arch/um/os-Linux/sigio.c - kernel/msm - Gitiles

 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Licensed under the GPL
  */

 #include <unistd.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <poll.h>
 #include <pty.h>
 #include <sched.h>
 #include <signal.h>
 #include <string.h>
 #include "kern_constants.h"
 #include "kern_util.h"
 #include "init.h"
 #include "os.h"
 #include "sigio.h"
 #include "um_malloc.h"
 #include "user.h"

 /*
  * Protected by sigio_lock(), also used by sigio_cleanup, which is an
  * exitcall.
  */
 static int write_sigio_pid = -1;
 static unsigned long write_sigio_stack;

 /*
  * These arrays are initialized before the sigio thread is started, and
  * the descriptors closed after it is killed.  So, it can't see them change.
  * On the UML side, they are changed under the sigio_lock.
  */
 #define SIGIO_FDS_INIT {-1, -1}

 static int write_sigio_fds[2] = SIGIO_FDS_INIT;
 static int sigio_private[2] = SIGIO_FDS_INIT;

 struct pollfds {
 	struct pollfd *poll;
 	int size;
 	int used;
 };

 /*
  * Protected by sigio_lock().  Used by the sigio thread, but the UML thread
  * synchronizes with it.
  */
 static struct pollfds current_poll;
 static struct pollfds next_poll;
 static struct pollfds all_sigio_fds;

 static int write_sigio_thread(void *unused)
 {
 	struct pollfds *fds, tmp;
 	struct pollfd *p;
 	int i, n, respond_fd;
 	char c;

 	signal(SIGWINCH, SIG_IGN);
 	fds = &current_poll;
 	while (1) {
 		n = poll(fds->poll, fds->used, -1);
 		if (n < 0) {
 			if (errno == EINTR)
 				continue;
 			printk(UM_KERN_ERR "write_sigio_thread : poll returned "
 			       "%d, errno = %d\n", n, errno);
 		}
 		for (i = 0; i < fds->used; i++) {
 			p = &fds->poll[i];
 			if (p->revents == 0)
 				continue;
 			if (p->fd == sigio_private[1]) {
 				CATCH_EINTR(n = read(sigio_private[1], &c,
 						     sizeof(c)));
 				if (n != sizeof(c))
 					printk(UM_KERN_ERR
 					       "write_sigio_thread : "
 					       "read on socket failed, "
 					       "err = %d\n", errno);
 				tmp = current_poll;
 				current_poll = next_poll;
 				next_poll = tmp;
 				respond_fd = sigio_private[1];
 			}
 			else {
 				respond_fd = write_sigio_fds[1];
 				fds->used--;
 				memmove(&fds->poll[i], &fds->poll[i + 1],
 					(fds->used - i) * sizeof(*fds->poll));
 			}

 			CATCH_EINTR(n = write(respond_fd, &c, sizeof(c)));
 			if (n != sizeof(c))
 				printk(UM_KERN_ERR "write_sigio_thread : "
 				       "write on socket failed, err = %d\n",
 				       errno);
 		}
 	}

 	return 0;
 }

 static int need_poll(struct pollfds *polls, int n)
 {
 	struct pollfd *new;

 	if (n <= polls->size)
 		return 0;

 	new = kmalloc(n * sizeof(struct pollfd), UM_GFP_ATOMIC);
 	if (new == NULL) {
 		printk(UM_KERN_ERR "need_poll : failed to allocate new "
 		       "pollfds\n");
 		return -ENOMEM;
 	}

 	memcpy(new, polls->poll, polls->used * sizeof(struct pollfd));
 	kfree(polls->poll);

 	polls->poll = new;
 	polls->size = n;
 	return 0;
 }

 /*
  * Must be called with sigio_lock held, because it's needed by the marked
  * critical section.
  */
 static void update_thread(void)
 {
 	unsigned long flags;
 	int n;
 	char c;

 	flags = set_signals(0);
 	CATCH_EINTR(n = write(sigio_private[0], &c, sizeof(c)));
 	if (n != sizeof(c)) {
 		printk(UM_KERN_ERR "update_thread : write failed, err = %d\n",
 		       errno);
 		goto fail;
 	}

