Add norwfs version of rewritePackedRefsWhileLocked

Signed-off-by: Javi Fontan <jfontan@gmail.com>

Author: jfontan

storage/filesystem/internal/dotgit/dotgit.go

@@ -458,7 +458,10 @@ func (d *DotGit) openAndLockPackedRefs(doCreate bool) (
 		}
 	}()
 
-	openFlags := os.O_RDWR
+	// File mode is retrieved from a constant defined in the target specific
+	// files (dotgit_rewrite_packed_refs_*). Some modes are not available
+	// in all filesystems.
+	openFlags := openAndLockPackedRefsMode
 	if doCreate {
 		openFlags |= os.O_CREATE
 	}

storage/filesystem/internal/dotgit/dotgit_rewrite_packed_refs_nix.go

@@ -1,8 +1,14 @@
-// +build !windows
+// +build !windows,!norwfs
 
 package dotgit
 
-import "gopkg.in/src-d/go-billy.v4"
+import (
+	"os"
+
+	"gopkg.in/src-d/go-billy.v4"
+)
+
+const openAndLockPackedRefsMode = os.O_RDWR
 
 func (d *DotGit) rewritePackedRefsWhileLocked(
 	tmp billy.File, pr billy.File) error {

storage/filesystem/internal/dotgit/dotgit_rewrite_packed_refs_norwfs.go

@@ -0,0 +1,34 @@
+// +build norwfs
+
+package dotgit
+
+import (
+	"io"
+	"os"
+
+	"gopkg.in/src-d/go-billy.v4"
+)
+
+const openAndLockPackedRefsMode = os.O_RDONLY
+
+// Instead of renaming that can not be supported in simpler filesystems
+// a full copy is done.
+func (d *DotGit) rewritePackedRefsWhileLocked(
+	tmp billy.File, pr billy.File) error {
+
+	prWrite, err := d.fs.Create(pr.Name())
+	if err != nil {
+		return err
+	}
+
+	defer prWrite.Close()
+
+	_, err = tmp.Seek(0, io.SeekStart)
+	if err != nil {
+		return err
+	}
+
+	_, err = io.Copy(prWrite, tmp)
+
+	return err
+}

storage/filesystem/internal/dotgit/dotgit_rewrite_packed_refs_windows.go

@@ -1,13 +1,16 @@
-// +build windows
+// +build windows,!norwfs
 
 package dotgit
 
 import (
 	"io"
+	"os"
 
 	"gopkg.in/src-d/go-billy.v4"
 )
 
+const openAndLockPackedRefsMode = os.O_RDWR
+
 func (d *DotGit) rewritePackedRefsWhileLocked(
 	tmp billy.File, pr billy.File) error {
 	// If we aren't using the bare Windows filesystem as the storage