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chan_user.c

/*
 * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
 * Licensed under the GPL
 */

#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sched.h>
#include <signal.h>
#include <termios.h>
#include <sys/ioctl.h>
#include "chan_user.h"
#include "os.h"
#include "um_malloc.h"
#include "user.h"

void generic_close(int fd, void *unused)
{
      close(fd);
}

int generic_read(int fd, char *c_out, void *unused)
{
      int n;

      n = read(fd, c_out, sizeof(*c_out));
      if (n > 0)
            return n;
      else if (errno == EAGAIN)
            return 0;
      else if (n == 0)
            return -EIO;
      return -errno;
}

/* XXX Trivial wrapper around write */

int generic_write(int fd, const char *buf, int n, void *unused)
{
      int err;

      err = write(fd, buf, n);
      if (err > 0)
            return err;
      else if (errno == EAGAIN)
            return 0;
      else if (err == 0)
            return -EIO;
      return -errno;
}

int generic_window_size(int fd, void *unused, unsigned short *rows_out,
                  unsigned short *cols_out)
{
      struct winsize size;
      int ret;

      if (ioctl(fd, TIOCGWINSZ, &size) < 0)
            return -errno;

      ret = ((*rows_out != size.ws_row) || (*cols_out != size.ws_col));

      *rows_out = size.ws_row;
      *cols_out = size.ws_col;

      return ret;
}

void generic_free(void *data)
{
      kfree(data);
}

int generic_console_write(int fd, const char *buf, int n)
{
      sigset_t old, no_sigio;
      struct termios save, new;
      int err;

      if (isatty(fd)) {
            sigemptyset(&no_sigio);
            sigaddset(&no_sigio, SIGIO);
            if (sigprocmask(SIG_BLOCK, &no_sigio, &old))
                  goto error;

            CATCH_EINTR(err = tcgetattr(fd, &save));
            if (err)
                  goto error;
            new = save;
            /*
             * The terminal becomes a bit less raw, to handle \n also as
             * "Carriage Return", not only as "New Line". Otherwise, the new
             * line won't start at the first column.
             */
            new.c_oflag |= OPOST;
            CATCH_EINTR(err = tcsetattr(fd, TCSAFLUSH, &new));
            if (err)
                  goto error;
      }
      err = generic_write(fd, buf, n, NULL);
      /*
       * Restore raw mode, in any case; we *must* ignore any error apart
       * EINTR, except for debug.
       */
      if (isatty(fd)) {
            CATCH_EINTR(tcsetattr(fd, TCSAFLUSH, &save));
            sigprocmask(SIG_SETMASK, &old, NULL);
      }

      return err;
error:
      return -errno;
}

/*
 * UML SIGWINCH handling
 *
 * The point of this is to handle SIGWINCH on consoles which have host
 * ttys and relay them inside UML to whatever might be running on the
 * console and cares about the window size (since SIGWINCH notifies
 * about terminal size changes).
 *
 * So, we have a separate thread for each host tty attached to a UML
 * device (side-issue - I'm annoyed that one thread can't have
 * multiple controlling ttys for the purpose of handling SIGWINCH, but
 * I imagine there are other reasons that doesn't make any sense).
 *
 * SIGWINCH can't be received synchronously, so you have to set up to
 * receive it as a signal.  That being the case, if you are going to
 * wait for it, it is convenient to sit in sigsuspend() and wait for
 * the signal to bounce you out of it (see below for how we make sure
 * to exit only on SIGWINCH).
 */

static void winch_handler(int sig)
{
}

struct winch_data {
      int pty_fd;
      int pipe_fd;
};

static int winch_thread(void *arg)
{
      struct winch_data *data = arg;
      sigset_t sigs;
      int pty_fd, pipe_fd;
      int count;
      char c = 1;

      pty_fd = data->pty_fd;
      pipe_fd = data->pipe_fd;
      count = write(pipe_fd, &c, sizeof(c));
      if (count != sizeof(c))
            printk(UM_KERN_ERR "winch_thread : failed to write "
                   "synchronization byte, err = %d\n", -count);

