nullfs and named pipes.

[Robert Watson]

On Thu, 15 Feb 2007, Kostik Belousov wrote:

> On Thu, Feb 15, 2007 at 03:22:59PM +0000, Josef Karthauser wrote:
>> On Thu, Feb 15, 2007 at 02:57:50PM +0100, Jeremie Le Hen wrote:
>>>
>>> Note that all processes within a jail can only intefere with processes 
>>> from another jail or host as if they were on different machines.  This 
>>> means they can communicate through PF_INET for instance but not PF_LOCAL.
>>
>> You might think so!  However that's not what's going on here.
>>
>> The named pipe/nullfs issue is nothing to do with jails.  It's just that 
>> nullfs is broken with respect to named pipes as I've previously reported. 
>> However with this patch:
>>
>>     cvs diff: Diffing .
>>     Index: null_subr.c
>>     ===================================================================
>>     RCS file: /home/ncvs/src/sys/fs/nullfs/null_subr.c,v
>>     retrieving revision 1.48.2.1
>>     diff -u -r1.48.2.1 null_subr.c
>>     --- null_subr.c 13 Mar 2006 03:05:17 -0000      1.48.2.1
>>     +++ null_subr.c 14 Feb 2007 00:02:28 -0000
>>     @@ -235,6 +235,8 @@
>> 	    xp->null_vnode = vp;
>> 	    xp->null_lowervp = lowervp;
>> 	    vp->v_type = lowervp->v_type;
>>     +       if (vp->v_type == VSOCK || vp->v_type == VFIFO)
>>     +               vp->v_un = lowervp->v_un;
>
> I'm wondering is some reference counting needed there ?

Yes, I find this a bit worrying also, but I don't know enough about how nullfs 
works to reason about it.  What happens when a vnode in the bottom layer has 
its on-disk reference count drop to zero -- is the vnode in the top layer 
invalidated somehow?

Robert N M Watson
Computer Laboratory
University of Cambridge