13 #include <string.h>
14 #include <kern_util.h>
15 #include <init.h>
16 #include <os.h>
17 #include <sigio.h>
18 #include <um_malloc.h>
19 
20 /*
21  * Protected by sigio_lock(), also used by sigio_cleanup, which is an
22  * exitcall.
23  */
24 static int write_sigio_pid = -1;
25 static unsigned long write_sigio_stack;
26 
27 /*
28  * These arrays are initialized before the sigio thread is started, and
29  * the descriptors closed after it is killed.  So, it can't see them change.
30  * On the UML side, they are changed under the sigio_lock.
31  */
32 #define SIGIO_FDS_INIT {-1, -1}
33 
34 static int write_sigio_fds[2] = SIGIO_FDS_INIT;
35 static int sigio_private[2] = SIGIO_FDS_INIT;
36 
37 struct pollfds {
38 	struct pollfd *poll;
39 	int size;
40 	int used;
41 };
42 
43 /*
44  * Protected by sigio_lock().  Used by the sigio thread, but the UML thread
45  * synchronizes with it.
46  */
47 static struct pollfds current_poll;
48 static struct pollfds next_poll;
49 static struct pollfds all_sigio_fds;
50 
write_sigio_thread(void * unused)51 static int write_sigio_thread(void *unused)
52 {
53 	struct pollfds *fds, tmp;
54 	struct pollfd *p;
55 	int i, n, respond_fd;
56 	char c;
57 
58 	os_fix_helper_signals();
59 	fds = &current_poll;
60 	while (1) {
61 		n = poll(fds->poll, fds->used, -1);
62 		if (n < 0) {
63 			if (errno == EINTR)
64 				continue;
65 			printk(UM_KERN_ERR "write_sigio_thread : poll returned "
66 			       "%d, errno = %d\n", n, errno);
67 		}
68 		for (i = 0; i < fds->used; i++) {
69 			p = &fds->poll[i];
70 			if (p->revents == 0)
71 				continue;
72 			if (p->fd == sigio_private[1]) {
73 				CATCH_EINTR(n = read(sigio_private[1], &c,
74 						     sizeof(c)));
75 				if (n != sizeof(c))
76 					printk(UM_KERN_ERR
77 					       "write_sigio_thread : "
78 					       "read on socket failed, "
79 					       "err = %d\n", errno);
80 				tmp = current_poll;
81 				current_poll = next_poll;
82 				next_poll = tmp;
83 				respond_fd = sigio_private[1];
84 			}
85 			else {
86 				respond_fd = write_sigio_fds[1];
87 				fds->used--;
88 				memmove(&fds->poll[i], &fds->poll[i + 1],
89 					(fds->used - i) * sizeof(*fds->poll));
90 			}
91 
92 			CATCH_EINTR(n = write(respond_fd, &c, sizeof(c)));
93 			if (n != sizeof(c))
94 				printk(UM_KERN_ERR "write_sigio_thread : "
95 				       "write on socket failed, err = %d\n",
96 				       errno);
97 		}
98 	}
99 
100 	return 0;
101 }
102 
need_poll(struct pollfds * polls,int n)103 static int need_poll(struct pollfds *polls, int n)
104 {
105 	struct pollfd *new;
106 
107 	if (n <= polls->size)
108 		return 0;
109 
110 	new = uml_kmalloc(n * sizeof(struct pollfd), UM_GFP_ATOMIC);
111 	if (new == NULL) {
112 		printk(UM_KERN_ERR "need_poll : failed to allocate new "
113 		       "pollfds\n");
114 		return -ENOMEM;
115 	}
116 
117 	memcpy(new, polls->poll, polls->used * sizeof(struct pollfd));
118 	kfree(polls->poll);
119 
120 	polls->poll = new;
121 	polls->size = n;
122 	return 0;
123 }
124 
125 /*
126  * Must be called with sigio_lock held, because it's needed by the marked
127  * critical section.
