lvmetad: add helper process and uevent monitordev-dct-lvmetad-helper4

so that lvmetad can keep its cache updated (and
autoactivate LVs) by itself without the assistance
of externally generated pvscan commands.

- the lvm udev rule sets the LVM_DO_PVSCAN label on
  devs that should be scanned.

- the lvmetad uevent monitor watches for devs with
  the LVM_DO_PVSCAN label.

- when an LVM_DO_PVSCAN event is seen, the lvmetad helper
  is told to run pvscan --cache -aay on that device.

TODO: error and failure handling -- if anything
fails related to the helper or uevents, lvmetad
should simply exit.

7 files changed, 706 insertions, 34 deletions

diff --git a/daemons/lvmetad/Makefile.in b/daemons/lvmetad/Makefile.in
index fa3bdf1da..9e039c93e 100644
--- a/daemons/lvmetad/Makefile.in
+++ b/daemons/lvmetad/Makefile.in
@@ -15,7 +15,7 @@ srcdir = @srcdir@
 top_srcdir = @top_srcdir@
 top_builddir = @top_builddir@
 
-SOURCES = lvmetad-core.c
+SOURCES = lvmetad-core.c lvmetad-helper.c
 SOURCES2 = testclient.c
 
 TARGETS = lvmetad lvmetactl
@@ -31,7 +31,7 @@ include $(top_builddir)/make.tmpl
 INCLUDES += -I$(top_srcdir)/libdaemon/server
 LVMLIBS = -ldaemonserver $(LVMINTERNAL_LIBS) -ldevmapper
 
-LIBS += $(PTHREAD_LIBS)
+LIBS += $(PTHREAD_LIBS) -ludev
 
 LDFLAGS += -L$(top_builddir)/libdaemon/server $(EXTRA_EXEC_LDFLAGS)
 CLDFLAGS += -L$(top_builddir)/libdaemon/server
diff --git a/daemons/lvmetad/lvmetactl.c b/daemons/lvmetad/lvmetactl.c
index dd2ee1e6d..1e42335cc 100644
--- a/daemons/lvmetad/lvmetactl.c
+++ b/daemons/lvmetad/lvmetactl.c
@@ -12,6 +12,8 @@
 
 #include "lvmetad-client.h"
 
+#define ARGS_SIZE 128 /* FIXME: get from header */
+
 daemon_handle h;
 
 static void print_reply(daemon_reply reply)
@@ -45,6 +47,7 @@ int main(int argc, char **argv)
 		printf("lvmetactl set_global_disable 0|1\n");
 		printf("lvmetactl set_vg_version <uuid> <name> <version>\n");
 		printf("lvmetactl vg_lock_type <uuid>\n");
+		printf("lvmetactl helper_run <path> <args>\n");
 		return -1;
 	}
 
@@ -237,6 +240,37 @@ int main(int argc, char **argv)
 					   NULL);
 		printf("%s\n", reply.buffer.mem);
 
+	} else if (!strcmp(cmd, "helper_run")) {
+		char args[ARGS_SIZE];
+		int i;
+
+		memset(args, 0, ARGS_SIZE);
+
+		if (argc < 3) {
+			printf("helper_run <path> [<args>]\n");
+			return -1;
+		}
+
+		if (argc > 3) {
+			for (i = 3; i < argc; i++) {
+				if (strlen(argv[i]) + strlen(args) + 2 > ARGS_SIZE) {
+					printf("args too long\n");
+					return -1;
+				}
+				strcat(args, argv[i]);
+				strcat(args, " ");
+			}
+		}
+
+		reply = daemon_send_simple(h, "helper_run",
+					   "token = %s", "skip",
+					   "pid = " FMTd64, (int64_t)getpid(),
+					   "cmd = %s", "lvmetactl",
+					   "runpath = %s", argv[2],
+					   "runargs = %s", args[0] ? args : "",
+					   NULL);
+		printf("%s\n", reply.buffer.mem);
+
 	} else {
 		printf("unknown command\n");
 		goto out_close;
diff --git a/daemons/lvmetad/lvmetad-core.c b/daemons/lvmetad/lvmetad-core.c
index ebaca7872..84c015580 100644
--- a/daemons/lvmetad/lvmetad-core.c
+++ b/daemons/lvmetad/lvmetad-core.c
@@ -22,6 +22,7 @@
 #include "daemon-server.h"
 #include "daemon-log.h"
 #include "lvm-version.h"
+#include "lvmetad-internal.h"
 #include "lvmetad-client.h"
 
