From: David Howells <dhowells@redhat.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: dhowells@redhat.com, linux-fsdevel@vger.kernel.org, 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: Tue, 14 Jan 2020 18:06:10 +0000 [thread overview]
Message-ID: <9351.1579025170@warthog.procyon.org.uk> (raw)
In-Reply-To: <20200114170250.GA8904@ZenIV.linux.org.uk>
Al Viro <viro@zeniv.linux.org.uk> wrote:
> > 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.
>
> Umm... I don't like the idea of linkat() doing that - you suddenly get new
> fun cases to think about (what should happen when the target is a mountpoint,
> for starters?
Don't allow it onto directories, S_AUTOMOUNT-marked inodes or anything that's
got something mounted on it.
> ) _and_ you would have to add a magical flag to vfs_link() so
> that it would know which tests to do.
Yes, I suggested AT_LINK_REPLACE as said magical flag.
> As for rename...
Yeah - with further thought, rename() doesn't really work as an interface,
particularly if a link has already been made.
Do you have an alternative suggestion? There are two things I want to avoid:
(1) Doing unlink-link or unlink-create as that leaves a window where the
cache file is absent.
(2) Creating replacement files in a temporary directory and renaming from
there over the top of the target file as the temp dir would then be a
bottleneck that spends a lot of time locked for creations and renames.
David
next prev parent reply other threads:[~2020-01-14 18:06 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-14 16:34 Making linkat() able to overwrite the target David Howells
2020-01-14 17:02 ` Al Viro
2020-01-14 18:06 ` David Howells [this message]
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
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