From: Al Viro <viro@zeniv.linux.org.uk>
To: Trond Myklebust <trondmy@hammerspace.com>
Cc: "dhowells@redhat.com" <dhowells@redhat.com>,
"hch@lst.de" <hch@lst.de>,
"osandov@osandov.com" <osandov@osandov.com>,
"miklos@szeredi.hu" <miklos@szeredi.hu>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"amir73il@gmail.com" <amir73il@gmail.com>,
"lsf-pc@lists.linux-foundation.org"
<lsf-pc@lists.linux-foundation.org>
Subject: Re: [LSF/MM/BPF TOPIC] Allowing linkat() to replace the destination
Date: Fri, 17 Jan 2020 16:01:09 +0000 [thread overview]
Message-ID: <20200117160109.GL8904@ZenIV.linux.org.uk> (raw)
In-Reply-To: <18dad9903c4f5c63300048e9ed2a8706ad31bc73.camel@hammerspace.com>
On Fri, Jan 17, 2020 at 02:56:05PM +0000, Trond Myklebust wrote:
> It sounds to me like we rather need a meta-topic about "How do we get
> simple things done in the Linux fs community?"
>
> It shouldn't take a ticket to Palm Springs to perform something simple
> like adding a new flag to a syscall.
Sure - adding a new flag is trivial. Coming up with sane semantics for
it, OTOH, can be rather non-trivial and in this case it is, unfortunately.
"something like link(2), only it tolerates the existing target and
atomically replaces it" does _not_ specify the semantics. Try to sit
down for a few minutes and come up with the cases when behaviour is
undefined by the above; it won't take longer than that.
We can do it by asking the proponent to come up with full description to
be included into the proposal, then have at it on fsdevel/linux-abi (as
well as security lists). Doable, but not a small amount of PITA for
original poster and dealing with questions/objections/etc. is certain
to grow a large thread with many branches (and lots of bikeshedding
thrown in) _and_ would include tons of roundtrips, so the latency
(especially early on, while the proposal is still raw) will be a factor.
It's not the question of how to implement it; it's what should it _do_.
And "we'll tweak the behaviour in corner cases later on" is good in
a lot of situations, but not for userland ABI. I'd been guilty of
such fuckups several times and they are not cheap to fix afterwards ;-/
prev parent reply other threads:[~2020-01-17 16:01 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
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 [this message]
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