From: Al Viro <viro@zeniv.linux.org.uk>
To: Trond Myklebust <trondmy@hammerspace.com>
Cc: "osandov@osandov.com" <osandov@osandov.com>,
"amir73il@gmail.com" <amir73il@gmail.com>,
"dhowells@redhat.com" <dhowells@redhat.com>,
"lsf-pc@lists.linux-foundation.org"
<lsf-pc@lists.linux-foundation.org>, "hch@lst.de" <hch@lst.de>,
"miklos@szeredi.hu" <miklos@szeredi.hu>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [LSF/MM/BPF TOPIC] Allowing linkat() to replace the destination
Date: Fri, 17 Jan 2020 15:46:57 +0000 [thread overview]
Message-ID: <20200117154657.GK8904@ZenIV.linux.org.uk> (raw)
In-Reply-To: <d2730b78cf0eac685c3719909df34d8d1b0bc347.camel@hammerspace.com>
On Fri, Jan 17, 2020 at 02:33:01PM +0000, Trond Myklebust wrote:
> On Fri, 2020-01-17 at 12:49 +0000, David Howells wrote:
> > It may be worth a discussion of whether linkat() could be given a
> > flag to
> > allow the destination to be replaced or if a new syscall should be
> > made for
> > this - or whether it should be disallowed entirely.
> >
> > A set of patches has been posted by Omar Sandoval that makes this
> > possible:
> >
> >
> > https://lore.kernel.org/linux-fsdevel/cover.1524549513.git.osandov@fb.com/
> >
> > though it only includes filesystem support for btrfs.
> >
> > This could be useful for cachefiles:
> >
> >
> > https://lore.kernel.org/linux-fsdevel/3326.1579019665@warthog.procyon.org.uk/
> >
> > and overlayfs.
> >
>
> That seems to me like a "just go ahead and do it if you can justify it"
> kind of thing. It has plenty of precedent, and fits easily into the
> existing syscall, so why do we need a face-to-face discussion?
Unfortunately, it does *not* fit easily. And IMO that's linux-abi fodder more
than anything else. The problem is in coming up with sane semantics - there's
a plenty of corner cases with that one. What to do when destination is
a dangling symlink, for example? Or has something mounted on it (no, saying
"we'll just reject directories" is not enough). What should happen when
destination is already a hardlink to the same object?
It's less of a horror than rename() would've been, but that's not saying
much.
next prev parent reply other threads:[~2020-01-17 15:47 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-17 12:49 [LSF/MM/BPF TOPIC] Allowing linkat() to replace the destination David Howells
2020-01-17 14:33 ` Trond Myklebust
2020-01-17 15:46 ` Al Viro [this message]
2020-01-17 16:12 ` Trond Myklebust
2020-01-17 16:48 ` Al Viro
2020-01-17 16:36 ` Omar Sandoval
2020-01-17 16:59 ` Al Viro
2020-01-17 17:28 ` Omar Sandoval
2020-01-17 18:17 ` Al Viro
2020-01-17 20:22 ` Omar Sandoval
2020-01-17 22:22 ` Al Viro
2020-01-17 23:54 ` Omar Sandoval
2020-01-18 0:47 ` Al Viro
2020-01-18 1:17 ` Omar Sandoval
2020-01-18 2:20 ` Al Viro
2020-01-21 23:05 ` Omar Sandoval
2020-01-22 6:57 ` Amir Goldstein
2020-01-22 22:10 ` Omar Sandoval
2020-01-23 3:47 ` Al Viro
2020-01-23 7:16 ` Dave Chinner
2020-01-23 7:47 ` Amir Goldstein
2020-01-24 21:25 ` Dave Chinner
2020-01-31 5:24 ` Darrick J. Wong
2020-01-31 5:29 ` hch
2020-01-31 7:00 ` Amir Goldstein
2020-01-31 20:33 ` Omar Sandoval
2020-01-31 21:55 ` Amir Goldstein
2020-01-28 1:27 ` Omar Sandoval
2020-01-28 14:35 ` David Howells
2020-01-31 5:31 ` hch
2020-01-31 8:04 ` David Howells
2020-01-31 8:56 ` Amir Goldstein
2020-01-22 9:53 ` David Howells
2020-01-17 14:47 ` David Howells
2020-01-17 14:56 ` Trond Myklebust
2020-01-17 16:01 ` Al Viro
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