TAKE - start of support for drive cache control

[Steve Lord <lord@sgi.com>]

This is a basic implementation of something to flush drive write
caches when writing the log. It is dependent on other code which
is not in the mainline kernel right now. So basically just storing the
code in the tree for now.

This comes from Andi Kleen.

Steve

Date:  Fri May 24 07:30:21 PDT 2002
Workarea:  jen.americas.sgi.com:/src/lord/xfs-linux.2.4

The following file(s) were checked into:
  bonnie.engr.sgi.com:/isms/slinx/2.4.x-xfs


Modid:  2.4.x-xfs:slinx:120152a
linux/fs/xfs/xfs_log.c - 1.247
	- On log writes specify cache flushing

linux/fs/xfs/xfs_buf.h - 1.86
	- Wrappers for PBF_FLUSH

linux/fs/xfs/xfs_vfsops.c - 1.345
	- NOLOGFLUSH option processing

linux/fs/xfs/xfs_clnt.h - 1.28
	- NOLOGFLUSH  defines

linux/fs/xfs/xfs_mount.h - 1.140
	- defines for new mount option

linux/fs/xfs/linux/xfs_super.c - 1.170
	- Add nologflush mount option - noflush meaning the drive write cache

linux/fs/xfs/pagebuf/page_buf_io.c - 1.38
	- Use PBF_FLUSH

linux/fs/xfs/pagebuf/page_buf.c - 1.26
	- Add support for drive write cache flushing - should the kernel         
	  have the infrastructure

linux/fs/xfs/pagebuf/page_buf.h - 1.14
	- New PBF_FLUSH define