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Re: [COMMITTED PATCH] Clean up POSIX.1 implementation of truncate.
- From: Rich Felker <dalias at aerifal dot cx>
- To: Roland McGrath <roland at hack dot frob dot com>
- Cc: "GNU C. Library" <libc-alpha at sourceware dot org>
- Date: Tue, 7 May 2013 07:10:53 -0400
- Subject: Re: [COMMITTED PATCH] Clean up POSIX.1 implementation of truncate.
- References: <20130506215703 dot B2E2C2C07D at topped-with-meat dot com>
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