sigio.c

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/*
 * 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_util.h>
#include <init.h>
#include <os.h>
#include <sigio.h>
#include <um_malloc.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]);
}

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();
}

/* 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 */
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);
    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();
}