TAKE - pagebuf_iozero

[Eric Sandeen <sandeen@sgi.com>]

pagebuf_iozero handles zeroing for xfs_zero_eof and xfs_zero_last_block
(both deal with zeroing unwritten portions when a write extends filesize).

But pagebuf_iozero wasn't setting up pages correctly, it was calling
pagebuf_commit_write_core w/o first setting up buffers on pages with
__pb_block_prepare_write_async.  

xfs_zero_eof and xfs_zero_last_block were also forcing writes on these
pagebufs, which was probably causing double i/o...

Date:  Wed Feb 20 13:27:57 PST 2002
Workarea:  stout.americas.sgi.com:/localhome/eric/2.4.x-xfs/workarea-reallyclean

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


Modid:  2.4.x-xfs:slinx:112227a
linux/fs/xfs/linux/xfs_lrw.c - 1.123
	- Prepare pagebuf bmap to pass to pagebuf_iozero
	  Don't force writing the pagebuf

linux/fs/xfs/pagebuf/page_buf_io.c - 1.13
	- do a __pb_block_prepare_write_async before pagebuf_commit_write_core

linux/fs/xfs/pagebuf/page_buf.h - 1.4
	- Add pb_bmap_t to pagebuf_iozero arguments