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Date:   Fri, 27 Dec 2019 00:42:06 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 03/10] fs: add namei support for doing a non-blocking
 path lookup
Message-ID: <20191227004206.GT4203@ZenIV.linux.org.uk>
References: <20191213183632.19441-1-axboe@kernel.dk>
 <20191213183632.19441-4-axboe@kernel.dk>
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On Fri, Dec 13, 2019 at 11:36:25AM -0700, Jens Axboe wrote:
> If the fast lookup fails, then return -EAGAIN to have the caller retry
> the path lookup. This is in preparation for supporting non-blocking
> open.

NAK.  We are not littering fs/namei.c with incremental broken bits
and pieces with uncertain eventual use.

And it's broken - lookup_slow() is *NOT* the only place that can and
does block.  For starters, ->d_revalidate() can very well block and
it is called outside of lookup_slow().  So does ->d_automount().
So does ->d_manage().

I'm rather sceptical about the usefulness of non-blocking open, to be
honest, but in any case, one thing that is absolutely not going to
happen is piecewise introduction of such stuff without a discussion
of the entire design.