kern/159663: sockets don't work though nullfs mounts

[Mikolaj Golub]

The following reply was made to PR kern/159663; it has been noted by GNATS.

From: Mikolaj Golub <trociny at freebsd.org>
To: Robert Millan <rmh at freebsd.org>
Cc: Mikolaj Golub <trociny at freebsd.org>,  FreeBSD-gnats-submit at freebsd.org,  freebsd-bugs at freebsd.org,  Kostik Belousov <kostikbel at gmail.com>,  Josef Karthauser <joe at freebsd.org>,  Adrian Chadd <adrian at freebsd.org>,  freebsd-fs at freebsd.org
Subject: Re: kern/159663: sockets don't work though nullfs mounts
Date: Tue, 27 Sep 2011 09:49:08 +0300

 --=-=-=
 
 
 On Tue, 27 Sep 2011 07:36:28 +0200 Robert Millan wrote:
 
  RM> 2011/9/25 Mikolaj Golub <trociny at freebsd.org>:
  >> As a proof of concept below is a patch that implements it.
 
  RM> This works very well, I'm currently using your patch to run X11 over a
  RM> nullfs-mounted /tmp.
 
  >> The issues with this approach I see so far:
  >>
  >> - we need an additional flag for namei;
 
  RM> What does this involve?
 
 Well, adding yet another flag just to handle this one case might be not very
 good idea :-)
 
 But actually it is possible to do without the additional flag, with the only
 hack in nullfs code: in lookup and create return lower vnode if it is a
 socket, like in the patch below. It works for me but I have not tested much
 and not checked yet if use cases are possible when this makes undesirable
 effect.
 
 -- 
 Mikolaj Golub
 
 
 --=-=-=
 Content-Type: text/x-diff
 Content-Disposition: inline; filename=nullfs.VSOCK.patch
 
 Index: sys/fs/nullfs/null_vnops.c
 ===================================================================
 --- sys/fs/nullfs/null_vnops.c	(revision 225757)
 +++ sys/fs/nullfs/null_vnops.c	(working copy)
 @@ -365,16 +365,38 @@ null_lookup(struct vop_lookup_args *ap)
  			vrele(lvp);
  		} else {
  			error = null_nodeget(dvp->v_mount, lvp, &vp);
 -			if (error)
 +			if (error) {
  				vput(lvp);
 -			else
 +			} else if (vp->v_type == VSOCK) {
 +				vref(lvp);
 +				vrele(vp);
 +				*ap->a_vpp =  lvp;
 +			} else {
  				*ap->a_vpp = vp;
 +			}
  		}
  	}
  	return (error);
  }
  
  static int
 +null_create(struct vop_create_args *ap)
 +{
 +	struct vnode *vp, *lvp;
 +	int retval;
 +
 +	retval = null_bypass(&ap->a_gen);
 +	vp = *ap->a_vpp;
 +	if (retval == 0 && vp->v_type == VSOCK) {
 +		lvp = NULLVPTOLOWERVP(vp);
 +		vref(lvp);
 +		vrele(vp);
 +		*ap->a_vpp = lvp;
 +	}
 +	return (retval);
 +}
 +
 +static int
  null_open(struct vop_open_args *ap)
  {
  	int retval;
 @@ -826,6 +848,7 @@ struct vop_vector null_vnodeops = {
  	.vop_accessx =		null_accessx,
  	.vop_advlockpurge =	vop_stdadvlockpurge,
  	.vop_bmap =		VOP_EOPNOTSUPP,
 +	.vop_create =           null_create,
  	.vop_getattr =		null_getattr,
  	.vop_getwritemount =	null_getwritemount,
  	.vop_inactive =		null_inactive,
 
 --=-=-=--