Re: Diskless setup with NFS_V4

Slawa Olhovchenkov wrote:
> Its posible use currentle FreeBSD on NFS_V4 root?
> 
> Explain:
> 
> pxeboot do NFS_v3 (not NFS_v4) mount and pass fd to kernel.
> In this setup kernel can use only configured (established) nfs fh.
> This is not allowed to switch version or some options.
> 
> When pxeboot use TFTP (not NFS) kernel (in nfs/bootp_subr.c) do DHCP
> discover and don't allow (in nfs/nfs_diskless.c:nfs_parse_options)
> 'nfsv4' option.
> 
> nfs/nfs_diskless.c:nfs_setup_diskless also initialy set
> 
> nd3->root_args.flags = (NFSMNT_NFSV3 | NFSMNT_WSIZE | NFSMNT_RSIZE |
> NFSMNT_RESVPORT);
> 
> and don't allow 'nfsv4' option.
> 
> Where I be wrong?
> How I can use diskless setup with R/O root on NFS_V4 share?
No. There are a couple of problems that would need to be resolved
for an NFSv4 root fs to work.
1 - An NFSv4 mount needs a unique identifier for the client machine.
    It currently uses the host uuid, but that is filled in by a
    userland utility run from the root fs (ie. not available soon enough).
    Linux uses the ip host address for this, which I believe is bogus
    and inappropriate.
2 - Without the nfsuserd daemon running, there is currently no uid/gid<-->name
    mappings available. This might work, but there would be a lot of "file owned
    by nobody" situations that could cause problems.
    I suspect this can be fixed by hardwiring a few mappings (root, bin,...),
    but there is currently no code to do this.
    The Linux solution for this is to put the number in a string on the wire
    and the updated draft of RFC3530 (called rfc3530bis, not yet an RFC) allows
    this, so eventually this will be supported by most/all servers.

Until 1 and 2 are resolved, doing an NFSv4 root fs mount is not practical.
To be honest, I don't see a need for it, since I'm "old fashioned" and still
believe that the root fs should be a small volume of critical system utilities
only, so an NFSv3 mount of it should be sufficient. (ie. If /var and any
other subtrees where files might get byte range locked are on separate volumes,
I think it should be fine with a NFSv3 root fs mount, even without running rpc.lockd.)

rick

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