/**
* 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-respawn.h"
#include <libmdsserver/macros.h>
#include <libmdsserver/util.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
#include <time.h>
#define MDS_RESPAWN_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 = 0,
.require_display = 0,
.require_respawn_info = 1,
.sanity_check_argc = 0,
.fork_for_safety = 0,
.danger_is_deadly = 0
};
/**
* Do not respawn crashed servers that did not live this many seconds
*/
static int interval = RESPAWN_TIME_LIMIT_SECONDS;
/**
* The number of servers managed by this process
*/
static size_t servers = 0;
/**
* Command line arguments, for each server — concatenated, with NULL termination
*/
static char** commands_args = NULL;
/**
* Mapping elements in `commands_args` that are the first
* argument for each server to run
*/
static char*** commands = NULL;
/**
* States of managed servers
*/
static server_state_t* states = NULL;
/**
* Whether a revive request has been received but not processed
*/
static volatile sig_atomic_t reviving = 0;
/**
* The number of servers that are alive
*/
static size_t live_count = 0;
/**
* Parse command line arguments
*
* @return Non-zero on error
*/
int parse_cmdline(void)
{
/* Parse command line arguments. */
int i;
size_t j, args = 0, stack = 0;
for (i = 1; i < argc; i++)
{
char* arg = argv[i];
if (startswith(arg, "--alarm=")) /* Schedule an alarm signal for forced abort. */
alarm((unsigned)min(atou(arg + strlen("--alarm=")), 60)); /* At most 1 minute. */
else if (startswith(arg, "--interval="))
interval = min(atoi(arg + strlen("--interval=")), 60); /* At most 1 minute. */
else if (strequals(arg, "--re-exec")) /* Re-exec state-marshal. */
is_reexec = 1;
else if (strequals(arg, "{"))
servers += stack++ == 0 ? 1 : 0;
else if (strequals(arg, "}"))
{
exit_if (stack-- == 0, eprint("Terminating non-started command, aborting."););
exit_if (stack == 0 && strequals(argv[i - 1], "{"),
eprint("Zero argument command specified, aborting."););
}
else if (stack == 0)
eprintf("Unrecognised option: %s, did you forget `='?", arg);
else
args++;
}
if (is_reexec)
{
is_respawn = 1;
eprint("re-exec performed.");
}
/* Validate command line arguments. */
exit_if (stack > 0, eprint("Non-terminated command specified, aborting."););
exit_if (servers == 0, eprint("No programs to spawn, aborting."););
/* Allocate arrays. */
fail_if (xmalloc(commands_args, args + servers, char*));
fail_if (xmalloc(commands, servers, char**));
fail_if (xmalloc(states, servers, server_state_t));
/* Fill command arrays. */
for (i = 1, args = j = 0; i < argc; i++)
{
char* arg = argv[i];
if (strequals(arg, "}")) commands_args[args++] = --stack == 0 ? NULL : arg;
else if (stack > 0) commands_args[args++] = arg;
else if (strequals(arg, "{") && (stack++ == 0))
commands[j++] = commands_args + args;
}
return 0;
fail:
xperror(*argv);
return 1;
}
/**
* Spawn a server
*
* @param index The index of the server
*/
static void spawn_server(size_t index)
{
struct timespec started;
pid_t pid;
/* When did the spawned server start? */
if (monotone(&started) < 0)
{
xperror(*argv);
eprintf("cannot read clock when starting %s, burying.", commands[index][0]);
states[index].state = DEAD_AND_BURIED;
return;
}
states[index].started = started;
/* Fork process to spawn the server. */
pid = fork();
if (pid == (pid_t)-1)
{
xperror(*argv);
eprintf("cannot fork in order to start %s, burying.", commands[index][0]);
states[index].state = DEAD_AND_BURIED;
return;
}
/* In the parent process (respawner): store spawned server information. */
if (pid)
{
states[index].pid = pid;
states[index].state = ALIVE;
live_count++;
return;
}
/* In the child process (server): remove the alarm and change execution image to the server.. */
alarm(0);
execvp(commands[index][0], commands[index]);
xperror(commands[index][0]);
_exit(1);
}
/**
* This function is called when a signal that
* signals the program to respawn all
* `DEAD_AND_BURIED` server is received
*
* @param signo The signal that has been received
*/
static void received_revive(int signo)
{
(void) signo;
reviving = 1;
eprint("revive signal received.");
}
/**
* 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 preinitialise_server(void)
{
/* Make the server revive all `DEAD_AND_BURIED` servers on SIGUSR2. */
fail_if (xsigaction(SIGUSR2, received_revive) < 0);
return 0;
fail:
xperror(*argv);
return 1;
}
/**
* This function should initialise the server,
* and it not invoked after a re-exec.
*
* @return Non-zero on error
*/
int initialise_server(void)
{
#if UNBORN != 0
size_t i;
#endif
memset(states, 0, servers * sizeof(server_state_t));
#if UNBORN != 0
for (i = 0; i < servers; i++)
states[i].state = UNBORN;
#endif
return 0;
}
/**
* 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)
{
size_t i, j;
/* Spawn servers that has not been spawned yet. */
for (i = 0; i < servers; i++)
if (states[i].state == UNBORN)
spawn_server(i);
/* Forever mark newly spawned services (after this point in time)
as respawned. */
for (i = j = 0; j < servers; i++)
if (commands_args[i] == NULL)
j++;
else if (strequals(commands_args[i], "--initial-spawn"))
fail_if (xstrdup(commands_args[i], "--respawn"));
/* Respawn dead and dead and buried servers.*/
for (i = 0; i < servers; i++)
if ((states[i].state == DEAD) ||
(states[i].state == DEAD_AND_BURIED))
spawn_server(i);
return 0;
fail:
xperror(*argv);
return 1;
}
/**
* 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 = sizeof(int) + sizeof(sig_atomic_t);
rc += sizeof(time_t) + sizeof(long);
rc += servers * sizeof(server_state_t);
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)
{
size_t i;
struct timespec antiepoch;
antiepoch.tv_sec = 0;
antiepoch.tv_nsec = 0;
(void) monotone(&antiepoch);
buf_set_next(state_buf, int, MDS_RESPAWN_VARS_VERSION);
buf_set_next(state_buf, sig_atomic_t, reviving);
buf_set_next(state_buf, time_t, antiepoch.tv_sec);
buf_set_next(state_buf, long, antiepoch.tv_nsec);
for (i = 0; i < servers; i++)
{
buf_set_next(state_buf, pid_t, states[i].pid);
buf_set_next(state_buf, int, states[i].state);
buf_set_next(state_buf, time_t, states[i].started.tv_sec);
buf_set_next(state_buf, long, states[i].started.tv_nsec);
}
free(states);
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)
{
size_t i;
struct timespec antiepoch;
struct timespec epoch;
epoch.tv_sec = 0;
epoch.tv_nsec = 0;
(void) monotone(&epoch);
/* buf_get_next(state_buf, int, MDS_RESPAWN_VARS_VERSION); */
buf_next(state_buf, int, 1);
buf_get_next(state_buf, sig_atomic_t, reviving);
buf_get_next(state_buf, time_t, antiepoch.tv_sec);
buf_get_next(state_buf, long, antiepoch.tv_nsec);
epoch.tv_sec -= antiepoch.tv_sec;
epoch.tv_nsec -= antiepoch.tv_nsec;
for (i = 0; i < servers; i++)
{
buf_get_next(state_buf, pid_t, states[i].pid);
buf_get_next(state_buf, int, states[i].state);
buf_get_next(state_buf, time_t, states[i].started.tv_sec);
buf_get_next(state_buf, long, states[i].started.tv_nsec);
if (validate_state(states[i].state) == 0)
{
states[i].state = CREMATED;
eprintf("invalid state unmarshallaed for `%s', cremating.", commands[i][0]);
}
else if (states[i].state == ALIVE)
{
live_count++;
/* Monotonic time epoch adjusment, the epoch of the monotonic
clock is unspecified, so we cannot know whether an exec
with cause a time jump. */
states[i].started.tv_sec -= epoch.tv_sec;
states[i].started.tv_nsec -= epoch.tv_nsec;
if (states[i].started.tv_nsec < 0)
{
states[i].started.tv_sec -= 1;
states[i].started.tv_nsec += 1000000000;
}
else if (states[i].started.tv_nsec > 0)
{
states[i].started.tv_sec += 1;
states[i].started.tv_nsec -= 1000000000;
}
}
}
return 0;
}
/**
* 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__((cold, const)) reexec_failure_recover(void)
{
/* Re-exec cannot fail. */
return 0;
}
/**
* Respawn a server that has exited if appropriate
*
* @param pid The process ID of the server that has exited
* @param status The server's death status
*/
static void joined_with_server(pid_t pid, int status)
{
struct timespec ended;
size_t i;
/* Find index of reaped server. */
for (i = 0; i < servers; i++)
if (states[i].pid == pid)
break;
if (i == servers)
{
eprintf("joined with unknown child process: %i", pid);
return;
}
/* Do nothing if the server is cremated. */
if (states[i].state == CREMATED)
{
eprintf("cremated child process `%s' exited, ignoring.", commands[i][0]);
return;
}
/* Mark server as dead if it was alive. */
if (states[i].state == ALIVE)
live_count--;
states[i].state = DEAD;
/* Cremate server if it exited normally or was killed nicely. */
if (WIFEXITED(status) ? (WEXITSTATUS(status) == 0) :
((WTERMSIG(status) == SIGTERM) || (WTERMSIG(status) == SIGINT)))
{
eprintf("child process `%s' exited normally, cremating.", commands[i][0]);
states[i].state = CREMATED;
return;
}
/* Print exit status of the reaped server. */
if (WIFEXITED(status))
eprintf("`%s' exited with code %i.", commands[i][0], WEXITSTATUS(status));
else
eprintf("`%s' died by signal %i.", commands[i][0], WTERMSIG(status));
/* When did the server exit. */
if (monotone(&ended) < 0)
{
xperror(*argv);
eprintf("`%s' died abnormally, burying because we could not read the time.", commands[i][0]);
states[i].state = DEAD_AND_BURIED;
return;
}
/* Bury the server if it died abnormally too fast. */
if (ended.tv_sec - states[i].started.tv_sec < interval)
{
eprintf("`%s' died abnormally, burying because it died too fast.", commands[i][0]);
states[i].state = DEAD_AND_BURIED;
return;
}
/* Respawn server if it died abnormally in a responable time. */
eprintf("`%s' died abnormally, respawning.", commands[i][0]);
spawn_server(i);
}
/**
* Perform the server's mission
*
* @return Non-zero on error
*/
int master_loop(void)
{
int status, rc = 0;
size_t i;
while (!reexecing && !terminating && live_count)
{
pid_t pid = uninterruptable_waitpid(-1, &status, 0);
if (reviving)
for (reviving = 0, i = 0; i < servers; i++)
if (states[i].state == DEAD_AND_BURIED)
spawn_server(i);
if (pid == (pid_t)-1)
{
xperror(*argv);
rc = 1;
break;
}
joined_with_server(pid, status);
}
free(commands_args);
free(commands);
if (reexecing == 0)
free(states);
return rc;
}