 #include <assert.h>
@@ -203,38 +204,10 @@ struct vg_info {
 #define GLFL_DISABLE_REASON_LVM1       0x00000008
 #define GLFL_DISABLE_REASON_DUPLICATES 0x00000010
 #define GLFL_DISABLE_REASON_VGRESTORE  0x00000020
-
 #define GLFL_DISABLE_REASON_ALL (GLFL_DISABLE_REASON_DIRECT | GLFL_DISABLE_REASON_LVM1 | GLFL_DISABLE_REASON_DUPLICATES | GLFL_DISABLE_REASON_VGRESTORE)
 
 #define VGFL_INVALID 0x00000001
 
-#define CMD_NAME_SIZE 32
-
-typedef struct {
-	daemon_idle *idle;
-	log_state *log; /* convenience */
-	const char *log_config;
-
-	struct dm_hash_table *pvid_to_pvmeta;
-	struct dm_hash_table *device_to_pvid; /* shares locks with above */
-
-	struct dm_hash_table *vgid_to_metadata;
-	struct dm_hash_table *vgid_to_vgname;
-	struct dm_hash_table *vgid_to_outdated_pvs;
-	struct dm_hash_table *vgid_to_info;
-	struct dm_hash_table *vgname_to_vgid;
-	struct dm_hash_table *pvid_to_vgid;
-	char token[128];
-	char update_cmd[CMD_NAME_SIZE];
-	int update_pid;
-	int update_timeout;
-	uint64_t update_begin;
-	uint32_t flags; /* GLFL_ */
-	pthread_mutex_t token_lock;
-	pthread_mutex_t info_lock;
-	pthread_rwlock_t cache_lock;
-} lvmetad_state;
-
 static uint64_t _monotonic_seconds(void)
 {
 	struct timespec ts;
@@ -2655,7 +2628,9 @@ static response dump(lvmetad_state *s)
 	return res;
 }
 
-static response handler(daemon_state s, client_handle h, request r)
+/* called in context of a per-connection thread */
+
+static response client_handler(daemon_state s, client_handle h, request r)
 {
 	response res;
 	lvmetad_state *state = s.private;
@@ -2822,7 +2797,8 @@ static response handler(daemon_state s, client_handle h, request r)
 	}
 
 	if (!strcmp(rq, "set_global_info") ||
-	    !strcmp(rq, "get_global_info")) {
+	    !strcmp(rq, "get_global_info") ||
+	    !strcmp(rq, "helper_run")) {
 		pthread_mutex_lock(&state->info_lock);
 		info_lock = 1;
 		goto do_rq;
@@ -2872,6 +2848,11 @@ static response handler(daemon_state s, client_handle h, request r)
 	else if (!strcmp(rq, "dump"))
 		res = dump(state);
 
+	else if (!strcmp(rq, "helper_run")) {
+		send_helper_request(&s, r);
+		res = daemon_reply_simple("OK", NULL );
+	}
+
 	else
 		res = reply_fail("request not implemented");
 
@@ -2909,6 +2890,9 @@ static int init(daemon_state *s)
 	if (ls->idle)
 		ls->idle->is_idle = 1;
 
+	if (ls->enable_udev_monitor)
+		setup_udev_monitor(s);
+
 	return 1;
 }
 
@@ -2943,6 +2927,8 @@ static void usage(const char *prog, FILE *file)
 		"   -V       Show version of lvmetad\n"
 		"   -h       Show this help information\n"
 		"   -f       Don't fork, run in the foreground\n"
+		"   -u 0|1   Enable udev monitor and running pvscan on new devs\n"
+		"   -a 0|1   Enable LV autoactivation with pvscan\n"
 		"   -l       Logging message levels (all,fatal,error,warn,info,wire,debug)\n"
 		"   -p       Set path to the pidfile\n"
 		"   -s       Set path to the socket to listen on\n"
@@ -2958,7 +2944,7 @@ int main(int argc, char *argv[])
 	daemon_state s = {
 		.daemon_fini = fini,
 		.daemon_init = init,
-		.handler = handler,
+		.handler = client_handler,
 		.name = "lvmetad",
 		.pidfile = getenv("LVM_LVMETAD_PIDFILE") ? : LVMETAD_PIDFILE,
 		.private = &ls,
@@ -2968,7 +2954,7 @@ int main(int argc, char *argv[])
 	};
 
