path: root/server.c

/* SPDX-License-Identifier: GPL-2.0 */

/** \file server.c Paraslash's main server.
 *
 * This file implements the main function of para_server(1) and its core
 * functionality, including signal handling and task setup/teardown and TCP
 * socket management.
 *
 * The file also contains a few helpers for other subsystems.
 */

#include <netinet/in.h>
#include <sys/socket.h>
#include <signal.h>
#include <osl.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <sys/un.h>
#include <netdb.h>
#include <lopsub.h>

#include "server.lsg.h"
#include "para.h"
#include "error.h"
#include "lsu.h"
#include "crypt.h"
#include "afh.h"
#include "string.h"
#include "afs.h"
#include "net.h"
#include "list.h"
#include "server.h"
#include "sched.h"
#include "send.h"
#include "vss.h"
#include "daemon.h"
#include "ipc.h"
#include "fd.h"
#include "signal.h"
#include "color.h"

/** \cond doxygen_ignore */
/* Get a reference to the supercommand of para_server. */
#define CMD_PTR (lls_cmd(0, server_suite))

/* Array of error strings. */
DEFINE_PARA_ERRLIST;

__printf_2_3 void (*para_log)(int, const char*, ...) = daemon_log;


/** \endcond */

/**
 * Pointer to shared memory area for communication between para_server
 * and its children. Exported to vss.c, command.c and to afs.
 */
struct misc_meta_data *mmd;

/**
 * The active value for all config options of para_server.
 *
 * It is computed by merging the parse result of the command line options with
 * the parse result of the config file.
 */
struct lls_parse_result *server_lpr = NULL;

/* Command line options (no config file options). Used in handle_sighup(). */
static struct lls_parse_result *cmdline_lpr;

/** The mutex protecting the shared memory area containing the mmd struct. */
int mmd_mutex;

/* Serializes log output. */
static int log_mutex;

/** The process id of the audio file selector process. */
pid_t afs_pid = 0;

/* The main server process (parent of afs and the command handlers). */
static pid_t server_pid;

static INITIALIZED_LIST_HEAD(user_list);

/** Initialized from the argument to --announce-time. */
struct timeval announce_tv;

/*
 * Wrapper for fgets(3).
 *
 * Unlike fgets(3), an integer value is returned. On success, this function
 * returns 1. On errors, -E_FGETS is returned. A zero return value indicates an
 * end of file condition.
 */
static int xfgets(char *line, int size, FILE *f)
{
again:
	if (fgets(line, size, f))
		return 1;
	if (feof(f))
		return 0;
	if (!ferror(f))
		return -E_FGETS;
	if (errno != EINTR) {
		PARA_ERROR_LOG("%s\n", strerror(errno));
		return -E_FGETS;
	}
	clearerr(f);
	goto again;
}

/*
 * Remove all entries from the user list. This is called on shutdown and
 * when the user list is reloaded because the server received SIGHUP.
 */
static void user_list_deplete(void)
{
	struct user *u, *tmpu;

	list_for_each_entry_safe(u, tmpu, &user_list, node) {
		list_del(&u->node);
		free(u->name);
		apc_free_pubkey(u->pubkey);
		free(u);
	}
}

/*
 * Initialize the list of users allowed to connect. This function may be
 * called more than once. Subsequent calls reload the user list by removing
 * any existing entries of the user list. The function either succeeds or
 * calls exit(3).
 */
static void user_list_init(const char *user_list_file)
{
	int ret = -E_USERLIST;
	FILE *file_ptr = fopen(user_list_file, "r");
	struct user *u;

	if (!file_ptr)
		goto err;

	user_list_deplete();
	for (;;) {
		int num;
		char line[255];
		/* keyword, name, key, perms */
		char w[255], n[255], k[255], p[255], tmp[4][255];
		struct asymmetric_key *pubkey;

		ret = xfgets(line, sizeof(line), file_ptr);
		if (ret <= 0)
			break;
		if (sscanf(line,"%200s %200s %200s %200s", w, n, k, p) < 3)
			continue;
		if (strcmp(w, "user"))
			continue;
		PARA_INFO_LOG("loading pubkey %s for user %s\n", k, n);
		ret = apc_get_pubkey(k, &pubkey);
		if (ret < 0) {
			PARA_NOTICE_LOG("skipping entry for user %s: %s\n", n,
				para_strerror(-ret));
			continue;
		}
		/*
		 * In order to encrypt len := APC_CHALLENGE_SIZE + 2 * SESSION_KEY_LEN
		 * bytes using RSA_public_encrypt() with EME-OAEP padding mode,
		 * RSA_size(rsa) must be greater than len + 41. So ignore keys
		 * which are too short. For details see RSA_public_encrypt(3).
		 */
		if (ret <= APC_CHALLENGE_SIZE + 2 * SESSION_KEY_LEN + 41) {
			PARA_WARNING_LOG("public key %s too short (%d)\n",
				k, ret);
			apc_free_pubkey(pubkey);
			continue;
		}
		u = alloc(sizeof(*u));
		u->name = para_strdup(n);
		u->pubkey = pubkey;
		u->perms = 0;
		num = sscanf(p, "%200[A-Z_],%200[A-Z_],%200[A-Z_],%200[A-Z_]",
			tmp[0], tmp[1], tmp[2], tmp[3]);
		PARA_DEBUG_LOG("found %i perm entries\n", num);
		while (num > 0) {
			num--;
			if (!strcmp(tmp[num], "VSS_READ"))
				u->perms |= VSS_READ;
			else if (!strcmp(tmp[num], "VSS_WRITE"))
				u->perms |= VSS_WRITE;
			else if (!strcmp(tmp[num], "AFS_READ"))
				u->perms |= AFS_READ;
			else if (!strcmp(tmp[num], "AFS_WRITE"))
				u->perms |= AFS_WRITE;
			else /* unknown permission */
				PARA_WARNING_LOG("ignoring unknown permission: %s\n",
					tmp[num]);
		}
		para_list_add(&u->node, &user_list);
	}
	fclose(file_ptr);
	if (ret >= 0)
		return;
err:
	PARA_EMERG_LOG("%s\n", para_strerror(-ret));
	exit(EXIT_FAILURE);
}

/**
 * Look up a user in the user list.
 *
 * \param name The name of the user.
 *
 * \return A pointer to the corresponding user struct if the user was found,
 * NULL otherwise.
 */
const struct user *user_list_lookup(const char *name)
{
	const struct user *u;
	list_for_each_entry(u, &user_list, node) {
		if (strcmp(u->name, name))
			continue;
		return u;
	}
	return NULL;
}


static INITIALIZED_LIST_HEAD(close_on_fork_list);

/* Describes an element of the close-on-fork list. */
struct close_on_fork_entry {
	int fd; /* The file descriptor which should be closed after fork(). */
	struct list_head node; /* The position in the close-on-fork list. */
};

/**
 * Add one file descriptor to the close-on-fork list.
 *
 * \param fd The file descriptor to add.
 */
void add_close_on_fork_list(int fd)
{
	struct close_on_fork_entry *e = alloc(sizeof(*e));

	e->fd = fd;
	para_list_add(&e->node, &close_on_fork_list);
}

/**
 * Delete one file descriptor from the close-on-fork list.
 *
 * \param fd The file descriptor to delete.
 *
 * Noop if fd does not belong to the close-on-fork list.
 */
void del_close_on_fork_list(int fd)
{
	struct close_on_fork_entry *e, *tmp;

	list_for_each_entry_safe(e, tmp, &close_on_fork_list, node) {
		if (fd != e->fd)
			continue;
		list_del(&e->node);
		free(e);
	}
}

/* Destroy all entries, optionally close the fds as we go. */
static void deplete_cof_list(bool close_fds)
{
	struct close_on_fork_entry *e, *tmp;

	list_for_each_entry_safe(e, tmp, &close_on_fork_list, node) {
		PARA_DEBUG_LOG("closing fd %d\n", e->fd);
		if (close_fds)
			close(e->fd);
		list_del(&e->node);
		free(e);
	}
}

static int parse_fec_parms(const char *arg, struct sender_command_data *scd)
{
	int32_t val;
	char *a = para_strdup(arg), *b = strchr(a, ':'), *c = strrchr(a, ':');
	int ret = -E_COMMAND_SYNTAX;

	if (!b || !c)
		goto out;
	*b = *c = '\0';

	ret = para_atoi32(a, &val);
	if (ret < 0)
		goto out;

	/* optional max_slice_bytes (0 means "use MTU") */
	if (b == c) {
		scd->max_slice_bytes = 0;
	} else {
		if (val < 0 || val > 65535)
			goto fec_einval;
		scd->max_slice_bytes = val;

		ret = para_atoi32(b + 1, &val);
		if (ret < 0)
			goto out;
	}

	/* k = data_slices_per_group */
	if (val < 0 || val > 255)
		goto fec_einval;
	scd->data_slices_per_group = val;

	/* n = slices_per_group */
	ret = para_atoi32(c + 1, &val);
	if (ret < 0)
		goto out;
	if (val < 0 || val < scd->data_slices_per_group)
		goto fec_einval;
	scd->slices_per_group = val;
	ret = 0;
out:
	free(a);
	return ret;
fec_einval:
	ret = -ERRNO_TO_PARA_ERROR(EINVAL);
	goto out;
}

/**
 * Parse a FEC URL string.
 *
 * \param arg the URL string to parse.
 * \param scd The structure containing host, port and the FEC parameters.
 *
 * \return Standard.
 *
 * A FEC URL consists of an ordinary URL string according to RFC 3986,
 * optionally followed by a slash and the three FEC parameters slice_size,
 * data_slices_per_group and slices_per_group. The three FEC parameters are
 * separated by colons.
 *
 * \sa \ref parse_url().
 */
int parse_fec_url(const char *arg, struct sender_command_data *scd)
{
	char *a = para_strdup(arg), *p = strchr(a, '/');
	int ret = 0;

	/* default fec parameters */
	scd->max_slice_bytes	   = 0;
	scd->data_slices_per_group = 14;
	scd->slices_per_group	   = 16;

	if (p) {
		*p = '\0';
		ret = parse_fec_parms(p + 1, scd);
		if (ret < 0)
			goto out;
	}
	if (!parse_url(a, scd->host, sizeof(scd->host), &scd->port))
		ret = -ERRNO_TO_PARA_ERROR(EINVAL);
out:
	free(a);
	return ret;
}

/**
 * Tell whether the executing process is a command handler.
 *
 * Cleanup on exit must be performed differently for command handlers.
 *
 * \return True if the pid of the executing process is neither the server pid
 * nor the afs pid.
 */
bool process_is_command_handler(void)
{
	pid_t pid = getpid();

	return pid != afs_pid && pid != server_pid;
}

/** The task responsible for server command handling. */
struct server_command_task {
	unsigned num_listen_fds; /* only one by default */
	/** TCP socket(s) on which para_server listens for connections. */
	int *listen_fds;
	int afs_fd;
	/* Obtained by accepting a connection on the listening socket. */
	int client_fd;
	/** Copied from para_server's main function. */
	int argc;
	/** Argument vector passed to para_server's main function. */
	char **argv;
	/** The command task structure for scheduling. */
	struct task *task;
};

static void pre_log_hook(void)
{
	mutex_lock(log_mutex);
}

static void post_log_hook(void)
{
	mutex_unlock(log_mutex);
}

/* Setup shared memory area and init mutexes */
static void init_ipc_or_die(void)
{
	void *shm;
	int shmid, ret = shm_new(sizeof(struct misc_meta_data));

	if (ret < 0)
		goto err_out;
	shmid = ret;
	ret = shm_attach(shmid, ATTACH_RW, &shm);
	shm_destroy(shmid);
	if (ret < 0)
		goto err_out;
	mmd = shm;

	ret = mutex_new();
	if (ret < 0)
		goto err_out;
	mmd_mutex = ret;
	ret = mutex_new();
	if (ret < 0)
		goto destroy_mmd_mutex;
	log_mutex = ret;

	mmd->num_played = 0;
	mmd->num_commands = 0;
	mmd->events = 0;
	mmd->num_connects = 0;
	mmd->active_connections = 0;
	mmd->vss_status_flags = VSS_NEXT;
	mmd->new_vss_status_flags = VSS_NEXT;
	mmd->loglevel = OPT_UINT32_VAL(LOGLEVEL);
	return;
destroy_mmd_mutex:
	mutex_destroy(mmd_mutex);
err_out:
	PARA_EMERG_LOG("%s\n", para_strerror(-ret));
	exit(EXIT_FAILURE);
}

/**
 * (Re-)read the server configuration files.
 *
 * \param reload Whether config file overrides command line.
 *
 * This function also re-opens the logfile and the user list. On SIGHUP it is
 * called from both server and afs context.
 */
void parse_config_or_die(bool reload)
{
	int ret;
	unsigned flags = MCF_DONT_FREE;

	if (server_lpr != cmdline_lpr)
		lls_free_parse_result(server_lpr, CMD_PTR);
	server_lpr = cmdline_lpr;
	if (reload)
		flags |= MCF_OVERRIDE;
	ret = lsu_merge_config_file_options(OPT_STRING_VAL(CONFIG_FILE),
		"server.conf", &server_lpr, CMD_PTR, server_suite, flags);
	if (ret < 0) {
		PARA_EMERG_LOG("failed to parse config file: %s\n",
			para_strerror(-ret));
		exit(EXIT_FAILURE);
	}
	daemon_set_loglevel(OPT_UINT32_VAL(LOGLEVEL));
	if (OPT_GIVEN(LOGFILE)) {
		daemon_set_logfile(OPT_STRING_VAL(LOGFILE));
		daemon_open_log_or_die();
	}
	if (daemon_init_colors_or_die(OPT_UINT32_VAL(COLOR), COLOR_AUTO,
			COLOR_NO, OPT_GIVEN(LOGFILE))) {
		int i;
		for (i = 0; i < OPT_GIVEN(LOG_COLOR); i++)
			daemon_set_log_color_or_die(lls_string_val(i,
				OPT_RESULT(LOG_COLOR)));
	}
	daemon_set_flag(DF_LOG_PID);
	daemon_set_flag(DF_LOG_LL);
	daemon_set_flag(DF_LOG_TIME);
	if (OPT_GIVEN(LOG_TIMING))
		daemon_set_flag(DF_LOG_TIMING);
	daemon_set_priority(OPT_UINT32_VAL(PRIORITY));
	if (!reload || getpid() != afs_pid) {
		char *user_list_file;
		if (OPT_GIVEN(USER_LIST))
			user_list_file = para_strdup(OPT_STRING_VAL(USER_LIST));
		else {
			char *home = para_homedir();
			user_list_file = make_message("%s/.paraslash/server.users", home);
			free(home);
		}
		user_list_init(user_list_file);
		free(user_list_file);
	}
}

/* Called when server receives SIGHUP or user runs the hup subcommand. */
static void handle_sighup(void)
{
	PARA_NOTICE_LOG("SIGHUP\n");
	parse_config_or_die(true);
	ms2tv(OPT_UINT32_VAL(ANNOUNCE_TIME), &announce_tv);
	if (afs_pid != 0)
		kill(afs_pid, SIGHUP);
}

/*
 * Returns negative error code on errors, zero if no child died, one
 * otherwise. It is considered a fatal error if the afs process died.
 */
static int reap_child(void)
{
	const char *child_name;
	int status, ll, ret;
	pid_t pid = waitpid(-1, &status, WNOHANG);

	if (pid < 0)
		return -ERRNO_TO_PARA_ERROR(errno);
	if (pid == 0)
		return 0;
	if (pid == afs_pid) {
		child_name = "afs";
		ll = LL_ERROR;
		ret = -ERRNO_TO_PARA_ERROR(ECHILD);
	} else {
		child_name = "command handler";
		ll = LL_INFO;
		ret = 1;
	}
	if (WIFEXITED(status))
		para_log(ll, "%s exited. Exit status: %i\n", child_name,
			WEXITSTATUS(status));
	else if (WIFSIGNALED(status))
		para_log(ll, "%s was killed by signal %i\n", child_name,
			WTERMSIG(status));
	else
		para_log(ll, "%s terminated abormally\n", child_name);
	return ret;
}

static int signal_post_monitor(struct sched *s, void *context)
{
	struct signal_task *st = context;
	int ret, signum;

	ret = task_get_notification(st->task);
	if (ret < 0)
		return ret;
	signum = para_next_signal();
	switch (signum) {
	case 0:
		return 0;
	case SIGHUP:
		handle_sighup();
		return 0;
	case SIGCHLD:
		for (;;) {
			ret = reap_child();
			if (ret < 0)
				goto genocide;
			if (ret == 0)
				return 0;
		}
	/* die on sigint/sigterm. Kill all children too. */
	case SIGINT:
	case SIGTERM:
		PARA_EMERG_LOG("terminating on signal %d\n", signum);
genocide:
		kill(0, SIGTERM);
		/*
		 * We must wait for all of our children to die. For the afs
		 * process or a command handler might want to use the
		 * shared memory area and the mmd mutex.  If we destroy this
		 * mutex too early and afs tries to lock the shared memory
		 * area, the call to mutex_lock() will fail and terminate the
		 * afs process. This leads to dirty osl tables.
		 */
		PARA_INFO_LOG("waiting for child processes to die\n");
		mutex_unlock(mmd_mutex);
		while (wait(NULL) != -1 || errno != ECHILD)
			; /* still at least one child alive */
		mutex_lock(mmd_mutex);
		free(mmd->afd.afhi.chunk_table);
		task_notify_all(s, E_DEADLY_SIGNAL);
		return -E_DEADLY_SIGNAL;
	}
	assert(0);
}

static void register_signal_task(struct sched *sched)
{
	static struct signal_task signal_task;

	signal_task.fd = signal_init();
	para_install_sighandler(SIGINT);
	para_install_sighandler(SIGTERM);
	para_install_sighandler(SIGHUP);
	para_install_sighandler(SIGCHLD);
	para_sigaction(SIGPIPE, SIG_IGN);
	add_close_on_fork_list(signal_task.fd);
	signal_task.task = task_register(&(struct task_info) {
		.name = "signal",
		.pre_monitor = signal_pre_monitor,
		.post_monitor = signal_post_monitor,
		.context = &signal_task,
	}, sched);
}

static void command_pre_monitor(struct sched *s, void *context)
{
	unsigned n;
	struct server_command_task *sct = context;

	for (n = 0; n < sct->num_listen_fds; n++)
		sched_monitor_readfd(sct->listen_fds[n], s);
}

static int command_task_accept(unsigned listen_idx, struct sched *s,
		struct server_command_task *sct)
{
	int new_fd, ret, i;
	char *peer_name;
	pid_t child_pid;
	uint32_t *chunk_table;

	ret = para_accept(sct->listen_fds[listen_idx], NULL, 0, &new_fd);
	if (ret <= 0)
		goto out;
	mmd->num_connects++;
	mmd->active_connections++;
	/*
	 * The chunk table is a pointer located in the mmd struct that points
	 * to dynamically allocated memory, i.e. it must be freed by the parent
	 * and the child. However, as the mmd struct is in a shared memory
	 * area, there's no guarantee that after the fork this pointer is still
	 * valid in child context. As it is not used in the child anyway, we
	 * save it to a local variable before the fork and free the memory via
	 * that copy in the child directly after the fork.
	 */
	chunk_table = mmd->afd.afhi.chunk_table;
	child_pid = fork();
	if (child_pid < 0) {
		ret = -ERRNO_TO_PARA_ERROR(errno);
		goto out;
	}
	if (child_pid) {
		/* avoid problems with non-fork-safe PRNGs */
		unsigned char buf[16];
		get_random_bytes_or_die(buf, sizeof(buf));
		close(new_fd);
		/* parent keeps accepting connections */
		return 0;
	}
	peer_name = remote_name(new_fd);
	PARA_INFO_LOG("accepted connection from %s\n", peer_name);
	/* mmd might already have changed at this point */
	free(chunk_table);
	sct->client_fd = new_fd;
	/*
	 * put info on who we are serving into argv[0] to make
	 * client ip visible in top/ps
	 */
	for (i = sct->argc - 1; i >= 0; i--)
		memset(sct->argv[i], 0, strlen(sct->argv[i]));
	i = sct->argc - 1 - lls_num_inputs(cmdline_lpr);
	sprintf(sct->argv[i], "para_server (serving %s)", peer_name);
	/* ask other tasks to terminate */
	task_notify_all(s, E_CHILD_CONTEXT);
	/*
	 * After we return, the scheduler calls server_select() with a minimal
	 * timeout value, because the remaining tasks have a notification
	 * pending. Next it calls the ->post_monitor method of these tasks,
	 * which will return negative in view of the notification. This causes
	 * schedule() to return as there are no more runnable tasks.
	 *
	 * Note that semaphores are not inherited across a fork(), so we don't
	 * hold the lock at this point. Since server_poll() drops the lock
	 * prior to calling poll(), we need to acquire it here.
	 */
	mutex_lock(mmd_mutex);
	return -E_CHILD_CONTEXT;
out:
	if (ret < 0)
		PARA_CRIT_LOG("%s\n", para_strerror(-ret));
	return 0;
}

static int command_post_monitor(struct sched *s, void *context)
{
	struct server_command_task *sct = context;
	unsigned n;
	int ret;

	ret = task_get_notification(sct->task);
	if (ret < 0)
		goto fail;
	for (n = 0; n < sct->num_listen_fds; n++) {
		ret = command_task_accept(n, s, sct);
		if (ret < 0)
			goto fail;
	}
	return 0;
fail:
	free(sct->listen_fds);
	return ret;
}

static void register_command_task(struct server_command_task *sct,
		struct sched *sched, int argc, char **argv)
{
	int ret;
	unsigned n;
	uint32_t port = OPT_UINT32_VAL(PORT);

	PARA_NOTICE_LOG("initializing tcp command socket\n");
	sct->client_fd = -1;
	sct->argc = argc;
	sct->argv = argv;
	if (!OPT_GIVEN(LISTEN_ADDRESS)) {
		sct->num_listen_fds = 1;
		sct->listen_fds = alloc(sizeof(int));
		ret = para_listen_simple(IPPROTO_TCP, port);
		if (ret < 0)
			goto err;
		sct->listen_fds[0] = ret;
	} else {
		sct->num_listen_fds = OPT_GIVEN(LISTEN_ADDRESS);
		sct->listen_fds = alloc(sct->num_listen_fds * sizeof(int));
		for (n = 0; n < OPT_GIVEN(LISTEN_ADDRESS); n++) {
			const char *arg;
			arg = lls_string_val(n, OPT_RESULT(LISTEN_ADDRESS));
			ret = para_listen(IPPROTO_TCP, arg, port);
			if (ret < 0)
				goto err;
			sct->listen_fds[n] = ret;
		}
	}
	for (n = 0; n < sct->num_listen_fds; n++) {
		ret = mark_fd_nonblocking(sct->listen_fds[n]);
		if (ret < 0)
			goto err;
		/* child doesn't need the listener */
		add_close_on_fork_list(sct->listen_fds[n]);
	}

	sct->task = task_register(&(struct task_info) {
		.name = "server command",
		.pre_monitor = command_pre_monitor,
		.post_monitor = command_post_monitor,
		.context = sct,
	}, sched);
	/*
	 * Detect whether the abstract Unix domain socket space is supported,
	 * but do not create the socket. We check this once in server context
	 * so that the command handlers inherit this bit of information and
	 * don't need to check again.
	 */
	create_local_socket(NULL);
	return;
err:
	PARA_EMERG_LOG("%s\n", para_strerror(-ret));
	exit(EXIT_FAILURE);
}

static int init_afs(int argc, char **argv)
{
	int ret, afs_server_socket[2];
	char c;

	ret = socketpair(PF_UNIX, SOCK_STREAM, 0, afs_server_socket);
	if (ret < 0)
		exit(EXIT_FAILURE);
	afs_pid = fork();
	if (afs_pid < 0)
		exit(EXIT_FAILURE);
	if (afs_pid == 0) { /* child (afs) */
		int i;

		afs_pid = getpid();
		crypt_shutdown();
		user_list_deplete();
		for (i = argc - 1; i >= 0; i--)
			memset(argv[i], 0, strlen(argv[i]));
		i = argc - lls_num_inputs(cmdline_lpr) - 1;
		sprintf(argv[i], "para_server (afs)");
		close(afs_server_socket[0]);
		afs_init(afs_server_socket[1]);
	}
	close(afs_server_socket[1]);
	if (read(afs_server_socket[0], &c, 1) <= 0) {
		PARA_EMERG_LOG("early afs exit\n");
		exit(EXIT_FAILURE);
	}
	ret = mark_fd_nonblocking(afs_server_socket[0]);
	if (ret < 0)
		exit(EXIT_FAILURE);
	return afs_server_socket[0];
}

static void handle_help_flags(void)
{
	char *help;
	bool d = OPT_GIVEN(DETAILED_HELP);

	if (d)
		help = lls_long_help(CMD_PTR);
	else if (OPT_GIVEN(HELP))
		help = lls_short_help(CMD_PTR);
	else
		return;
	printf("%s\n", help);
	free(help);
	exit(EXIT_SUCCESS);
}

static int server_poll(struct pollfd *fds, nfds_t nfds, int timeout)
{
	static int prev_events = -1;
	int ret;

	daemon_set_loglevel(mmd->loglevel);
	if (prev_events != mmd->events)
		goto force_update;
	if (mmd->new_vss_status_flags == mmd->vss_status_flags)
		goto poll;
	mmd->events++;
force_update:
	prev_events = mmd->events;
	mmd->vss_status_flags = mmd->new_vss_status_flags;
	PARA_DEBUG_LOG("%u events, forcing status update\n", mmd->events);
	killpg(0, SIGUSR1);
poll:
	mutex_unlock(mmd_mutex);
	ret = xpoll(fds, nfds, timeout);
	mutex_lock(mmd_mutex);
	return ret;
}

/* exit on errors, never return NULL */
static struct sched *server_init(int argc, char **argv,
		struct server_command_task *sct)
{
	int ret, daemon_pipe = -1;
	char *errctx;
	struct sched *sched;

	valid_fd_012();
	/* parse command line options */
	ret = lls(lls_parse(argc, argv, CMD_PTR, &cmdline_lpr, &errctx));
	if (ret < 0)
		goto fail;
	server_lpr = cmdline_lpr;
	daemon_set_loglevel(OPT_UINT32_VAL(LOGLEVEL));
	daemon_drop_privileges_or_die(OPT_STRING_VAL(USER),
		OPT_STRING_VAL(GROUP));
	version_handle_flag("server", OPT_GIVEN(VERSION));
	handle_help_flags();
	parse_config_or_die(false);
	/* become daemon */
	if (OPT_GIVEN(DAEMON))
		daemon_pipe = daemonize(true /* parent waits for SIGTERM */);
	server_pid = getpid();
	crypt_init();
	daemon_log_welcome("server");
	init_ipc_or_die(); /* init mmd struct, mmd and log mutex */
	daemon_set_start_time();
	daemon_set_hooks(pre_log_hook, post_log_hook);
	/*
	 * Although afs uses its own signal handling we must ignore SIGUSR1
	 * _before_ the afs child process gets born by init_afs() below.  It's
	 * racy to do this in the child because the parent might send SIGUSR1
	 * before the child gets a chance to ignore this signal.
	 *
	 * We also have to block SIGCHLD before the afs process is created
	 * because otherwise para_server does not notice if afs dies before the
	 * SIGCHLD handler has been installed for the parent process by
	 * register_signal_task() below.
	 */
	para_sigaction(SIGUSR1, SIG_IGN);
	para_block_signal(SIGCHLD);
	PARA_NOTICE_LOG("initializing the audio file selector\n");
	sct->afs_fd = init_afs(argc, argv);
	sched = sched_new(server_poll);
	register_signal_task(sched);
	para_unblock_signal(SIGCHLD);
	ms2tv(OPT_UINT32_VAL(ANNOUNCE_TIME), &announce_tv);
	PARA_NOTICE_LOG("initializing virtual streaming system\n");
	vss_init(sct->afs_fd, sched);
	register_command_task(sct, sched, argc, argv);
	if (daemon_pipe >= 0) {
		if (write(daemon_pipe, "\0", 1) < 0) {
			PARA_EMERG_LOG("daemon_pipe: %s", strerror(errno));
			exit(EXIT_FAILURE);
		}
		close(daemon_pipe);
	}
	PARA_NOTICE_LOG("server init complete\n");
	return sched;
fail:
	assert(ret < 0);
	if (errctx)
		PARA_ERROR_LOG("%s\n", errctx);
	PARA_EMERG_LOG("%s\n", para_strerror(-ret));
	exit(EXIT_FAILURE);
}

/**
 * Deallocate all lopsub parse results.
 *
 * The server allocates a parse result for command line options and optionally
 * a second parse result for the effective configuration, defined by merging
 * the command line options with the options stored in the configuration file.
 * This function frees both structures.
 */
void free_lpr(void)
{
	lls_free_parse_result(server_lpr, CMD_PTR);
	if (server_lpr != cmdline_lpr)
		lls_free_parse_result(cmdline_lpr, CMD_PTR);
}

/**
 * The main function of para_server.
 *
 * \param argc Options are defined in the server lopsub suite.
 * \param argv Subcommands are defined in the server_command suite.
 *
 * We fork once at startup to create the afs process. The child calls \ref
 * afs_init() of \ref afs.c to initialize the audio file selector. Both
 * processes define and register their own set of tasks to the scheduler.
 *
 * The server processes registers three tasks to handle signals, stream audio,
 * or dispatch command requests at the command socket. Incoming requests
 * are handled without blocking by forking and having the child call \ref
 * handle_connect() of \ref command.c.
 *
 * \return EXIT_SUCCESS or EXIT_FAILURE.
 */
int main(int argc, char *argv[])
{
	int ret;
	struct server_command_task server_command_task_struct,
		*sct = &server_command_task_struct;
	struct sched *sched = server_init(argc, argv, sct);

	mutex_lock(mmd_mutex);
	ret = schedule(sched);
	/*
	 * We hold the mmd lock: it was re-acquired in server_poll()
	 * after the poll(2) call.
	 */
	mutex_unlock(mmd_mutex);
	sched_shutdown(sched);
	crypt_shutdown();
	if (!process_is_command_handler()) { /* parent (server) */
		mutex_destroy(mmd_mutex);
		daemon_set_hooks(NULL, NULL); /* only one process remaining */
		mutex_destroy(log_mutex);
		deplete_cof_list(false /* don't close fds */);
		if (ret < 0)
			PARA_EMERG_LOG("%s\n", para_strerror(-ret));
	} else {
		deplete_cof_list(true /* close fds */);
		ret = handle_connect(sct->client_fd, sct->afs_fd);
	}
	vss_shutdown();
	shm_detach(mmd);
	user_list_deplete();
	free_lpr();
	exit(ret < 0? EXIT_FAILURE : EXIT_SUCCESS);
}