arch/um/drivers/chan_user.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
   4  */
   5
   6 #include <stdlib.h>
   7 #include <unistd.h>
   8 #include <errno.h>
   9 #include <sched.h>
  10 #include <signal.h>
  11 #include <termios.h>
  12 #include <sys/ioctl.h>
  13 #include "chan_user.h"
  14 #include <os.h>
  15 #include <um_malloc.h>
  16
  17 void generic_close(int fd, void *unused)
  18 {
  19         close(fd);
  20 }
  21
  22 int generic_read(int fd, char *c_out, void *unused)
  23 {
  24         int n;
  25
  26         n = read(fd, c_out, sizeof(*c_out));
  27         if (n > 0)
  28                 return n;
  29         else if (errno == EAGAIN)
  30                 return 0;
  31         else if (n == 0)
  32                 return -EIO;
  33         return -errno;
  34 }
  35
  36 /* XXX Trivial wrapper around write */
  37
  38 int generic_write(int fd, const char *buf, int n, void *unused)
  39 {
  40         int err;
  41
  42         err = write(fd, buf, n);
  43         if (err > 0)
  44                 return err;
  45         else if (errno == EAGAIN)
  46                 return 0;
  47         else if (err == 0)
  48                 return -EIO;
  49         return -errno;
  50 }
  51
  52 int generic_window_size(int fd, void *unused, unsigned short *rows_out,
  53                         unsigned short *cols_out)
  54 {
  55         struct winsize size;
  56         int ret;
  57
  58         if (ioctl(fd, TIOCGWINSZ, &size) < 0)
  59                 return -errno;
  60
  61         ret = ((*rows_out != size.ws_row) || (*cols_out != size.ws_col));
  62
  63         *rows_out = size.ws_row;
  64         *cols_out = size.ws_col;
  65
  66         return ret;
  67 }
  68
  69 void generic_free(void *data)
  70 {
  71         kfree(data);
  72 }
  73
  74 int generic_console_write(int fd, const char *buf, int n)
  75 {
  76         sigset_t old, no_sigio;
  77         struct termios save, new;
  78         int err;
  79
  80         if (isatty(fd)) {
  81                 sigemptyset(&no_sigio);
  82                 sigaddset(&no_sigio, SIGIO);
  83                 if (sigprocmask(SIG_BLOCK, &no_sigio, &old))
  84                         goto error;
  85
  86                 CATCH_EINTR(err = tcgetattr(fd, &save));
  87                 if (err)
  88                         goto error;
  89                 new = save;
  90                 /*
  91                  * The terminal becomes a bit less raw, to handle \n also as
  92                  * "Carriage Return", not only as "New Line". Otherwise, the new
  93                  * line won't start at the first column.
  94                  */
  95                 new.c_oflag |= OPOST;
  96                 CATCH_EINTR(err = tcsetattr(fd, TCSAFLUSH, &new));
  97                 if (err)
  98                         goto error;
  99         }
 100         err = generic_write(fd, buf, n, NULL);
 101         /*
 102          * Restore raw mode, in any case; we *must* ignore any error apart
 103          * EINTR, except for debug.
 104          */
 105         if (isatty(fd)) {
 106                 CATCH_EINTR(tcsetattr(fd, TCSAFLUSH, &save));
 107                 sigprocmask(SIG_SETMASK, &old, NULL);
 108         }
 109
 110         return err;
 111 error:
 112         return -errno;
 113 }
 114
 115 /*
 116  * UML SIGWINCH handling
 117  *
 118  * The point of this is to handle SIGWINCH on consoles which have host
 119  * ttys and relay them inside UML to whatever might be running on the
 120  * console and cares about the window size (since SIGWINCH notifies
 121  * about terminal size changes).
 122  *
 123  * So, we have a separate thread for each host tty attached to a UML
 124  * device (side-issue - I'm annoyed that one thread can't have
 125  * multiple controlling ttys for the purpose of handling SIGWINCH, but
 126  * I imagine there are other reasons that doesn't make any sense).
 127  *
 128  * SIGWINCH can't be received synchronously, so you have to set up to
 129  * receive it as a signal.  That being the case, if you are going to
 130  * wait for it, it is convenient to sit in sigsuspend() and wait for
 131  * the signal to bounce you out of it (see below for how we make sure
 132  * to exit only on SIGWINCH).
 133  */
 134
 135 static void winch_handler(int sig)
 136 {
 137 }
 138
 139 struct winch_data {
 140         int pty_fd;
 141         int pipe_fd;
 142 };
 143
 144 static int winch_thread(void *arg)
 145 {
 146         struct winch_data *data = arg;
 147         sigset_t sigs;
 148         int pty_fd, pipe_fd;
 149         int count;
 150         char c = 1;
 151
 152         pty_fd = data->pty_fd;
 153         pipe_fd = data->pipe_fd;
 154         count = write(pipe_fd, &c, sizeof(c));
 155         if (count != sizeof(c))
 156                 printk(UM_KERN_ERR "winch_thread : failed to write "
 157                        "synchronization byte, err = %d\n", -count);
 158
 159         /*
 160          * We are not using SIG_IGN on purpose, so don't fix it as I thought to
 161          * do! If using SIG_IGN, the sigsuspend() call below would not stop on
 162          * SIGWINCH.