 	CATCH_EINTR(n = read(sigio_private[0], &c, sizeof(c)));
 	if (n != sizeof(c)) {
 		printk(UM_KERN_ERR "update_thread : read failed, err = %d\n",
 		       errno);
 		goto fail;
 	}

 	set_signals(flags);
 	return;
  fail:
 	/* Critical section start */
 	if (write_sigio_pid != -1) {
 		os_kill_process(write_sigio_pid, 1);
 		free_stack(write_sigio_stack, 0);
 	}
 	write_sigio_pid = -1;
 	close(sigio_private[0]);
 	close(sigio_private[1]);
 	close(write_sigio_fds[0]);
 	close(write_sigio_fds[1]);
 	/* Critical section end */
 	set_signals(flags);
 }

 int add_sigio_fd(int fd)
 {
 	struct pollfd *p;
 	int err = 0, i, n;

 	sigio_lock();
 	for (i = 0; i < all_sigio_fds.used; i++) {
 		if (all_sigio_fds.poll[i].fd == fd)
 			break;
 	}
 	if (i == all_sigio_fds.used)
 		goto out;

 	p = &all_sigio_fds.poll[i];

 	for (i = 0; i < current_poll.used; i++) {
 		if (current_poll.poll[i].fd == fd)
 			goto out;
 	}

 	n = current_poll.used;
 	err = need_poll(&next_poll, n + 1);
 	if (err)
 		goto out;

 	memcpy(next_poll.poll, current_poll.poll,
 	       current_poll.used * sizeof(struct pollfd));
 	next_poll.poll[n] = *p;
 	next_poll.used = n + 1;
 	update_thread();
  out:
 	sigio_unlock();
 	return err;
 }

 int ignore_sigio_fd(int fd)
 {
 	struct pollfd *p;
 	int err = 0, i, n = 0;

 	/*
 	 * This is called from exitcalls elsewhere in UML - if
 	 * sigio_cleanup has already run, then update_thread will hang
 	 * or fail because the thread is no longer running.
 	 */
 	if (write_sigio_pid == -1)
 		return -EIO;

 	sigio_lock();
 	for (i = 0; i < current_poll.used; i++) {
 		if (current_poll.poll[i].fd == fd)
 			break;
 	}
 	if (i == current_poll.used)
 		goto out;

 	err = need_poll(&next_poll, current_poll.used - 1);
 	if (err)
 		goto out;

 	for (i = 0; i < current_poll.used; i++) {
 		p = &current_poll.poll[i];
 		if (p->fd != fd)
 			next_poll.poll[n++] = *p;
 	}
 	next_poll.used = current_poll.used - 1;

 	update_thread();
  out:
 	sigio_unlock();
 	return err;
 }

 static struct pollfd *setup_initial_poll(int fd)
 {
 	struct pollfd *p;

 	p = kmalloc(sizeof(struct pollfd), UM_GFP_KERNEL);
 	if (p == NULL) {
 		printk(UM_KERN_ERR "setup_initial_poll : failed to allocate "
 		       "poll\n");
 		return NULL;
 	}
 	*p = ((struct pollfd) { .fd		= fd,
 				.events 	= POLLIN,
 				.revents 	= 0 });
 	return p;
 }

 static void write_sigio_workaround(void)
 {
 	struct pollfd *p;
 	int err;
 	int l_write_sigio_fds[2];
 	int l_sigio_private[2];
 	int l_write_sigio_pid;

