From: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Date: Tue, 26 Nov 2019 20:08:01 +0000 (-0500)
Subject: relayd: add fd-cap option to limit the number of opened FDs
X-Git-Tag: v2.12.0-rc1~67
X-Git-Url: https://git.lttng.org/?p=lttng-tools.git;a=commitdiff_plain;h=896010e38f60e85d757a43778e25a51b890a7443

relayd: add fd-cap option to limit the number of opened FDs

Add an --fd-cap option to the relay daemon in order to allow the
launch of the relay daemon with a maximal number of file descriptors
to be open at any given moment.

When the value of the --fd-cap parameter is left unset, the maximal
number of file descriptors is set to the system's NOFILE soft limit
(see GETRLIMIT(3P)).

A minimal number of file descriptors of 30 is imposed, mainly to
prevent absurd configurations (someone setting 1 fd) which would not
even allow one target to connect and stream traces. This also allows
a bit of leverage to open file descriptors that could be needed by
future changes without "breaking" an existing configuration.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: Ibaf49b25ccf3e3a8013115c9478744ca3646e306
---

diff --git a/src/bin/lttng-relayd/main.c b/src/bin/lttng-relayd/main.c
index 4e30ac498..f61f1f13e 100644
--- a/src/bin/lttng-relayd/main.c
+++ b/src/bin/lttng-relayd/main.c
@@ -34,6 +34,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <sys/resource.h>
 #include <inttypes.h>
 #include <urcu/futex.h>
 #include <urcu/uatomic.h>
@@ -41,6 +42,7 @@
 #include <unistd.h>
 #include <fcntl.h>
 #include <strings.h>
+#include <ctype.h>
 
 #include <lttng/lttng.h>
 #include <common/common.h>
@@ -160,6 +162,9 @@ static uint64_t last_relay_stream_id;
  */
 static struct relay_conn_queue relay_conn_queue;
 
+/* Cap of file desriptors to be in simultaneous use by the relay daemon. */
+static unsigned int lttng_opt_fd_cap;
+
 /* Global relay stream hash table. */
 struct lttng_ht *relay_streams_ht;
 
@@ -181,6 +186,7 @@ static struct option long_options[] = {
 	{ "daemonize", 0, 0, 'd', },
 	{ "background", 0, 0, 'b', },
 	{ "group", 1, 0, 'g', },
+	{ "fd-cap", 1, 0, '\0', },
 	{ "help", 0, 0, 'h', },
 	{ "output", 1, 0, 'o', },
 	{ "verbose", 0, 0, 'v', },
@@ -224,9 +230,34 @@ static int set_option(int opt, const char *arg, const char *optname)
 
 	switch (opt) {
 	case 0:
-		fprintf(stderr, "option %s", optname);
-		if (arg) {
-			fprintf(stderr, " with arg %s\n", arg);
+		if (!strcmp(optname, "fd-cap")) {
+			unsigned long v;
+
+			errno = 0;
+			v = strtoul(arg, NULL, 0);
+			if (errno != 0 || !isdigit(arg[0])) {
+				ERR("Wrong value in --fd-cap parameter: %s",
+						arg);
+				ret = -1;
+				goto end;
+			}
+			if (v < DEFAULT_RELAYD_MINIMAL_FD_CAP) {
+				ERR("File descriptor cap must be set to at least %d",
+						DEFAULT_RELAYD_MINIMAL_FD_CAP);
+			}
+			if (v >= UINT_MAX) {
+				ERR("File descriptor cap overflow in --fd-cap parameter: %s",
+						arg);
+				ret = -1;
+				goto end;
+			}
+			lttng_opt_fd_cap = (unsigned int) v;
+			DBG3("File descriptor cap set to %u", lttng_opt_fd_cap);
+		} else {
+			fprintf(stderr, "unknown option %s", optname);
+			if (arg) {
+				fprintf(stderr, " with arg %s\n", arg);
+			}
 		}
 		break;
 	case 'C':
@@ -563,6 +594,18 @@ static int set_options(int argc, char **argv)
 			goto exit;
 		}
 	}
+	if (lttng_opt_fd_cap == 0) {
+		int ret;
+		struct rlimit rlimit;
+
+		ret = getrlimit(RLIMIT_NOFILE, &rlimit);
+		if (ret) {
+			PERROR("Failed to get file descriptor limit");
+			retval = -1;
+		}
+
+		lttng_opt_fd_cap = rlimit.rlim_cur;
+	}
 
 	if (opt_group_output_by == RELAYD_GROUP_OUTPUT_BY_UNKNOWN) {
 		opt_group_output_by = RELAYD_GROUP_OUTPUT_BY_HOST;
diff --git a/src/common/defaults.h b/src/common/defaults.h
index 2c3e80f43..e57e6495f 100644
--- a/src/common/defaults.h
+++ b/src/common/defaults.h
@@ -93,6 +93,8 @@
 #define DEFAULT_RELAYD_RUNDIR			"%s"
 #define DEFAULT_RELAYD_PATH			DEFAULT_RELAYD_RUNDIR "/relayd"
 
+#define DEFAULT_RELAYD_MINIMAL_FD_CAP		30
+
 /* Default lttng run directory */
 #define DEFAULT_LTTNG_HOME_ENV_VAR              "LTTNG_HOME"
 #define DEFAULT_LTTNG_FALLBACK_HOME_ENV_VAR	"HOME"