.

wcfs/notes.txt

@@ -41,6 +41,13 @@ https://lwn.net/ml/linux-fsdevel/20190315212556.9315-1-kirr%40nexedi.com/
 Invalidations to wcfs clients are delayed until block access
 ============================================================
 
+XXX patial invalidations (only for those blocks that are in OS cache) could be
+still handled at zδhandle (txn boundary) time. The reason we handle them lazily
+is probably to avoid unneccessary notifications (i.e. if part of a file is
+mmaped, but changed block is out of mmaped region - there won't be reads
+covering that block and thus no pin messages with that block at all)
+XXX -> describe that in text.
+
 Initially it was planned that wcfs would send invalidation messages to its
 clients right after receiving invalidation message from ZODB at transaction
 boundary time. That simplifies logic but requires that for a particular file,

wcfs/wcfs.go

@@ -289,7 +289,7 @@ package main
 //	won't be served from OS file cache and instead will trigger a FUSE read
 //	request to wcfs.
 //
-//    4.5) no invalidation messages are sent to wcfs clients at this point(+).
+//    4.5) no invalidation messages are sent to wcfs clients at this point(+).	XXX rethink
 //
 //    4.6) processing ZODB invalidations and serving file reads (see 7) are
 //      organized to be mutually exclusive.
@@ -471,6 +471,8 @@ type Head struct {
 
 	// XXX move zconn's current transaction to Head here?
 
+	// XXX move watchTab here?
+
 }
 
 // /head/watch				- served by Watch.
@@ -487,6 +489,9 @@ type Watcher struct {
 	sk *FileSock
 
 	// XXX
+	// fileTab:	BigFile ->
+	//			at
+	//			pinned = ...		XXX
 }
 
 // /(head|<rev>)/bigfile/		- served by BigFileDir.
@@ -1615,9 +1620,19 @@ func main() {
 	gmntpt  = mntpt
 
 	// we require proper pagecache control (added to Linux 2.6.36 in 2010)
-	supports := fssrv.KernelSettings().SupportsNotify
+	kinit := fssrv.KernelSettings()
+	kfuse := fmt.Sprintf("kernel FUSE (API %d.%d)", kinit.Major, kinit.Minor)
+	supports := kinit.SupportsNotify
 	if !(supports(fuse.NOTIFY_STORE_CACHE) && supports(fuse.NOTIFY_RETRIEVE_CACHE)) {
-		log.Fatalf("kernel FUSE does not support pagecache control")
+		log.Fatalf("%s does not support pagecache control", kfuse)
+	}
+	// make a bold warning if kernel does not support precise cache invalidation
+	// (patch sent upstream; see notes.txt -> "Notes on OS pagecache control")
+	if kinit.Flags & fuse.CAP_PRECISE_INVAL_DATA == 0 {
+		w1 := fmt.Sprintf("%s does not support precise data cache invalidation", kfuse)
+		w2 := "-> performance will be AWFUL."
+		log.Error(w1); log.Error(w2)
+		fmt.Fprintf(os.Stderr, "W: wcfs: %s\nW: wcfs: %s\n", w1, w2)
 	}
 
 	// add entries to /

wcfs/wcfs_test.py

@@ -594,10 +594,22 @@ def test_wcfs():
     assert w.sendReq(b"watch %s @%s" % (h(zf._p_oid), h(at1))) == "ok"
     done.recv()
 
+    # XXX test watch with all at variants
+    # XXX both from scratch and going e.g. at1 -> at2 -> at3
+    # XXX going not only up, but also down at1 <- at2 <- at3
     w = t.watch(zf, at1)  # XXX <- pin @at2 @at3
     #t.watch(zf, at1, {2: at1, 3: at1})  # XXX <- pin @at2 @at3
 
+    # XXX 2 (or more) opened watch for 1 file at the same time
+    # XXX watch for 2 files via single watch open
 
+    # XXX watch with @at > head - must wait for head to become >= at
+    # XXX watch with @at < δtail.tail -> rejected
+    # XXX watch with at="-" -> stop watching
+
+    # XXX drop file[blk] from cache, access again -> no pin message sent the second time
+
+    # XXX mmap f; change f[blk] on pin message while under pagefault - should get changed page