 	/* We call this *tons* of times - and most ones we must just fail. */
 	sigio_lock();
 	l_write_sigio_pid = write_sigio_pid;
 	sigio_unlock();

 	if (l_write_sigio_pid != -1)
 		return;

 	err = os_pipe(l_write_sigio_fds, 1, 1);
 	if (err < 0) {
 		printk(UM_KERN_ERR "write_sigio_workaround - os_pipe 1 failed, "
 		       "err = %d\n", -err);
 		return;
 	}
 	err = os_pipe(l_sigio_private, 1, 1);
 	if (err < 0) {
 		printk(UM_KERN_ERR "write_sigio_workaround - os_pipe 2 failed, "
 		       "err = %d\n", -err);
 		goto out_close1;
 	}

 	p = setup_initial_poll(l_sigio_private[1]);
 	if (!p)
 		goto out_close2;

 	sigio_lock();

 	/*
 	 * Did we race? Don't try to optimize this, please, it's not so likely
 	 * to happen, and no more than once at the boot.
 	 */
 	if (write_sigio_pid != -1)
 		goto out_free;

 	current_poll = ((struct pollfds) { .poll 	= p,
 					   .used 	= 1,
 					   .size 	= 1 });

 	if (write_sigio_irq(l_write_sigio_fds[0]))
 		goto out_clear_poll;

 	memcpy(write_sigio_fds, l_write_sigio_fds, sizeof(l_write_sigio_fds));
 	memcpy(sigio_private, l_sigio_private, sizeof(l_sigio_private));

 	write_sigio_pid = run_helper_thread(write_sigio_thread, NULL,
 					    CLONE_FILES | CLONE_VM,
 					    &write_sigio_stack);

 	if (write_sigio_pid < 0)
 		goto out_clear;

 	sigio_unlock();
 	return;

 out_clear:
 	write_sigio_pid = -1;
 	write_sigio_fds[0] = -1;
 	write_sigio_fds[1] = -1;
 	sigio_private[0] = -1;
 	sigio_private[1] = -1;
 out_clear_poll:
 	current_poll = ((struct pollfds) { .poll	= NULL,
 					   .size	= 0,
 					   .used	= 0 });
 out_free:
 	sigio_unlock();
 	kfree(p);
 out_close2:
 	close(l_sigio_private[0]);
 	close(l_sigio_private[1]);
 out_close1:
 	close(l_write_sigio_fds[0]);
 	close(l_write_sigio_fds[1]);
 }

 /* Changed during early boot */
 static int pty_output_sigio = 0;
 static int pty_close_sigio = 0;

 void maybe_sigio_broken(int fd, int read)
 {
 	int err;

 	if (!isatty(fd))
 		return;

 	if ((read || pty_output_sigio) && (!read || pty_close_sigio))
 		return;

 	write_sigio_workaround();

 	sigio_lock();
 	err = need_poll(&all_sigio_fds, all_sigio_fds.used + 1);
 	if (err) {
 		printk(UM_KERN_ERR "maybe_sigio_broken - failed to add pollfd "
 		       "for descriptor %d\n", fd);
 		goto out;
 	}

 	all_sigio_fds.poll[all_sigio_fds.used++] =
 		((struct pollfd) { .fd  	= fd,
 				   .events 	= read ? POLLIN : POLLOUT,
 				   .revents 	= 0 });
 out:
 	sigio_unlock();
 }

 static void sigio_cleanup(void)
 {
 	if (write_sigio_pid == -1)
 		return;

 	os_kill_process(write_sigio_pid, 1);
 	free_stack(write_sigio_stack, 0);
 	write_sigio_pid = -1;
 }

 __uml_exitcall(sigio_cleanup);

 /* Used as a flag during SIGIO testing early in boot */
 static volatile int got_sigio = 0;

 static void __init handler(int sig)
 {
 	got_sigio = 1;
 }

 struct openpty_arg {
 	int master;
 	int slave;
 	int err;
 };

 static void openpty_cb(void *arg)
 {
 	struct openpty_arg *info = arg;

 	info->err = 0;
 	if (openpty(&info->master, &info->slave, NULL, NULL, NULL))
 		info->err = -errno;
 }

 static int async_pty(int master, int slave)
 {
 	int flags;

 	flags = fcntl(master, F_GETFL);
 	if (flags < 0)
 		return -errno;

 	if ((fcntl(master, F_SETFL, flags | O_NONBLOCK | O_ASYNC) < 0) ||
 	    (fcntl(master, F_SETOWN, os_getpid()) < 0))
 		return -errno;

 	if ((fcntl(slave, F_SETFL, flags | O_NONBLOCK) < 0))
 		return -errno;

 	return 0;
 }

 static void __init check_one_sigio(void (*proc)(int, int))
 {
 	struct sigaction old, new;
 	struct openpty_arg pty = { .master = -1, .slave = -1 };
 	int master, slave, err;

 	initial_thread_cb(openpty_cb, &pty);
 	if (pty.err) {
 		printk(UM_KERN_ERR "check_one_sigio failed, errno = %d\n",
 		       -pty.err);
 		return;
 	}

 	master = pty.master;
 	slave = pty.slave;

 	if ((master == -1) || (slave == -1)) {
 		printk(UM_KERN_ERR "check_one_sigio failed to allocate a "
 		       "pty\n");
 		return;
 	}

 	/* Not now, but complain so we now where we failed. */
 	err = raw(master);
 	if (err < 0) {
 		printk(UM_KERN_ERR "check_one_sigio : raw failed, errno = %d\n",
 		      -err);
 		return;
 	}

 	err = async_pty(master, slave);
 	if (err < 0) {
 		printk(UM_KERN_ERR "check_one_sigio : sigio_async failed, "
 		       "err = %d\n", -err);
 		return;
 	}

 	if (sigaction(SIGIO, NULL, &old) < 0) {
 		printk(UM_KERN_ERR "check_one_sigio : sigaction 1 failed, "
 		       "errno = %d\n", errno);
 		return;
 	}

 	new = old;
 	new.sa_handler = handler;
 	if (sigaction(SIGIO, &new, NULL) < 0) {
 		printk(UM_KERN_ERR "check_one_sigio : sigaction 2 failed, "
 		       "errno = %d\n", errno);
 		return;
 	}

 	got_sigio = 0;
 	(*proc)(master, slave);

 	close(master);
 	close(slave);

 	if (sigaction(SIGIO, &old, NULL) < 0)
 		printk(UM_KERN_ERR "check_one_sigio : sigaction 3 failed, "
 		       "errno = %d\n", errno);
 }

 static void tty_output(int master, int slave)
 {
 	int n;
 	char buf[512];

 	printk(UM_KERN_INFO "Checking that host ptys support output SIGIO...");

 	memset(buf, 0, sizeof(buf));

 	while (write(master, buf, sizeof(buf)) > 0) ;
 	if (errno != EAGAIN)
 		printk(UM_KERN_ERR "tty_output : write failed, errno = %d\n",
 		       errno);
 	while (((n = read(slave, buf, sizeof(buf))) > 0) && !got_sigio)
 		;

 	if (got_sigio) {
 		printk(UM_KERN_CONT "Yes\n");
 		pty_output_sigio = 1;
 	} else if (n == -EAGAIN)
 		printk(UM_KERN_CONT "No, enabling workaround\n");
 	else
 		printk(UM_KERN_CONT "tty_output : read failed, err = %d\n", n);
 }

 static void tty_close(int master, int slave)
 {
 	printk(UM_KERN_INFO "Checking that host ptys support SIGIO on "
 	       "close...");

 	close(slave);
 	if (got_sigio) {
 		printk(UM_KERN_CONT "Yes\n");
 		pty_close_sigio = 1;
 	} else
 		printk(UM_KERN_CONT "No, enabling workaround\n");
 }

 void __init check_sigio(void)
 {
 	if ((access("/dev/ptmx", R_OK) < 0) &&
 	    (access("/dev/ptyp0", R_OK) < 0)) {
 		printk(UM_KERN_WARNING "No pseudo-terminals available - "
 		       "skipping pty SIGIO check\n");
 		return;
 	}
 	check_one_sigio(tty_output);
 	check_one_sigio(tty_close);
 }

