TAKE - Small I/O path cleanups

[Steve Lord <lord@sgi.com>]

This is worth a few percent on write performance, and about 15% on
O_SYNC writes. Basically get more information about the type of I/O
we are doing down to the block layer code.

Date:  Fri May 17 10:20:52 PDT 2002
Workarea:  jen.americas.sgi.com:/src/lord/xfs-baseline

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


Modid:  2.4.x-xfs:slinx:119446a
linux/fs/xfs/linux/xfs_lrw.c - 1.136
	- Pass info on the expected new file size down to the allocator

linux/fs/xfs/linux/xfs_iops.c - 1.140
	- Add getblock case for passing O_SYNC information down to the allocator,
	  don't just use 64K as the default preallocation size.

linux/fs/xfs/pagebuf/page_buf_io.c - 1.35
	- pass file pointer into prepare and commit write so they can get
	  O_SYNC information.