linux-ext4 - Re: Making linkat() able to overwrite the target

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Message-ID: <469671.1579279148@warthog.procyon.org.uk>
Date:   Fri, 17 Jan 2020 16:39:08 +0000
From:   David Howells <dhowells@...hat.com>
To:     Omar Sandoval <osandov@...ndov.com>
Cc:     dhowells@...hat.com, Colin Walters <walters@...bum.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        Theodore Ts'o <tytso@....edu>, adilger.kernel@...ger.ca,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Chris Mason <clm@...com>, josef@...icpanda.com,
        dsterba@...e.com, linux-ext4 <linux-ext4@...r.kernel.org>,
        xfs <linux-xfs@...r.kernel.org>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Making linkat() able to overwrite the target

Omar Sandoval <osandov@...ndov.com> wrote:

> Yes I still have those patches lying around and I'd be happy to dust
> them off and resend them.

That would be great if you could.  I could use them here:

	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=fscache-iter

I'm performing invalidation by creating a vfs_tmpfile() and then replacing the
on-disk file whilst letting ops resume on the temporary file.  Replacing the
on-disk file currently, however, involves unlinking the old one before I can
link in a new one - which leaves a window in which nothing is there.  I could
use one or more side dirs in which to create new files and rename them over,
but that has potential lock bottleneck issues - and is particularly fun if an
entire volume is invalidated (e.g. AFS vos release).

David