 	// use getopt_long
-	while ((opt = getopt(argc, argv, "?fhVl:p:s:t:")) != EOF) {
+	while ((opt = getopt(argc, argv, "?fhVl:p:s:t:u:a:")) != EOF) {
 		switch (opt) {
 		case 'h':
 			usage(argv[0], stdout);
@@ -2997,13 +2983,22 @@ int main(int argc, char *argv[])
 			if (di.max_timeouts)
 				s.idle = ls.idle = &di;
 			break;
+		case 'u':
+			ls.enable_udev_monitor = atoi(optarg);
+			break;
+		case 'a':
+			ls.enable_autoactivate = atoi(optarg);
+			break;
 		case 'V':
 			printf("lvmetad version: " LVM_VERSION "\n");
 			exit(1);
 		}
 	}
 
+	setup_helper(&s);
+
 	daemon_start(s);
 
 	return 0;
 }
+
diff --git a/daemons/lvmetad/lvmetad-helper.c b/daemons/lvmetad/lvmetad-helper.c
new file mode 100644
index 000000000..1dbb86440
--- /dev/null
+++ b/daemons/lvmetad/lvmetad-helper.c
@@ -0,0 +1,535 @@
+/*
+ * Copyright (C) 2016 Red Hat, Inc.
+ *
+ * This file is part of LVM2.
+ *
+ * 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#define _XOPEN_SOURCE 500  /* pthread */
+#define _GNU_SOURCE
+#define _REENTRANT
+
+#include <inttypes.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <stddef.h>
+#include <poll.h>
+#include <fcntl.h>
+#include <string.h>
+#include <errno.h>
+#include <limits.h>
+#include <time.h>
+#include <stdarg.h>
+#include <signal.h>
+#include <ctype.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/prctl.h>
+#include <grp.h>
+#include <assert.h>
+#include <errno.h>
+
+#include "libudev.h"
+
+#include "tool.h"
+
+#include "daemon-io.h"
+#include "daemon-server.h"
+#include "daemon-log.h"
+#include "lvm-version.h"
+#include "lvmetad-internal.h"
+#include "lvmetad-client.h"
+
+/*
+ * lvmetad_main is the main process that:
+ * . forks threads to handle client (command) connections
+ * . receives client requests from socket
+ * . reads/writes cache state
+ * . receives uevent messages
+ * . sends lvmetad_helper pvscan requests for uevents
+ * . sends lvmetad_helper client requests from lvmetactl
+ *
+ * lvmetad_helper is the helper process that:
+ * . receives pvscan requests from lvmetad_main
+ * . forks/execs pvscan commands for each request
+ */
+
+#define MAX_AV_COUNT 8
+
+static int _log_debug_stderr;
+
+#define log_debug(fmt, args...) \
+do { \
+	if (_log_debug_stderr) \
+		fprintf(stderr, fmt "\n", ##args); \
+} while (0)
+
+static void run_path(struct helper_msg *hm)
+{
+	char arg[HELPER_ARGS_LEN];
+	char *args = hm->args;
+	char *av[MAX_AV_COUNT + 1]; /* +1 for NULL */
+	int av_count = 0;
+	int i, arg_len, args_len;
+
+	for (i = 0; i < MAX_AV_COUNT + 1; i++)
+		av[i] = NULL;
+
+	av[av_count++] = strdup(hm->path);
+
+	if (!args[0])
+		goto run;
+
+	/* this should already be done, but make sure */
+	args[HELPER_ARGS_LEN - 1] = '\0';
+
+	memset(&arg, 0, sizeof(arg));
+	arg_len = 0;
+	args_len = strlen(args);
+
+	for (i = 0; i < args_len; i++) {
+		if (!args[i])
+			break;
+
+		if (av_count == MAX_AV_COUNT)
+			break;
+
+		if (args[i] == '\\') {
+			if (i == (args_len - 1))
+				break;
+			i++;
+
+			if (args[i] == '\\') {
+				arg[arg_len++] = args[i];
+				continue;
+			}
+			if (isspace(args[i])) {
+				arg[arg_len++] = args[i];
+				continue;
+			} else {
+				break;
+			}
+		}
+
