nfs v2/v3 and diskless boot problem

[Danny Braniss]

> Danny Braniss wrote:
> >> Danny Braniss wrote:
> >>>> Danny Braniss wrote:
> >>>>> there is an undocumented option:
> >>>>> 	boot-nfsroot-options
> >>>>> that the diskeless boot can use. I tried 
> >>>>> 	boot-nfsroot-options = "nfsv3"
> >>>>> since the pxeboot does the initial mount via nfsv2, and this has at least
> >>>>> one problem: removing a file from the readonly / will hang the system.
> >>>>>
> >>>>> so, the remount to v3 works in the case that the root is served by a Freebsd
> >>>>> nfs server, but fails if it's NetAPP. The reason is that the v2 filehandle
> >>>>> is 32 bytes, and when switching to V3 it becomes 28bytes - sizeof(fhandle_t).
> >>>>> This is not liked by the NetApp, which correctly gives error 1001: BADHANDLE 
> >>>>> :-)
> >>>>>
> >>>>> While I'm trying to come up with a solution, I am wondering if someone
> >>>>> can shed some light:
> >>>>>  - is sizeof(fhandle_t) == 28 bytes is mystical, or changing it to
> >>>>>    32 bytes will start WW3?
> >>>> NFSv3 file handles (by spec) can be up to 64bytes.
> >>> true, but in freebsd, look at sys/nfs/nfsproto.h
> >>> #define	NFSX_V2FH	32
> >>> #define NFSX_V3FH		(sizeof (fhandle_t))
> >>> #define NFSX_V4FH		128
> >>>
> >>> so for v3 it's 28 bytes. (fhandle_t is defined in sys/mount.h)
> >>>
> >>>
> >>>> I'm not 100% sure what is happening, but it sounds like the file handle 
> >>>> for the mount point or maybe one of the directories is not getting reset 
> >>>> on remount.
> >>>>
> >>>> When do you get the BADHANDLE error?  Can you capture a 
> >>>> tshark/wireshark/tcpdump of the remount and error?
> >>> I did, and if you look in sys/nfsclient/nfs_vfsops.c, nfs_convert_diskless is responsible
> >>> for chopping off the 4 extra bytes. BTW, I tried to change the bcopy count to NFSX_V2FH/32, and
> >>> it panics the kernel :-(
> >>>
> >>> danny
> >>
> >> oh - looks like this says it all:
> >> http://fxr.googlebit.com/source/sys/nfsclient/nfsdiskless.h?v=8-CURRENT#L51
> >>
> > that's where the boot-nfsroot-options comes from:-)
> > if you notice, the filehandle for v3 is 64 bytes, but
> > only 28 are used.
> > 
> > but as I mentioned initially, this ONLY works when the server is FreeBSD, and
> > breaks for other servers, ie NetAPP. AND the initial question stands:
> > what's in a filehandle, or can it be > 28bytes.
> 
> 
> Yea, FreeBSD is making the assumption that all NFS servers will use the 
> same size FH for NFSv3.  That is just wrong.
> 
carful, I think this is the case only if fsb is the server, it will 'probably' 
accept
filehandles of other sizes from other servers.

> The FH is a server created opaque handle that it can create however it 
> wishes.  Most servers use information like inode, generation, fsid, etc 
> to create it, but it's something that you can't necessarily decode.
> 
yes, but the FH has information that the server can/must use to figure out
which local filesystem it refers to - remember that v2/v3 are stateless.

> I've created a patch that might fix this, but I'm still testing and QEMU 
> (which I use for my testing) keeps making my system either panic or lock 
> up, so hopefully I should have something for you to try tonight.
> 
> Also - can you tell me the exact 'mount' command you tried to do the 
> remount/update?
> 
it's only in the diskless boot, where setting
	boot-nfsroot-options = "nfsv3"
in /boot/loader.conf will do the remount.

cheers,
	danny