 163          */
 164
 165         signal(SIGWINCH, winch_handler);
 166         sigfillset(&sigs);
 167         /* Block all signals possible. */
 168         if (sigprocmask(SIG_SETMASK, &sigs, NULL) < 0) {
 169                 printk(UM_KERN_ERR "winch_thread : sigprocmask failed, "
 170                        "errno = %d\n", errno);
 171                 exit(1);
 172         }
 173         /* In sigsuspend(), block anything else than SIGWINCH. */
 174         sigdelset(&sigs, SIGWINCH);
 175
 176         if (setsid() < 0) {
 177                 printk(UM_KERN_ERR "winch_thread : setsid failed, errno = %d\n",
 178                        errno);
 179                 exit(1);
 180         }
 181
 182         if (ioctl(pty_fd, TIOCSCTTY, 0) < 0) {
 183                 printk(UM_KERN_ERR "winch_thread : TIOCSCTTY failed on "
 184                        "fd %d err = %d\n", pty_fd, errno);
 185                 exit(1);
 186         }
 187
 188         if (tcsetpgrp(pty_fd, os_getpid()) < 0) {
 189                 printk(UM_KERN_ERR "winch_thread : tcsetpgrp failed on "
 190                        "fd %d err = %d\n", pty_fd, errno);
 191                 exit(1);
 192         }
 193
 194         /*
 195          * These are synchronization calls between various UML threads on the
 196          * host - since they are not different kernel threads, we cannot use
 197          * kernel semaphores. We don't use SysV semaphores because they are
 198          * persistent.
 199          */
 200         count = read(pipe_fd, &c, sizeof(c));
 201         if (count != sizeof(c))
 202                 printk(UM_KERN_ERR "winch_thread : failed to read "
 203                        "synchronization byte, err = %d\n", errno);
 204
 205         while(1) {
 206                 /*
 207                  * This will be interrupted by SIGWINCH only, since
 208                  * other signals are blocked.
 209                  */
 210                 sigsuspend(&sigs);
 211
 212                 count = write(pipe_fd, &c, sizeof(c));
 213                 if (count != sizeof(c))
 214                         printk(UM_KERN_ERR "winch_thread : write failed, "
 215                                "err = %d\n", errno);
 216         }
 217 }
 218
 219 static int winch_tramp(int fd, struct tty_port *port, int *fd_out,
 220                        unsigned long *stack_out)
 221 {
 222         struct winch_data data;
 223         int fds[2], n, err;
 224         char c;
 225
 226         err = os_pipe(fds, 1, 1);
 227         if (err < 0) {
 228                 printk(UM_KERN_ERR "winch_tramp : os_pipe failed, err = %d\n",
 229                        -err);
 230                 goto out;
 231         }
 232
 233         data = ((struct winch_data) { .pty_fd           = fd,
 234                                       .pipe_fd          = fds[1] } );
 235         /*
 236          * CLONE_FILES so this thread doesn't hold open files which are open
 237          * now, but later closed in a different thread.  This is a
 238          * problem with /dev/net/tun, which if held open by this
 239          * thread, prevents the TUN/TAP device from being reused.
 240          */
 241         err = run_helper_thread(winch_thread, &data, CLONE_FILES, stack_out);
 242         if (err < 0) {
 243                 printk(UM_KERN_ERR "fork of winch_thread failed - errno = %d\n",
 244                        -err);
 245                 goto out_close;
 246         }
 247
 248         *fd_out = fds[0];
 249         n = read(fds[0], &c, sizeof(c));
 250         if (n != sizeof(c)) {
 251                 printk(UM_KERN_ERR "winch_tramp : failed to read "
 252                        "synchronization byte\n");
 253                 printk(UM_KERN_ERR "read failed, err = %d\n", errno);
 254                 printk(UM_KERN_ERR "fd %d will not support SIGWINCH\n", fd);
 255                 err = -EINVAL;
 256                 goto out_close;
 257         }
 258
 259         if (os_set_fd_block(*fd_out, 0)) {
 260                 printk(UM_KERN_ERR "winch_tramp: failed to set thread_fd "
 261                        "non-blocking.\n");
 262                 goto out_close;
 263         }
 264
 265         return err;
 266
 267  out_close:
 268         close(fds[1]);
 269         close(fds[0]);
 270  out:
 271         return err;
 272 }
 273
 274 void register_winch(int fd, struct tty_port *port)
 275 {
 276         unsigned long stack;
 277         int pid, thread, count, thread_fd = -1;
 278         char c = 1;
 279
 280         if (!isatty(fd))
 281                 return;
 282
 283         pid = tcgetpgrp(fd);
 284         if (is_skas_winch(pid, fd, port)) {
 285                 register_winch_irq(-1, fd, -1, port, 0);
 286                 return;
 287         }
 288
 289         if (pid == -1) {
 290                 thread = winch_tramp(fd, port, &thread_fd, &stack);
 291                 if (thread < 0)
 292                         return;
 293
 294                 register_winch_irq(thread_fd, fd, thread, port, stack);
 295
 296                 count = write(thread_fd, &c, sizeof(c));
 297                 if (count != sizeof(c))
 298                         printk(UM_KERN_ERR "register_winch : failed to write "
 299                                "synchronization byte, err = %d\n", errno);
 300         }
 301 }