MFH: 285685
Add support to the jail framework to be able to mount linsysfs(5) and linprocfs(5).

PR: 207179
Requested by: thomas@gibfest.dk
Reviewed by: jamie, bapt
Approved by: re (gjb)
Sponsored by: gandi.net
Differential Revision: https://reviews.freebsd.org/D5390

MFC r283421:

Introduce a new module linux_common.ko which is intended for the
following primary purposes:

1. Remove the dependency of linsysfs and linprocfs modules from linux.ko,
which will be architecture specific on amd64.

2. Incorporate into linux_common.ko general code for platforms on which
we'll support two Linuxulator modules (for both instruction set - 32 & 64 bit).

3. Move malloc(9) declaration to linux_common.ko, to enable getting memory
usage statistics properly.

Currently linux_common.ko incorporates a code from linux_mib.c and linux_util.c
and linprocfs, linsysfs and linux kernel modules depend on linux_common.ko.

Temporarily remove dtrace garbage from linux_mib.c and linux_util.c

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

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

Add procfs to jail-mountable filesystems.

Reviewed by: jamie
MFC after: 1 week

Remove no-op assignment.

Submitted by: clang via arundel@
MFC after: 2 weeks

Add a pn_destroy field to pfs_node. This field points to a destructor
function which is called from pfs_destroy() before the node is reclaimed.

Modify pfs_create_{dir,file,link}() to accept a pointer to a destructor
function in addition to the usual attr / fill / vis pointers.

This breaks both the programming and binary interfaces between pseudofs
and its consumers. It is believed that there are no pseudofs consumers
outside the source tree, so that the impact of this change is minimal.

Submitted by: Aniruddha Bohra <bohra@cs.rutgers.edu>

MFP4 (110957)

Use TAILQ_FOREACH_SAFE instead of the unsafe one where an item is removed
from the queue.

This prevents a panic on kldunload.

Submitted by: rdivacky
Tested by: bsam

Remove the dependency on procfs since it isn't used.

Noticed by: des

Add in linsysfs. A linux 2.6 like sys filesystem to pacify the Linux
LSI MegaRAID SAS utility.

Sponsored by: IronPort Systems
Man page help from: brueffer