[newlib-cygwin] Cygwin: pipes: don't call NtQueryInformationFile on read side of pipes

Corinna Vinschen corinna@sourceware.org
Wed Sep 15 13:42:27 GMT 2021


https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=34b14470406cb9551f98707bf63175811a506523

commit 34b14470406cb9551f98707bf63175811a506523
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Wed Sep 15 14:17:59 2021 +0200

    Cygwin: pipes: don't call NtQueryInformationFile on read side of pipes
    
    NtQueryInformationFile hangs if it's called on the read side handle of
    a pipe while another thread or process is performing a blocking read.
    
    Avoid select potentially hanging by calling NtQueryInformationFile
    only on the write side of the pipe and using PeekNamedPipe otherwise.
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/select.cc | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc
index a09d8a34d..566cf66d6 100644
--- a/winsup/cygwin/select.cc
+++ b/winsup/cygwin/select.cc
@@ -587,6 +587,14 @@ no_verify (select_record *, fd_set *, fd_set *, fd_set *)
 static int
 pipe_data_available (int fd, fhandler_base *fh, HANDLE h, bool writing)
 {
+  if (fh->get_device () == FH_PIPER)
+    {
+      DWORD nbytes_in_pipe;
+      if (!writing && PeekNamedPipe (h, NULL, 0, NULL, &nbytes_in_pipe, NULL))
+	return nbytes_in_pipe > 0;
+      return -1;
+    }
+
   IO_STATUS_BLOCK iosb = {{0}, 0};
   FILE_PIPE_LOCAL_INFORMATION fpli = {0};
   NTSTATUS status;


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