lvm2/daemons/dmeventd/libdevmapper-event.c

/*
 * Copyright (C) 2005 Red Hat, Inc. All rights reserved.
 *
 * This file is part of the device-mapper userspace tools.
 *
 * This copyrighted material is made available to anyone wishing to use,
 * modify, copy, or redistribute it subject to the terms and conditions
 * of the GNU Lesser General Public License v.2.1.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include "lib.h"
#include "libdevmapper-event.h"
//#include "libmultilog.h"
#include "dmeventd.h"

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <sys/file.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <sys/wait.h>
#include <arpa/inet.h> /* for htonl, ntohl */

/* Set by any of the external fxns the first time one of them is called */
/* FIXME Unused */
// static int _logging = 0;

/* Fetch a string off src and duplicate it into *dest. */
/* FIXME: move to seperate module to share with the daemon. */
static const char delimiter = ' ';
static char *fetch_string(char **src)
{
	char *p, *ret;

	if ((p = strchr(*src, delimiter)))
		*p = 0;

	if ((ret = dm_strdup(*src)))
		*src += strlen(ret) + 1;

	if (p)
		*p = delimiter;

	return ret;
}

/* Parse a device message from the daemon. */
static int parse_message(struct dm_event_daemon_message *msg, char **dso_name,
			 char **device, enum dm_event_type *events)
{
	char *p = msg->data;

	if ((*dso_name = fetch_string(&p)) &&
	    (*device   = fetch_string(&p))) {
		*events = atoi(p);

		return 0;
	}

	return -ENOMEM;
}

/*
 * daemon_read
 * @fifos
 * @msg
 *
 * Read message from daemon.
 *
 * Returns: 0 on failure, 1 on success
 */
static int daemon_read(struct dm_event_fifos *fifos, struct dm_event_daemon_message *msg)
{
	unsigned bytes = 0;
	int ret, i;
	fd_set fds;
	struct timeval tval = {0, 0};
	size_t size = 2 * sizeof(uint32_t); // status + size
	char *buf = alloca(size);
	int header = 1;

	while (bytes < size) {
		for (i = 0, ret = 0; (i < 20) && (ret < 1); i++) {
			/* Watch daemon read FIFO for input. */
			FD_ZERO(&fds);
			FD_SET(fifos->server, &fds);
			tval.tv_sec = 1;
			ret = select(fifos->server+1, &fds, NULL, NULL, &tval);
			if (ret < 0 && errno != EINTR) {
				log_error("Unable to read from event server");
				return 0;
			}
		}
		if (ret < 1) {
			log_error("Unable to read from event server.");
			return 0;
		}

		ret = read(fifos->server, buf + bytes, size);
		if (ret < 0) {
			if ((errno == EINTR) || (errno == EAGAIN))
				continue;
			else {
				log_error("Unable to read from event server.");
				return 0;
			}
		}

		bytes += ret;
		if (bytes == 2*sizeof(uint32_t) && header) {
			msg->cmd = ntohl(*((uint32_t *)buf));
			msg->size = ntohl(*((uint32_t *)buf + 1));
			buf = msg->data = dm_malloc(msg->size);
			size = msg->size;
			bytes = 0;
			header = 0;
		}
	}

	if (bytes != size) {
		if (msg->data)
			dm_free(msg->data);
		msg->data = NULL;
	}

	return bytes == size;
}

/* Write message to daemon. */
static int daemon_write(struct dm_event_fifos *fifos, struct dm_event_daemon_message *msg)
{
	unsigned bytes = 0;
	int ret = 0;
	fd_set fds;

	size_t size = 2*sizeof(uint32_t) + msg->size;
	char *buf = alloca(size);

	*((uint32_t *)buf) = htonl(msg->cmd);
	*((uint32_t *)buf + 1) = htonl(msg->size);
	memcpy(buf + 2*sizeof(uint32_t), msg->data, msg->size);

	while (bytes < size) {
		do {
			/* Watch daemon write FIFO to be ready for output. */
			FD_ZERO(&fds);
			FD_SET(fifos->client, &fds);
			ret = select(fifos->client +1, NULL, &fds, NULL, NULL);
			if ((ret < 0) && (errno != EINTR)) {
				log_error("Unable to talk to event daemon");
				return 0;
			}
		} while (ret < 1);

		ret = write(fifos->client, ((char *) buf) + bytes, size - bytes);
		if (ret < 0) {
			if ((errno == EINTR) || (errno == EAGAIN))
				continue;
			else {
				log_error("Unable to talk to event daemon");
				return 0;
			}
		}

		bytes += ret;
	}

	return bytes == size;
}

static int daemon_talk(struct dm_event_fifos *fifos, struct dm_event_daemon_message *msg,
		       int cmd, const char *dso_name, const char *device,
		       enum dm_event_type events, uint32_t timeout)
{
	char test[1];
	const char *dso = dso_name ? dso_name : "";
	const char *dev = device ? device : "";
	const char *fmt = "%s %s %u %"PRIu32;
	memset(msg, 0, sizeof(*msg));

