Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Staticize functions which are not used somewhere else, move the
corresponding prototypes from the header to the code file.

Do not export AT_CLKTCK when emulating Linux kernel prior
to 2.4.0, as it has appeared in the 2.4.0-rc7 first time.
Being exported, AT_CLKTCK is returned by sysconf(_SC_CLK_TCK),
glibc falls back to the hard-coded CLK_TCK value when aux entry
is not present.

Glibc versions prior to 2.2.1 always use hard-coded CLK_TCK value.

For older applications/libc's which depends on hard-coded CLK_TCK
value user should set compat.linux.osrelease less than 2.4.0.

Approved by: kib (mentor)

Introduce linux_kernver() interface which is intended for an exact
designation of the emulated kernel version.

linux_kernver() returns integer value formatted as 'VVVMMMIII' where
VVV - version, MMM - major revision, III - minor revision.

Approved by: kib (mentor)

Move the per-prison Linux MIB from a private one-off pointer to the new
OSD-based jail extensions. This allows the Linux MIB to accessed via
jail_set and jail_get, and serves as a demonstration of adding jail support
to a module.

Reviewed by: dchagin, kib
Approved by: bz (mentor)

MFp4 (111746+):
Redo the checking for 2.6 emulation. We now cache the value of
use26 and replace calls to linux_get_osrelease() + parsing with
a call to linux_use26(). Typical path is lockless now.

Pointed out by: kib

This allows to ship RELENG_7_0 with a default osrelease of 2.4.2 and the
possibility to enable 2.6.x emulation without the possible performance
impact of the previous version of the check.

Submitted by: rdivacky

Remove linux_mib_destroy() (which I actually added in between 5.0 and 5.1)
which existed to cleanup the linux_osname mutex. Now that MTX_SYSINIT()
has grown a SYSUNINIT to destroy mutexes on unload, the extra destroy here
was redundant and resulted in panics in debug kernels.

MFC after: 1 week
Reported by: Goran Gajic ggajic at afrodita dot rcub dot bg dot ac dot yu

Add a cleanup function to destroy the osname_lock and call it on module
unload.

Submitted by: gallatin
Reported by: Martin Karlsson <mk-freebsd@bredband.net>

- Change the linux_[gs]et_os{name, release, s_version}() functions to
take a thread instead of a proc for their first argument.
- Add a mutex to protect the system-wide Linux osname, osrelease, and
oss_version variables.
- Change linux_get_prison() to take a thread instead of a proc for its
first argument and to use td_ucred rather than p_ucred. This is ok
because a thread's prison does not change even though it's ucred might.
- Also, change linux_get_prison() to return a struct prison * instead of
a struct linux_prison * since it returns with the struct prison locked
and this makes it easier to safely unlock the prison when we are done
messing with it.

Fixed some style bugs in the removal of __P(()). Tabs before "__P(("
were not removed.

Remove __P.

o Introduce pr_mtx into struct prison, providing protection for the
mutable contents of struct prison (hostname, securelevel, refcount,
pr_linux, ...)
o Generally introduce mtx_lock()/mtx_unlock() calls throughout kern/
so as to enforce these protections, in particular, in kern_mib.c
protection sysctl access to the hostname and securelevel, as well as
kern_prot.c access to the securelevel for access control purposes.
o Rewrite linux emulator abstractions for accessing per-jail linux
mib entries (osname, osrelease, osversion) so that they don't return
a pointer to the text in the struct linux_prison, rather, a copy
to an array passed into the calls. Likewise, update linprocfs to
use these primitives.
o Update in_pcb.c to always use prison_getip() rather than directly
accessing struct prison.

Reviewed by: jhb

Fix typo in license.

$Id$ -> $FreeBSD$

Add sysctl variables for the Linuxulator. These reside under `compat.linux' as
discussed on current.

The following variables are defined (for now):

osname (defaults to "Linux")
Allow users to change the name of the OS as returned by uname(2),
specially added for all those Linux Netscape users and statistics
maniacs :-) We now have what we all wanted!

osrelease (defaults to "2.2.5")
Allow users to change the version of the OS as returned by uname(2).
Since -current supports glibc2.1 now, change the default to 2.2.5
(was 2.0.36).

oss_version (defaults to 198144 [0x030600])
This one will be used by the OSS_GETVERSION ioctl (PR 12917) which I
can commit now that we have the MIB. The default version number is the
lowest version possible with the current 'encoding'.

A note about imprisoned processes (see jail(2)):
These variables are copy-on-write (as suggested by phk). This means that
imprisoned processes will use the system wide value unless it is written/set
by the process. From that moment on, a copy local to the prison will be
used.

A note about the implementation:
I choose to add a single pointer to struct prison, because I didn't like the
idea of changing struct prison every time I come up with a new variable. As
a side effect, the extra storage is only needed when a variable is set from
within the prison. This also minimizes kernel bloat when the Linuxulator is
not used; both compiled in or as a module.

Reviewed by: bde (first version only) and phk