From f661efa7fa2e718aea2ab800f108179da7090fb4 Mon Sep 17 00:00:00 2001
From: frm <frm@gordijn.org>
Date: Sat, 28 Jan 2017 16:28:29 +0100
Subject: [PATCH] Support for hardlinks with the restore command

---
 src/restic/fs/file.go         |  6 +++
 src/restic/hardlinks_index.go | 91 +++++++++++++++++++++++++++++++++++
 src/restic/node.go            | 19 ++++++++
 src/restic/restorer.go        |  4 +-
 4 files changed, 119 insertions(+), 1 deletion(-)
 create mode 100644 src/restic/hardlinks_index.go

diff --git a/src/restic/fs/file.go b/src/restic/fs/file.go
index b7e81a38b..ba2a27192 100644
--- a/src/restic/fs/file.go
+++ b/src/restic/fs/file.go
@@ -102,6 +102,12 @@ func Symlink(oldname, newname string) error {
 	return os.Symlink(fixpath(oldname), fixpath(newname))
 }
 
+// Hardlink creates newname as a hard link to oldname.
+// If there is an error, it will be of type *LinkError.
+func Hardlink(oldname, newname string) error {
+	return os.Link(fixpath(oldname), fixpath(newname))
+}
+
 // Stat returns a FileInfo structure describing the named file.
 // If there is an error, it will be of type *PathError.
 func Stat(name string) (os.FileInfo, error) {
diff --git a/src/restic/hardlinks_index.go b/src/restic/hardlinks_index.go
new file mode 100644
index 000000000..907d65950
--- /dev/null
+++ b/src/restic/hardlinks_index.go
@@ -0,0 +1,91 @@
+package restic
+
+import (
+	"sync"
+	"fmt"
+)
+
+type HardlinkKey struct {
+    Inode, Device uint64
+}
+
+type HardlinkData struct {
+    Links uint64
+    Name string
+}
+
+var (
+	hardLinkIndex      = make(map[HardlinkKey]*HardlinkData)
+	hardLinkIndexMutex = sync.RWMutex{}
+)
+
+func ExistsLink(inode uint64, device uint64) bool {
+	hardLinkIndexMutex.RLock()
+	defer hardLinkIndexMutex.RUnlock()
+	_, ok := hardLinkIndex[HardlinkKey{inode, device}]
+	
+	return ok
+}
+
+func AddLink(inode uint64, device uint64, links uint64, name string) {
+	hardLinkIndexMutex.RLock()
+	_, ok := hardLinkIndex[HardlinkKey{inode, device}]
+	hardLinkIndexMutex.RUnlock()
+	
+	if !ok {
+		hardLinkIndexMutex.Lock()
+		hardLinkIndex[HardlinkKey{inode,device}] = &HardlinkData{links, name};
+		hardLinkIndexMutex.Unlock()
+	} 	
+}
+
+func GetLink(inode uint64, device uint64) *HardlinkData {
+	hardLinkIndexMutex.RLock()
+	defer hardLinkIndexMutex.RUnlock()
+	return hardLinkIndex[HardlinkKey{inode, device}]
+}
+
+func RemoveLink(inode uint64, device uint64) {
+	hardLinkIndexMutex.Lock()
+	defer hardLinkIndexMutex.Unlock()
+	delete(hardLinkIndex, HardlinkKey{inode, device})
+}
+
+func DecrementLink(inode uint64, device uint64) {
+	hardLinkIndexMutex.RLock()
+	_, ok := hardLinkIndex[HardlinkKey{inode, device}]
+	hardLinkIndexMutex.RUnlock()
+	
+	if ok {
+		hardLinkIndexMutex.RLock()
+		if hardLinkIndex[HardlinkKey{inode, device}].Links > 0 {
+			hardLinkIndexMutex.RUnlock()
+			hardLinkIndexMutex.Lock()
+			hardLinkIndex[HardlinkKey{inode, device}].Links--
+			hardLinkIndexMutex.Unlock()
+		} else {
+			hardLinkIndexMutex.RUnlock()
+		}
+	}
+}
+
+/* return the number of links for a given inode-device combination */
+func CountLink(inode uint64, device uint64) uint64 {
+	hardLinkIndexMutex.RLock()
+	defer hardLinkIndexMutex.RUnlock()
+	
+	_, ok := hardLinkIndex[HardlinkKey{inode, device}]
+	if ok {
+		return hardLinkIndex[HardlinkKey{inode, device}].Links
+	}
+	return 0
+}
+
+func PrintLinkSummary() {
+	hardLinkIndexMutex.RLock()
+	defer hardLinkIndexMutex.RUnlock()
+	
+	for _, value := range hardLinkIndex {
+	    fmt.Printf("File %v has unrestored links; probably you did not backup the complete volume\n", value.Name)
+	}
+}
diff --git a/src/restic/node.go b/src/restic/node.go
index bf41f4201..f5c8dbbea 100644
--- a/src/restic/node.go
+++ b/src/restic/node.go
@@ -192,6 +192,24 @@ func (node Node) createDirAt(path string) error {
 }
 
 func (node Node) createFileAt(path string, repo Repository) error {
+	
+	if node.Links > 1 {
+		if !ExistsLink(node.Inode, node.Device) {
+			AddLink(node.Inode, node.Device, node.Links, path)
+			DecrementLink(node.Inode, node.Device)
+		} else {
+			err :=fs.Hardlink(GetLink(node.Inode, node.Device).Name, path)
+			if err != nil {
+				return errors.Wrap(err, "CreateHardlink")
+			}
+			DecrementLink(node.Inode, node.Device)
+			if CountLink(node.Inode, node.Device) == 0 {
+				RemoveLink(node.Inode, node.Device)
+			}
+			return nil
+		}
+	}
+		
 	f, err := fs.OpenFile(path, os.O_CREATE|os.O_WRONLY, 0600)
 	defer f.Close()
 
@@ -482,6 +500,7 @@ func (node *Node) fillExtra(path string, fi os.FileInfo) error {
 	case "file":
 		node.Size = uint64(stat.size())
 		node.Links = uint64(stat.nlink())
+		node.Device = uint64(stat.dev())
 	case "dir":
 	case "symlink":
 		node.LinkTarget, err = fs.Readlink(path)
diff --git a/src/restic/restorer.go b/src/restic/restorer.go
index 5397c8d52..8b600fdd6 100644
--- a/src/restic/restorer.go
+++ b/src/restic/restorer.go
@@ -119,7 +119,9 @@ func (res *Restorer) restoreNodeTo(node *Node, dir string, dst string) error {
 // RestoreTo creates the directories and files in the snapshot below dir.
 // Before an item is created, res.Filter is called.
 func (res *Restorer) RestoreTo(dir string) error {
-	return res.restoreTo(dir, "", *res.sn.Tree)
+	err := res.restoreTo(dir, "", *res.sn.Tree)
+	PrintLinkSummary();
+	return err
 }
 
 // Snapshot returns the snapshot this restorer is configured to use.