Re: [9fans] openat()

[Gorka Guardiola <paurea@gmail.com>]

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On Fri, Apr 5, 2024, 23:49 Alyssa M via 9fans <9fans@9fans.net> wrote:

> Are you thinking narrowly about "What changes to the Plan 9 kernel would
> you make to emulate the Linux openat() system call" or more generally about
> "How would you design a facility for plan 9 that provides an equivalent
> service?
>

Yes, this is what I understood between my first answer and the second. You
don't want to rewalk the path and you already have the fid with the
directory part walked in the chan of dirfd. I think that if you walk the
remaining path from that chan (cloning it) you preserve the same guarantees
provided by openat.



> As I understand it from the rationale section on the linux man page, the
> call exists to avoid a race condition between checking that a directory
> exists and doing something to a path containing it. An additional motivator
> is providing the effect of additional current working directories notably
> for Linux threads (which presumably don't have their own. I think
> 'threads'  (processes that share memory) on Plan 9 do???).
>
> This is all based on the assumption that holding a file/directory open
> keeps it alive and in existence... which on Plan 9, I think it doesn't,
> does it? As I understand it, remove can remove a file or directory that is
> open, which is not like UNIX/Linux...
>
> Sorry, I'm just trying to understand the question.
>
>
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