      /*
       * We are not using SIG_IGN on purpose, so don't fix it as I thought to
       * do! If using SIG_IGN, the sigsuspend() call below would not stop on
       * SIGWINCH.
       */

      signal(SIGWINCH, winch_handler);
      sigfillset(&sigs);
      /* Block all signals possible. */
      if (sigprocmask(SIG_SETMASK, &sigs, NULL) < 0) {
            printk(UM_KERN_ERR "winch_thread : sigprocmask failed, "
                   "errno = %d\n", errno);
            exit(1);
      }
      /* In sigsuspend(), block anything else than SIGWINCH. */
      sigdelset(&sigs, SIGWINCH);

      if (setsid() < 0) {
            printk(UM_KERN_ERR "winch_thread : setsid failed, errno = %d\n",
                   errno);
            exit(1);
      }

      if (ioctl(pty_fd, TIOCSCTTY, 0) < 0) {
            printk(UM_KERN_ERR "winch_thread : TIOCSCTTY failed on "
                   "fd %d err = %d\n", pty_fd, errno);
            exit(1);
      }

      if (tcsetpgrp(pty_fd, os_getpid()) < 0) {
            printk(UM_KERN_ERR "winch_thread : tcsetpgrp failed on "
                   "fd %d err = %d\n", pty_fd, errno);
            exit(1);
      }

      /*
       * These are synchronization calls between various UML threads on the
       * host - since they are not different kernel threads, we cannot use
       * kernel semaphores. We don't use SysV semaphores because they are
       * persistent.
       */
      count = read(pipe_fd, &c, sizeof(c));
      if (count != sizeof(c))
            printk(UM_KERN_ERR "winch_thread : failed to read "
                   "synchronization byte, err = %d\n", errno);

      while(1) {
            /*
             * This will be interrupted by SIGWINCH only, since
             * other signals are blocked.
             */
            sigsuspend(&sigs);

            count = write(pipe_fd, &c, sizeof(c));
            if (count != sizeof(c))
                  printk(UM_KERN_ERR "winch_thread : write failed, "
                         "err = %d\n", errno);
      }
}

static int winch_tramp(int fd, struct tty_struct *tty, int *fd_out,
                   unsigned long *stack_out)
{
      struct winch_data data;
      int fds[2], n, err;
      char c;

      err = os_pipe(fds, 1, 1);
      if (err < 0) {
            printk(UM_KERN_ERR "winch_tramp : os_pipe failed, err = %d\n",
                   -err);
            goto out;
      }

      data = ((struct winch_data) { .pty_fd           = fd,
                              .pipe_fd          = fds[1] } );
      /*
       * CLONE_FILES so this thread doesn't hold open files which are open
       * now, but later closed in a different thread.  This is a
       * problem with /dev/net/tun, which if held open by this
       * thread, prevents the TUN/TAP device from being reused.
       */
      err = run_helper_thread(winch_thread, &data, CLONE_FILES, stack_out);
      if (err < 0) {
            printk(UM_KERN_ERR "fork of winch_thread failed - errno = %d\n",
                   -err);
            goto out_close;
      }

      *fd_out = fds[0];
      n = read(fds[0], &c, sizeof(c));
      if (n != sizeof(c)) {
            printk(UM_KERN_ERR "winch_tramp : failed to read "
                   "synchronization byte\n");
            printk(UM_KERN_ERR "read failed, err = %d\n", errno);
            printk(UM_KERN_ERR "fd %d will not support SIGWINCH\n", fd);
            err = -EINVAL;
            goto out_close;
      }

      if (os_set_fd_block(*fd_out, 0)) {
            printk(UM_KERN_ERR "winch_tramp: failed to set thread_fd "
                   "non-blocking.\n");
            goto out_close;
      }

      return err;

 out_close:
      close(fds[1]);
      close(fds[0]);
 out:
      return err;
}

void register_winch(int fd, struct tty_struct *tty)
{
      unsigned long stack;
      int pid, thread, count, thread_fd = -1;
      char c = 1;

      if (!isatty(fd))
            return;

      pid = tcgetpgrp(fd);
      if (!is_skas_winch(pid, fd, tty) && (pid == -1)) {
            thread = winch_tramp(fd, tty, &thread_fd, &stack);
            if (thread < 0)
                  return;

            register_winch_irq(thread_fd, fd, thread, tty, stack);

            count = write(thread_fd, &c, sizeof(c));
            if (count != sizeof(c))
                  printk(UM_KERN_ERR "register_winch : failed to write "
                         "synchronization byte, err = %d\n", errno);
      }
}

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