	/*
	 * Set command and pack the arguments
	 * into ASCII message string.
	 */
	msg->cmd = cmd;
	/* FIXME depends on glibc 2.1+ */
	msg->size = snprintf(test, 1, fmt, dso, dev, events, timeout);
	msg->data = alloca(msg->size);
	snprintf(msg->data, msg->size, fmt, dso, dev, events, timeout);

	/*
	 * Write command and message to and
	 * read status return code from daemon.
	 */
	if (!daemon_write(fifos, msg)) {
		stack;
		return -EIO;
	}

	if (!daemon_read(fifos, msg)) {
		stack;
		return -EIO;
	}

	return (int32_t) msg->cmd;
}

/*
 * start_daemon
 *
 * This function forks off a process (dmeventd) that will handle
 * the events.  I am currently test opening one of the fifos to
 * ensure that the daemon is running and listening...  I thought
 * this would be less expensive than fork/exec'ing every time.
 * Perhaps there is an even quicker/better way (no, checking the
 * lock file is _not_ a better way).
 *
 * Returns: 1 on success, 0 otherwise
 */
static int start_daemon(struct dm_event_fifos *fifos)
{
	int pid, ret = 0;
	int status;
	struct stat statbuf;

	if (stat(fifos->client_path, &statbuf))
		goto start_server;

	if (!S_ISFIFO(statbuf.st_mode)) {
		log_error("%s is not a fifo.", fifos->client_path);
		return 0;
	}

	/* Anyone listening?  If not, errno will be ENXIO */
	fifos->client = open(fifos->client_path, O_WRONLY | O_NONBLOCK);
	if (fifos->client >= 0) {
		/* server is running and listening */

		close(fifos->client);
		return 1;
	} else if (errno != ENXIO) {
		/* problem */

		log_error("%s: Can't open client fifo %s: %s",
			  __func__, fifos->client_path, strerror(errno));
		stack;
		return 0;
	}

start_server:
	/* server is not running */
	pid = fork();

	if (pid < 0)
		log_error("Unable to fork.");

	else if (!pid) {
		execvp("dmeventd", NULL); /* security risk if admin has bad PATH */
		exit(EXIT_FAILURE);
	} else {
		if (waitpid(pid, &status, 0) < 0)
			log_error("Unable to start dmeventd: %s", strerror(errno));
		else if (WEXITSTATUS(status))
			log_error("Unable to start dmeventd.");
		else
			ret = 1;
	}

	return ret;
}

/* Initialize client. */
static int init_client(struct dm_event_fifos *fifos)
{
	/* FIXME Is fifo the most suitable method? */
	/* FIXME Why not share comms/daemon code with something else e.g. multipath? */

	/* init fifos */
	memset(fifos, 0, sizeof(*fifos));
	fifos->client_path = DM_EVENT_FIFO_CLIENT;
	fifos->server_path = DM_EVENT_FIFO_SERVER;

	if (!start_daemon(fifos)) {
		stack;
		return 0;
	}

	/* Open the fifo used to read from the daemon. */
	if ((fifos->server = open(fifos->server_path, O_RDWR)) < 0) {
		log_error("%s: open server fifo %s",
			__func__, fifos->server_path);
		stack;
		return 0;
	}

	/* Lock out anyone else trying to do communication with the daemon. */
	if (flock(fifos->server, LOCK_EX) < 0){
		log_error("%s: flock %s", __func__, fifos->server_path);
		close(fifos->server);
		return 0;
	}

/*	if ((fifos->client = open(fifos->client_path,
  O_WRONLY | O_NONBLOCK)) < 0) {*/
	if ((fifos->client = open(fifos->client_path, O_RDWR | O_NONBLOCK)) < 0) {
		log_error("%s: Can't open client fifo %s: %s",
			  __func__, fifos->client_path, strerror(errno));
		close(fifos->server);
		stack;
		return 0;
	}
	
	return 1;
}

static void dtr_client(struct dm_event_fifos *fifos)
{
	if (flock(fifos->server, LOCK_UN))
		log_error("flock unlock %s", fifos->server_path);

	close(fifos->client);
	close(fifos->server);
}

/* Check, if a block device exists. */
static int device_exists(const char *device)
{
	struct stat st_buf;
	char path2[PATH_MAX];

	if (!device)
		return 0;

	if (device[0] == '/') /* absolute path */
		return !stat(device, &st_buf) && S_ISBLK(st_buf.st_mode);

	if (PATH_MAX <= snprintf(path2, PATH_MAX, "%s/%s", dm_dir(), device))
		return 0;

	return !stat(path2, &st_buf) && S_ISBLK(st_buf.st_mode);
}

/* Handle the event (de)registration call and return negative error codes. */
static int do_event(int cmd, struct dm_event_daemon_message *msg,
		    const char *dso_name, const char *device, enum dm_event_type events,
		    uint32_t timeout)
{
	int ret;
	struct dm_event_fifos fifos;

