.

wcfs/wcfs.go

@@ -127,6 +127,7 @@
 //
 //	S: <2·k> pin <bigfileX> #<blk> @<rev_max>
 //	XXX @head means unpin.
+//	XXX or use `unpin <bigfileX> #<blk>` ?
 //
 // and waits until all clients confirm that changed file block can be updated
 // in global OS cache.
@@ -1354,7 +1355,9 @@ func (w *Watch) _pin(ctx context.Context, blk int64, rev zodb.Tid) (err error) {
 		if rev == zodb.TidMax {
 			panicf("f<%s>: wlink%d: pinned[#%d] = @head", foid, w.link.id, blk)
 		}
-		return nil // already pinned	XXX for simultaneous calls?
+		// already pinned
+		// (e.g. os cache for block was evicted and read called the second time)
+		return nil
 	}
 
 	ack, err := w.link.sendReq(ctx, fmt.Sprintf("pin %s #%d @%s", foid, blk, revstr))