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From:   David Howells <dhowells@redhat.com>
To:     linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, hch@lst.de,
        tytso@mit.edu, adilger.kernel@dilger.ca, darrick.wong@oracle.com,
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        linux-xfs@vger.kernel.org, linux-btrfs@vger.kernel.org,
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Subject: Making linkat() able to overwrite the target
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Date:   Tue, 14 Jan 2020 16:34:25 +0000
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With my rewrite of fscache and cachefiles:

	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log=
/?h=3Dfscache-iter

when a file gets invalidated by the server - and, under some circumstances=
,
modified locally - I have the cache create a temporary file with vfs_tmpfi=
le()
that I'd like to just link into place over the old one - but I can't becau=
se
vfs_link() doesn't allow you to do that.  Instead I have to either unlink =
the
old one and then link the new one in or create it elsewhere and rename acr=
oss.

Would it be possible to make linkat() take a flag, say AT_LINK_REPLACE, th=
at
causes the target to be replaced and not give EEXIST?  Or make it so that
rename() can take a tmpfile as the source and replace the target with that=
.  I
presume that, either way, this would require journal changes on ext4, xfs =
and
btrfs.

Thanks,
David