linux-kernel - Re: namei.c LOOKUP_NONBLOCK (was "Re: [GIT PULL] io

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Date:   Thu, 10 Dec 2020 12:21:28 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        io-uring <io-uring@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: namei.c LOOKUP_NONBLOCK (was "Re: [GIT PULL] io_uring fixes for
 5.10-rc")

On 12/10/20 11:55 AM, Linus Torvalds wrote:
> On Thu, Dec 10, 2020 at 9:32 AM Jens Axboe <axboe@...nel.dk> wrote:
>>
>> Here's a potentially better attempt - basically we allow LOOKUP_NONBLOCK
>> with LOOKUP_RCU, and if we end up dropping LOOKUP_RCU, then we generally
>> return -EAGAIN if LOOKUP_NONBLOCK is set as we can no longer guarantee
>> that we won't block.
> 
> Looks sane to me.
> 
> I don't love the "__unlazy_walk vs unlazy_walk" naming - I think it
> needs to be more clear about what the difference is, but I think the
> basic patch looks sane, and looks about as big as I would have
> expected it to be.

Agree, would probably make more sense as __unlazy_walk ->
complete_walk_rcu(), which then also falls out naturally from
complete_walk() being the sole caller of that.

> But yes, I'll leave it to Al.
> 
> And if we do this - and I think we should - I'd also love to see a new
> flag in 'struct open_how' to openat2(), even if it's only to enable
> tests. RESOLVE_NONBLOCK?

Sure, enabling cached opens from userspace through regular openat2().
Let's wrap up this one first though, that needs to be a separate patch
anyway. I'll follow up with that once this is in.

-- 
Jens Axboe