1 files changed, 84 insertions, 0 deletions
diff --git a/vendor/github.com/coreos/go-iptables/iptables/lock.go b/vendor/github.com/coreos/go-iptables/iptables/lock.go
new file mode 100644
index 000000000..a88e92b4e
--- /dev/null
+++ b/vendor/github.com/coreos/go-iptables/iptables/lock.go
@@ -0,0 +1,84 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package iptables
+
+import (
+	"os"
+	"sync"
+	"syscall"
+)
+
+const (
+	// In earlier versions of iptables, the xtables lock was implemented
+	// via a Unix socket, but now flock is used via this lockfile:
+	// http://git.netfilter.org/iptables/commit/?id=aa562a660d1555b13cffbac1e744033e91f82707
+	// Note the LSB-conforming "/run" directory does not exist on old
+	// distributions, so assume "/var" is symlinked
+	xtablesLockFilePath = "/var/run/xtables.lock"
+
+	defaultFilePerm = 0600
+)
+
+type Unlocker interface {
+	Unlock() error
+}
+
+type nopUnlocker struct{}
+
+func (_ nopUnlocker) Unlock() error { return nil }
+
+type fileLock struct {
+	// mu is used to protect against concurrent invocations from within this process
+	mu sync.Mutex
+	fd int
+}
+
+// tryLock takes an exclusive lock on the xtables lock file without blocking.
+// This is best-effort only: if the exclusive lock would block (i.e. because
+// another process already holds it), no error is returned. Otherwise, any
+// error encountered during the locking operation is returned.
+// The returned Unlocker should be used to release the lock when the caller is
+// done invoking iptables commands.
+func (l *fileLock) tryLock() (Unlocker, error) {
+	l.mu.Lock()
+	err := syscall.Flock(l.fd, syscall.LOCK_EX|syscall.LOCK_NB)
+	switch err {
+	case syscall.EWOULDBLOCK:
+		l.mu.Unlock()
+		return nopUnlocker{}, nil
+	case nil:
+		return l, nil
+	default:
+		l.mu.Unlock()
+		return nil, err
+	}
+}
+
+// Unlock closes the underlying file, which implicitly unlocks it as well. It
+// also unlocks the associated mutex.
+func (l *fileLock) Unlock() error {
+	defer l.mu.Unlock()
+	return syscall.Close(l.fd)
+}
+
+// newXtablesFileLock opens a new lock on the xtables lockfile without
+// acquiring the lock
+func newXtablesFileLock() (*fileLock, error) {
+	fd, err := syscall.Open(xtablesLockFilePath, os.O_CREATE, defaultFilePerm)
+	if err != nil {
+		return nil, err
+	}
+	return &fileLock{fd: fd}, nil
+}