Cygwin: pipes: drop "tiny pipe" handling

Given we return 1 already if WriteQuotaAvailable is > 0, the condition
for tiny pipes is never true.  Fix the comments.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc
index ac2fd227eb175ed17dd12e3e900b4d6185442b08..5e338e43f8d8434f39bfe0bf207ea43db42dcdfa 100644 (file)
--- a/winsup/cygwin/select.cc
+++ b/winsup/cygwin/select.cc
@@ -608,10 +608,12 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, bool writing)
     }
   if (writing)
     {
-       /* If there is anything available in the pipe buffer then signal
-          that.  This means that a pipe could still block since you could
-          be trying to write more to the pipe than is available in the
-          buffer but that is the hazard of select().  */
+      /* WriteQuotaAvailable is decremented by the number of bytes requested
+        by a blocking reader on the other side of the pipe.  Cygwin readers
+        are serialized and never request a number of bytes equivalent to the
+        full buffer size.  So WriteQuotaAvailable is 0 only if either the
+        read buffer on the other side is really full, or if we have non-Cygwin
+        readers. */
       if (fpli.WriteQuotaAvailable > 0)
        {
          paranoid_printf ("fd %d, %s, write: size %u, avail %u", fd,
@@ -619,17 +621,7 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, bool writing)
                           fpli.WriteQuotaAvailable);
          return 1;
        }
-      /* If we somehow inherit a tiny pipe (size < PIPE_BUF), then consider
-        the pipe writable only if it is completely empty, to minimize the
-        probability that a subsequent write will block.  */
-      if (fpli.OutboundQuota < PIPE_BUF
-         && fpli.WriteQuotaAvailable == fpli.OutboundQuota)
-       {
-         select_printf ("fd, %s, write tiny pipe: size %u, avail %u",
-                        fd, fh->get_name (), fpli.OutboundQuota,
-                        fpli.WriteQuotaAvailable);
-         return 1;
-       }
+      /* TODO: Buffer really full or non-Cygwin reader? */
     }
   else if (fpli.ReadDataAvailable)
     {