From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <ee9e417a0610090857y40e2a25bic2ab448767cef83c@mail.gmail.com>
Date: Mon,  9 Oct 2006 11:57:21 -0400
From: "Russ Cox" <rsc@swtch.com>
To: "Fans of the OS Plan 9 from Bell Labs" <9fans@cse.psu.edu>
Subject: Re: [9fans] non-truncating create
In-Reply-To: <49c8e5f6ae1f50391b40e6465b4a8818@plan9.jp>
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References: <ee9e417a0610082100n256719c6j568ce455859414e@mail.gmail.com>
	<49c8e5f6ae1f50391b40e6465b4a8818@plan9.jp>
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Rc says something like:

if ((fd =3D open(file, OWRITE)) < 0 && (fd =3D create(file, OWRITE, 0666)) =
< 0) {
    complain(...);
    return;
}
seek(fd, 0, 2);

You don't really mean ~0 as the argument to create.

Russ


On 10/9/06, Joel "chesky" Salomon <JoelCSalomon@gmail.com> wrote:
> > Rc just tries the open, and if that fails, tries the create.
> > It doesn't even bother looking at the error code.
> > If the open failed due to permissions, so will the create.
>
> Drawterm barfed on me and I lost the bit of code this suggested; when
> I tried to recreate it I ended up checking for OTRUNC a few times.
> Not pretty.
>
> > Or use create with OEXCL if you really care.
>
> Sort of the way create(2) calls create(5) first, then open(5) if that
> failed?  My code now looks like:
>         o =3D create(oname, omode|OEXCL, ~0);     /* fails if file exists=
 */
>         if(o < 0)
>                 o =3D open(oname, omode);
>         if(o < 0){
>                 complain("can't open %s for writing: %r", oname);
>                 return;
>         }
> which has no special-case code depending on OTRUNC being set or no.
>
> I suppose I ought to look at /sys/src/cmd/rc to see how it's really
> done.  Ma=F1ana.
>
> Thanks for the assist.
>
> --Joel
>
>