.

wcfs/wcfs.go

@@ -521,6 +521,8 @@ func (bfdata *BigFileData) Read(_ nodefs.File, dest []byte, off int64, fctx *fus
 
 // readBlk serves Read to read 1 ZBlk #blk into destination buffer.
 func (bfdata *BigFileData) readBlk(ctx context.Context, blk int64, dest []byte) error {
+	// XXX errctx?
+
 	// check if someone else is already loading this block
 	bfdata.loadMu.Lock()
 	loading, already := bfdata.loading[blk]
@@ -532,7 +534,7 @@ func (bfdata *BigFileData) readBlk(ctx context.Context, blk int64, dest []byte)
 	}
 	bfdata.loadMu.Unlock()
 
-	// if it is already loading - wait for it
+	// if it is already loading - just wait for it
 	if already {
 		select {
 		case <-ctx.Done():
@@ -581,13 +583,20 @@ func (bfdata *BigFileData) readBlk(ctx context.Context, blk int64, dest []byte)
 	// and thus would trigger DB access again.
 	go func() {
 		// XXX locking - invalidation must make sure this workers are finished.
+
+		// XXX if direct-io: don't touch pagecache
 		st := gfsconn.FileNotifyStoreCache(bfdata.Inode(), blk*blksize, blkdata)
 
 		bfdata.loadMu.Lock()
 		delete(bfdata.loading, blk)
 		bfdata.loadMu.Unlock()
 
-		// XXX where to report error
+		// XXX where to report error (-> log)
+
+		// XXX st == ENOSYS -> log once + disable pagecache update?
+		// EINVAL | ENOENT -> bug
+		// ENOMEN - kernel is already under memory pressure - we must not keep here
+
 		if st != fuse.OK {
 			return fmt.Errorf("bigfile %s: blk %d: -> pagecache: %s", zbf.POid(), blk, st)
 		}
@@ -681,6 +690,11 @@ func main() {
 	}
 	gfsconn = fsconn	// FIXME temp workaround (see ^^^)
 
+	supports := fssrv.KernelSettings().SupportsNotify
+	if !(supports(fuse.NOTIFY_STORE) && supports(fuse.NOTIFY_RETRIEVE)) {
+		log.Fatalf("kernel FUSE does not support cache control") // XXX more details?
+	}
+
 	// add entries to /
 	mkfile(root, ".wcfs", NewStaticFile([]byte(zurl)))
 	mkdir(root, "bigfile", &BigFileRoot{