nfs v2/v3 and diskless boot problem

[Danny Braniss]

> 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