[newlib-cygwin] Always try to write complete incoming buffer on pipes and fifos

[Corinna Vinschen <corinna at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=688d943a520cf79b04e67d890cdeeefaf90d269c

commit 688d943a520cf79b04e67d890cdeeefaf90d269c
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Sat Jan 14 16:29:06 2017 +0100

    Always try to write complete incoming buffer on pipes and fifos
    
    This patch fixes the following problem:
    
    Commit 9636c426 refactored the pipe code especially to make sure
    to call WriteFile only with chunks matching the maximum atomic write
    count.  This accidentally introduced a small change in behaviour
    on blocking pipes due to the success case falling through into the
    error case.  Rather then writing atomic chunks until all bytes are
    written, the code immediately broke from the loop after writing
    the first chunk, basically the same as in case of non-blocking
    writes.  This behaviour is not compliant to POSIX which requires
    
     "Write requests to a pipe or FIFO [...]
    
      * If the O_NONBLOCK flag is clear, a write request may cause the
        thread to block, but on normal completion it shall return nbyte."
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/fhandler.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/winsup/cygwin/fhandler.cc b/winsup/cygwin/fhandler.cc
index 9ab52ad..a8fe3b6 100644
--- a/winsup/cygwin/fhandler.cc
+++ b/winsup/cygwin/fhandler.cc
@@ -2155,7 +2155,7 @@ fhandler_base_overlapped::raw_write (const void *ptr, size_t len)
 	    case overlapped_success:
 	      ptr = ((char *) ptr) + chunk;
 	      nbytes += nbytes_now;
-	      /* fall through intentionally */
+	      break;
 	    case overlapped_error:
 	      len = 0;		/* terminate loop */
 	    case overlapped_unknown: