Cygwin: pipe: Make pipe_data_available() return PDA_UNKNOWN

... rather than 1 when the pipe space estimation fails, so that
select() and raw_wrie() can perform appropriate fallback handling.
In select(), even if pipe space is unknown, return writable to avoid
deadlock.  Even with select() returns writable, write() can blocked
anyway, if data is larger than pipe space. In raw_write(), if the
pipe is real non-blocking mode, attempting to write larger data than
pipe space is safe. Otherwise, return error.

Reviewed-by:
Signed-off-by: Takashi Yano <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>

Author: tyan0

winsup/cygwin/fhandler/pipe.cc

@@ -663,12 +663,13 @@ fhandler_pipe_fifo::raw_write (const void *ptr, size_t len)
 	     in a very implementation-defined way we can't emulate, but it
 	     resembles it closely enough to get useful results. */
 	  avail = pipe_data_available (-1, this, get_handle (), PDA_WRITE);
-	  if (avail < 1)	/* error or pipe closed */
+	  if (avail == PDA_UNKNOWN && real_non_blocking_mode)
+	    avail = len1;
+	  else if (avail == 0 || !PDA_NOERROR (avail))
+	    /* error or pipe closed */
 	    break;
 	  if (avail > len1)	/* somebody read from the pipe */
 	    avail = len1;
-	  if (avail == 1)	/* 1 byte left or non-Cygwin pipe */
-	    len1 >>= 1;
 	  else if (avail >= PIPE_BUF)
 	    len1 = avail & ~(PIPE_BUF - 1);
 	  else

winsup/cygwin/local_includes/select.h

@@ -143,5 +143,8 @@ ssize_t pipe_data_available (int, fhandler_base *, HANDLE, int);
 
 #define PDA_READ	0x00
 #define PDA_WRITE	0x01
+#define PDA_ERROR	-1
+#define PDA_UNKNOWN	-2
+#define PDA_NOERROR(x)	(x >= 0)
 
 #endif /* _SELECT_H_ */

winsup/cygwin/select.cc

@@ -601,7 +601,7 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, int mode)
       if (mode == PDA_READ
 	  && PeekNamedPipe (h, NULL, 0, NULL, &nbytes_in_pipe, NULL))
 	return nbytes_in_pipe;
-      return -1;
+      return PDA_ERROR;
     }
 
   IO_STATUS_BLOCK iosb = {{0}, 0};
@@ -618,7 +618,7 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, int mode)
 	 access on the write end.  */
       select_printf ("fd %d, %s, NtQueryInformationFile failed, status %y",
 		     fd, fh->get_name (), status);
-      return (mode == PDA_WRITE) ? 1 : -1;
+      return (mode == PDA_WRITE) ? PDA_UNKNOWN : PDA_ERROR;
     }
   if (mode == PDA_WRITE)
     {
@@ -660,7 +660,7 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, int mode)
 	    return fpli.WriteQuotaAvailable; /* Not empty */
 	  else if (!NT_SUCCESS (status))
 	    /* We cannot know actual write pipe space. */
-	    return 1;
+	    return PDA_UNKNOWN;
 	  /* Restore pipe mode to blocking mode */
 	  ((fhandler_pipe *) fh)->set_pipe_non_blocking (false);
 	  /* Empty */
@@ -684,7 +684,7 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, int mode)
       return fpli.ReadDataAvailable;
     }
   if (fpli.NamedPipeState & FILE_PIPE_CLOSING_STATE)
-    return -1;
+    return PDA_ERROR;
   return 0;
 }
 
@@ -734,7 +734,7 @@ peek_pipe (select_record *s, bool from_select)
       if (n == 0 && fh->get_echo_handle ())
 	n = pipe_data_available (s->fd, fh, fh->get_echo_handle (), PDA_READ);
 
-      if (n < 0)
+      if (n == PDA_ERROR)
 	{
 	  select_printf ("read: %s, n %d", fh->get_name (), n);
 	  if (s->except_selected)
@@ -775,8 +775,8 @@ peek_pipe (select_record *s, bool from_select)
 	}
       ssize_t n = pipe_data_available (s->fd, fh, h, PDA_WRITE);
       select_printf ("write: %s, n %d", fh->get_name (), n);
-      gotone += s->write_ready = (n > 0);
-      if (n < 0 && s->except_selected)
+      gotone += s->write_ready = (n > 0 || n == PDA_UNKNOWN);
+      if (n == PDA_ERROR && s->except_selected)
 	gotone += s->except_ready = true;
     }
   return gotone;
@@ -989,7 +989,7 @@ peek_fifo (select_record *s, bool from_select)
       ssize_t n = pipe_data_available (s->fd, fh, fh->get_handle (), PDA_WRITE);
       select_printf ("write: %s, n %d", fh->get_name (), n);
       gotone += s->write_ready = (n > 0);
-      if (n < 0 && s->except_selected)
+      if (n == PDA_ERROR && s->except_selected)
 	gotone += s->except_ready = true;
     }
   return gotone;
@@ -1415,7 +1415,7 @@ peek_pty_slave (select_record *s, bool from_select)
       ssize_t n = pipe_data_available (s->fd, fh, h, PDA_WRITE);
       select_printf ("write: %s, n %d", fh->get_name (), n);
       gotone += s->write_ready = (n > 0);
-      if (n < 0 && s->except_selected)
+      if (n == PDA_ERROR && s->except_selected)
 	gotone += s->except_ready = true;
     }
   return gotone;