Cygwin: pipe: Switch pipe mode to blocking mode by default

Previously, cygwin read pipe used non-blocking mode although non-
cygwin app uses blocking-mode by default. Despite this requirement,
if a cygwin app is executed from a non-cygwin app and the cygwin
app exits, read pipe remains on non-blocking mode because of the
commit fc691d0246b9. Due to this behaviour, the non-cygwin app
cannot read the pipe correctly after that. Similarly, if a non-
cygwin app is executed from a cygwin app and the non-cygwin app
exits, the read pipe mode remains on blocking mode although cygwin
read pipe should be non-blocking mode.

These bugs were provoked by pipe mode toggling between cygwin and
non-cygwin apps. To make management of pipe mode simpler, this
patch has re-designed the pipe implementation. In this new
implementation, both read and write pipe basically use only blocking
mode and the behaviour corresponding to the pipe mode is simulated
in raw_read() and raw_write(). Only when NtQueryInformationFile
(FilePipeLocalInformation) fails for some reasons, the raw_read()/
raw_write() cannot simulate non-blocking access. Therefore, the pipe
mode is temporarily changed to non-blocking mode.

Moreover, because the fact that NtSetInformationFile() in
set_pipe_non_blocking(true) fails with STATUS_PIPE_BUSY if the pipe
is not empty has been found, query handle is not necessary anymore.
This allows the implementation much simpler than before.

Addresses: https://github.com/git-for-windows/git/issues/5115
Fixes: fc691d0246b9 ("Cygwin: pipe: Make sure to set read pipe non-blocking for cygwin apps.");
Reported-by: isaacag, Johannes Schindelin <Johannes.Schindelin@gmx.de>
Reviewed-by: Corinna Vinschen <corinna@vinschen.de>, Ken Brown <kbrown@cornell.edu>
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>

1 files changed, 2 insertions, 42 deletions

diff --git a/winsup/cygwin/local_includes/fhandler.h b/winsup/cygwin/local_includes/fhandler.h
index 5b025f8..4e274d8 100644
--- a/winsup/cygwin/local_includes/fhandler.h
+++ b/winsup/cygwin/local_includes/fhandler.h
@@ -1197,6 +1197,7 @@ class fhandler_pipe_fifo: public fhandler_base
 {
  protected:
   size_t pipe_buf_size;
+  HANDLE pipe_mtx; /* Used only in the pipe case */
   virtual void release_select_sem (const char *) {};
 
  public:
@@ -1209,15 +1210,8 @@ class fhandler_pipe_fifo: public fhandler_base
 class fhandler_pipe: public fhandler_pipe_fifo
 {
 private:
-  HANDLE read_mtx;
   pid_t popen_pid;
-  HANDLE query_hdl;
-  HANDLE hdl_cnt_mtx;
-  HANDLE query_hdl_proc;
-  HANDLE query_hdl_value;
-  HANDLE query_hdl_close_req_evt;
   void release_select_sem (const char *);
-  HANDLE get_query_hdl_per_process (OBJECT_NAME_INFORMATION *);
 public:
   fhandler_pipe ();
 
@@ -1234,13 +1228,11 @@ public:
   int open (int flags, mode_t mode = 0);
   bool open_setup (int flags);
   void fixup_after_fork (HANDLE);
-  void fixup_after_exec ();
   int dup (fhandler_base *child, int);
   void set_close_on_exec (bool val);
   int close ();
   void raw_read (void *ptr, size_t& len);
   int ioctl (unsigned int cmd, void *);
-  int fcntl (int cmd, intptr_t);
   int fstat (struct stat *buf);
   int fstatvfs (struct statvfs *buf);
   int fadvise (off_t, off_t, int);
@@ -1265,39 +1257,7 @@ public:
     fh->copy_from (this);
     return fh;
   }
-  void set_pipe_non_blocking (bool nonblocking);
-  HANDLE get_query_handle () const { return query_hdl; }
-  void close_query_handle ()
-  {
-    if (query_hdl)
-      {
-	CloseHandle (query_hdl);
-	query_hdl = NULL;
-      }
-    if (query_hdl_close_req_evt)
-      {
-	CloseHandle (query_hdl_close_req_evt);
-	query_hdl_close_req_evt = NULL;
-      }
-  }
-  bool reader_closed ();
-  HANDLE temporary_query_hdl ();
-  bool need_close_query_hdl ()
-    {
-      return query_hdl_close_req_evt ?
-	IsEventSignalled (query_hdl_close_req_evt) : false;
-    }
-  bool request_close_query_hdl ()
-    {
-      if (query_hdl_close_req_evt)
-	{
-	  SetEvent (query_hdl_close_req_evt);
-	  return true;
-	}
-      return false;
-    }
-  static void spawn_worker (int fileno_stdin, int fileno_stdout,
-			    int fileno_stderr);
+  NTSTATUS set_pipe_non_blocking (bool nonblocking);
 };
 
 #define CYGWIN_FIFO_PIPE_NAME_LEN     47