linux/arch/um/kernel/sigio_user.c

/*
 * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
 * Licensed under the GPL
 */

#include <unistd.h>
#include <stdlib.h>
#include <termios.h>
#include <pty.h>
#include <signal.h>
#include <errno.h>
#include <string.h>
#include <sched.h>
#include <sys/socket.h>
#include <sys/poll.h>
#include "init.h"
#include "user.h"
#include "kern_util.h"
#include "user_util.h"
#include "sigio.h"
#include "os.h"

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

/* 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.
 */
static int write_sigio_fds[2] = { -1, -1 };
static int sigio_private[2] = { -1, -1 };

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.
 */
struct pollfds current_poll = {
	.poll  		= NULL,
	.size 		= 0,
	.used 		= 0
};

struct pollfds next_poll = {
	.poll  		= NULL,
	.size 		= 0,
	.used 		= 0
};

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("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]){
				n = os_read_file(sigio_private[1], &c, sizeof(c));
				if(n != sizeof(c))
					printk("write_sigio_thread : "
					       "read failed, err = %d\n", -n);
				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));
			}

			n = os_write_file(respond_fd, &c, sizeof(c));
			if(n != sizeof(c))
				printk("write_sigio_thread : write failed, "
				       "err = %d\n", -n);
		}
	}

	return 0;
}

static int need_poll(int n)
{
	if(n <= next_poll.size){
		next_poll.used = n;
		return(0);
	}
	kfree(next_poll.poll);
	next_poll.poll = um_kmalloc_atomic(n * sizeof(struct pollfd));
	if(next_poll.poll == NULL){
		printk("need_poll : failed to allocate new pollfds\n");
		next_poll.size = 0;
		next_poll.used = 0;
		return(-1);
	}
	next_poll.size = n;
	next_poll.used = 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);
	n = os_write_file(sigio_private[0], &c, sizeof(c));
	if(n != sizeof(c)){
		printk("update_thread : write failed, err = %d\n", -n);
		goto fail;
	}

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

	set_signals(flags);
	return;
 fail:
	/* Critical section start */
	if(write_sigio_pid != -1) 
		os_kill_process(write_sigio_pid, 1);
	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, int read)
{
	int err = 0, i, n, events;

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

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

	for(i = 0; i < current_poll.used; i++)
		next_poll.poll[i] = current_poll.poll[i];

	if(read) events = POLLIN;
	else events = POLLOUT;

	next_poll.poll[n - 1] = ((struct pollfd) { .fd  	= fd,
						   .events 	= events,
						   .revents 	= 0 });
	update_thread();
 out:
	sigio_unlock();
	return(err);
}

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

	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(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++] = current_poll.poll[i];
	}
	if(n == i){
		printk("ignore_sigio_fd : fd %d not found\n", fd);
		err = -1;
		goto out;
	}

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

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

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

void write_sigio_workaround(void)
{
	unsigned long stack;
	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("write_sigio_workaround - os_pipe 1 failed, "
		       "err = %d\n", -err);
		return;
	}
	err = os_pipe(l_sigio_private, 1, 1);
	if(err < 0){
		printk("write_sigio_workaround - os_pipe 1 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_unlock;

	write_sigio_pid = run_helper_thread(write_sigio_thread, NULL,
					    CLONE_FILES | CLONE_VM, &stack, 0);

	if (write_sigio_pid < 0)
		goto out_clear;

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

	/* Success, finally. */
	memcpy(write_sigio_fds, l_write_sigio_fds, sizeof(l_write_sigio_fds));
	memcpy(sigio_private, l_sigio_private, sizeof(l_sigio_private));

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

	sigio_unlock();
	return;

 out_kill:
	l_write_sigio_pid = write_sigio_pid;
	write_sigio_pid = -1;
	sigio_unlock();
	/* Going to call waitpid, avoid holding the lock. */
	os_kill_process(l_write_sigio_pid, 1);
	goto out_free;

 out_clear:
	write_sigio_pid = -1;
 out_unlock:
	sigio_unlock();
 out_free:
	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]);
	return;
}

void sigio_cleanup(void)
{
	if (write_sigio_pid != -1) {
		os_kill_process(write_sigio_pid, 1);
		write_sigio_pid = -1;
	}
}