kern/167905: zfs set canmount=on UNMOUNTS dataset

[vermaden]

>Number:         167905
>Category:       kern
>Synopsis:       zfs set canmount=on UNMOUNTS dataset
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue May 15 06:20:02 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator:     vermaden
>Release:        9.0-RELEASE
>Organization:
>Environment:
9.0-RELEASE
>Description:
Its possible to change CANMOUNT from ON to NOAUTO on a mounted filesystem, but its not possible to change CANMOUNT from NOAUTO to ON as it REMOUNTS that dataset even if its ALREADY MOUNTED.
>How-To-Repeat:
# mount | head -1
zroot/ROOT/default on / (zfs, local, noatime, nfsv4acls)

# zfs get canmount zroot/ROOT/default
NAME                PROPERTY  VALUE     SOURCE
zroot/ROOT/default  canmount  noauto    local

# zfs set canmount=on zroot/ROOT/default
cannot unmount '/': Invalid argument

>Fix:
Do not remount dataset after setting CANMOUNT to ON from NOAUTO when its already mounted.

>Release-Note:
>Audit-Trail:
>Unformatted: