Re: [9fans] non-truncating create

["G. David Butler" <gdb@dbsystems.com>]

And if you are interested in a much deeper discussion, look at the archives from 1999.

>-----Original Message-----
>From: Russ Cox [mailto:rsc@swtch.com]
>Sent: Monday, October 9, 2006 10:57 AM
>To: 'Fans of the OS Plan 9 from Bell Labs'
>Subject: Re: [9fans] non-truncating create
>
>Rc says something like:
>
>if ((fd = open(file, OWRITE)) < 0 && (fd = 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 = create(oname, omode|OEXCL, ~0);     /* fails if file exists */
>>         if(o < 0)
>>                 o = 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.  Mañana.
>>
>> Thanks for the assist.
>>
>> --Joel
>>
>>
>