mountinfo: add GetMountsForPID, deprecate PidMountInfo

Function PidMountInfo is not named correctly (it should be PID not Pid,
and we already have mountinfo in the package name so it's tautological),
and can not accept FilterFunc.

Introduce GetMountsForPid, and deprecate PidMountInfo.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

mountinfo/mountinfo_linux.go

@@ -148,17 +148,28 @@ func parseMountTable(filter FilterFunc) ([]*Info, error) {
 	return GetMountsFromReader(f, filter)
 }
 
-// PidMountInfo collects the mounts for a specific process ID. If the process
-// ID is unknown, it is better to use `GetMounts` which will inspect
-// "/proc/self/mountinfo" instead.
-func PidMountInfo(pid int) ([]*Info, error) {
+// GetMountsForPID retrieves the list of mounts from a given process' mount
+// namespace. Unless there is a need to get mounts from a mount namespace
+// different from that of a calling process, use GetMounts.
+//
+// This function is Linux-specific.
+func GetMountsForPID(pid int, filter FilterFunc) ([]*Info, error) {
 	f, err := os.Open(fmt.Sprintf("/proc/%d/mountinfo", pid))
 	if err != nil {
 		return nil, err
 	}
 	defer f.Close()
 
-	return GetMountsFromReader(f, nil)
+	return GetMountsFromReader(f, filter)
+}
+
+// PidMountInfo collects the mounts for a specific process ID. If the process
+// ID is unknown, it is better to use `GetMounts` which will inspect
+// "/proc/self/mountinfo" instead.
+//
+// Deprecated: this will be removed before v1; use GetMountsForPID instead.
+func PidMountInfo(pid int) ([]*Info, error) {
+	return GetMountsForPID(pid, nil)
 }
 
 // A few specific characters in mountinfo path entries (root and mountpoint)