128  */
update_thread(void)129 static void update_thread(void)
130 {
131 	unsigned long flags;
132 	int n;
133 	char c;
134 
135 	flags = um_set_signals_trace(0);
136 	CATCH_EINTR(n = write(sigio_private[0], &c, sizeof(c)));
137 	if (n != sizeof(c)) {
138 		printk(UM_KERN_ERR "update_thread : write failed, err = %d\n",
139 		       errno);
140 		goto fail;
141 	}
142 
143 	CATCH_EINTR(n = read(sigio_private[0], &c, sizeof(c)));
144 	if (n != sizeof(c)) {
145 		printk(UM_KERN_ERR "update_thread : read failed, err = %d\n",
146 		       errno);
147 		goto fail;
148 	}
149 
150 	um_set_signals_trace(flags);
151 	return;
152  fail:
153 	/* Critical section start */
154 	if (write_sigio_pid != -1) {
155 		os_kill_process(write_sigio_pid, 1);
156 		free_stack(write_sigio_stack, 0);
157 	}
158 	write_sigio_pid = -1;
159 	close(sigio_private[0]);
160 	close(sigio_private[1]);
161 	close(write_sigio_fds[0]);
162 	close(write_sigio_fds[1]);
163 	/* Critical section end */
164 	um_set_signals_trace(flags);
165 }
166 
__add_sigio_fd(int fd)167 int __add_sigio_fd(int fd)
168 {
169 	struct pollfd *p;
170 	int err, i, n;
171 
172 	for (i = 0; i < all_sigio_fds.used; i++) {
173 		if (all_sigio_fds.poll[i].fd == fd)
174 			break;
175 	}
176 	if (i == all_sigio_fds.used)
177 		return -ENOSPC;
178 
179 	p = &all_sigio_fds.poll[i];
180 
181 	for (i = 0; i < current_poll.used; i++) {
182 		if (current_poll.poll[i].fd == fd)
183 			return 0;
184 	}
185 
186 	n = current_poll.used;
187 	err = need_poll(&next_poll, n + 1);
188 	if (err)
189 		return err;
190 
191 	memcpy(next_poll.poll, current_poll.poll,
192 	       current_poll.used * sizeof(struct pollfd));
193 	next_poll.poll[n] = *p;
194 	next_poll.used = n + 1;
195 	update_thread();
196 
197 	return 0;
198 }
199 
200 
add_sigio_fd(int fd)201 int add_sigio_fd(int fd)
202 {
203 	int err;
204 
205 	sigio_lock();
206 	err = __add_sigio_fd(fd);
207 	sigio_unlock();
208 
209 	return err;
210 }
211 
__ignore_sigio_fd(int fd)212 int __ignore_sigio_fd(int fd)
213 {
214 	struct pollfd *p;
215 	int err, i, n = 0;
216 
217 	/*
218 	 * This is called from exitcalls elsewhere in UML - if
219 	 * sigio_cleanup has already run, then update_thread will hang
220 	 * or fail because the thread is no longer running.
221 	 */
222 	if (write_sigio_pid == -1)
223 		return -EIO;
224 
225 	for (i = 0; i < current_poll.used; i++) {
226 		if (current_poll.poll[i].fd == fd)
227 			break;
228 	}
229 	if (i == current_poll.used)
230 		return -ENOENT;
231 
232 	err = need_poll(&next_poll, current_poll.used - 1);
233 	if (err)
234 		return err;
235 
236 	for (i = 0; i < current_poll.used; i++) {
237 		p = &current_poll.poll[i];
238 		if (p->fd != fd)
239 			next_poll.poll[n++] = *p;
240 	}
241 	next_poll.used = current_poll.used - 1;
242 
243 	update_thread();
244 
245 	return 0;
246 }
247 
ignore_sigio_fd(int fd)248 int ignore_sigio_fd(int fd)
249 {
250 	int err;
251 
252 	sigio_lock();
253 	err = __ignore_sigio_fd(fd);
254 	sigio_unlock();
255 
256 	return err;
257 }
258 
setup_initial_poll(int fd)259 static struct pollfd *setup_initial_poll(int fd)
260 {
261 	struct pollfd *p;
262 
263 	p = uml_kmalloc(sizeof(struct pollfd), UM_GFP_KERNEL);
264 	if (p == NULL) {
265 		printk(UM_KERN_ERR "setup_initial_poll : failed to allocate "
266 		       "poll\n");
267 		return NULL;
268 	}
269 	*p = ((struct pollfd) { .fd		= fd,
270 				.events 	= POLLIN,
271 				.revents 	= 0 });
272 	return p;
273 }
274 
write_sigio_workaround(void)275 static void write_sigio_workaround(void)
276 {
277 	struct pollfd *p;
278 	int err;
279 	int l_write_sigio_fds[2];
280 	int l_sigio_private[2];
281 	int l_write_sigio_pid;
282 
283 	/* We call this *tons* of times - and most ones we must just fail. */
284 	sigio_lock();
285 	l_write_sigio_pid = write_sigio_pid;
286 	sigio_unlock();
287 
288 	if (l_write_sigio_pid != -1)
289 		return;
290 
291 	err = os_pipe(l_write_sigio_fds, 1, 1);
292 	if (err < 0) {
293 		printk(UM_KERN_ERR "write_sigio_workaround - os_pipe 1 failed, "
294 		       "err = %d\n", -err);
295 		return;
296 	}
297 	err = os_pipe(l_sigio_private, 1, 1);
298 	if (err < 0) {
299 		printk(UM_KERN_ERR "write_sigio_workaround - os_pipe 2 failed, "
300 		       "err = %d\n", -err);
301 		goto out_close1;
302 	}
303 
304 	p = setup_initial_poll(l_sigio_private[1]);
305 	if (!p)
306 		goto out_close2;
307 
308 	sigio_lock();
309 
310 	/*
311 	 * Did we race? Don't try to optimize this, please, it's not so likely
312 	 * to happen, and no more than once at the boot.
