[COMMITTED PATCH] Clean up POSIX.1 implementation of truncate.

[Rich Felker]

On Mon, May 06, 2013 at 02:57:03PM -0700, Roland McGrath wrote:
> 2013-05-06  Roland McGrath  <roland@hack.frob.com>
> 
> 	* sysdeps/posix/truncate.c (__truncate): Renamed from truncate.
> 	Call __ names for open, ftruncate, and close.
> 	For LENGTH==0 case, just use O_TRUNC rather than calling ftruncate.
> 	(truncate): Define as weak alias.
> 
> --- a/sysdeps/posix/truncate.c
> +++ b/sysdeps/posix/truncate.c
> @@ -1,4 +1,5 @@
> -/* Copyright (C) 1995-2013 Free Software Foundation, Inc.
> +/* Truncate a file given by name.  Generic POSIX.1 version.
> +   Copyright (C) 1995-2013 Free Software Foundation, Inc.
>     This file is part of the GNU C Library.
>  
>     The GNU C Library is free software; you can redistribute it and/or
> @@ -22,20 +23,22 @@
>  
>  /* Truncate PATH to LENGTH bytes.  */
>  int
> -truncate (path, length)
> -     const char *path;
> -     off_t length;
> +__truncate (const char *path, off_t length)
>  {
>    int fd, ret, save;
>  
> -  fd = open (path, O_WRONLY);
> +  fd = __open (path, O_WRONLY | (length == 0 ? O_TRUNC : 0));

This code is buggy both before and after since it can leak a file
descriptor if another thread or a signal handler performs exec while
the file is open.

I understand this code is just the "generic POSIX implementation" in
terms of other POSIX functions and not actually used anywhere, but I
question the value of having buggy, nonconforming implementations like
this.

Note that it can be fixed with O_CLOEXEC assuming the underlying
implementation supports that.

Rich