macos: mount snapshots - UNTESTED!

  - when the flag '-mount-snapshots' was given
  - and the snapshot is not mounted, mount it

this does not work under linux and freebsd:

    $ zfs mount pool/ds@snap
    cannot open 'pool/ds@snap': snapshot delimiter '@' is not expected here

the used command is somethink like: `zfs mount pool/ds@snap`
see: https://openzfsonosx.org/wiki/FAQ#Q.29_How_can_I_access_the_.zfs_snapshot_directories.3F

cmd/zfs-snap-diff/main.go

@@ -90,7 +90,7 @@ func parseFlags() (CliConfig, config.Config) {
 	// zfs
 	zfsCfg := &zsdCfg.ZFS
 	flag.BoolVar(&zfsCfg.UseSudo, "use-sudo", zfsCfg.UseSudo, "use sudo when executing 'zfs' commands")
-	flag.BoolVar(&zfsCfg.MountSnapshot, "mount-snapshot", zfsCfg.MountSnapshot,
+	flag.BoolVar(&zfsCfg.MountSnapshots, "mount-snapshots", zfsCfg.MountSnapshots,
 		"mount snapshot (only necessary if it's not mounted by zfs automatically")
 
 	flag.Parse()

pkg/config/zfs_config.go

@@ -5,18 +5,18 @@ import (
 )
 
 type ZFSConfig struct {
-	UseSudo       bool
-	MountSnapshot bool
+	UseSudo        bool
+	MountSnapshots bool
 }
 
 func NewDefaultZFSConfig() ZFSConfig {
-	mountSnapshot := false
+	mountSnapshots := false
 	if runtime.GOOS == "darwin" {
-		mountSnapshot = true
+		mountSnapshots = true
 	}
 
 	return ZFSConfig{
 		UseSudo:       false,
-		MountSnapshot: mountSnapshot,
+		MountSnapshots: mountSnapshots,
 	}
 }

pkg/scanner/scanner.go

@@ -12,9 +12,10 @@ import (
 var log = plog.GlobalLogger()
 
 type Scanner struct {
-	dateRange     DateRange
-	compareMethod string
-	dataset       zfs.Dataset
+	dateRange      DateRange
+	compareMethod  string
+	dataset        zfs.Dataset
+	zfs            zfs.ZFS
 }
 
 type ScanResult struct {
@@ -32,8 +33,8 @@ type FileVersion struct {
 	Snapshot zfs.Snapshot  `json:"snapshot"`
 }
 
-func NewScanner(dateRange DateRange, compareMethod string, dataset zfs.Dataset) Scanner {
-	return Scanner{dateRange, compareMethod, dataset}
+func NewScanner(dateRange DateRange, compareMethod string, dataset zfs.Dataset, zfs zfs.ZFS) Scanner {
+	return Scanner{dateRange, compareMethod, dataset, zfs}
 }
 
 func (self *Scanner) FindFileVersions(pathActualVersion string) (ScanResult, error) {
@@ -50,6 +51,9 @@ func (self *Scanner) FindFileVersions(pathActualVersion string) (ScanResult, err
 	var cmp Comparator
 	snapsSkipped := 0
 	for idx, snap := range snaps {
+
+		// search is data-range based - check if the actual checked snapshot
+		// was created in the given range
 		if self.dateRange.IsBefore(snap.Created) {
 			snapsSkipped = snapsSkipped + 1
 			log.Tracef("skip snapshot - snapshot is younger (%s) than the time-range: %s",
@@ -58,8 +62,31 @@ func (self *Scanner) FindFileVersions(pathActualVersion string) (ScanResult, err
 			continue
 		}
 
+		if self.dateRange.IsAfter(snap.Created) {
+			log.Debugf("abort search - snapshot is older (%s) than the time-range %s",
+				snap.Created, self.dateRange.String())
+			break
+		}
+
+		// mount the snapshot if necessary
+		if self.zfs.MountSnapshots() {
+			isMounted, err := snap.IsMounted()
+			if err != nil {
+				log.Errorf("unable to check if snapshot: %s is mounted - %v", snap.Name, err)
+			}
+
+			if ! isMounted {
+				if err := self.zfs.MountSnapshot(snap); err != nil {
+					log.Errorf("unable to mount snapshot: %s - %v", snap.Name, err)
+
+					// skip this snapshot
+					continue
+				}
+			}
+		}
+
+		// initialize the file-content comparator
 		if cmp == nil {
-			// init comparator
 
 			var pathInitVersion string
 			if p, ok := self.findLastPathInSnap(pathActualVersion, idx-1, snaps); ok {
@@ -79,27 +106,26 @@ func (self *Scanner) FindFileVersions(pathActualVersion string) (ScanResult, err
 			}
 		}
 
-		if self.dateRange.IsAfter(snap.Created) {
-			log.Debugf("abort search - snapshot is older (%s) than the time-range %s",
-				snap.Created, self.dateRange.String())
-			break
-		}
-
-		sr.SnapsScanned = sr.SnapsScanned + 1
-		sr.LastScannedSnapshot = snap
 
+		// get the file-handle to the backup version in the snapshot
 		fh, err := fs.NewFileHandle(self.pathInSnapshot(pathActualVersion, snap))
 		if err != nil {
-			// not every snapshot has a version of the file - ignore errors
+			// not every snapshot MUST have a version of the file.
+			// maybe the file was deleted and restored - so ignore the error
 			sr.SnapsFileMissing = sr.SnapsFileMissing + 1
 			continue
 		}
 