313 	 */
314 	if (write_sigio_pid != -1)
315 		goto out_free;
316 
317 	current_poll = ((struct pollfds) { .poll 	= p,
318 					   .used 	= 1,
319 					   .size 	= 1 });
320 
321 	if (write_sigio_irq(l_write_sigio_fds[0]))
322 		goto out_clear_poll;
323 
324 	memcpy(write_sigio_fds, l_write_sigio_fds, sizeof(l_write_sigio_fds));
325 	memcpy(sigio_private, l_sigio_private, sizeof(l_sigio_private));
326 
327 	write_sigio_pid = run_helper_thread(write_sigio_thread, NULL,
328 					    CLONE_FILES | CLONE_VM,
329 					    &write_sigio_stack);
330 
331 	if (write_sigio_pid < 0)
332 		goto out_clear;
333 
334 	sigio_unlock();
335 	return;
336 
337 out_clear:
338 	write_sigio_pid = -1;
339 	write_sigio_fds[0] = -1;
340 	write_sigio_fds[1] = -1;
341 	sigio_private[0] = -1;
342 	sigio_private[1] = -1;
343 out_clear_poll:
344 	current_poll = ((struct pollfds) { .poll	= NULL,
345 					   .size	= 0,
346 					   .used	= 0 });
347 out_free:
348 	sigio_unlock();
349 	kfree(p);
350 out_close2:
351 	close(l_sigio_private[0]);
352 	close(l_sigio_private[1]);
353 out_close1:
354 	close(l_write_sigio_fds[0]);
355 	close(l_write_sigio_fds[1]);
356 }
357 
sigio_broken(int fd)358 void sigio_broken(int fd)
359 {
360 	int err;
361 
362 	write_sigio_workaround();
363 
364 	sigio_lock();
365 	err = need_poll(&all_sigio_fds, all_sigio_fds.used + 1);
366 	if (err) {
367 		printk(UM_KERN_ERR "maybe_sigio_broken - failed to add pollfd "
368 		       "for descriptor %d\n", fd);
369 		goto out;
370 	}
371 
372 	all_sigio_fds.poll[all_sigio_fds.used++] =
373 		((struct pollfd) { .fd  	= fd,
374 				   .events 	= POLLIN,
375 				   .revents 	= 0 });
376 out:
377 	sigio_unlock();
378 }
379 
380 /* Changed during early boot */
381 static int pty_output_sigio;
382 
maybe_sigio_broken(int fd)383 void maybe_sigio_broken(int fd)
384 {
385 	if (!isatty(fd))
386 		return;
387 
388 	if (pty_output_sigio)
389 		return;
390 
391 	sigio_broken(fd);
392 }
393 
sigio_cleanup(void)394 static void sigio_cleanup(void)
395 {
396 	if (write_sigio_pid == -1)
397 		return;
398 
399 	os_kill_process(write_sigio_pid, 1);
400 	free_stack(write_sigio_stack, 0);
401 	write_sigio_pid = -1;
402 }
403 
404 __uml_exitcall(sigio_cleanup);
405 
406 /* Used as a flag during SIGIO testing early in boot */
407 static int got_sigio;
408 
handler(int sig)409 static void __init handler(int sig)
410 {
411 	got_sigio = 1;
412 }
413 
414 struct openpty_arg {
415 	int master;
416 	int slave;
417 	int err;
418 };
419 
openpty_cb(void * arg)420 static void openpty_cb(void *arg)
421 {
422 	struct openpty_arg *info = arg;
423 
424 	info->err = 0;
425 	if (openpty(&info->master, &info->slave, NULL, NULL, NULL))
426 		info->err = -errno;
427 }
428 
async_pty(int master,int slave)429 static int async_pty(int master, int slave)
430 {
431 	int flags;
432 
433 	flags = fcntl(master, F_GETFL);
434 	if (flags < 0)
435 		return -errno;
436 
437 	if ((fcntl(master, F_SETFL, flags | O_NONBLOCK | O_ASYNC) < 0) ||
438 	    (fcntl(master, F_SETOWN, os_getpid()) < 0))
439 		return -errno;
440 
