/**
* mds — A micro-display server
* Copyright © 2014 Mattias Andrée (maandree@member.fsf.org)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "mds-vt.h"
#include <libmdsserver/config.h>
#include <libmdsserver/macros.h>
#include <libmdsserver/util.h>
#include <libmdsserver/mds-message.h>
#include <errno.h>
#include <inttypes.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <linux/kd.h>
#include <limits.h>
#include <fcntl.h>
#include <unistd.h>
#include <signal.h>
#define reconnect_to_display() -1
#define MDS_VT_VARS_VERSION 0
/**
* This variable should declared by the actual server implementation.
* It must be configured before `main` is invoked.
*
* This tells the server-base how to behave
*/
server_characteristics_t server_characteristics =
{
.require_privileges = 1, /* we want to open the new tty (the rest is fine without root for some reason) */
.require_display = 1,
.require_respawn_info = 1,
.sanity_check_argc = 1,
.fork_for_safety = 0,
.danger_is_deadly = 0
};
/**
* Value of the ‘Message ID’ header for the next message
*/
static uint32_t message_id = 1;
/**
* Buffer for received messages
*/
static mds_message_t received;
/**
* Whether the server is connected to the display
*/
static int connected = 1;
/**
* The index of the VT used for the display
*/
static int display_vt;
/**
* The file descriptor the display's TTY is opened on
*/
static int display_tty_fd = -1;
/**
* Whether the display's TTY is in the foreground
*/
static int vt_is_active = 1;
/**
* The stat for the TTY of the display's VT before we toke it
*/
static struct stat old_vt_stat;
/**
* -1 if switching to our VT, 1 if switching to another VT, 0 otherwise
*/
static volatile int switching_vt = 0;
/**
* The pathname for the file containing VT information
*/
static char vtfile_path[PATH_MAX];
/**
* This function will be invoked before `initialise_server` (if not re-exec:ing)
* or before `unmarshal_server` (if re-exec:ing)
*
* @return Non-zero on error
*/
int __attribute__((const)) preinitialise_server(void)
{
return 0;
}
/**
* Write persistent data about the VT and TTY to a file
*
* @return Zero on success, -1 on error
*/
static int write_vt_file(void)
{
char buf[(sizeof(int) + sizeof(struct stat)) / sizeof(char)];
int fd, r, old_errno;
int* intbuf = (int*)buf;
*intbuf = display_vt;
*(struct stat*)(buf + sizeof(int) / sizeof(char)) = old_vt_stat;
fd = open(vtfile_path, O_WRONLY | O_CREAT);
if (fd < 0)
return -1;
r = full_write(fd, buf, sizeof(buf));
old_errno = errno;
close(fd);
errno = old_errno;
return r;
}
/**
* Read persistent data about the VT and TTY from a file
*
* @return Zero on success, -1 on error
*/
static int read_vt_file(void)
{
char* buf;
size_t len;
int fd;
fd = open(vtfile_path, O_RDONLY);
if (fd < 0)
return -1;
buf = full_read(fd, &len);
if (buf == NULL)
return -1;
if (len != sizeof(int) + sizeof(struct stat))
{
eprint("VT file is of wrong size.");
errno = 0;
return -1;
}
display_vt = *(int*)buf;
old_vt_stat = *(struct stat*)(buf + sizeof(int) / sizeof(char));
return 0;
}
/**
* This function should initialise the server,
* and it not invoked after a re-exec.
