linux/arch/um/os-Linux/sigio.c

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/*
uml: random driver fixes The random driver would essentially hang if the host's /dev/random returned -EAGAIN. There was a test of need_resched followed by a schedule inside the loop, but that didn't help and it's the wrong way to work anyway. The right way is to ask for an interrupt when there is input available from the host and handle it then rather than polling. Now, when the host's /dev/random returns -EAGAIN, the driver asks for a wakeup when there's randomness available again and sleeps. The interrupt routine just wakes up whatever processes are sleeping on host_read_wait. There is an atomic_t, host_sleep_count, which counts the number of processes waiting for randomness. When this reaches zero, the interrupt is disabled. An added complication is that async I/O notification was only recently added to /dev/random (by me), so essentially all hosts will lack it. So, we use the sigio workaround here, which is to have a separate thread poll on the descriptor and send an interrupt when there is input on it. This mechanism is activated when a process gets -EAGAIN (activating this multiple times is harmless, if a bit wasteful) and deactivated by the last process still waiting. The module name was changed from "random" to "hw_random" in order for udev to recognize it. The sigio workaround needed some changes. sigio_broken was added for cases when we know that async notification doesn't work. This is now called from maybe_sigio_broken, which deals with pts devices. Signed-off-by: Jeff Dike <jdike@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-05-12 21:01:58 +00:00
* Copyright (C) 2002 - 2008 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"
uml: random driver fixes The random driver would essentially hang if the host's /dev/random returned -EAGAIN. There was a test of need_resched followed by a schedule inside the loop, but that didn't help and it's the wrong way to work anyway. The right way is to ask for an interrupt when there is input available from the host and handle it then rather than polling. Now, when the host's /dev/random returns -EAGAIN, the driver asks for a wakeup when there's randomness available again and sleeps. The interrupt routine just wakes up whatever processes are sleeping on host_read_wait. There is an atomic_t, host_sleep_count, which counts the number of processes waiting for randomness. When this reaches zero, the interrupt is disabled. An added complication is that async I/O notification was only recently added to /dev/random (by me), so essentially all hosts will lack it. So, we use the sigio workaround here, which is to have a separate thread poll on the descriptor and send an interrupt when there is input on it. This mechanism is activated when a process gets -EAGAIN (activating this multiple times is harmless, if a bit wasteful) and deactivated by the last process still waiting. The module name was changed from "random" to "hw_random" in order for udev to recognize it. The sigio workaround needed some changes. sigio_broken was added for cases when we know that async notification doesn't work. This is now called from maybe_sigio_broken, which deals with pts devices. Signed-off-by: Jeff Dike <jdike@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-05-12 21:01:58 +00:00
#include "process.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 = uml_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 = uml_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]);
}
uml: random driver fixes The random driver would essentially hang if the host's /dev/random returned -EAGAIN. There was a test of need_resched followed by a schedule inside the loop, but that didn't help and it's the wrong way to work anyway. The right way is to ask for an interrupt when there is input available from the host and handle it then rather than polling. Now, when the host's /dev/random returns -EAGAIN, the driver asks for a wakeup when there's randomness available again and sleeps. The interrupt routine just wakes up whatever processes are sleeping on host_read_wait. There is an atomic_t, host_sleep_count, which counts the number of processes waiting for randomness. When this reaches zero, the interrupt is disabled. An added complication is that async I/O notification was only recently added to /dev/random (by me), so essentially all hosts will lack it. So, we use the sigio workaround here, which is to have a separate thread poll on the descriptor and send an interrupt when there is input on it. This mechanism is activated when a process gets -EAGAIN (activating this multiple times is harmless, if a bit wasteful) and deactivated by the last process still waiting. The module name was changed from "random" to "hw_random" in order for udev to recognize it. The sigio workaround needed some changes. sigio_broken was added for cases when we know that async notification doesn't work. This is now called from maybe_sigio_broken, which deals with pts devices. Signed-off-by: Jeff Dike <jdike@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-05-12 21:01:58 +00:00
void sigio_broken(int fd, int read)
{
int err;
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();
}