 /* Here because it only does the SIGIO testing for now */
 void __init os_check_bugs(void)
 {
 	check_sigio();
 }
	/*
	* Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
	* Licensed under the GPL
	*/

	#include <unistd.h>
	#include <errno.h>
	#include <fcntl.h>
	#include <poll.h>
	#include <pty.h>
	#include <sched.h>
	#include <signal.h>
	#include <string.h>
	#include "kern_constants.h"
	#include "kern_util.h"
	#include "init.h"
	#include "os.h"
	#include "sigio.h"
	#include "um_malloc.h"
	#include "user.h"

	/*
	* Protected by sigio_lock(), also used by sigio_cleanup, which is an
	* exitcall.
	*/
	static int write_sigio_pid = -1;
	static unsigned long write_sigio_stack;

	/*
	* These arrays are initialized before the sigio thread is started, and
	* the descriptors closed after it is killed. So, it can't see them change.
	* On the UML side, they are changed under the sigio_lock.
	*/
	#define SIGIO_FDS_INIT {-1, -1}

	static int write_sigio_fds[2] = SIGIO_FDS_INIT;
	static int sigio_private[2] = SIGIO_FDS_INIT;

	struct pollfds {
	struct pollfd *poll;
	int size;
	int used;
	};

	/*
	* Protected by sigio_lock(). Used by the sigio thread, but the UML thread
	* synchronizes with it.
	*/
	static struct pollfds current_poll;
	static struct pollfds next_poll;
	static struct pollfds all_sigio_fds;

	static int write_sigio_thread(void *unused)
	{
	struct pollfds *fds, tmp;
	struct pollfd *p;
	int i, n, respond_fd;
	char c;

	signal(SIGWINCH, SIG_IGN);
	fds = &current_poll;
	while (1) {
	n = poll(fds->poll, fds->used, -1);
	if (n < 0) {
	if (errno == EINTR)
	continue;
	printk(UM_KERN_ERR "write_sigio_thread : poll returned "
	"%d, errno = %d\n", n, errno);
	}
	for (i = 0; i < fds->used; i++) {
	p = &fds->poll[i];
	if (p->revents == 0)
	continue;
	if (p->fd == sigio_private[1]) {
	CATCH_EINTR(n = read(sigio_private[1], &c,
	sizeof(c)));
	if (n != sizeof(c))
	printk(UM_KERN_ERR
	"write_sigio_thread : "
	"read on socket failed, "
	"err = %d\n", errno);
	tmp = current_poll;
	current_poll = next_poll;
	next_poll = tmp;
	respond_fd = sigio_private[1];
	}
	else {
	respond_fd = write_sigio_fds[1];
	fds->used--;
	memmove(&fds->poll[i], &fds->poll[i + 1],
	(fds->used - i) * sizeof(*fds->poll));
	}

	CATCH_EINTR(n = write(respond_fd, &c, sizeof(c)));
	if (n != sizeof(c))
	printk(UM_KERN_ERR "write_sigio_thread : "
	"write on socket failed, err = %d\n",
	errno);
	}
	}

	return 0;
	}

	static int need_poll(struct pollfds *polls, int n)
	{
	struct pollfd *new;

	if (n <= polls->size)
	return 0;

	new = kmalloc(n * sizeof(struct pollfd), UM_GFP_ATOMIC);
	if (new == NULL) {
	printk(UM_KERN_ERR "need_poll : failed to allocate new "
	"pollfds\n");
	return -ENOMEM;
	}

	memcpy(new, polls->poll, polls->used * sizeof(struct pollfd));
	kfree(polls->poll);

	polls->poll = new;
	polls->size = n;
	return 0;
	}

	/*
	* Must be called with sigio_lock held, because it's needed by the marked
	* critical section.
	*/
	static void update_thread(void)
	{
	unsigned long flags;
	int n;
	char c;

	flags = set_signals(0);
	CATCH_EINTR(n = write(sigio_private[0], &c, sizeof(c)));
	if (n != sizeof(c)) {
	printk(UM_KERN_ERR "update_thread : write failed, err = %d\n",
	errno);
	goto fail;
	}

	CATCH_EINTR(n = read(sigio_private[0], &c, sizeof(c)));
	if (n != sizeof(c)) {
	printk(UM_KERN_ERR "update_thread : read failed, err = %d\n",
	errno);
	goto fail;
	}

	set_signals(flags);
	return;
	fail:
	/* Critical section start */
	if (write_sigio_pid != -1) {
	os_kill_process(write_sigio_pid, 1);
	free_stack(write_sigio_stack, 0);
	}
	write_sigio_pid = -1;
	close(sigio_private[0]);
	close(sigio_private[1]);
	close(write_sigio_fds[0]);
	close(write_sigio_fds[1]);
	/* Critical section end */
	set_signals(flags);
	}

	int add_sigio_fd(int fd)
	{
	struct pollfd *p;
	int err = 0, i, n;

	sigio_lock();
	for (i = 0; i < all_sigio_fds.used; i++) {
	if (all_sigio_fds.poll[i].fd == fd)
	break;
	}
	if (i == all_sigio_fds.used)
	goto out;

	p = &all_sigio_fds.poll[i];

	for (i = 0; i < current_poll.used; i++) {
	if (current_poll.poll[i].fd == fd)
	goto out;
	}

	n = current_poll.used;
	err = need_poll(&next_poll, n + 1);
	if (err)
	goto out;

	memcpy(next_poll.poll, current_poll.poll,
	current_poll.used * sizeof(struct pollfd));
	next_poll.poll[n] = *p;
	next_poll.used = n + 1;
	update_thread();
	out:
	sigio_unlock();
	return err;
	}

	int ignore_sigio_fd(int fd)
	{
	struct pollfd *p;
	int err = 0, i, n = 0;

	/*
	* This is called from exitcalls elsewhere in UML - if
	* sigio_cleanup has already run, then update_thread will hang
	* or fail because the thread is no longer running.
	*/
	if (write_sigio_pid == -1)
	return -EIO;

	sigio_lock();
	for (i = 0; i < current_poll.used; i++) {
	if (current_poll.poll[i].fd == fd)
	break;
	}
	if (i == current_poll.used)
	goto out;

	err = need_poll(&next_poll, current_poll.used - 1);
	if (err)
	goto out;

	for (i = 0; i < current_poll.used; i++) {
	p = &current_poll.poll[i];
	if (p->fd != fd)
	next_poll.poll[n++] = *p;
	}
	next_poll.used = current_poll.used - 1;

	update_thread();
	out:
	sigio_unlock();
	return err;
	}

	static struct pollfd *setup_initial_poll(int fd)
	{
	struct pollfd *p;

	p = kmalloc(sizeof(struct pollfd), UM_GFP_KERNEL);
	if (p == NULL) {
	printk(UM_KERN_ERR "setup_initial_poll : failed to allocate "
	"poll\n");
	return NULL;
	}
	*p = ((struct pollfd) { .fd = fd,
	.events = POLLIN,
	.revents = 0 });
	return p;
	}

	static void write_sigio_workaround(void)
	{
	struct pollfd *p;
	int err;
	int l_write_sigio_fds[2];
	int l_sigio_private[2];
	int l_write_sigio_pid;