*
* @return Non-zero on error
*/
int initialise_server(void)
{
struct vt_mode mode;
char* display_env;
const char* const message =
"Command: intercept\n"
"Message ID: 0\n"
"Length: 38\n"
"\n"
"Command: get-vt\n"
"Command: configure-vt\n";
display_env = getenv("MDS_DISPLAY");
display_env = display_env ? strchr(display_env, ':') : NULL;
if ((display_env == NULL) || (strlen(display_env) < 2))
goto no_display;
memset(vtfile_path, 0, sizeof(vtfile_path));
xsnprintf(vtfile_path, "%s/%s.vt", MDS_RUNTIME_ROOT_DIRECTORY, display_env + 1);
if (is_respawn == 0)
{
display_vt = vt_get_next_available();
if (display_vt == 0)
{
eprint("out of available virtual terminals, I am stymied.");
goto fail;
}
else if (display_vt < 0)
goto pfail;
display_tty_fd = vt_open(display_vt, &old_vt_stat);
fail_if (write_vt_file() < 0);
fail_if (vt_set_active(display_vt) < 0);
}
else
{
fail_if (read_vt_file() < 0);
vt_is_active = (display_vt == vt_get_active());
fail_if (vt_is_active < 0);
}
if (full_send(message, strlen(message)))
return 1;
fail_if (server_initialised() < 0);
fail_if (mds_message_initialise(&received));
fail_if (xsigaction(SIGRTMIN + 1, received_switch_vt) < 0);
fail_if (xsigaction(SIGRTMIN + 2, received_switch_vt) < 0);
vt_construct_mode(1, SIGRTMIN + 1, SIGRTMIN + 2, &mode);
fail_if (vt_get_set_mode(display_tty_fd, 1, &mode) < 0);
if (vt_set_exclusive(display_tty_fd, 1) < 0)
xperror(*argv);
return 0;
no_display:
eprint("no display has been set, how did this happen.");
return 1;
pfail:
xperror(*argv);
fail:
unlink(vtfile_path);
if (display_tty_fd >= 0)
vt_close(display_tty_fd, &old_vt_stat);
mds_message_destroy(&received);
return 1;
}
/**
* This function will be invoked after `initialise_server` (if not re-exec:ing)
* or after `unmarshal_server` (if re-exec:ing)
*
* @return Non-zero on error
*/
int postinitialise_server(void)
{
if (connected)
return 0;
if (reconnect_to_display())
{
mds_message_destroy(&received);
return 1;
}
connected = 1;
return 0;
}
/**
* Calculate the number of bytes that will be stored by `marshal_server`
*
* On failure the program should `abort()` or exit by other means.
* However it should not be possible for this function to fail.
*
* @return The number of bytes that will be stored by `marshal_server`
*/
size_t marshal_server_size(void)
{
size_t rc = 5 * sizeof(int) + sizeof(uint32_t);
rc += sizeof(struct stat);
rc += PATH_MAX * sizeof(char);
rc += mds_message_marshal_size(&received);
return rc;
}
/**
* Marshal server implementation specific data into a buffer
*
* @param state_buf The buffer for the marshalled data
* @return Non-zero on error
*/
int marshal_server(char* state_buf)
{
buf_set_next(state_buf, int, MDS_VT_VARS_VERSION);
buf_set_next(state_buf, int, connected);
buf_set_next(state_buf, uint32_t, message_id);
buf_set_next(state_buf, int, display_vt);
buf_set_next(state_buf, int, display_tty_fd);
buf_set_next(state_buf, int, vt_is_active);
buf_set_next(state_buf, struct stat, old_vt_stat);
memcpy(state_buf, vtfile_path, PATH_MAX * sizeof(char));
state_buf += PATH_MAX;
mds_message_marshal(&received, state_buf);
mds_message_destroy(&received);
return 0;
}
/**
* Unmarshal server implementation specific data and update the servers state accordingly
*
* On critical failure the program should `abort()` or exit by other means.
* That is, do not let `reexec_failure_recover` run successfully, if it unrecoverable
* error has occurred or one severe enough that it is better to simply respawn.
*
* @param state_buf The marshalled data that as not been read already
* @return Non-zero on error
*/
int unmarshal_server(char* state_buf)
{
int r;
/* buf_get_next(state_buf, int, MDS_VT_VARS_VERSION); */
buf_next(state_buf, int, 1);
buf_get_next(state_buf, int, connected);
buf_get_next(state_buf, uint32_t, message_id);
buf_get_next(state_buf, int, display_vt);
buf_get_next(state_buf, int, display_tty_fd);
buf_get_next(state_buf, int, vt_is_active);
buf_get_next(state_buf, struct stat, old_vt_stat);
memcpy(vtfile_path, state_buf, PATH_MAX * sizeof(char));
state_buf += PATH_MAX;
r = mds_message_unmarshal(&received, state_buf);
if (r)
{
xperror(*argv);
mds_message_destroy(&received);
}
return r;
}
/**
* Attempt to recover from a re-exec failure that has been
* detected after the server successfully updated it execution image
*
* @return Non-zero on error
*/
