linux-kernel - Re: [PATCH 10/11] readahead: dont do start-of-file readahead after lseek()

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Date:	Tue, 2 Feb 2010 19:48:31 +0100
From:	Olivier Galibert <galibert@...ox.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/11] readahead: dont do start-of-file readahead after lseek()

On Tue, Feb 02, 2010 at 10:40:41AM -0800, Linus Torvalds wrote:
> IOW, if you start off with a SEEK_END, I think it's reasonable to expect 
> it to _not_ read the whole thing.

I've seen a lot of:
  int fd = open(...);
  size = lseek(fd, 0, SEEK_END);
  lseek(fd, 0, SEEK_SET);

  data = malloc(size);
  read(fd, data, size);
  close(fd);

Why not fstat?  I don't know.  Perhaps a case of cargo culting,
perhaps a case of "other unixes suck for portability"[1].  But it's
probably still there a lot in real code.

  OG.

[1] In the hpux, dgux, sunos, etc sense.  Not to be taken as a comment
    on modern BSDs.
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