2411: Add copyright notices to everything.

[arvados.git] / services / keepstore / volume_unix.go

diff --git a/services/keepstore/volume_unix.go b/services/keepstore/volume_unix.go
index fa28ee272ff7b00948557ca8177288f518d255bf..da9b110c56e80f1c4572aceb09b65c6dd29e8578 100644 (file)
--- a/services/keepstore/volume_unix.go
+++ b/services/keepstore/volume_unix.go
@@ -1,3 +1,7 @@
+// Copyright (C) The Arvados Authors. All rights reserved.
+//
+// SPDX-License-Identifier: AGPL-3.0
+
 package main
 
 import (
@@ -8,6 +12,7 @@ import (
        "io"
        "io/ioutil"
        "os"
+       "os/exec"
        "path/filepath"
        "regexp"
        "strconv"
@@ -115,6 +120,82 @@ type UnixVolume struct {
        os osWithStats
 }
 
+// DeviceID returns a globally unique ID for the volume's root
+// directory, consisting of the filesystem's UUID and the path from
+// filesystem root to storage directory, joined by "/". For example,
+// the DeviceID for a local directory "/mnt/xvda1/keep" might be
+// "fa0b6166-3b55-4994-bd3f-92f4e00a1bb0/keep".
+func (v *UnixVolume) DeviceID() string {
+       giveup := func(f string, args ...interface{}) string {
+               log.Printf(f+"; using blank DeviceID for volume %s", append(args, v)...)
+               return ""
+       }
+       buf, err := exec.Command("findmnt", "--noheadings", "--target", v.Root).CombinedOutput()
+       if err != nil {
+               return giveup("findmnt: %s (%q)", err, buf)
+       }
+       findmnt := strings.Fields(string(buf))
+       if len(findmnt) < 2 {
+               return giveup("could not parse findmnt output: %q", buf)
+       }
+       fsRoot, dev := findmnt[0], findmnt[1]
+
+       absRoot, err := filepath.Abs(v.Root)
+       if err != nil {
+               return giveup("resolving relative path %q: %s", v.Root, err)
+       }
+       realRoot, err := filepath.EvalSymlinks(absRoot)
+       if err != nil {
+               return giveup("resolving symlinks in %q: %s", absRoot, err)
+       }
+
+       // Find path from filesystem root to realRoot
+       var fsPath string
+       if strings.HasPrefix(realRoot, fsRoot+"/") {
+               fsPath = realRoot[len(fsRoot):]
+       } else if fsRoot == "/" {
+               fsPath = realRoot
+       } else if fsRoot == realRoot {
+               fsPath = ""
+       } else {
+               return giveup("findmnt reports mount point %q which is not a prefix of volume root %q", fsRoot, realRoot)
+       }
+
+       if !strings.HasPrefix(dev, "/") {
+               return giveup("mount %q device %q is not a path", fsRoot, dev)
+       }
+
+       fi, err := os.Stat(dev)
+       if err != nil {
+               return giveup("stat %q: %s\n", dev, err)
+       }
+       ino := fi.Sys().(*syscall.Stat_t).Ino
+
+       // Find a symlink in /dev/disk/by-uuid/ whose target is (i.e.,
+       // has the same inode as) the mounted device
+       udir := "/dev/disk/by-uuid"
+       d, err := os.Open(udir)
+       if err != nil {
+               return giveup("opening %q: %s", udir, err)
+       }
+       uuids, err := d.Readdirnames(0)
+       if err != nil {
+               return giveup("reading %q: %s", udir, err)
+       }
+       for _, uuid := range uuids {
+               link := filepath.Join(udir, uuid)
+               fi, err = os.Stat(link)
+               if err != nil {
+                       log.Printf("error: stat %q: %s", link, err)
+                       continue
+               }
+               if fi.Sys().(*syscall.Stat_t).Ino == ino {
+                       return uuid + fsPath
+               }
+       }
+       return giveup("could not find entry in %q matching %q", udir, dev)
+}
+
 // Examples implements VolumeWithExamples.
 func (*UnixVolume) Examples() []Volume {
        return []Volume{