Linux emulation enhancement to emulate device nodes and some SCSI stuff

[Doug Ambrisko]

To get the LSI RAID SAS to work under Linux emulation we need to emulate
more of Linux type stuff.  I've put patches up at:
	http://www.ambrisko.com/doug/linux.patches

I've added back the proc/devices to the emulator although really emulated
since with devfs are majors are not as Linux app's expect.  So I've used a
"linux_ioctl_handle" type paradigm to add a new "linux_device_handle" thing.
Each entry is of type:
  struct linux_device_handler {
	char	*bsd_driver_name;
	char	*linux_driver_name;
	char	*bsd_device_name;
	char	*linux_device_name;
	int	linux_major;
	int	linux_minor;
	int	linux_char_device;
  };

An example of usage is:
  static struct linux_device_handler mfi_device_handler =
	{ "mfi", "megaraid_sas", "mfi0", "megaraid_sas_ioctl_node", -1, 0, 1};

  SYSINIT  (mfi_register2,   SI_SUB_KLD, SI_ORDER_MIDDLE,
	  linux_device_register_handler, &mfi_device_handler);
  SYSUNINIT(mfi_unregister2, SI_SUB_KLD, SI_ORDER_MIDDLE,
	  linux_device_unregister_handler, &mfi_device_handler);

The -1 major means allocate dynamically.  This then shows up in proc/devices
as:

  Character devices:
    1 null
  200 megaraid_sas_ioctl_node

  Block devices:

I needed a entry to /dev/null so I created a static entry for that.

In the new proc/sys there is a class & devices tree.  The devices tree
runs the PCI space sort-of like Linux and builds a tree.  The class/scsi_host
links into that tree.  It only fills in things for PCI storage classes
and fills in the "proc_name" for the driver if known like:
  %cat class/scsi_host/host0/proc_name
  megaraid_sas
  %ls -l class/scsi_host/host0
  total 0
  lr--r--r--  1 root  wheel  0 Apr 27 15:07 device -> ../../../devices/pci0000:03/0001:00.0/0002:0e.0/host0
  -r--r--r--  1 root  wheel  0 Apr 27 15:07 proc_name
  %ls -l devices/pci0000:03/0001:00.0/0002:0e.0
  total 0
  dr-xr-xr-x  1 root  wheel  0 Apr 27 15:07 host0
  %

I had to add code to linux_stat stuff to intercept and return the expected
major/minor number if a device_handler was defined.

With this and some changes to mfi(4) driver I can run the Linux MegaCli
binary from LSI on FreeBSD.

Please let me know how this patch looks.

Note this is following the Linux 2.6 style.

Doug A.