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sigio.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 <fcntl.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 "sigio.h"
#include "os.h"
#include "um_malloc.h"
#include "init.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("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("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("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("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);
      n = write(sigio_private[0], &c, sizeof(c));
      if(n != sizeof(c)){
            printk("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("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("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("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 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("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("openpty failed, errno = %d\n", -pty.err);
            return;
      }

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

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

      /* Not now, but complain so we now where we failed. */
      err = raw(master);
      if (err < 0)
            panic("check_sigio : __raw failed, errno = %d\n", -err);

      err = async_pty(master, slave);
      if(err < 0)
            panic("tty_fds : sigio_async failed, err = %d\n", -err);

      if(sigaction(SIGIO, NULL, &old) < 0)
            panic("check_sigio : sigaction 1 failed, errno = %d\n", errno);
      new = old;
      new.sa_handler = handler;
      if(sigaction(SIGIO, &new, NULL) < 0)
            panic("check_sigio : sigaction 2 failed, errno = %d\n", errno);

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

      close(master);
      close(slave);

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

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

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

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

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

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

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

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

void __init check_sigio(void)
{
      if((os_access("/dev/ptmx", OS_ACC_R_OK) < 0) &&
         (os_access("/dev/ptyp0", OS_ACC_R_OK) < 0)){
            printk("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();
}

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