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To: Andrew Morton <>
Subject: Re: Bug in open() function (?)
Date: Sat, 12 Jul 2003 01:11:12 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: Your message of "Fri, 11 Jul 2003 20:38:09 PDT." <>

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On Fri, 11 Jul 2003 20:38:09 PDT, Andrew Morton said:
> "J.C. Wren" <> wrote:
> >
> > I was playing around today and found that if an existing file is opened wit
> >  O_TRUNC | O_RDONLY, the existing file is truncated.
> Well that's fairly idiotic, isn't it?

Not idiotic at all, and even if it was, it's still contrary to specific
language in the manpage.

I could *easily* see some program having a line of code:

	if (do_ro_testing) openflags |= O_RDONLY;

I'd not be surprised if J.C. was playing around because a file unexpectedly
shrank to zero size because of code like this.  There's a LOT of programs that
implement some sort of "don't really do it" option, from "/bin/bash -n" to
"cdrecord -dummy".  So you do something like the above to make your
file R/O - and O_TRUNC *STILL* zaps the file, in *direct violation* of
the language in the manpage.

Whoops.  Ouch. Where's the backup tapes?

> The Open Group go on to say "The result of using O_TRUNC with O_RDONLY is
> undefined" which is also rather silly.
> I'd be inclined to leave it as-is, really.

I hate to think how many programmers are relying on the *documented* behavior to
prevent data loss during debugging/test runs....


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  reply	other threads:[~2003-07-12  4:56 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-07-12  1:17 [PATCH] [2.5] adding ppp xon/xoff support Samuel Thibault
2003-07-12  1:30 ` Paul Mackerras
2003-07-12  2:42   ` Samuel Thibault
2003-07-12  3:09     ` Bug in open() function (?) J.C. Wren
2003-07-12  3:38       ` Andrew Morton
2003-07-12  5:11         ` Valdis.Kletnieks [this message]
2003-07-12  5:23           ` Andrew Morton
2003-07-12  6:14             ` Valdis.Kletnieks
2003-07-12  9:37               ` Andries Brouwer
2003-07-12 12:04                 ` jw schultz
2003-07-12  5:39           ` J.C. Wren
2003-07-26 21:35     ` [PATCH] [2.6] adding xon/xoff support to ppp Samuel Thibault
2003-07-17  7:54 Bug in open() function (?) Michael Kerrisk
2003-07-17 10:54 ` Andries Brouwer

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