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From: Christoph Hellwig <hch@lst.de>
To: David Howells <dhowells@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk,
	hch@lst.de, tytso@mit.edu, adilger.kernel@dilger.ca,
	darrick.wong@oracle.com, clm@fb.com, josef@toxicpanda.com,
	dsterba@suse.com, linux-ext4@vger.kernel.org,
	linux-xfs@vger.kernel.org, linux-btrfs@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: Making linkat() able to overwrite the target
Date: Wed, 15 Jan 2020 09:36:19 +0100	[thread overview]
Message-ID: <20200115083619.GA23039@lst.de> (raw)
In-Reply-To: <3326.1579019665@warthog.procyon.org.uk>

On Tue, Jan 14, 2020 at 04:34:25PM +0000, David Howells wrote:
> 
> when a file gets invalidated by the server - and, under some circumstances,
> modified locally - I have the cache create a temporary file with vfs_tmpfile()
> that I'd like to just link into place over the old one - but I can't because
> 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 across.
> 
> Would it be possible to make linkat() take a flag, say AT_LINK_REPLACE, that
> 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.

This sounds like a very useful primitive, and from the low-level XFS
point of view should be very easy to implement and will not require any
on-disk changes.  I can't really think of any good userspace interface but
a new syscall, though.

      parent reply	other threads:[~2020-01-15  8:36 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-14 16:34 David Howells
2020-01-14 17:02 ` Al Viro
2020-01-14 18:06 ` David Howells
2020-01-14 19:37   ` Miklos Szeredi
2020-01-17  0:46   ` Colin Walters
2020-01-17  9:57     ` Amir Goldstein
2020-01-17 11:42   ` David Howells
2020-01-17 16:22     ` Omar Sandoval
2020-01-17 16:39     ` David Howells
2020-01-15  8:36 ` Christoph Hellwig [this message]

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