sys: Remove $FreeBSD$: two-line .h pattern

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

sglist: Add sglist_append_single_mbuf().

This function appends the contents of a single mbuf to an sglist
rather than an entire mbuf chain.

Reviewed by: gallatin, markj
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D30135

Step 2.2:
o Shrink sglist(9) functions to work with multipage mbufs down from
four functions to two.
o Don't use 'struct mbuf_ext_pgs *' as argument, use struct mbuf.
o Rename to something matching _epg.

Reviewed by: gallatin
Differential Revision: https://reviews.freebsd.org/D24598

Continuation of multi page mbuf redesign from r359919.

The following series of patches addresses three things:

Now that array of pages is embedded into mbuf, we no longer need
separate structure to pass around, so struct mbuf_ext_pgs is an
artifact of the first implementation. And struct mbuf_ext_pgs_data
is a crutch to accomodate the main idea r359919 with minimal churn.

Also, M_EXT of type EXT_PGS are just a synonym of M_NOMAP.

The namespace for the newfeature is somewhat inconsistent and
sometimes has a lengthy prefixes. In these patches we will
gradually bring the namespace to "m_epg" prefix for all mbuf
fields and most functions.

Step 1 of 4:

o Anonymize mbuf_ext_pgs_data, embed in m_ext
o Embed mbuf_ext_pgs
o Start documenting all this entanglement

Reviewed by: gallatin
Differential Revision: https://reviews.freebsd.org/D24598

Add an external mbuf buffer type that holds multiple unmapped pages.

Unmapped mbufs allow sendfile to carry multiple pages of data in a
single mbuf, without mapping those pages. It is a requirement for
Netflix's in-kernel TLS, and provides a 5-10% CPU savings on heavy web
serving workloads when used by sendfile, due to effectively
compressing socket buffers by an order of magnitude, and hence
reducing cache misses.

For this new external mbuf buffer type (EXT_PGS), the ext_buf pointer
now points to a struct mbuf_ext_pgs structure instead of a data
buffer. This structure contains an array of physical addresses (this
reduces cache misses compared to an earlier version that stored an
array of vm_page_t pointers). It also stores additional fields needed
for in-kernel TLS such as the TLS header and trailer data that are
currently unused. To more easily detect these mbufs, the M_NOMAP flag
is set in m_flags in addition to M_EXT.

Various functions like m_copydata() have been updated to safely access
packet contents (using uiomove_fromphys()), to make things like BPF
safe.

NIC drivers advertise support for unmapped mbufs on transmit via a new
IFCAP_NOMAP capability. This capability can be toggled via the new
'nomap' and '-nomap' ifconfig(8) commands. For NIC drivers that only
transmit packet contents via DMA and use bus_dma, adding the
capability to if_capabilities and if_capenable should be all that is
required.

If a NIC does not support unmapped mbufs, they are converted to a
chain of mapped mbufs (using sf_bufs to provide the mapping) in
ip_output or ip6_output. If an unmapped mbuf requires software
checksums, it is also converted to a chain of mapped mbufs before
computing the checksum.

Submitted by: gallatin (earlier version)
Reviewed by: gallatin, hselasky, rrs
Discussed with: ae, kp (firewalls)
Relnotes: yes
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D20616

sys: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 3-Clause license.

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.

Special thanks to Wind River for providing access to "The Duke of
Highlander" tool: an older (2014) run over FreeBSD tree was useful as a
starting point.

sglist.h: Fix sg_refs signedness to match refcount(9)

PR: 220122
Reported by: Mark Millard <markmi at dsl-only.net>
Sponsored by: Dell EMC Isilon

Add sglist_append_sglist().

This function permits a range of one scatter/gather list to be appended to
another sglist. This can be used to construct a scatter/gather list that
reorders or duplicates ranges from one or more existing scatter/gather
lists.

Sponsored by: Chelsio Communications

Add sglist functions for working with arrays of VM pages.

sglist_count_vmpages() determines the number of segments required for
a buffer described by an array of VM pages. sglist_append_vmpages()
adds the segments described by such a buffer to an sglist. The latter
function is largely pulled from sglist_append_bio(), and
sglist_append_bio() now uses sglist_append_vmpages().

Reviewed by: kib
Sponsored by: Chelsio Communications

Add sglist_append_bio(9) to append a struct bio's data to a sglist

Reviewed by: jhb, kib (long ago)

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

MFC 196404:
Change the 'resid' parameter to sglist_consume_uio() from an int to a
size_t to match the recent type change of the uio_resid member of struct
uio.

Approved by: re (kib)

Change the 'resid' parameter to sglist_consume_uio() from an int to a
size_t to match the recent type change of the uio_resid member of struct
uio.

Approved by: re (kib)

Add a simple API to manage scatter/gather lists of phyiscal addresses.
Each list describes a logical memory object that is backed by one or more
physical address ranges. To minimize locking, the sglist objects
themselves are immutable once they are shared.

These objects may be used in the future to facilitate I/O requests using
physically-addressed buffers. For the immediate future I plan to use them
to implement a new type of VM object and pager.

Reviewed by: jeff, scottl
MFC after: 1 month