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Date:   Thu, 23 Jan 2020 03:47:45 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Omar Sandoval <osandov@osandov.com>
Cc:     Amir Goldstein <amir73il@gmail.com>,
        Trond Myklebust <trondmy@hammerspace.com>,
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        "Darrick J. Wong" <darrick.wong@oracle.com>
Subject: Re: [LSF/MM/BPF TOPIC] Allowing linkat() to replace the destination
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On Wed, Jan 22, 2020 at 02:10:03PM -0800, Omar Sandoval wrote:

> > Sorry for not reading all the thread again, some API questions:
> > - We intend to allow AT_REPLACE only with O_TMPFILE src. Right?
> 
> I wasn't planning on having that restriction. It's not too much effort
> for filesystems to support it for normal files, so I wouldn't want to
> place an artificial restriction on a useful primitive.

I'm not sure; that's how we ended up with the unspeakable APIs like
rename(2), after all...

Said that, in this particular case I would suggest allowing it for
any source - what matters is not the _origin_ of that thing, but the
current state.  And linkat() (including the already existing variant)
can change that at any time...