+		// compare the file content
 		log.Tracef("check if file was changed under path: %s", fh.Path)
 		if cmp.HasChanged(fh) {
 			log.Debugf("file was changed in snapshot: %s", fh.Path)
 			sr.FileVersions = append(sr.FileVersions, FileVersion{fh, snap})
 		}
+
+		// update stats
+		sr.SnapsScanned = sr.SnapsScanned + 1
+		sr.LastScannedSnapshot = snap
 	}
 
 	sr.ScanDuration = time.Now().Sub(startTs)

pkg/webapp/webapi.go

@@ -100,7 +100,7 @@ func (self *WebApp) findFileVersionsHndl(w http.ResponseWriter, r *http.Request)
 	}
 
 	// scan for other file versions
-	sc := scanner.NewScanner(payload.DateRange, payload.CompareMethod, ds)
+	sc := scanner.NewScanner(payload.DateRange, payload.CompareMethod, ds, self.zfs)
 	versions, err := sc.FindFileVersions(payload.Path)
 	if err != nil {
 		log.Errorf("File versions search failed - %v", err)

pkg/zfs/dataset.go

@@ -42,23 +42,24 @@ func (self *Dataset) ScanSnapshots() (Snapshots, error) {
 
 	snapshots := Snapshots{}
 	for _, line := range strings.Split(stdout, "\n") {
-		if snapName, creation, ok := parse(line); ok {
+		if fullName, creation, ok := parse(line); ok {
 			// remove dataset name from snapshot
-			fields := strings.Split(snapName, "@")
-			snapName := fields[len(fields)-1]
+			fields := strings.Split(fullName, "@")
+			name := fields[len(fields)-1]
 
             // create the dir-handle per hand.
 			// this prevents a unnecessary 'os.Stat' call for each snapshot
+			// (which takes some time with thousands snapshots on spinning disks)
 			dir := fs.DirHandle{fs.FSHandle{
-				Name: snapName,
-				Path: self.MountPoint.Path + "/.zfs/snapshot/" + snapName,
+				Name: name,
+				Path: self.MountPoint.Path + "/.zfs/snapshot/" + name,
 				Kind: fs.DIR,
 				Size: 0,
 				ModTime: creation,
 			}}
 
 			// append new snap to snapshots
-			snapshots = append(snapshots, Snapshot{snapName, creation, dir})
+			snapshots = append(snapshots, Snapshot{name, fullName, creation, dir})
 		}
 
 	}

pkg/zfs/snapshot.go

@@ -3,15 +3,39 @@ package zfs
 import (
 	"github.com/j-keck/zfs-snap-diff/pkg/fs"
 	"time"
+	"os"
 )
 
 // Snapshot - zfs snapshot
 type Snapshot struct {
-	Name    string       `json:"name"`
-	Created time.Time    `json:"created"`
-	Dir     fs.DirHandle `json:"dir"`
+	Name     string       `json:"name"`
+	FullName string       `json:"fullName"`
+	Created  time.Time    `json:"created"`
+	Dir      fs.DirHandle `json:"dir"`
 }
 
+
+// Check if the snaphot is mounted
+func (s *Snapshot) IsMounted() (bool, error) {
+	log.Tracef("check if snapshot: %s is mounted", s.Name)
+
+	// to check if the snapshot is mounted, list
+	// the directory content. use 'File.Readdirnames'
+	// for the directrory listing, because it has less overhead
+
+	fh, err := os.Open(s.Dir.Path)
+	if err != nil {
+		return false, err
+	}
+
+	names, _ := fh.Readdirnames(10)
+	isMounted := len(names) > 0
+	log.Tracef("snapshot: %s is mounted = %v", s.Name, isMounted)
+	return isMounted, nil
+}
+
+
+
 // Snapshots represents snapshots from a zfs dataset
 type Snapshots []Snapshot
 
@@ -34,3 +58,4 @@ func (s *Snapshots) Filter(f func(Snapshot) bool) Snapshots {
 	}
 	return newS
 }
+

pkg/zfs/zfs.go

@@ -17,6 +17,7 @@ var log = plog.GlobalLogger()
 type ZFS struct {
 	datasets Datasets
 	cmd      ZFSCmd
+	cfg      config.Config
 }
 
 // NewZFS returns a handler for a zfs filesystem
@@ -29,6 +30,7 @@ func NewZFS(name string, cfg config.Config) (ZFS, error) {
 		return self, err
 	}
 	self.datasets = datasets
+	self.cfg = cfg
 	return self, nil
 }
 
@@ -142,6 +144,19 @@ func (self *ZFS) scanDatasets(name string) (Datasets, error) {
 	return datasets, nil
 }
 
+
+func (self *ZFS) MountSnapshots() bool {
+	return self.cfg.ZFS.MountSnapshots
+}
+
+func (self *ZFS) MountSnapshot(snap Snapshot) error {
+	log.Debugf("mount snapshot: %s", snap.Name)
+	stdout, stderr, err := self.cmd.Exec("mount", snap.FullName)
+	log.Tracef("mount snapshot stdout: %s", stdout)
+	log.Tracef("mount snapshot stderr: %s", stderr)
+	return err
+}
+
 type SortByPathDesc Datasets
 
 func (s SortByPathDesc) Len() int {

webapp/src/ZSD/Model/Snapshot.purs

@@ -9,9 +9,10 @@ import ZSD.Model.DateTime (DateTime)
 import ZSD.Model.FSEntry (FSEntry)
 
 type Snapshot =
-  { name    :: String
-  , created :: DateTime
-  , dir     :: FSEntry
+  { name     :: String
+  , fullName :: String
+  , created  :: DateTime
+  , dir      :: FSEntry
   }