fusefrontend: use sync.Once for one-time warnings

Using a simple boolean was racy (which was harmless
in this case) and non-idomatic.

internal/fusefrontend/file.go

@@ -472,15 +472,14 @@ func (f *file) GetAttr(a *fuse.Attr) fuse.Status {
 	return fuse.OK
 }
 
-// Allocate - FUSE call, fallocate(2)
-var allocateWarned bool
+// Only warn once
+var allocateWarnOnce sync.Once
 
+// Allocate - FUSE call, fallocate(2)
 func (f *file) Allocate(off uint64, sz uint64, mode uint32) fuse.Status {
-	// Only warn once
-	if !allocateWarned {
+	allocateWarnOnce.Do(func() {
 		toggledlog.Warn.Printf("fallocate(2) is not supported, returning ENOSYS - see https://github.com/rfjakob/gocryptfs/issues/1")
-		allocateWarned = true
-	}
+	})
 	return fuse.ENOSYS
 }
 

internal/fusefrontend/fs.go

@@ -208,14 +208,13 @@ func (fs *FS) Mknod(path string, mode uint32, dev uint32, context *fuse.Context)
 	return fs.FileSystem.Mknod(cPath, mode, dev, context)
 }
 
-var truncateWarned bool
+// Only warn once
+var truncateWarnOnce sync.Once
 
 func (fs *FS) Truncate(path string, offset uint64, context *fuse.Context) (code fuse.Status) {
-	// Only warn once
-	if !truncateWarned {
+	truncateWarnOnce.Do(func() {
 		toggledlog.Warn.Printf("truncate(2) is not supported, returning ENOSYS - use ftruncate(2)")
-		truncateWarned = true
-	}
+	})
 	return fuse.ENOSYS
 }