Date: Thu, 12 Sep 2002 20:40:54 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Nate Lawson <nate@root.org> Cc: phk@FreeBSD.ORG, <des@FreeBSD.ORG>, <arch@FreeBSD.ORG> Subject: Re: PATCH: vnode->v_tag to const char * Message-ID: <20020912202409.Y5891-100000@gamplex.bde.org> In-Reply-To: <Pine.BSF.4.21.0209111342510.22368-100000@root.org>
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On Wed, 11 Sep 2002, Nate Lawson wrote:
> On Thu, 12 Sep 2002, Bruce Evans wrote:
> > On Tue, 10 Sep 2002, Nate Lawson wrote:
> > > * kern/vfs_bio.c, vm/vm_swap.c - detecting NFS vnode is now done via:
> > > vp->v_mount->mnt_stat.f_type == nfs_mount_type
> > > Since NFS does this itself, I'm guessing it's the accepted way.
> >
> > I don't like this. I can't find where nfs does this now, but remember
> > thinking that this method doesn't work in general because nfs's variable
> > can only be referenced if nfs is loaded.
>
> Here are the current places that reference nfs_mount_type:
>
> kern/vfs_subr.c:int nfs_mount_type = -1;
> sys/mount.h:extern int nfs_mount_type; /* vfc_typenum for nfs, or -1 */
> vm/vnode_pager.c: (vp->v_mount->mnt_stat.f_type !=
> nfs_mount_type)) {
>
> As you can see, NFS does not need to be loaded and this var is already
> ref'd in the vm code. For vm_swap.c, the code is seeing if it is enabling
> swapping to a file on an NFS-mounted fs, so v_mount has to be non-NULL.
This would be more convincing if the variable were actually initialized
to something other than -1 :-). The non-null initialization was removed
without comment in nfsclient/nfs_subs.c rev.1.105 (after a repo copy from
nfs/nfs_subs.c rev.1.104), perhaps because the variable appeared to be a
private to nfs and its one user in nfs (nfs_nqlease.c) went away. I wonder
why no one noticed the effect of this on vm_swap.c.
> The only other option I considered was checking v_op == nfsv2_vnodeop_p
> but that has huge problems in that the vops for NFS are only present when
> NFS is loaded.
>
> If you have a better solution, I'm open to it.
I guess the global is the least of evils.
Bruce
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