filesystem: add device number utilities

Add a utility type and functions for handling device numbers.

1 files changed, 26 insertions, 0 deletions

diff --git a/filesystem/path.go b/filesystem/path.go
index cfc3dc0..a99b743 100644
--- a/filesystem/path.go
+++ b/filesystem/path.go
@@ -20,6 +20,7 @@
 package filesystem
 
 import (
+	"fmt"
 	"log"
 	"os"
 	"path/filepath"
@@ -99,3 +100,28 @@ func isRegularFile(path string) bool {
 	info, err := loggedStat(path)
 	return err == nil && info.Mode().IsRegular()
 }
+
+// DeviceNumber represents a combined major:minor device number.
+type DeviceNumber uint64
+
+func (num DeviceNumber) String() string {
+	return fmt.Sprintf("%d:%d", unix.Major(uint64(num)), unix.Minor(uint64(num)))
+}
+
+func newDeviceNumberFromString(str string) (DeviceNumber, error) {
+	var major, minor uint32
+	if count, _ := fmt.Sscanf(str, "%d:%d", &major, &minor); count != 2 {
+		return 0, errors.Errorf("invalid device number string %q", str)
+	}
+	return DeviceNumber(unix.Mkdev(major, minor)), nil
+}
+
+// getDeviceNumber returns the device number of the device node at the given
+// path.  If there is a symlink at the path, it is dereferenced.
+func getDeviceNumber(path string) (DeviceNumber, error) {
+	var stat unix.Stat_t
+	if err := unix.Stat(path, &stat); err != nil {
+		return 0, err
+	}
+	return DeviceNumber(stat.Rdev), nil
+}