Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

Mark usage function as __dead2 in programs where it does not return

In most cases, usage does not return, so mark them as __dead2. For the
cases where they do return, they have not been marked __dead2.

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/735

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

Add a new "-m" option to pnfsdsfile(8) to prepare a file for mirroring.

When pnfsdscopymr(8) is used to create a mirror of a file on a mirrored
pNFS service, it expects to find an entry in the extended attribute for
IP address 0.0.0.0.
This patch adds a "-m" option which can be used to create these entrie(s).
It also tightens up the checks for use of incompatible command line options.

Add a command the displays and modifies the pNFS server's extended attribute.

This command allows a sysadmin to display or modify the pnfsd.dsfile extended
attribute used by the pNFS MDS server in various ways.
Its main use is to set a DS's IP address to 0.0.0.0 when that DS has failed,
so that it will not be used for the file when brought back online after
being repaired.