TAKE - make XFS use the generic write code

[Steve Lord <lord@sgi.com>]

This removes the XFS specific write path by modifying the
generic path to be usable by XFS. Also a couple of O_DIRECT
related fixes, and a locking change in pagebuf which should
protect the cases where the block device and the filesystem
path are being accessed in parallel.

Date:  Mon Jul  8 19:59:39 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:122679a
linux/mm/filemap.c - 1.113
	- break generic_file_write apart for use by xfs. Fix direct read end of
	  file handling.

linux/include/linux/fs.h - 1.152
	- prototype for do_generic_file_write

linux/fs/xfs/xfs_dmapi.c - 1.64
	- Get max direct I/O size from a different place

linux/fs/xfs/linux/xfs_lrw.c - 1.152
	- replace call to pagebuf_generic_file_write with do_generic_file_write.

linux/fs/xfs/linux/xfs_file.c - 1.69
	- since we now call the generic write path in xfs remove the checks
	  here which duplicate its functionality. Grab the i_sem lock in the
	  non O_DIRECT case, we need it in the vmtruncate call out of
	  do_generic_file_write.

linux/fs/xfs/linux/xfs_iops.c - 1.157
	- Add a truncate operation, change setattr to use vmtruncate and
	  not call inode_setattr

linux/fs/xfs/linux/xfs_ioctl.c - 1.65
	- Get max direct I/O size from a different place

linux/fs/xfs/pagebuf/page_buf_io.c - 1.48
	- remove write path

linux/fs/xfs/pagebuf/page_buf.c - 1.35
	- leave pages locked when reading it in.

linux/fs/xfs/pagebuf/page_buf.h - 1.23
	- remove prototypes

linux/fs/xfs/pagebuf/page_buf_internal.h - 1.10
	- remove direct I/O config option