Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Implement lockless resource limits.

Use the same scheme implemented to manage credentials.

Code needing to look at process's credentials (as opposed to thred's) is
provided with *_proc variants of relevant functions.

Places which possibly had to take the proc lock anyway still use the proc
pointer to access limits.

Generalised support for copy-on-write structures shared by threads.

Thread credentials are maintained as follows: each thread has a pointer to
creds and a reference on them. The pointer is compared with proc's creds on
userspace<->kernel boundary and updated if needed.

This patch introduces a counter which can be compared instead, so that more
structures can use this scheme without adding more comparisons on the boundary.

Fix up module unload for syscall_module_handler consumers.

After r273707 it was registering syscalls as static.

This fixes hwpmc module unload.

Reported by: markj

Avoid dynamic syscall overhead for statically compiled modules.

The kernel tracks syscall users so that modules can safely unregister them.

But if the module is not unloadable or was compiled into the kernel, there is
no need to do this.

Achieve this by adding SY_THR_STATIC_KLD macro which expands to SY_THR_STATIC
during kernel build and 0 otherwise.

Reviewed by: kib (previous version)
MFC after: 2 weeks

Call chainevh callback when we are invoked with neither MOD_LOAD nor
MOD_UNLOAD. This makes it possible to add custom hooks for other module
events.

Return EOPNOTSUPP when there is no callback available.

Pointed out by: jhb
Reviewed by: jhb
MFC after: 1 month

In syscall_module_handler(): all switch branches return, remove
unreached code as pointed out in a Chinese forum [1].

[1] http://www.freebsdchina.org/forum/viewtopic.php?t=50619

Pointed out by: btw616 <btw s qq com>
MFC after: 1 month

Count number of threads that enter and leave dynamically registered
syscalls. On the dynamic syscall deregistration, wait until all
threads leave the syscall code. This somewhat increases the safety
of the loadable modules unloading.

Reviewed by: jhb
Tested by: pho
MFC after: 1 month

Introduce SYSCALL_INIT_HELPER and SYSCALL32_INIT_HELPER macros and
neccessary support functions to allow registering dynamically loaded
syscalls from the MOD_LOAD handlers. Helpers handle registration
failures semi-automatically.

Reviewed by: jhb
MFC after: 2 weeks

Various style fixes. 7 space indent is just odd.

Make system call modules a bit more robust:
- If we fail to register the system call during MOD_LOAD, then note that
so that we don't try to deregister it or invoke the chained event handler
during the subsequent MOD_UNLOAD event. Doing the deregister when the
register failed could result in trashing system call entries.
- Add a SI_SUB_SYSCALLS just before starting up init and use that to
register syscall modules instead of SI_SUB_DRIVERS. Registering system
calls as late as possible increases the chances that any other module
event handlers or SYSINITs in a module are executed to initialize the
data in a kld before a syscall dependent on that data is able to be
invoked.

MFC after: 3 days

Do a pass over all modules in the kernel and make them return EOPNOTSUPP
for unknown events.

A number of modules return EINVAL in this instance, and I have left
those alone for now and instead taught MOD_QUIESCE to accept this
as "didn't do anything".

Use __FBSDID().

- Lock down the ``module'' structure by adding an SX lock that is used by
all the global bits of ``module'' data. This commit adds a few generic
macros, MOD_SLOCK, MOD_XLOCK, etc., that are meant to be used as ways
of accessing the SX lock. It is also the first step in helping to lock
down the kernel linker and module systems.

Reviewed by: jhb, jake, smp@

KSE Milestone 2
Note ALL MODULES MUST BE RECOMPILED
make the kernel aware that there are smaller units of scheduling than the
process. (but only allow one thread per process at this time).
This is functionally equivalent to teh previousl -current except
that there is a thread associated with each process.

Sorry john! (your next MFC will be a doosie!)

Reviewed by: peter@freebsd.org, dillon@freebsd.org

X-MFC after: ha ha ha ha

sysvipc loadable.

new syscall entry lkmressys - "reserved loadable syscall"

Make syscall_register allow overwriting of such entries (lkmressys).

Trim unused options (or #ifdef for undoc options).

Submitted by: phk

$Id$ -> $FreeBSD$

Call the chained module handler before unregistering the syscall so that
errors can be detected.

Submitted by: "A.Yu.Isupov" <isupov@moonhe.jinr.ru>
PR: kern/12239

Move lkmnosys() from kern_lkm.c to here.

Implement a mechanism for a module to report a small amount of module
specific data back to the user via kldstat(2). Use that mechanism in
the syscall handler to report the syscall number used.

Implement support for adding syscalls in KLD modules.

Submitted by: Assar Westerlund <assar@sics.se>