lib: add startup option to limit fds

Add a startup-time option to limit the number of fds used
by the thread/event infrastructure. If nothing is configured,
the system ulimit is used.

Signed-off-by: Mark Stapp <mjs@voltanet.io>

4 files changed, 31 insertions, 3 deletions

diff --git a/doc/user/basic.rst b/doc/user/basic.rst
index 7a450bec53..4d34c82895 100644
--- a/doc/user/basic.rst
+++ b/doc/user/basic.rst
@@ -712,6 +712,12 @@ These options apply to all |PACKAGE_NAME| daemons.
 
    Enable the transactional CLI mode.
 
+.. option:: --limit-fds <number>
+
+   Limit the number of file descriptors that will be used internally
+   by the FRR daemons. By default, the daemons use the system ulimit
+   value.
+
 .. _loadable-module-support:
 
 Loadable Module Support
diff --git a/lib/libfrr.c b/lib/libfrr.c
index 800596c563..8e7777a1a9 100644
--- a/lib/libfrr.c
+++ b/lib/libfrr.c
@@ -99,6 +99,7 @@ static void opt_extend(const struct optspec *os)
 #define OPTION_TCLI      1005
 #define OPTION_DB_FILE   1006
 #define OPTION_LOGGING   1007
+#define OPTION_LIMIT_FDS 1008
 
 static const struct option lo_always[] = {
 	{"help", no_argument, NULL, 'h'},
@@ -113,6 +114,7 @@ static const struct option lo_always[] = {
 	{"log-level", required_argument, NULL, OPTION_LOGLEVEL},
 	{"tcli", no_argument, NULL, OPTION_TCLI},
 	{"command-log-always", no_argument, NULL, OPTION_LOGGING},
+	{"limit-fds", required_argument, NULL, OPTION_LIMIT_FDS},
 	{NULL}};
 static const struct optspec os_always = {
 	"hvdM:F:N:",
@@ -126,7 +128,8 @@ static const struct optspec os_always = {
 	"      --moduledir    Override modules directory\n"
 	"      --log          Set Logging to stdout, syslog, or file:<name>\n"
 	"      --log-level    Set Logging Level to use, debug, info, warn, etc\n"
-	"      --tcli         Use transaction-based CLI\n",
+	"      --tcli         Use transaction-based CLI\n"
+	"      --limit-fds    Limit number of fds supported\n",
 	lo_always};
 
 
@@ -552,6 +555,9 @@ static int frr_opt(int opt)
 	case OPTION_LOGGING:
 		di->log_always = true;
 		break;
+	case OPTION_LIMIT_FDS:
+		di->limit_fds = strtoul(optarg, &err, 0);
+		break;
 	default:
 		return 1;
 	}
@@ -739,6 +745,11 @@ enum frr_cli_mode frr_get_cli_mode(void)
 	return di ? di->cli_mode : FRR_CLI_CLASSIC;
 }
 
+uint32_t frr_get_fd_limit(void)
+{
+	return di ? di->limit_fds : 0;
+}
+
 static int rcvd_signal = 0;
 
 static void rcv_signal(int signum)
diff --git a/lib/libfrr.h b/lib/libfrr.h
index ab72299206..2e4dcbe093 100644
--- a/lib/libfrr.h
+++ b/lib/libfrr.h
@@ -102,6 +102,9 @@ struct frr_daemon_info {
 	size_t n_yang_modules;
 
 	bool log_always;
+
+	/* Optional upper limit on the number of fds used in select/poll */
+	uint32_t limit_fds;
 };
 
 /* execname is the daemon's executable (and pidfile and configfile) name,
@@ -134,6 +137,7 @@ extern __attribute__((__noreturn__)) void frr_help_exit(int status);
 extern struct thread_master *frr_init(void);
 extern const char *frr_get_progname(void);
 extern enum frr_cli_mode frr_get_cli_mode(void);
+uint32_t frr_get_fd_limit(void);
 
 DECLARE_HOOK(frr_late_init, (struct thread_master * tm), (tm))
 DECLARE_HOOK(frr_very_late_init, (struct thread_master * tm), (tm))
diff --git a/lib/thread.c b/lib/thread.c
index e71fd74bd9..c886058355 100644
--- a/lib/thread.c
+++ b/lib/thread.c
@@ -36,6 +36,7 @@
 #include "frr_pthread.h"
 #include "lib_errors.h"
 #include "libfrr_trace.h"
+#include "libfrr.h"
 
 DEFINE_MTYPE_STATIC(LIB, THREAD, "Thread")
 DEFINE_MTYPE_STATIC(LIB, THREAD_MASTER, "Thread master")
@@ -442,8 +443,14 @@ struct thread_master *thread_master_create(const char *name)
 	rv->name = XSTRDUP(MTYPE_THREAD_MASTER, name);
 
 	/* Initialize I/O task data structures */
-	getrlimit(RLIMIT_NOFILE, &limit);
-	rv->fd_limit = (int)limit.rlim_cur;
+
+	/* Use configured limit if present, ulimit otherwise. */
+	rv->fd_limit = frr_get_fd_limit();
+	if (rv->fd_limit == 0) {
+		getrlimit(RLIMIT_NOFILE, &limit);
+		rv->fd_limit = (int)limit.rlim_cur;
+	}
+
 	rv->read = XCALLOC(MTYPE_THREAD_POLL,
 			   sizeof(struct thread *) * rv->fd_limit);