Remove ancient SCCS tags from the tree, automated scripting, with two
minor fixup to keep things compiling. All the common forms in the tree
were removed with a perl script.

Sponsored by:		Netflix

The MNT_IGNORE flag can be used to mark certain filesystem mounts so
that utilities such as df(1) and mount(8) can filter out those mounts by
default. This can be used, for instance, to reduce the noise from
running container workloads inside jails which often have at least three
and sometimes as many as ten mounts per container.

The flag is supplied by the nmount(2) system call and is recorded so
that it can be reported by statfs(2). Unfortunately several filesystems
override the default behaviour and mask out the flag, defeating its
purpose. This change preserves the MNT_IGNORE flag for those filesystems
so that it can be reported correctly.

MFC after:	1 week

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

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

The pseudo file systems (devfs, fdescfs, procfs, etc.) report total
and available blocks and inodes despite being synthetic with no
underlying storage device to which those values could be applied.

The current code of these file systems tends to report a fixed number
of total blocks but no free blocks, and in the case of procfs,
libprocfs, linsysfs also no free inodes.

This can be irritating in e.g. the "df" output, since 100% of the
resources seem to be in use, but it can also create warnings in
monitoring tools used for capacity management.

This patch makes these file systems return the same value for the
total and free parameters, leading to 0% in use being displayed by
"df". Since there is no resource that can be exhausted, this appears
to be a sensible result.

Reviewed by:	mckusick
Differential Revision:	https://reviews.freebsd.org/D39442

Filesystems which want to use it in limited capacity can employ the
VOP_UNLOCK_FLAGS macro.

Reviewed by:	kib (previous version)
Differential Revision:	https://reviews.freebsd.org/D21427

Reviewed by:	kib
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D22009

See r353150.

Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D21646

by doing most of the work in a new function prison_add_vfs in kern_jail.c
Now a jail-enabled filesystem need only mark itself with VFCF_JAIL, and
the rest is taken care of.  This includes adding a jail parameter like
allow.mount.foofs, and a sysctl like security.jail.mount_foofs_allowed.
Both of these used to be a static list of known filesystems, with
predefined permission bits.

Reviewed by:	kib
Differential Revision:	D14681

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.