From e951043084937c42421debf457e33b3db3b5bac4 Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher
Date: Sun, 1 Jul 2018 19:13:28 +0200
Subject: fusefrontend: add File.SeekData() function

This function will enable "gocryptfs -fsck" to handle
sparse files efficiently.
---
 internal/fusefrontend/file_holes.go | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

(limited to 'internal/fusefrontend')

diff --git a/internal/fusefrontend/file_holes.go b/internal/fusefrontend/file_holes.go
index 2b95c5c..04a00ec 100644
--- a/internal/fusefrontend/file_holes.go
+++ b/internal/fusefrontend/file_holes.go
@@ -3,6 +3,9 @@ package fusefrontend
 // Helper functions for sparse files (files with holes)
 
 import (
+	"runtime"
+	"syscall"
+
 	"github.com/hanwen/go-fuse/fuse"
 
 	"github.com/rfjakob/gocryptfs/internal/tlog"
@@ -53,3 +56,15 @@ func (f *File) zeroPad(plainSize uint64) fuse.Status {
 	_, status := f.doWrite(pad, int64(plainSize))
 	return status
 }
+
+// SeekData calls the lseek syscall with SEEK_DATA. It returns the offset of the
+// next data bytes, skipping over file holes.
+func (f *File) SeekData(oldOffset int64) (int64, error) {
+	if runtime.GOOS != "linux" {
+		// Does MacOS support something like this?
+		return 0, syscall.EOPNOTSUPP
+	}
+	const SEEK_DATA = 3
+	fd := f.intFd()
+	return syscall.Seek(fd, oldOffset, SEEK_DATA)
+}
-- 
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