// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2002 - 2008 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 */

#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;

        os_fix_helper_signals();
        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_trace(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_trace(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_trace(flags);
}

int __add_sigio_fd(int fd)
{
        struct pollfd *p;
        int err, i, n;

        for (i = 0; i < all_sigio_fds.used; i++) {
                if (all_sigio_fds.poll[i].fd == fd)
                        break;
        }
        if (i == all_sigio_fds.used)
                return -ENOSPC;

        p = &all_sigio_fds.poll[i];

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

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

        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();

        return 0;
}


int add_sigio_fd(int fd)
{
        int err;

        sigio_lock();
        err = __add_sigio_fd(fd);
        sigio_unlock();

        return err;
}

int __ignore_sigio_fd(int fd)
{
        struct pollfd *p;
        int err, 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;

        for (i = 0; i < current_poll.used; i++) {
                if (current_poll.poll[i].fd == fd)
                        break;
        }
        if (i == current_poll.used)
                return -ENOENT;

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

        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();

        return 0;
}

int ignore_sigio_fd(int fd)
{
        int err;

        sigio_lock();
        err = __ignore_sigio_fd(fd);
        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 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      = POLLIN,
                                   .revents     = 0 });
out:
        sigio_unlock();
}

/* Changed during early boot */
static int pty_output_sigio;

void maybe_sigio_broken(int fd)
{
        if (!isatty(fd))
                return;

        if (pty_output_sigio)
                return;

        sigio_broken(fd);
}

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 __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);
}

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