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

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

- Add 32-bit compat system calls for VFS_AIO. The system calls live in the
aio code and are registered via the recently added SYSCALL32_*() helpers.
- Since the aio code likes to invoke fuword and suword a lot down in the
"bowels" of system calls, add a structure holding a set of operations for
things like storing errors, copying in the aiocb structure, storing
status, etc. The 32-bit system calls use a separate operations vector to
handle fuword32 vs fuword, etc. Also, the oldsigevent handling is now
done by having seperate operation vectors with different aiocb copyin
routines.
- Split out kern_foo() functions for the various AIO system calls so the
32-bit front ends can manage things like copying in and converting
timespec structures, etc.
- For both the native and 32-bit aio_suspend() and lio_listio() calls,
just use copyin() to read the array of aiocb pointers instead of using
a for loop that iterated over fuword/fuword32. The error handling in
the old case was incomplete (lio_listio() just ignored any aiocb's that
it got an EFAULT trying to read rather than reporting an error), and
possibly slower.

MFC after: 1 month

MFP4 (with some minor changes):

Implement the linux_io_* syscalls (AIO). They are only enabled if the native
AIO code is available (either compiled in to the kernel or as a module) at
the time the functions are used. If the AIO stuff is not available there
will be a ENOSYS.

From the submitter:
---snip---
DESIGN NOTES:

1. Linux permits a process to own multiple AIO queues (distinguished by
"context"), but FreeBSD creates only one single AIO queue per process.
My code maintains a request queue (STAILQ of queue(3)) per "context",
and throws all AIO requests of all contexts owned by a process into
the single FreeBSD per-process AIO queue.

When the process calls io_destroy(2), io_getevents(2), io_submit(2) and
io_cancel(2), my code can pick out requests owned by the specified context
from the single FreeBSD per-process AIO queue according to the per-context
request queues maintained by my code.

2. The request queue maintained by my code stores contrast information between
Linux IO control blocks (struct linux_iocb) and FreeBSD IO control blocks
(struct aiocb). FreeBSD IO control block actually exists in userland memory
space, required by FreeBSD native aio_XXXXXX(2).

3. It is quite troubling that the function io_getevents() of libaio-0.3.105
needs to use Linux-specific "struct aio_ring", which is a partial mirror
of context in user space. I would rather take the address of context in
kernel as the context ID, but the io_getevents() of libaio forces me to
take the address of the "ring" in user space as the context ID.

To my surprise, one comment line in the file "io_getevents.c" of
libaio-0.3.105 reads:

Ben will hate me for this

REFERENCE:

1. Linux kernel source code: http://www.kernel.org/pub/linux/kernel/v2.6/
(include/linux/aio_abi.h, fs/aio.c)

2. Linux manual pages: http://www.kernel.org/pub/linux/docs/manpages/
(io_setup(2), io_destroy(2), io_getevents(2), io_submit(2), io_cancel(2))

3. Linux Scalability Effort: http://lse.sourceforge.net/io/aio.html
The design notes: http://lse.sourceforge.net/io/aionotes.txt

4. The package libaio, both source and binary:
http://rpmfind.net/linux/rpm2html/search.php?query=libaio
Simple transparent interface to Linux AIO system calls.

5. Libaio-oracle: http://oss.oracle.com/projects/libaio-oracle/
POSIX AIO implementation based on Linux AIO system calls (depending on
libaio).
---snip---

Submitted by: Li, Xiao <intron@intron.ac>

Make AIO a loadable module.

Remove the explicit call to aio_proc_rundown() from exit1(), instead AIO
will use at_exit(9).

Add functions at_exec(9), rm_at_exec(9) which function nearly the
same as at_exec(9) and rm_at_exec(9), these functions are called
on behalf of modules at the time of execve(2) after the image
activator has run.

Use a modified version of tegge's suggestion via at_exec(9) to close
an exploitable race in AIO.

Fix SYSCALL_MODULE_HELPER such that it's archetecuterally neutral,
the problem was that one had to pass it a paramater indicating the
number of arguments which were actually the number of "int". Fix
it by using an inline version of the AS macro against the syscall
arguments. (AS should be available globally but we'll get to that
later.)

Add a primative system for dynamically adding kqueue ops, it's really
not as sophisticated as it should be, but I'll discuss with jlemon when
he's around.