.

wcfs/notes.txt

@@ -25,10 +25,14 @@ invalidating pagecache - e.g. it will invalidate whole cache on file size change
 
 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/fuse/inode.c?id=e0bc833d10#n233
 
-we can currently workaround it with using writeback mode (see !is_wb in the
+(XXX no) we can currently workaround it with using writeback mode (see !is_wb in the
 link above), but better we have proper FUSE flag for filesystem server to
 tell the kernel it is fully responsible for invalidating pagecache.
 
+XXX ^^^ we cannot workaround with writeback mode - in writeback mode the kernel
+does not trust us for size that we report via getattr, and thus we cannot even
+update the file from being 0 size to having some data.
+
 
 Invalidations to wcfs clients are delayed until block access
 ============================================================

wcfs/wcfs.go

@@ -809,7 +809,7 @@ retry:
 	zhead.txnCtx = ctx
 
 	// 2. restat invalidated ZBigFile
-	// XXX -> parallel?
+	// XXX -> parallel
 	// XXX locking
 	for file := range toinvalidate {
 		size, treePath, err := file.zfile.Size(ctx)

wcfs/wcfs_test.py

@@ -377,6 +377,8 @@ def test_wcfs():
     t.commit()
     t.wcsync()    # sync wcfs to ZODB
 
+
+    print(t.stat(zf))
     assert f.cached() == [0,0,0]  # initially not cached
     f.assertData ([b'',b'',s], mtime=t.head)
     # XXX assertCache all present?