[Mingw-msys] bash input buffering

[Howard C. <hy...@hi...>]

I just noticed while building under VMware that my system was processing 
some 80,000 reads per second while running a Makefile, spending 90+% 
time in kernel mode and only about 6% in user mode. This was with the 
previous bash 2.x, but I installed bash 3.1 and got the same behavior. 
Basically bash is never using buffered I/O; it's reading script files 
one character at a time. This behavior is totally unnecessary.

This patch fixes the behavior:
Index: input.c
===================================================================
RCS file: /cvsroot/mingw/msys/packages/bash/3.1/input.c,v
retrieving revision 1.2
diff -u -r1.2 input.c
--- input.c     11 Aug 2006 17:21:39 -0000      1.2
+++ input.c     13 Mar 2007 02:00:16 -0000
@@ -337,7 +337,7 @@
  #if ! (__CYGWIN__ || __MSYS__)
  #  define fd_is_seekable(fd) (lseek ((fd), 0L, SEEK_CUR) >= 0)
  #else
-#  define fd_is_seekable(fd) 0
+#  define fd_is_seekable(fd) 1
  #endif /* __CYGWIN__ */

  /* Take FD, a file descriptor, and create and return a buffered stream

Note that fd_is_seekable() is only used in one place, to determine 
whether to buffer the input or not. Also there's no harm in always 
returning true, because a non-seekable descriptor will return a 0 in 
statbuf.st_size, and there's already a check for that condition, which 
will revert to the single-character reads.
-- 
   -- Howard Chu
   Chief Architect, Symas Corp.  http://www.symas.com
   Director, Highland Sun        http://highlandsun.com/hyc
   Chief Architect, OpenLDAP     http://www.openldap.org/project/