Re: [9fans] non-truncating create

["Felipe Bichued" <bichued@gmail.com>]

Hello,

You might want to read this: http://lsub.org/who/nemo/9.intro.pdf

Regards.

On 10/9/06, Joel "chesky" Salomon <JoelCSalomon@gmail.com> wrote:
> Still for the Brain-Dead SHell homework assignment...
>
> I'm trying to implement output redirection, > and >>.  Truncating
> redirect (>) is easy; just use create(2) whether the file exists or
> no.  The non-truncing option is puzzling me, though.  If the file
> exists, I need to o = open(oname, OWRITE), then seek(o, 0, 2); if the
> file does not exist I need to create it.
>
> How do I check for the existence of a file?  I'm thinking about the
> following code snippet:
>         o = open(oname, OWRITE)
>         rerrstr(errbuf, ERRMAX);
>         if((strstr(errbuf, "file does not exist") == 0){
>                 complain("cannot open %s: %r", oname);
>                 return;
>         }else   o = create(oname, OWRITE, ~0);
>         if(o < 0)
>                 ...
> Is there a cleaner way to accomplish this?  Some form of stat(2) that has an explicit  "file does not exist" code outside parsing errstr
>
> Of secondary interest: Not that this is production code, but should I
> be concerned about race conditions where the file is created by
> somebody else between the failed open(2) and the create(2)?
>
> Of tertiary interest: Is there a general use for a library function
> complain() that behaves identically to sysfatal(2) except for not
> terminating the program?
>
>
> --Joel
>
>


-- 
Felipe