+		if (isalnum(args[i]) || ispunct(args[i])) {
+			arg[arg_len++] = args[i];
+		} else if (isspace(args[i])) {
+			if (arg_len)
+				av[av_count++] = strdup(arg);
+
+			memset(arg, 0, sizeof(arg));
+			arg_len = 0;
+		} else {
+			break;
+		}
+	}
+
+	if ((av_count < MAX_AV_COUNT) && arg_len) {
+		av[av_count++] = strdup(arg);
+	}
+run:
+	execvp(av[0], av);
+}
+
+static int read_from_main(int fd, struct helper_msg *hm)
+{
+	int rv;
+ retry:
+	rv = read(fd, hm, sizeof(struct helper_msg));
+	if (rv == -1 && errno == EINTR)
+		goto retry;
+
+	if (rv != sizeof(struct helper_msg))
+		return -1;
+	return 0;
+}
+
+static int send_to_main(int fd, int type)
+{
+	struct helper_status hs;
+	int rv;
+
+	memset(&hs, 0, sizeof(hs));
+
+	hs.type = type;
+
+	rv = write(fd, &hs, sizeof(hs));
+
+	if (rv == sizeof(hs))
+		return 0;
+	return -1;
+}
+
+#define INACTIVE_TIMEOUT_MS 10000
+#define ACTIVE_TIMEOUT_MS 1000
+
+int run_helper(int in_fd, int out_fd, int debug_stderr)
+{
+	char name[16];
+	struct pollfd pollfd;
+	struct helper_msg hm;
+	unsigned int fork_count = 0;
+	unsigned int wait_count = 0;
+	int timeout = INACTIVE_TIMEOUT_MS;
+	int rv, pid, status;
+
+	_log_debug_stderr = debug_stderr;
+
+	memset(name, 0, sizeof(name));
+	sprintf(name, "%s", "lvmetad_helper");
+	prctl(PR_SET_NAME, (unsigned long)name, 0, 0, 0);
+
+	memset(&pollfd, 0, sizeof(pollfd));
+	pollfd.fd = in_fd;
+	pollfd.events = POLLIN;
+
+	/* Tell the main process we've started. */
+	send_to_main(out_fd, HELPER_STARTED);
+
+	while (1) {
+		rv = poll(&pollfd, 1, timeout);
+		if (rv == -1 && errno == EINTR)
+			continue;
+
+		if (rv < 0)
+			exit(0);
+
+		memset(&hm, 0, sizeof(hm));
+
+		if (pollfd.revents & POLLIN) {
+			rv = read_from_main(in_fd, &hm);
+			if (rv)
+				continue;
+
+			if (hm.type == HELPER_MSG_RUNPATH) {
+				pid = fork();
+				if (!pid) {
+					run_path(&hm);
+					exit(-1);
+				}
+
+				fork_count++;
+
+				/*
+				log_debug("helper fork %d count %d %d %s %s",
+					  pid, fork_count, wait_count,
+					  hm.path, hm.args);
+				*/
+			}
+		}
+
+		if (pollfd.revents & (POLLERR | POLLHUP | POLLNVAL))
+			exit(0);
+
+		/* collect child exits until no more children exist (ECHILD)
+		   or none are ready (WNOHANG) */
+
+		while (1) {
+			rv = waitpid(-1, &status, WNOHANG);
+			if (rv > 0) {
+				wait_count++;
+
+				/*
+				log_debug("helper wait %d count %d %d",
+					  rv, fork_count, wait_count);
+				*/
+				continue;
+			}
+
+			/* no more children to wait for or no children
+			   have exited */
+
+			if (rv < 0 && errno == ECHILD)
+				timeout = INACTIVE_TIMEOUT_MS;
+			else
+				timeout = ACTIVE_TIMEOUT_MS;
+			break;
+		}
+	}
+
+	return 0;
+}
+
+void close_helper(daemon_state *s)
+{
+	lvmetad_state *ls = s->private;
+
+	close(ls->helper_pr_fd);
+	close(ls->helper_pw_fd);
+	ls->helper_pr_fd = -1;
+	ls->helper_pw_fd = -1;
+	s->helper_fd = -1;
+	s->helper_handler = NULL;
+}
+
+static void _send_helper_msg(daemon_state *s, struct helper_msg *hm)
+{
+	lvmetad_state *ls = s->private;
+	int rv;
+
+ retry:
+	rv = write(ls->helper_pw_fd, hm, sizeof(struct helper_msg));
+	if (rv == -1 && errno == EINTR)
+		goto retry;
+
+	if (rv == -1 && errno == EAGAIN) {
