fuserfrontend: support truncate(2) by wrapping ftruncate(2)

Support truncate(2) by opening the file and calling ftruncate(2)
While the glibc "truncate" wrapper seems to always use ftruncate, fsstress from
xfstests uses this a lot by calling "truncate64" directly.

2 files changed, 12 insertions, 7 deletions

diff --git a/internal/fusefrontend/file.go b/internal/fusefrontend/file.go
index 7f25172..780a792 100644
--- a/internal/fusefrontend/file.go
+++ b/internal/fusefrontend/file.go
@@ -489,6 +489,8 @@ func (f *file) GetAttr(a *fuse.Attr) fuse.Status {
 var allocateWarnOnce sync.Once
 
 // Allocate - FUSE call, fallocate(2)
+// This is not implemented yet in gocryptfs, but it is neither in EncFS. This
+// suggests that the user demand is low.
 func (f *file) Allocate(off uint64, sz uint64, mode uint32) fuse.Status {
 	allocateWarnOnce.Do(func() {
 		tlog.Warn.Printf("fallocate(2) is not supported, returning ENOSYS - see https://github.com/rfjakob/gocryptfs/issues/1")
diff --git a/internal/fusefrontend/fs.go b/internal/fusefrontend/fs.go
index 20079b2..640c45d 100644
--- a/internal/fusefrontend/fs.go
+++ b/internal/fusefrontend/fs.go
@@ -207,14 +207,17 @@ func (fs *FS) Mknod(path string, mode uint32, dev uint32, context *fuse.Context)
 	return fs.FileSystem.Mknod(cPath, mode, dev, context)
 }
 
-// Only warn once
-var truncateWarnOnce sync.Once
-
+// Support truncate(2) by opening the file and calling ftruncate(2)
+// While the glibc "truncate" wrapper seems to always use ftruncate, fsstress from
+// xfstests uses this a lot by calling "truncate64" directly.
 func (fs *FS) Truncate(path string, offset uint64, context *fuse.Context) (code fuse.Status) {
-	truncateWarnOnce.Do(func() {
-		tlog.Warn.Printf("truncate(2) is not supported, returning ENOSYS - use ftruncate(2)")
-	})
-	return fuse.ENOSYS
+	file, code := fs.Open(path, uint32(os.O_RDWR), context)
+	if code != fuse.OK {
+		return code
+	}
+	code = file.Truncate(offset)
+	file.Release()
+	return code
 }
 
 func (fs *FS) Utimens(path string, Atime *time.Time, Mtime *time.Time, context *fuse.Context) (code fuse.Status) {