uml: random driver fixes The random driver would essentially hang if the host's /dev/random returned -EAGAIN. There was a test of need_resched followed by a schedule inside the loop, but that didn't help and it's the wrong way to work anyway. The right way is to ask for an interrupt when there is input available from the host and handle it then rather than polling. Now, when the host's /dev/random returns -EAGAIN, the driver asks for a wakeup when there's randomness available again and sleeps. The interrupt routine just wakes up whatever processes are sleeping on host_read_wait. There is an atomic_t, host_sleep_count, which counts the number of processes waiting for randomness. When this reaches zero, the interrupt is disabled. An added complication is that async I/O notification was only recently added to /dev/random (by me), so essentially all hosts will lack it. So, we use the sigio workaround here, which is to have a separate thread poll on the descriptor and send an interrupt when there is input on it. This mechanism is activated when a process gets -EAGAIN (activating this multiple times is harmless, if a bit wasteful) and deactivated by the last process still waiting. The module name was changed from "random" to "hw_random" in order for udev to recognize it. The sigio workaround needed some changes. sigio_broken was added for cases when we know that async notification doesn't work. This is now called from maybe_sigio_broken, which deals with pts devices. Signed-off-by: Jeff Dike <jdike@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-05-12 21:01:58 +00:00
/* Changed during early boot */
static int pty_output_sigio;
static int pty_close_sigio;
void maybe_sigio_broken(int fd, int read)
{
if (!isatty(fd))
return;
if ((read || pty_output_sigio) && (!read || pty_close_sigio))
return;
sigio_broken(fd, read);
}
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 */
uml: random driver fixes The random driver would essentially hang if the host's /dev/random returned -EAGAIN. There was a test of need_resched followed by a schedule inside the loop, but that didn't help and it's the wrong way to work anyway. The right way is to ask for an interrupt when there is input available from the host and handle it then rather than polling. Now, when the host's /dev/random returns -EAGAIN, the driver asks for a wakeup when there's randomness available again and sleeps. The interrupt routine just wakes up whatever processes are sleeping on host_read_wait. There is an atomic_t, host_sleep_count, which counts the number of processes waiting for randomness. When this reaches zero, the interrupt is disabled. An added complication is that async I/O notification was only recently added to /dev/random (by me), so essentially all hosts will lack it. So, we use the sigio workaround here, which is to have a separate thread poll on the descriptor and send an interrupt when there is input on it. This mechanism is activated when a process gets -EAGAIN (activating this multiple times is harmless, if a bit wasteful) and deactivated by the last process still waiting. The module name was changed from "random" to "hw_random" in order for udev to recognize it. The sigio workaround needed some changes. sigio_broken was added for cases when we know that async notification doesn't work. This is now called from maybe_sigio_broken, which deals with pts devices. Signed-off-by: Jeff Dike <jdike@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-05-12 21:01:58 +00:00
static int got_sigio;
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);
uml: random driver fixes The random driver would essentially hang if the host's /dev/random returned -EAGAIN. There was a test of need_resched followed by a schedule inside the loop, but that didn't help and it's the wrong way to work anyway. The right way is to ask for an interrupt when there is input available from the host and handle it then rather than polling. Now, when the host's /dev/random returns -EAGAIN, the driver asks for a wakeup when there's randomness available again and sleeps. The interrupt routine just wakes up whatever processes are sleeping on host_read_wait. There is an atomic_t, host_sleep_count, which counts the number of processes waiting for randomness. When this reaches zero, the interrupt is disabled. An added complication is that async I/O notification was only recently added to /dev/random (by me), so essentially all hosts will lack it. So, we use the sigio workaround here, which is to have a separate thread poll on the descriptor and send an interrupt when there is input on it. This mechanism is activated when a process gets -EAGAIN (activating this multiple times is harmless, if a bit wasteful) and deactivated by the last process still waiting. The module name was changed from "random" to "hw_random" in order for udev to recognize it. The sigio workaround needed some changes. sigio_broken was added for cases when we know that async notification doesn't work. This is now called from maybe_sigio_broken, which deals with pts devices. Signed-off-by: Jeff Dike <jdike@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-05-12 21:01:58 +00:00
while (((n = read(slave, buf, sizeof(buf))) > 0) &&
!({ barrier(); 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");
}
static 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();
}