Modify vfs_register() to use a hash calculation

on vfc_name to set vfc_typenum, so that vfc_typenum doesn't
change when file systems are loaded in different orders. This
keeps NFS file handles from changing, for file systems that
use vfc_typenum in their fsid. This change is controlled via
a loader.conf variable called vfs.typenumhash, since vfc_typenum
will change once when this is enabled. It defaults to 1 for
9.0, but will default to 0 when MFC'd to stable/8.

Tested by:	hrs
Reviewed by:	jhb, pjd (earlier version)
Approved by:	re (kib)
MFC after:	1 month

1 files changed, 12 insertions, 0 deletions

diff --git a/UPDATING b/UPDATING
index f5c6f4d..dd35131 100644
--- a/UPDATING
+++ b/UPDATING
@@ -22,6 +22,18 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 9.x IS SLOW:
 	machines to maximize performance.  (To disable malloc debugging, run
 	ln -s aj /etc/malloc.conf.)
 
+20110913:
+	This commit modifies vfs_register() so that it uses a hash
+	calculation to set vfc_typenum, which is enabled by default.
+	The first time a system is booted after this change, the
+	vfc_typenum values will change for all file systems. The
+	main effect of this is a change to the NFS server file handles
+	for file systems that use vfc_typenum in their fsid, such as ZFS.
+	It will, however, prevent vfc_typenum from changing when file
+	systems are loaded in a different order for subsequent reboots.
+	To disable this, you can set vfs.typenumhash=0 in /boot/loader.conf
+	until you are ready to remount all NFS clients after a reboot.
+
 20110828:
 	Bump the shared library version numbers for libraries that
 	do not use symbol versioning, have changed the ABI compared