int __attribute__((const)) reexec_failure_recover(void)
{
return -1;
}
/**
* Perform the server's mission
*
* @return Non-zero on error
*/
int master_loop(void)
{
int rc = 1, r;
while (!reexecing && !terminating)
{
if (switching_vt)
{
/* FIXME */
}
r = mds_message_read(&received, socket_fd);
if (r == 0)
{
r = 0; /* FIXME */
if (r == 0)
continue;
}
if (r == -2)
{
eprint("corrupt message received, aborting.");
goto fail;
}
else if (errno == EINTR)
continue;
else if (errno != ECONNRESET)
goto pfail;
eprint("lost connection to server.");
mds_message_destroy(&received);
mds_message_initialise(&received);
connected = 0;
if (reconnect_to_display())
goto fail;
connected = 1;
}
rc = 0;
if (vt_set_exclusive(display_tty_fd, 0) < 0) xperror(*argv);
if (vt_set_graphical(display_tty_fd, 0) < 0) xperror(*argv);
if (unlink(vtfile_path) < 0)
xperror(*argv);
vt_close(display_tty_fd, &old_vt_stat);
goto fail;
pfail:
xperror(*argv);
fail:
if (rc || !reexecing)
mds_message_destroy(&received);
return rc;
}
/**
* This function is called when the kernel wants
* to switch foreground virtual terminal
*
* @param signo The received signal number
*/
void received_switch_vt(int signo)
{
int leaving = signo == (SIGRTMIN + 1);
switching_vt = leaving ? 1 : -1;
}
/**
* Send a full message even if interrupted
*
* @param message The message to send
* @param length The length of the message
* @return Non-zero on success
*/
int full_send(const char* message, size_t length)
{
size_t sent;
while (length > 0)
{
sent = send_message(socket_fd, message, length);
if (sent > length)
{
eprint("Sent more of a message than exists in the message, aborting.");
return -1;
}
else if ((sent < length) && (errno != EINTR))
{
xperror(*argv);
return -1;
}
message += sent;
length -= sent;
}
return 0;
}
/**
* Get the index of the next available virtual terminal
*
* @return -1 on error, 0 if the terminals are exhausted, otherwise the next terminal
*/
int vt_get_next_available(void)
{
int next_vt = -1;
int r = ioctl(STDIN_FILENO, VT_OPENQRY, &next_vt);
if (r < 0)
return r;
return ((next_vt < 0) || (MAX_NR_CONSOLES < next_vt)) ? 0 : next_vt;
}
/**
* Get the currently active virtual terminal
*
* @return -1 on error, otherwise the current terminal
*/
int vt_get_active(void)
{
struct vt_stat state;
if (ioctl(STDIN_FILENO, VT_GETSTATE, &state) < 0)
return -1;
return state.v_active;
}
/**
* Change currently active virtual terminal and wait for it to complete the switch
*
* @param vt The index of the terminal
* @return Zero on success, -1 on error
*/
int vt_set_active(int vt)
{
if (ioctl(STDIN_FILENO, VT_ACTIVATE, vt) < 0)
return -1;
if (ioctl(STDIN_FILENO, VT_WAITACTIVE, vt) < 0)
xperror(*argv);
return 0;
}
/**
* Open a virtual terminal
*
* @param vt The index of the terminal
* @param old_stat Output parameter for the old file stat for the terminal
* @return The file descriptor for the terminal, -1 on error
*/
int vt_open(int vt, struct stat* restrict old_stat)
{
char vtpath[64]; /* Should be small enought and large enought for any
lunatic alternative to /dev/ttyNNN, if not you
will need to apply a patch (or fix your system.) */
int fd;
sprintf(vtpath, VT_PATH_PATTERN, vt);
fd = open(vtpath, O_RDWR);
if (fd < 0)
return -1;
if ((fstat(fd, old_stat) < 0) ||
(fchown(fd, getuid(), getgid()) < 0))
{
close(fd);
return -1;
}
return fd;
}
/**
* Close a virtual terminal
*
* @param vt The index of the terminal
* @param old_stat The old file stat for the terminal
*/
void vt_close(int fd, struct stat* restrict old_stat)
{
if (fchown(fd, old_stat->st_uid, old_stat->st_gid) < 0)
{
xperror(*argv);
eprint("while resetting TTY ownership.");
}
close(fd);
}
/**
* Construct a virtual terminal mode that can be used in `vt_get_set_mode`
*
* @param vt_switch_control Whether we want to be able to block and delay VT switches
* @param vt_leave_signal The signal that should be send to us we a process is trying
* to switch terminal to another terminal
* @param vt_enter_signal The signal that should be send to us we a process is trying
* to switch terminal to our terminal
* @param mode Output parameter
*/
void vt_construct_mode(int vt_switch_control, int vt_leave_signal,
int vt_enter_signal, struct vt_mode* restrict mode)
{
mode->mode = vt_switch_control ? VT_PROCESS : VT_AUTO;
mode->waitv = 0;
mode->relsig = (short int)vt_leave_signal;
mode->acqsig = (short int)vt_enter_signal;
}
