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

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

fd: make fget_unlocked take a thread argument

Just like other fget routines. This enables embedding fd table pointer
in struct thread, avoiding taking a trip through proc.

LinuxKPI: Constantly use _LINUXKPI_ prefix in include guards

MFC after: 1 week
Reviewed by: bz, emaste, hselasky, manu
Differential Revision: https://reviews.freebsd.org/D33562

fd: remove the seq argument from fget_unlocked

It is almost always NULL.

Eliminate the overhead of gratuitous repeated reinitialization of cap_rights

- Add macros to allow preinitialization of cap_rights_t.

- Convert most commonly used code paths to use preinitialized cap_rights_t.
A 3.6% speedup in fstat was measured with this change.

Reported by: mjg
Reviewed by: oshogbo
Approved by: sbruno
MFC after: 1 month

Add more sanity checks to linux_fget() in the LinuxKPI. This prevents
returning pointers to file descriptors which were not created by the
LinuxKPI.

MFC after: 1 week
Sponsored by: Mellanox Technologies

Add generic kqueue() and kevent() support to the LinuxKPI character
devices. The implementation allows read and write filters to be
created and piggybacks on the poll() file operation to determine when
a filter should trigger. The piggyback mechanism is simply to check
for the EWOULDBLOCK or EAGAIN return code from read(), write() or
ioctl() system calls and then update the kqueue() polling state bits.
The implementation is similar to the one found in the cuse(3) module.
Refer to sys/fs/cuse/*.[ch] for more details.

MFC after: 1 week
Sponsored by: Mellanox Technologies

Fixes for refcounting "struct linux_file" in the LinuxKPI.

- Allow "struct linux_file" to be refcounted when its "_file" member
is NULL by using its "f_count" field. The reference counts are
transferred to the file structure when the file descriptor is
installed.

- Add missing vdrop() calls for error cases during open().

- Set the "_file" member of "struct linux_file" during open. This
allows use of refcounting through get_file() and fput() with LinuxKPI
character devices.

MFC after: 1 week
Sponsored by: Mellanox Technologies

Make the LinuxKPI task struct persistent accross system calls.

A set of helper functions have been added to manage the life of the
LinuxKPI task struct. When an external system call or task is invoked,
a check is made to create the task struct by demand. A thread
destructor callback is registered to free the task struct when a
thread exits to avoid memory leaks.

This change lays the ground for emulating the Linux kernel more
closely which is a dependency by the code using the LinuxKPI APIs.

Add new dedicated td_lkpi_task field has been added to struct thread
instead of abusing td_retval[1].

Fix some header file inclusions to make LINT kernel build properly
after this change.

Bump the __FreeBSD_version to force a rebuild of all kernel modules.

MFC after: 1 week
Sponsored by: Mellanox Technologies

Handle when filedescriptors are closed before initialized. An early
fdclose() call can cause fget_unlocked() to fail.

Found by: mjg @
MFC after: 1 week
Reviewed by: Mark Block <markb@mellanox.com>
Sponsored by: Mellanox Technologies
Differential Revision: https://reviews.freebsd.org/D4351

Add more functions and types to the LinuxKPI.

MFC after: 1 week
Sponsored by: Mellanox Technologies

Finish process of moving the LinuxKPI module into the default kernel build.

- Move all files related to the LinuxKPI into sys/compat/linuxkpi and
its subfolders.
- Update sys/conf/files and some Makefiles to use new file locations.
- Added description of COMPAT_LINUXKPI to sys/conf/NOTES which in turn
adds the LinuxKPI to all LINT builds.
- The LinuxKPI can be added to the kernel by setting the
COMPAT_LINUXKPI option. The OFED kernel option no longer builds the
LinuxKPI into the kernel. This was done to keep the build rules for
the LinuxKPI in sys/conf/files simple.
- Extend the LinuxKPI module to include support for USB by moving the
Linux USB compat from usb.ko to linuxkpi.ko.
- Bump the FreeBSD_version.
- A universe kernel build has been done.

Reviewed by: np @ (cxgb and cxgbe related changes only)
Sponsored by: Mellanox Technologies