svn commit: r325392 - head/etc/autofs

[Alan Somers]

On Sat, Nov 4, 2017 at 8:38 AM, Edward Tomasz Napierala
<trasz at freebsd.org> wrote:
> Author: trasz
> Date: Sat Nov  4 14:38:00 2017
> New Revision: 325392
> URL: https://svnweb.freebsd.org/changeset/base/325392
>
> Log:
>   Add NIS automounter map, which supports rewriting of self-hosted locations
>   to make them nullfs.
>
>   PR:           221010
>   Submitted by: G. Paul Ziemba
>   MFC after:    2 weeks

This is not generally safe with NFSv4.  If
vfs.nfsd.issue_delegations==1, then the server will allow NFS clients
to delay flushing writes back to the server.  The protocol handles
multiple clients that want delegations for the same file, but it
doesn't handle local access.  So if somebody tries to automount a
locally-hosted NFSv4 volume with delegations enabled, but accidentally
mounts it with nullfs instead, file corruption could result.  The
simplest solution would be to never use nullfs if
vfs.nfsd.issue_delgations==1.

-Alan