	/* FIXME Start the daemon here if it's not running e.g. exclusive lock file */
	/* FIXME Move this to separate 'dm_event_register_handler' - if no daemon here, fail */
	if (!init_client(&fifos)) {
		stack;
		return -ESRCH;
	}

	/* FIXME Use separate 'dm_event_register_handler' function to pass in dso? */
	ret = daemon_talk(&fifos, msg, cmd, dso_name, device, events, timeout);

	/* what is the opposite of init? */
	dtr_client(&fifos);
	
	return ret;
}

/* FIXME remove dso_name - use handle instead */
/* FIXME Use uuid not path! */
/* External library interface. */
int dm_event_register(const char *dso_name, const char *device_path,
		      enum dm_event_type events)
{
	int ret, err;
	struct dm_event_daemon_message msg;

	if (!device_exists(device_path)) {
		log_error("%s: device not found", device_path);
		return 0;
	}

	if ((err = do_event(DM_EVENT_CMD_REGISTER_FOR_EVENT, &msg,
			    dso_name, device_path, events, 0)) < 0) {
		log_error("%s: event registration failed: %s", device_path,
			  msg.data ? msg.data : strerror(-err));
		ret = 0;
	} else
		ret = 1;

	if (msg.data)
		dm_free(msg.data);

	return ret;
}

int dm_event_unregister(const char *dso_name, const char *device_path,
			enum dm_event_type events)
{
	int ret, err;
	struct dm_event_daemon_message msg;

	if (!device_exists(device_path)) {
		log_error("%s: device not found", device_path);
		return 0;
	}

	if ((err = do_event(DM_EVENT_CMD_UNREGISTER_FOR_EVENT, &msg,
			    dso_name, device_path, events, 0)) < 0) {
		log_error("%s: event deregistration failed: %s", device_path,
			  msg.data ? msg.data : strerror(-err));
		ret = 0;
	} else
		ret = 1;

	if (msg.data)
		dm_free(msg.data);
	return ret;
}

/*
 * dm_event_get_registered_device
 * @dso_name
 * @device_path
 * @events
 * @next
 *
 * FIXME: This function sucks.
 *
 * Returns: 1 if device found, 0 otherwise (even on error)
 */
int dm_event_get_registered_device(char **dso_name, char **device_path,
			     enum dm_event_type *events, int next)
{
	int ret;
	char *dso_name_arg = NULL, *device_path_arg = NULL;
	struct dm_event_daemon_message msg;

	if (!(ret = do_event(next ? DM_EVENT_CMD_GET_NEXT_REGISTERED_DEVICE :
				    DM_EVENT_CMD_GET_REGISTERED_DEVICE,
			     &msg, *dso_name, *device_path, *events, 0))) {
		ret = !parse_message(&msg, &dso_name_arg, &device_path_arg,
				     events);
	} else /* FIXME: Make sure this is ENOENT */
		ret = 0;

	if (msg.data)
		dm_free(msg.data);

	if (next) {
		if (*dso_name)
			dm_free(*dso_name);
		if (*device_path)
			dm_free(*device_path);
		*dso_name = dso_name_arg;
		*device_path = device_path_arg;
	} else {
		if (!(*dso_name))
			*dso_name = dso_name_arg;
		if (!(*device_path))
			*device_path = device_path_arg;
	}

	return ret;
}

int dm_event_set_timeout(const char *device_path, uint32_t timeout)
{
	struct dm_event_daemon_message msg;

	if (!device_exists(device_path))
		return -ENODEV;
	return do_event(DM_EVENT_CMD_SET_TIMEOUT, &msg,
			NULL, device_path, 0, timeout);
}

int dm_event_get_timeout(const char *device_path, uint32_t *timeout)
{
	int ret;
	struct dm_event_daemon_message msg;

	if (!device_exists(device_path))
		return -ENODEV;
	if (!(ret = do_event(DM_EVENT_CMD_GET_TIMEOUT, &msg, NULL, device_path, 0, 0)))
		*timeout = atoi(msg.data);
	if (msg.data)
		dm_free(msg.data);
	return ret;
}