+		return;
+	}
+
+	/* helper exited or closed fd, quit using helper */
+	if (rv == -1 && errno == EPIPE) {
+		ERROR(s, "send_helper EPIPE");
+		close_helper(s);
+		return;
+	}
+
+	if (rv != sizeof(struct helper_msg)) {
+		/* this shouldn't happen */
+		ERROR(s, "send_helper error %d %d", rv, errno);
+		close_helper(s);
+		return;
+	}
+}
+
+/* send a request to helper process */
+
+void send_helper_request(daemon_state *s, request r)
+{
+	struct helper_msg hm = { 0 };
+	char *runpath = daemon_request_str(r, "runpath", NULL);
+	char *runargs = daemon_request_str(r, "runargs", NULL);
+
+	hm.type = HELPER_MSG_RUNPATH;
+	memcpy(hm.path, runpath, HELPER_PATH_LEN);
+	if (runargs)
+		memcpy(hm.args, runargs, HELPER_ARGS_LEN);
+
+	_send_helper_msg(s, &hm);
+}
+
+static void send_helper_pvscan_cache_dev(daemon_state *s, dev_t devt)
+{
+	lvmetad_state *ls = s->private;
+	struct helper_msg hm = { 0 };
+
+	hm.type = HELPER_MSG_RUNPATH;
+	sprintf(hm.path, "pvscan");
+	snprintf(hm.args, HELPER_ARGS_LEN-1, "--cache %s --major %d --minor %d",
+		 ls->enable_autoactivate ? "-aay" : "",
+		 major(devt), minor(devt));
+
+	_send_helper_msg(s, &hm);
+}
+
+static void send_helper_pvscan_cache_all(daemon_state *s)
+{
+	lvmetad_state *ls = s->private;
+	struct helper_msg hm = { 0 };
+
+	hm.type = HELPER_MSG_RUNPATH;
+	sprintf(hm.path, "pvscan");
+	snprintf(hm.args, HELPER_ARGS_LEN-1, "--cache %s",
+		 ls->enable_autoactivate ? "-aay" : "");
+
+	_send_helper_msg(s, &hm);
+}
+
+/*
+ * called in context of main lvmetad process
+ * handles a message from helper process
+ */
+
+static int helper_handler(daemon_state *s)
+{
+	lvmetad_state *ls = s->private;
+	struct helper_status hs;
+	int rv;
+
+	memset(&hs, 0, sizeof(hs));
+
+	rv = read(ls->helper_pr_fd, &hs, sizeof(hs));
+	if (!rv || rv == -EAGAIN)
+		return -1;
+	if (rv < 0) {
+		ERROR(s, "handle_helper rv %d errno %d", rv, errno);
+		goto fail;
+	}
+	if (rv != sizeof(hs)) {
+		ERROR(s, "handle_helper recv size %d", rv);
+		goto fail;
+	}
+
+	DEBUGLOG(s, "helper message type %d status %d", hs.type, hs.status);
+
+	/*
+	 * Run initial pvscan --cache to populate lvmetad cache.
+	 *
+	 * (Upon receiving HELPER_STARTED we know that the helper
+	 * is ready to handle to running commands.)
+	 *
+	 * The udev monitor is enabled before this, so there should
+	 * be no gap where new devs could be missed.  It's possible
+	 * that new devs added during lvmetad startup could be scanned
+	 * by this initial pvscan --cache, and then scanned again
+	 * individually because of the monitor.  This possible repetition
+	 * is harmless.
+	 */
+	if (hs.type == HELPER_STARTED)
+		send_helper_pvscan_cache_all(s);
+
+	return 0;
+
+ fail:
+	ERROR(s, "close helper connection");
+	close_helper(s);
+	return -1;
+}
+
+/* create helper process */
+
+int setup_helper(daemon_state *s)
+{
+	lvmetad_state *ls = s->private;
+	int pid;
+	int pw_fd = -1; /* parent write */
+	int cr_fd = -1; /* child read */
+	int pr_fd = -1; /* parent read */
+	int cw_fd = -1; /* child write */
+	int pfd[2];
+
+	/* don't allow the main daemon thread to block */
+	if (pipe2(pfd, O_NONBLOCK | O_CLOEXEC))
+		return -errno;
+
+	/* only available on rhel7 */
