.

wcfs/notes.txt

@@ -141,6 +141,9 @@ Starting from Linux 5.1 mmap_sem should be generally released while doing any IO
 
 but before that the analysis remains FUSE-specific.
 
+The property that changing mmapping while under pagefault is possible is
+verified by wcfs testsuite in `test_wcfs_remmap_on_pin` test.
+
 
 Client cannot be ptraced while under pagefault
 ==============================================

wcfs/wcfs.go

@@ -359,18 +359,18 @@ package main
 //	using just cheap revmax estimate can frequently result in all watches
 //	being skipped.
 //
-//   7.2) for all registered client@at watchers of head/bigfile/file:
+//   7.2) for all registered client@at watches of head/bigfile/file:
 //
 //	- rev'(blk) ≤ at: -> do nothing
 //	- rev'(blk) > at:
-//	  - if blk ∈ watcher.pinned -> do nothing
+//	  - if blk ∈ watch.pinned -> do nothing
 //	  - rev = max(δtail.by(#blk) : _ ≤ at)	|| min(rev ∈ δtail : rev ≤ at)	|| at
-//	  - watcher.pin(file, #blk, @rev)
-//	  - watcher.pinned += blk
+//	  - watch.pin(file, #blk, @rev)
+//	  - watch.pinned += blk
 //
 //	where
 //
-//	  watcher.pin(file, #blk, @rev)
+//	  watch.pin(file, #blk, @rev)
 //
 //	sends pin message according to "Invalidation protocol", and is assumed
 //	to cause
@@ -1004,6 +1004,7 @@ func (f *BigFile) invalidateBlk(ctx context.Context, blk int64) (err error) {
 		delete(f.loading, blk)
 	}
 
+	// XXX skip retrieve/store if len(f.watches) == 0
 	// try to retrieve cache of current head/data[blk], if we got nothing from f.loading
 	if blkdata == nil {
 		blkdata = make([]byte, blksize)

wcfs/wcfs_test.py

@@ -1682,6 +1682,9 @@ def test_wcfs_watch_vs_access():
 # verify that on pin message, while under pagefault, we can mmap @at/f[blk]
 # into where head/f[blk] was mmaped; the result of original pagefaulting read
 # must be from newly insterted mapping.
+#
+# TODO same with two mappings to the same file, but only one changing blk mmap
+#      -> one read gets changed data, one read gets data from @head.
 @func
 def test_wcfs_remmap_on_pin():
     t = tDB(); zf = t.zfile