	/* We call this tons of times - and most ones we must just fail. */
	sigio_lock();
	l_write_sigio_pid = write_sigio_pid;
	sigio_unlock();

	if (l_write_sigio_pid != -1)
	return;

	err = os_pipe(l_write_sigio_fds, 1, 1);
	if (err < 0) {
	printk(UM_KERN_ERR "write_sigio_workaround - os_pipe 1 failed, "
	"err = %d\n", -err);
	return;
	}
	err = os_pipe(l_sigio_private, 1, 1);
	if (err < 0) {
	printk(UM_KERN_ERR "write_sigio_workaround - os_pipe 2 failed, "
	"err = %d\n", -err);
	goto out_close1;
	}

	p = setup_initial_poll(l_sigio_private[1]);
	if (!p)
	goto out_close2;

	sigio_lock();

	/*
	* Did we race? Don't try to optimize this, please, it's not so likely
	* to happen, and no more than once at the boot.
	*/
	if (write_sigio_pid != -1)
	goto out_free;

	current_poll = ((struct pollfds) { .poll = p,
	.used = 1,
	.size = 1 });

	if (write_sigio_irq(l_write_sigio_fds[0]))
	goto out_clear_poll;

	memcpy(write_sigio_fds, l_write_sigio_fds, sizeof(l_write_sigio_fds));
	memcpy(sigio_private, l_sigio_private, sizeof(l_sigio_private));

	write_sigio_pid = run_helper_thread(write_sigio_thread, NULL,
	CLONE_FILES \| CLONE_VM,
	&write_sigio_stack);

	if (write_sigio_pid < 0)
	goto out_clear;

	sigio_unlock();
	return;

	out_clear:
	write_sigio_pid = -1;
	write_sigio_fds[0] = -1;
	write_sigio_fds[1] = -1;
	sigio_private[0] = -1;
	sigio_private[1] = -1;
	out_clear_poll:
	current_poll = ((struct pollfds) { .poll = NULL,
	.size = 0,
	.used = 0 });
	out_free:
	sigio_unlock();
	kfree(p);
	out_close2:
	close(l_sigio_private[0]);
	close(l_sigio_private[1]);
	out_close1:
	close(l_write_sigio_fds[0]);
	close(l_write_sigio_fds[1]);
	}

	/* Changed during early boot */
	static int pty_output_sigio = 0;
	static int pty_close_sigio = 0;

	void maybe_sigio_broken(int fd, int read)
	{
	int err;

	if (!isatty(fd))
	return;

	if ((read \|\| pty_output_sigio) && (!read \|\| pty_close_sigio))
	return;

	write_sigio_workaround();

	sigio_lock();
	err = need_poll(&all_sigio_fds, all_sigio_fds.used + 1);
	if (err) {
	printk(UM_KERN_ERR "maybe_sigio_broken - failed to add pollfd "
	"for descriptor %d\n", fd);
	goto out;
	}

	all_sigio_fds.poll[all_sigio_fds.used++] =
	((struct pollfd) { .fd = fd,
	.events = read ? POLLIN : POLLOUT,
	.revents = 0 });
	out:
	sigio_unlock();
	}

	static void sigio_cleanup(void)
	{
	if (write_sigio_pid == -1)
	return;

	os_kill_process(write_sigio_pid, 1);
	free_stack(write_sigio_stack, 0);
	write_sigio_pid = -1;
	}

	__uml_exitcall(sigio_cleanup);

	/* Used as a flag during SIGIO testing early in boot */
	static volatile int got_sigio = 0;

	static void __init handler(int sig)
	{
	got_sigio = 1;
	}

	struct openpty_arg {
	int master;
	int slave;
	int err;
	};

	static void openpty_cb(void *arg)
	{
	struct openpty_arg *info = arg;

	info->err = 0;
	if (openpty(&info->master, &info->slave, NULL, NULL, NULL))
	info->err = -errno;
	}

	static int async_pty(int master, int slave)
	{
	int flags;

	flags = fcntl(master, F_GETFL);
	if (flags < 0)
	return -errno;