+	/* fcntl(pfd[1], F_SETPIPE_SZ, 1024*1024); */
+
+	cr_fd = pfd[0];
+	pw_fd = pfd[1];
+
+	if (pipe2(pfd, O_NONBLOCK | O_CLOEXEC)) {
+		close(cr_fd);
+		close(pw_fd);
+		return -errno;
+	}
+
+	pr_fd = pfd[0];
+	cw_fd = pfd[1];
+
+	pid = fork();
+	if (pid < 0) {
+		close(cr_fd);
+		close(pw_fd);
+		close(pr_fd);
+		close(cw_fd);
+		return -errno;
+	}
+
+	if (pid) {
+		close(cr_fd);
+		close(cw_fd);
+		ls->helper_pw_fd = pw_fd;
+		ls->helper_pr_fd = pr_fd;
+		ls->helper_pid = pid;
+		s->helper_fd = pr_fd; /* libdaemon uses helper_fd in select */
+		s->helper_handler = helper_handler;
+		return 0;
+	} else {
+		close(pr_fd);
+		close(pw_fd);
+		run_helper(cr_fd, cw_fd, (s->foreground && strstr(ls->log_config, "debug")));
+		exit(0);
+	}
+}
+
+/*
+ * called in context of main lvmetad process
+ * handles a message from udev monitor
+ * sends a message to lvmetad helper to scan a device
+ */
+
+static int monitor_handler(daemon_state *s)
+{
+	lvmetad_state *ls = s->private;
+	struct udev_device *dev;
+	const char *name;
+	dev_t devt;
+
+	dev = udev_monitor_receive_device(ls->udev_mon);
+	if (!dev)
+		return 0;
+
+	name = udev_device_get_devnode(dev);
+	devt = udev_device_get_devnum(dev);
+
+	DEBUGLOG(s, "monitor scan %d:%d %s", major(devt), minor(devt), name ?: "");
+	send_helper_pvscan_cache_dev(s, devt);
+
+	udev_device_unref(dev);
+	return 0;
+}
+
+/* create udev monitor */
+
+void setup_udev_monitor(daemon_state *s)
+{
+	lvmetad_state *ls = s->private;
+	int fd;
+	int ret;
+
+	/* FIXME: add error handling/cleanup */
+
+	ls->udevh = udev_new();
+	if (!ls->udevh) {
+		ERROR(s, "Failed to monitor udev: new.");
+		return;
+	}
+
+	ls->udev_mon = udev_monitor_new_from_netlink(ls->udevh, "udev");
+	if (!ls->udev_mon) {
+		ERROR(s, "Failed to monitor udev: netlink.");
+		return;
+	}
+
+	ret = udev_monitor_filter_add_match_subsystem_devtype(ls->udev_mon, "block", "disk");
+	if (ret < 0) {
+		ERROR(s, "Failed to monitor udev: devtype.");
+		return;
+	}
+
+	ret = udev_monitor_filter_add_match_tag(ls->udev_mon, "LVM_DO_PVSCAN");
+	if (ret < 0) {
+		ERROR(s, "Failed to monitor udev: tag.");
+		return;
+	}
+
+	ret = udev_monitor_enable_receiving(ls->udev_mon);
+	if (ret < 0) {
+		ERROR(s, "Failed to monitor udev: receive.");
+		return;
+	}
+
+	/* udev_monitor_set_receive_buffer_size? */
+
+	fd = udev_monitor_get_fd(ls->udev_mon);
+	if (fd < 0) {
+		ERROR(s, "Failed to monitor udev: fd.");
+		return;
+	}
+
+	ls->udev_fd = fd;
+	s->monitor_fd = fd;
+	s->monitor_handler = monitor_handler;
+}
+
diff --git a/daemons/lvmetad/lvmetad-internal.h b/daemons/lvmetad/lvmetad-internal.h
new file mode 100644
index 000000000..8308f9e68
--- /dev/null
+++ b/daemons/lvmetad/lvmetad-internal.h
@@ -0,0 +1,89 @@
+/*
+ * Copyright (C) 2016 Red Hat, Inc.
+ *
+ * This file is part of LVM2.
+ *
+ * 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.
+ */
+
+#ifndef _LVM_LVMETAD_INTERNAL_H
+#define _LVM_LVMETAD_INTERNAL_H
+
+#define CMD_NAME_SIZE 32
+
+typedef struct {
+	daemon_idle *idle;
+	log_state *log; /* convenience */
+	const char *log_config;
+	int enable_udev_monitor;
+	int enable_autoactivate;
+
+	struct dm_hash_table *pvid_to_pvmeta;
