linux-kernel - Re: [RFC, PATCH] Extensible AIO interface

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Date:	Mon, 1 Oct 2012 17:47:29 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Zach Brown <zab@...bo.net>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	tytso@...gle.com, tj@...nel.org,
	Dave Kleikamp <dave.kleikamp@...cle.com>,
	Dmitry Monakhov <dmonakhov@...nvz.org>,
	"Maxim V. Patlasov" <mpatlasov@...allels.com>,
	michael.mesnier@...el.com, jeffrey.d.skirvin@...el.com,
	Martin Petersen <martin.petersen@...cle.com>
Subject: Re: [RFC, PATCH] Extensible AIO interface

On Mon, Oct 01, 2012 at 04:44:39PM -0700, Zach Brown wrote:
> And what about duplicate instances of a given attribute id?  Use the
> first?  The last?  Error?  Depends on the id?

I thought of a better idea, instead of explicitly checking for
disallowed dups:

We want to return -ENOTHANDLED for not handled attributes anyways, so
let's just do that for dups - that'll catch erronious usage just fine
and a generic mechanism's better than a one off hack any day.

This does mean we can't punt on return values, which isn't a bad thing.

Also, if we've got duplicate attributes userspace needs to be able to
figure out which return value was for which attribute.

Two possibilities: one, return values come out in the same order
attributes went in. That'd work, but I dislike the subtlety and I expect
it'd be a pain for userspace.

Instead, let's just stick a u64 cookie in the attribute and include that
in the return, just like we do everywhere else.
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