Hiroki Sato <h...@freebsd.org> wrote in <20110819.002046.908756241495481148....@allbsd.org>:
hr> Hi,
hr>
hr> I have experienced "Stale NFS file handle" issue when switching
hr> between oldnfs and newnfs on a CURRENT box (NFS server exporting ZFS
hr> mountpoints). The cause was that fsid was changed in the following
hr> conditions and not in the NFS subsystem itself, but I am wondering if
hr> these are expected behavior...
hr>
hr> First, I tried the following configurations of NFS and ZFS, and saw
hr> if fsid of the same mountpoint (a mounted ZFS dataset) changed or
hr> not by using statfs(2):
hr>
hr> compile opts kld module fsid[0:1] kld
loaded by
hr>
----------------------------------------------------------------------------
hr> NFSSERVER+NFSCLIENT zfs 865798fa:8346ef02 loader
hr>
hr> NFSSERVER+NFSCLIENT zfs 865798fa:8346ef07
kldload(8)
hr>
hr> NFSSERVER+NFSCLIENT+
hr> NFSD+NFSCL zfs 865798fa:8346ef03 loader
hr>
hr> NFSSERVER+NFSCLIENT+
hr> NFSD+NFSCL zfs 865798fa:8346ef08 kldload(8)
hr>
hr> NFSSERVER+NFSCLIENT nfsd+nfscl+zfs 865798fa:8346ef08 loader
hr>
----------------------------------------------------------------------------
Ah, I found why this happened:
/*
* The fsid is 64 bits, composed of an 8-bit fs type, which
* separates our fsid from any other filesystem types, and a
* 56-bit objset unique ID. The objset unique ID is unique to
* all objsets open on this system, provided by unique_create().
* The 8-bit fs type must be put in the low bits of fsid[1]
* because that's where other Solaris filesystems put it.
*/
fsid_guid = dmu_objset_fsid_guid(zfsvfs->z_os);
ASSERT((fsid_guid & ~((1ULL<<56)-1)) == 0);
vfsp->vfs_fsid.val[0] = fsid_guid;
vfsp->vfs_fsid.val[1] = ((fsid_guid>>32) << 8) |
vfsp->mnt_vfc->vfc_typenum & 0xFF;
Since the vfc_typenum variable is incremented every time a new vfs is
installed, loading order of modules that call vfs_register() affects
ZFS's fsid.
Anyway, possibility of fsid change is troublesome especially for an
NFS server with a lot of clients running. Can zeroing or setting a
fixed value to the lowest 8-bit of vfs_fsid.val[1] be harmful?
-- Hiroki
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