Add GetFromPath to construct NsHandle from any path

Also makes other Get functions utilize GetFromPath
to avoid duplication.

Author: Eugene Yakubovich

netns_linux.go

@@ -52,33 +52,30 @@ func Get() (NsHandle, error) {
 	return GetFromThread(os.Getpid(), syscall.Gettid())
 }
 
-// GetFromName gets a handle to a named network namespace such as one
-// created by `ip netns add`.
-func GetFromName(name string) (NsHandle, error) {
-	fd, err := syscall.Open(fmt.Sprintf("/var/run/netns/%s", name), syscall.O_RDONLY, 0)
+// GetFromPath gets a handle to a network namespace
+// identified by the path
+func GetFromPath(path string) (NsHandle, error) {
+	fd, err := syscall.Open(path, syscall.O_RDONLY, 0)
 	if err != nil {
 		return -1, err
 	}
 	return NsHandle(fd), nil
 }
 
+// GetFromName gets a handle to a named network namespace such as one
+// created by `ip netns add`.
+func GetFromName(name string) (NsHandle, error) {
+	return GetFromPath(fmt.Sprintf("/var/run/netns/%s", name))
+}
+
 // GetFromPid gets a handle to the network namespace of a given pid.
 func GetFromPid(pid int) (NsHandle, error) {
-	fd, err := syscall.Open(fmt.Sprintf("/proc/%d/ns/net", pid), syscall.O_RDONLY, 0)
-	if err != nil {
-		return -1, err
-	}
-	return NsHandle(fd), nil
+	return GetFromPath(fmt.Sprintf("/proc/%d/ns/net", pid))
 }
 
 // GetFromThread gets a handle to the network namespace of a given pid and tid.
 func GetFromThread(pid, tid int) (NsHandle, error) {
-	name := fmt.Sprintf("/proc/%d/task/%d/ns/net", pid, tid)
-	fd, err := syscall.Open(name, syscall.O_RDONLY, 0)
-	if err != nil {
-		return -1, err
-	}
-	return NsHandle(fd), nil
+	return GetFromPath(fmt.Sprintf("/proc/%d/task/%d/ns/net", pid, tid))
 }
 
 // GetFromDocker gets a handle to the network namespace of a docker container.