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>

2 files changed, 2 insertions, 0 deletions

diff --git a/sys/conf/files.amd64 b/sys/conf/files.amd64
index 15c71b4..47d416f 100644
--- a/sys/conf/files.amd64
+++ b/sys/conf/files.amd64
@@ -240,6 +240,7 @@ amd64/linux32/linux32_locore.s	optional	compat_linux32		\
 amd64/linux32/linux32_machdep.c	optional	compat_linux32
 amd64/linux32/linux32_sysent.c	optional	compat_linux32
 amd64/linux32/linux32_sysvec.c	optional	compat_linux32
+compat/linux/linux_aio.c	optional	compat_linux32
 compat/linux/linux_emul.c       optional	compat_linux32
 compat/linux/linux_file.c	optional	compat_linux32
 compat/linux/linux_futex.c	optional	compat_linux32
diff --git a/sys/conf/files.i386 b/sys/conf/files.i386
index 11419d0..04a5080 100644
--- a/sys/conf/files.i386
+++ b/sys/conf/files.i386
@@ -85,6 +85,7 @@ rr232x_lib.o			optional	rr232x			\
 #
 compat/linprocfs/linprocfs.c	optional linprocfs
 compat/linsysfs/linsysfs.c	optional linsysfs
+compat/linux/linux_aio.c	optional compat_linux
 compat/linux/linux_emul.c	optional compat_linux
 compat/linux/linux_file.c	optional compat_linux
 compat/linux/linux_futex.c	optional compat_linux