Increase open file limit to maximum possible value

Opening a lot of kernel modules for processing requires high open-file-limit
value. The default value is 1024 which is too low.

Try to increase process limit to infinity first. If it does not work
then try to increase soft limit to hard limit value.

Closes #76

generator/kmod_test.go

@@ -20,6 +20,8 @@ import (
 func TestModuleNames(t *testing.T) {
 	t.Parallel()
 
+	increaseOpenFileLimit()
+
 	ver, err := readKernelVersion()
 	require.NoError(t, err)
 

generator/main.go

@@ -65,6 +65,8 @@ func runGenerator() error {
 		defer pprof.StopCPUProfile()
 	}
 
+	increaseOpenFileLimit()
+
 	conf, err := readGeneratorConfig(*configFile)
 	if err != nil {
 		return err

generator/util.go

@@ -1,6 +1,10 @@
 package main
 
-import "regexp"
+import (
+	"regexp"
+
+	"golang.org/x/sys/unix"
+)
 
 // parseProperties parses input in form of "PROP1=VAL1\nPROP2=VAL2\n..." into a map
 func parseProperties(data string) map[string]string {
@@ -13,3 +17,35 @@ func parseProperties(data string) map[string]string {
 
 	return result
 }
+
+// Opening a lot of module files in parallel requires high limit of open file descriptors
+func increaseOpenFileLimit() {
+	limit := unix.Rlimit{
+		Cur: unix.RLIM_INFINITY,
+		Max: unix.RLIM_INFINITY,
+	}
+
+	// first try to set the process limit to infinity
+	if err := unix.Setrlimit(unix.RLIMIT_NOFILE, &limit); err == nil {
+		// it worked!
+		return
+	}
+
+	// if the current process unprivileged then the only thing we can do is to set soft limit to max limit value
+
+	if err := unix.Getrlimit(unix.RLIMIT_NOFILE, &limit); err != nil {
+		warning("unable to get open file limit: %v", err)
+		return
+	}
+
+	if limit.Cur >= limit.Max {
+		return // nothing to increase
+	}
+
+	debug("increasing open file limit %d->%d", limit.Cur, limit.Max)
+	limit.Cur = limit.Max
+
+	if err := unix.Setrlimit(unix.RLIMIT_NOFILE, &limit); err != nil {
+		warning("unable to increase open file limit: %v", err)
+	}
+}