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Message-ID: <9c8bc740300964ffbd15a9b2ee39a0af26c6c7e5.camel@kernel.org>
Subject: Re: [PATCH RFC 06/24] vfs: break parent dir delegations in
 open(..., O_CREAT) codepath
From: Jeff Layton <jlayton@kernel.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>, Chuck
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Date: Sun, 17 Mar 2024 08:23:28 -0400
In-Reply-To: <20240317001942.GJ538574@ZenIV>
References: <20240315-dir-deleg-v1-0-a1d6209a3654@kernel.org>
	 <20240315-dir-deleg-v1-6-a1d6209a3654@kernel.org>
	 <20240317001942.GJ538574@ZenIV>
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On Sun, 2024-03-17 at 00:19 +0000, Al Viro wrote:
> On Fri, Mar 15, 2024 at 12:52:57PM -0400, Jeff Layton wrote:
> > In order to add directory delegation support, we need to break
> > delegations on the parent whenever there is going to be a change in the
> > directory.
> >=20
> > Add a delegated_inode parameter to lookup_open and have it break the
> > delegation. Then, open_last_lookups can wait for the delegation break
> > and retry the call to lookup_open once it's done.
>=20
> > @@ -3490,6 +3490,11 @@ static struct dentry *lookup_open(struct nameida=
ta *nd, struct file *file,
>=20
> Wait a sec - are you going to do anything to the atomic_open side of thin=
gs?
>=20
>=20

Hmm good point. I was thinking that all of the filesystems that had
atomic_open didn't support leases. I'm wrong though -- there are some
that currently do:

9p: It's a network filesystem, and I don't think it has any sort of
asynchronous notification or delegation-like object, does it? It might
be best though to just make it call simple_nosetlease.

fuse: fuse allows leases today. I doubt we can get away with turning
that off now. There probably ought to be a way for the userland driver
to opt-in or out of allowing built-in lease support maybe a flag or
something?

ntfs3: IDGI. Why does ntfs3 (which is a local filesystem, unless I'm
mistaken) have an atomic_open? Shouldn't lookup+open be fine, like with
most local filesystems?

vboxsf: Probably the same situation as 9p. Can we just disable leases?

I'll spin up a patchset soon to add proper setlease handlers to all of
the above. Then we can then guard against allowing generic_setlease on
filesystems by default on filesystems with an atomic_open handler.

Another (maybe better) idea might be to require filesystems to specify a
setlease handler if they want them enabled. We could just set the
existing local filesystems to generic_setlease. That would make lease
support a strictly opt-in thing, which is probably the best idea for
avoiding surprises with them.

> =20
> >  	/* Negative dentry, just create the file */
> >  	if (!dentry->d_inode && (open_flag & O_CREAT)) {
> > +		/* but break the directory lease first! */
> > +		error =3D try_break_deleg(dir_inode, delegated_inode);
> > +		if (error)
> > +			goto out_dput;

--=20
Jeff Layton <jlayton@kernel.org>