multipath-tools: Improvement to max_fds

Setting max_fds to unlimited doesn't actually work.  In the kernel, there is a
fixed limit to the maximum number of open fds a process can have.  If you try
to set max_fds to greater than this, it fails.  This patch replaces the special
value "unlimited" with a new special value, "max".  If you set max_fds to "max",
multipath will use the actual system limit, which it looks up from
/proc/sys/fs/nr_open.

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>

6 files changed, 49 insertions, 24 deletions

diff --git a/libmultipath/dict.c b/libmultipath/dict.c
index 2902e89..ee4de68 100644
--- a/libmultipath/dict.c
+++ b/libmultipath/dict.c
@@ -19,6 +19,7 @@
 #include "blacklist.h"
 #include "defaults.h"
 #include "prio.h"
+#include "errno.h"
 
 /*
  * default block handlers
@@ -156,23 +157,52 @@ def_minio_handler(vector strvec)
 }
 
 static int
+get_sys_max_fds(int *max_fds)
+{
+	FILE *file;
+	int nr_open;
+	int ret = 1;
+
+	file = fopen("/proc/sys/fs/nr_open", "r");
+	if (!file) {
+		fprintf(stderr, "Cannot open /proc/sys/fs/nr_open : %s\n",
+			strerror(errno));
+		return 1;
+	}
+	if (fscanf(file, "%d", &nr_open) != 1) {
+		fprintf(stderr, "Cannot read max open fds from /proc/sys/fs/nr_open");
+		if (ferror(file))
+			fprintf(stderr, " : %s\n", strerror(errno));
+		else
+			fprintf(stderr, "\n");
+	} else {
+		*max_fds = nr_open;
+		ret = 0;
+	}
+	fclose(file);
+	return ret;
+}
+
+
+static int
 max_fds_handler(vector strvec)
 {
 	char * buff;
+	int r = 0;
 
 	buff = set_value(strvec);
 
 	if (!buff)
 		return 1;
 
-	if (strlen(buff) == 9 &&
-	    !strcmp(buff, "unlimited"))
-		conf->max_fds = MAX_FDS_UNLIMITED;
+	if (strlen(buff) == 3 &&
+	    !strcmp(buff, "max"))
+		r = get_sys_max_fds(&conf->max_fds);
 	else
 		conf->max_fds = atoi(buff);
 	FREE(buff);
 
-	return 0;
+	return r;
 }
 
 static int
@@ -1755,8 +1785,6 @@ snprint_max_fds (char * buff, int len, void * data)
 	if (!conf->max_fds)
 		return 0;
 
-	if (conf->max_fds < 0)
-		return snprintf(buff, len, "unlimited");
 	return snprintf(buff, len, "%d", conf->max_fds);
 }
 
diff --git a/libmultipath/structs.h b/libmultipath/structs.h
index f7eca60..aafadba 100644
--- a/libmultipath/structs.h
+++ b/libmultipath/structs.h
@@ -24,7 +24,6 @@
 #define NO_PATH_RETRY_FAIL	-1
 #define NO_PATH_RETRY_QUEUE	-2
 
-#define MAX_FDS_UNLIMITED	-1
 
 enum free_path_switch {
 	KEEP_PATHS,
diff --git a/multipath.conf.annotated b/multipath.conf.annotated
index 1b8f7cc..2374d56 100644
--- a/multipath.conf.annotated
+++ b/multipath.conf.annotated
@@ -113,7 +113,7 @@
 #	# scope   : multipathd
 #	# desc    : Sets the maximum number of open file descriptors for the
 #	#           multipathd process.
-#	# values  : unlimited|n > 0
+#	# values  : max|n > 0
 #	# default : None
 #	#
 #	max_fds		8192
diff --git a/multipath/main.c b/multipath/main.c
index 707e2b9..d72e242 100644
--- a/multipath/main.c
+++ b/multipath/main.c
@@ -428,14 +428,9 @@ main (int argc, char *argv[])
 
 	if (conf->max_fds) {
 		struct rlimit fd_limit;
-		if (conf->max_fds > 0) {
-			fd_limit.rlim_cur = conf->max_fds;
-			fd_limit.rlim_max = conf->max_fds;
-		}
-		else {
-			fd_limit.rlim_cur = RLIM_INFINITY;
-			fd_limit.rlim_max = RLIM_INFINITY;
-		}
+
+		fd_limit.rlim_cur = conf->max_fds;
+		fd_limit.rlim_max = conf->max_fds;
 		if (setrlimit(RLIMIT_NOFILE, &fd_limit) < 0)
 			condlog(0, "can't set open fds limit to %d : %s\n",
 				conf->max_fds, strerror(errno));
diff --git a/multipath/multipath.conf.5 b/multipath/multipath.conf.5
index 6b1be81..df1f3b4 100644
--- a/multipath/multipath.conf.5
+++ b/multipath/multipath.conf.5
@@ -230,6 +230,14 @@ use the WWID as the alias. In either case this be will
 be overriden by any specific aliases in the \fImultipaths\fR section.
 Default is
 .I no
+.TP
+.B max_fds
+Specify the maximum number of file descriptors that can be opened by multipath
+and multipathd.  This is equivalent to ulimit -n. A value of \fImax\fR will set
+this to the system limit from /proc/sys/fs/nr_open. If this is not set, the
+maximum number of open fds is taken from the calling process. It is usually
+1024. To be safe, this should be set to the maximum number of paths plus 32,
+if that number is greated than 1024.
 .
 .SH "blacklist section"
 The
diff --git a/multipathd/main.c b/multipathd/main.c
index dfa1098..41a9bd0 100644
--- a/multipathd/main.c
+++ b/multipathd/main.c
@@ -1373,14 +1373,9 @@ child (void * param)
 
 	if (conf->max_fds) {
 		struct rlimit fd_limit;
-		if (conf->max_fds > 0) {
-			fd_limit.rlim_cur = conf->max_fds;
-			fd_limit.rlim_max = conf->max_fds;
-		}
-		else {
-			fd_limit.rlim_cur = RLIM_INFINITY;
-			fd_limit.rlim_max = RLIM_INFINITY;
-		}
+
+		fd_limit.rlim_cur = conf->max_fds;
+		fd_limit.rlim_max = conf->max_fds;
 		if (setrlimit(RLIMIT_NOFILE, &fd_limit) < 0)
 			condlog(0, "can't set open fds limit to %d : %s\n",
 				conf->max_fds, strerror(errno));