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From:   "NeilBrown" <neilb@suse.de>
To:     "J. Bruce Fields" <bfields@fieldses.org>
Cc:     "Christoph Hellwig" <hch@infradead.org>,
        "Josef Bacik" <josef@toxicpanda.com>,
        "Chuck Lever" <chuck.lever@oracle.com>, "Chris Mason" <clm@fb.com>,
        "David Sterba" <dsterba@suse.com>,
        "Alexander Viro" <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org,
        linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 07/11] exportfs: Allow filehandle lookup to cross internal
 mount points.
In-reply-to: <20210728191711.GC3152@fieldses.org>
References: <162742539595.32498.13687924366155737575.stgit@noble.brown>,
 <162742546554.32498.9309110546560807513.stgit@noble.brown>,
 <20210728191711.GC3152@fieldses.org>
Date:   Thu, 29 Jul 2021 08:25:29 +1000
Message-id: <162751112971.21659.13568311032380832336@noble.neil.brown.name>
Precedence: bulk

On Thu, 29 Jul 2021, J. Bruce Fields wrote:
> On Wed, Jul 28, 2021 at 08:37:45AM +1000, NeilBrown wrote:
> > @@ -232,6 +239,68 @@ reconnect_path(struct vfsmount *mnt, struct dentry *=
target_dir, char *nbuf)
> >  	}
> >  	dput(dentry);
> >  	clear_disconnected(target_dir);
>=20
> Minor nit--I'd prefer the following in a separate function.

Fair.  Are you thinking "a separate function that is called here" or "a
separate function that needs to be called by whoever called
exportfs_decode_fh_raw()" if they happen to want the vfsmnt to be
updated?

NeilBrown

>=20
> --b.
>=20
> > +
> > +	/* Need to find appropriate vfsmount, which might not exist yet.
> > +	 * We may need to trigger automount points.
> > +	 */
> > +	path.mnt =3D mnt;
> > +	path.dentry =3D target_dir;
> > +	vfs_getattr_nosec(&path, &stat, 0, AT_STATX_DONT_SYNC);
> > +	target_dev =3D stat.dev;
> > +
> > +	path.dentry =3D mnt->mnt_root;
> > +	vfs_getattr_nosec(&path, &stat, 0, AT_STATX_DONT_SYNC);
> > +
> > +	while (stat.dev !=3D target_dev) {
> > +		/* walk up the dcache tree from target_dir, recording the
> > +		 * location of the most recent change in dev number,
> > +		 * until we find a mountpoint.
> > +		 * If there was no change in show_dev result before the
> > +		 * mountpount, the vfsmount at the mountpoint is what we want.
> > +		 * If there was, we need to trigger an automount where the
> > +		 * show_dev() result changed.
> > +		 */