	if ((fcntl(master, F_SETFL, flags \| O_NONBLOCK \| O_ASYNC) < 0) \|\|
	(fcntl(master, F_SETOWN, os_getpid()) < 0))
	return -errno;

	if ((fcntl(slave, F_SETFL, flags \| O_NONBLOCK) < 0))
	return -errno;

	return 0;
	}

	static void __init check_one_sigio(void (*proc)(int, int))
	{
	struct sigaction old, new;
	struct openpty_arg pty = { .master = -1, .slave = -1 };
	int master, slave, err;

	initial_thread_cb(openpty_cb, &pty);
	if (pty.err) {
	printk(UM_KERN_ERR "check_one_sigio failed, errno = %d\n",
	-pty.err);
	return;
	}

	master = pty.master;
	slave = pty.slave;

	if ((master == -1) \|\| (slave == -1)) {
	printk(UM_KERN_ERR "check_one_sigio failed to allocate a "
	"pty\n");
	return;
	}

	/* Not now, but complain so we now where we failed. */
	err = raw(master);
	if (err < 0) {
	printk(UM_KERN_ERR "check_one_sigio : raw failed, errno = %d\n",
	-err);
	return;
	}

	err = async_pty(master, slave);
	if (err < 0) {
	printk(UM_KERN_ERR "check_one_sigio : sigio_async failed, "
	"err = %d\n", -err);
	return;
	}

	if (sigaction(SIGIO, NULL, &old) < 0) {
	printk(UM_KERN_ERR "check_one_sigio : sigaction 1 failed, "
	"errno = %d\n", errno);
	return;
	}

	new = old;
	new.sa_handler = handler;
	if (sigaction(SIGIO, &new, NULL) < 0) {
	printk(UM_KERN_ERR "check_one_sigio : sigaction 2 failed, "
	"errno = %d\n", errno);
	return;
	}

	got_sigio = 0;
	(*proc)(master, slave);

	close(master);
	close(slave);

	if (sigaction(SIGIO, &old, NULL) < 0)
	printk(UM_KERN_ERR "check_one_sigio : sigaction 3 failed, "
	"errno = %d\n", errno);
	}

	static void tty_output(int master, int slave)
	{
	int n;
	char buf[512];

	printk(UM_KERN_INFO "Checking that host ptys support output SIGIO...");

	memset(buf, 0, sizeof(buf));

	while (write(master, buf, sizeof(buf)) > 0) ;
	if (errno != EAGAIN)
	printk(UM_KERN_ERR "tty_output : write failed, errno = %d\n",
	errno);
	while (((n = read(slave, buf, sizeof(buf))) > 0) && !got_sigio)
	;

	if (got_sigio) {
	printk(UM_KERN_CONT "Yes\n");
	pty_output_sigio = 1;
	} else if (n == -EAGAIN)
	printk(UM_KERN_CONT "No, enabling workaround\n");
	else
	printk(UM_KERN_CONT "tty_output : read failed, err = %d\n", n);
	}

	static void tty_close(int master, int slave)
	{
	printk(UM_KERN_INFO "Checking that host ptys support SIGIO on "
	"close...");

	close(slave);
	if (got_sigio) {
	printk(UM_KERN_CONT "Yes\n");
	pty_close_sigio = 1;
	} else
	printk(UM_KERN_CONT "No, enabling workaround\n");
	}

	void __init check_sigio(void)
	{
	if ((access("/dev/ptmx", R_OK) < 0) &&
	(access("/dev/ptyp0", R_OK) < 0)) {
	printk(UM_KERN_WARNING "No pseudo-terminals available - "
	"skipping pty SIGIO check\n");
	return;
	}
	check_one_sigio(tty_output);
	check_one_sigio(tty_close);
	}

	/* Here because it only does the SIGIO testing for now */
	void __init os_check_bugs(void)
	{
	check_sigio();
	}