441 	if ((fcntl(slave, F_SETFL, flags | O_NONBLOCK) < 0))
442 		return -errno;
443 
444 	return 0;
445 }
446 
check_one_sigio(void (* proc)(int,int))447 static void __init check_one_sigio(void (*proc)(int, int))
448 {
449 	struct sigaction old, new;
450 	struct openpty_arg pty = { .master = -1, .slave = -1 };
451 	int master, slave, err;
452 
453 	initial_thread_cb(openpty_cb, &pty);
454 	if (pty.err) {
455 		printk(UM_KERN_ERR "check_one_sigio failed, errno = %d\n",
456 		       -pty.err);
457 		return;
458 	}
459 
460 	master = pty.master;
461 	slave = pty.slave;
462 
463 	if ((master == -1) || (slave == -1)) {
464 		printk(UM_KERN_ERR "check_one_sigio failed to allocate a "
465 		       "pty\n");
466 		return;
467 	}
468 
469 	/* Not now, but complain so we now where we failed. */
470 	err = raw(master);
471 	if (err < 0) {
472 		printk(UM_KERN_ERR "check_one_sigio : raw failed, errno = %d\n",
473 		      -err);
474 		return;
475 	}
476 
477 	err = async_pty(master, slave);
478 	if (err < 0) {
479 		printk(UM_KERN_ERR "check_one_sigio : sigio_async failed, "
480 		       "err = %d\n", -err);
481 		return;
482 	}
483 
484 	if (sigaction(SIGIO, NULL, &old) < 0) {
485 		printk(UM_KERN_ERR "check_one_sigio : sigaction 1 failed, "
486 		       "errno = %d\n", errno);
487 		return;
488 	}
489 
490 	new = old;
491 	new.sa_handler = handler;
492 	if (sigaction(SIGIO, &new, NULL) < 0) {
493 		printk(UM_KERN_ERR "check_one_sigio : sigaction 2 failed, "
494 		       "errno = %d\n", errno);
495 		return;
496 	}
497 
498 	got_sigio = 0;
499 	(*proc)(master, slave);
500 
501 	close(master);
502 	close(slave);
503 
504 	if (sigaction(SIGIO, &old, NULL) < 0)
505 		printk(UM_KERN_ERR "check_one_sigio : sigaction 3 failed, "
506 		       "errno = %d\n", errno);
507 }
508 
tty_output(int master,int slave)509 static void tty_output(int master, int slave)
510 {
511 	int n;
512 	char buf[512];
513 
514 	printk(UM_KERN_INFO "Checking that host ptys support output SIGIO...");
515 
516 	memset(buf, 0, sizeof(buf));
517 
518 	while (write(master, buf, sizeof(buf)) > 0) ;
519 	if (errno != EAGAIN)
520 		printk(UM_KERN_ERR "tty_output : write failed, errno = %d\n",
521 		       errno);
522 	while (((n = read(slave, buf, sizeof(buf))) > 0) &&
523 	       !({ barrier(); got_sigio; }))
524 		;
525 
526 	if (got_sigio) {
527 		printk(UM_KERN_CONT "Yes\n");
528 		pty_output_sigio = 1;
529 	} else if (n == -EAGAIN)
530 		printk(UM_KERN_CONT "No, enabling workaround\n");
531 	else
532 		printk(UM_KERN_CONT "tty_output : read failed, err = %d\n", n);
533 }
534 
check_sigio(void)535 static void __init check_sigio(void)
536 {
537 	if ((access("/dev/ptmx", R_OK) < 0) &&
538 	    (access("/dev/ptyp0", R_OK) < 0)) {
539 		printk(UM_KERN_WARNING "No pseudo-terminals available - "
540 		       "skipping pty SIGIO check\n");
541 		return;
542 	}
543 	check_one_sigio(tty_output);
544 }
545 
546 /* Here because it only does the SIGIO testing for now */
os_check_bugs(void)547 void __init os_check_bugs(void)
548 {
549 	check_sigio();
550 }
551