+	struct dm_hash_table *device_to_pvid; /* shares locks with above */
+
+	struct dm_hash_table *vgid_to_metadata;
+	struct dm_hash_table *vgid_to_vgname;
+	struct dm_hash_table *vgid_to_outdated_pvs;
+	struct dm_hash_table *vgid_to_info;
+	struct dm_hash_table *vgname_to_vgid;
+	struct dm_hash_table *pvid_to_vgid;
+	char token[128];
+	char update_cmd[CMD_NAME_SIZE];
+	int update_pid;
+	int update_timeout;
+	uint64_t update_begin;
+	uint32_t flags; /* GLFL_ */
+	pthread_mutex_t token_lock;
+	pthread_mutex_t info_lock;
+	pthread_rwlock_t cache_lock;
+
+	int helper_pid;
+	int helper_pw_fd; /* parent write to send message to helper */
+	int helper_pr_fd; /* parent read to recv message from helper */
+
+	struct udev *udevh;
+	struct udev_monitor *udev_mon;
+	int udev_fd;
+} lvmetad_state;
+
+/*
+ * helper process
+ * recvs 512 byte helper_msg on in_fd
+ * sends 4 byte helper_status on out_fd
+ */
+
+/* max length of path and args, includes terminate \0 byte */
+
+#define HELPER_PATH_LEN    128
+#define HELPER_ARGS_LEN    128
+#define HELPER_MSG_LEN     512
+#define HELPER_MSG_RUNPATH 1
+
+struct helper_msg {
+	uint8_t type;
+	uint8_t pad1;
+	uint16_t pad2;
+	uint32_t flags;
+	int pid;
+	int unused;
+	char path[HELPER_PATH_LEN]; /* 128 */
+	char args[HELPER_ARGS_LEN]; /* 128 */
+	char pad[240];
+};
+
+#define HELPER_STARTED 1
+
+struct helper_status {
+	uint8_t type;
+	uint8_t status;
+	uint16_t len;
+};
+
+void close_helper(daemon_state *s);
+void send_helper_request(daemon_state *s, request r);
+int setup_helper(daemon_state *s);
+void setup_udev_monitor(daemon_state *s);
+
+#endif
diff --git a/libdaemon/server/daemon-server.c b/libdaemon/server/daemon-server.c
index 4d6546633..00c23f5f6 100644
--- a/libdaemon/server/daemon-server.c
+++ b/libdaemon/server/daemon-server.c
@@ -630,12 +630,26 @@ void daemon_start(daemon_state s)
 		_reset_timeout(s);
 		FD_ZERO(&in);
 		FD_SET(s.socket_fd, &in);
+
+		if (s.helper_handler)
+			FD_SET(s.helper_fd, &in);
+		if (s.monitor_handler)
+			FD_SET(s.monitor_fd, &in);
+
 		if (select(FD_SETSIZE, &in, NULL, NULL, _get_timeout(s)) < 0 && errno != EINTR)
 			perror("select error");
 		if (FD_ISSET(s.socket_fd, &in)) {
 			timeout_count = 0;
 			handle_connect(s);
 		}
+		if (FD_ISSET(s.helper_fd, &in)) {
+			timeout_count = 0;
+			s.helper_handler(&s);
+		}
+		if (FD_ISSET(s.monitor_fd, &in)) {
+			timeout_count = 0;
+			s.monitor_handler(&s);
+		}
 
 		_reap(s, 0);
 
diff --git a/libdaemon/server/daemon-server.h b/libdaemon/server/daemon-server.h
index 2b9ceac36..ee8ca9c79 100644
--- a/libdaemon/server/daemon-server.h
+++ b/libdaemon/server/daemon-server.h
@@ -108,10 +108,15 @@ typedef struct daemon_state {
 	int (*daemon_init)(struct daemon_state *st);
 	int (*daemon_fini)(struct daemon_state *st);
 	int (*daemon_main)(struct daemon_state *st);
+	int (*helper_handler)(struct daemon_state *st);
+	int (*monitor_handler)(struct daemon_state *st);
 
 	/* Global runtime info maintained by the framework. */
 	int socket_fd;
 
+	int helper_fd;  /* used in select if helper_handler is set */
+	int monitor_fd; /* used in select if monitor_handler is set */
+
 	log_state *log;
 	struct thread_state *threads;