common/fdlimit: Move fdlimit files to separate package (#15850)

* common/fdlimit: Move fdlimit files to separate package

When go-ethereum is used as a library the calling program need to set
the FD limit.

This commit extract fdlimit files to a separate package so it can be
used outside of go-ethereum.

* common/fdlimit: Remove FdLimit from functions signature

* common/fdlimit: Rename fdlimit functions

1 files changed, 45 insertions, 0 deletions

diff --git a/common/fdlimit/fdlimit_test.go b/common/fdlimit/fdlimit_test.go
new file mode 100644
index 000000000..05e9f0b65
--- /dev/null
+++ b/common/fdlimit/fdlimit_test.go
@@ -0,0 +1,45 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of go-ethereum.
+//
+// go-ethereum is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// go-ethereum is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
+
+package fdlimit
+
+import (
+	"fmt"
+	"testing"
+)
+
+// TestFileDescriptorLimits simply tests whether the file descriptor allowance
+// per this process can be retrieved.
+func TestFileDescriptorLimits(t *testing.T) {
+	target := 4096
+	hardlimit, err := Maximum()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if hardlimit < target {
+		t.Skip(fmt.Sprintf("system limit is less than desired test target: %d < %d", hardlimit, target))
+	}
+
+	if limit, err := Current(); err != nil || limit <= 0 {
+		t.Fatalf("failed to retrieve file descriptor limit (%d): %v", limit, err)
+	}
+	if err := Raise(uint64(target)); err != nil {
+		t.Fatalf("failed to raise file allowance")
+	}
+	if limit, err := Current(); err != nil || limit < target {
+		t.Fatalf("failed to retrieve raised descriptor limit (have %v, want %v): %v", limit, target, err)
+	}
+}