/*
* linux/fs/nfs/write.c
*
* Writing file data over NFS.
*
* We do it like this: When a (user) process wishes to write data to an
* NFS file, a write request is allocated that contains the RPC task data
* plus some info on the page to be written, and added to the inode's
* write chain. If the process writes past the end of the page, an async
* RPC call to write the page is scheduled immediately; otherwise, the call
* is delayed for a few seconds.
*
* Just like readahead, no async I/O is performed if wsize < PAGE_SIZE.
*
* Write requests are kept on the inode's writeback list. Each entry in
* that list references the page (portion) to be written. When the
* cache timeout has expired, the RPC task is woken up, and tries to
* lock the page. As soon as it manages to do so, the request is moved
* from the writeback list to the writelock list.
*
* Note: we must make sure never to confuse the inode passed in the
* write_page request with the one in page->inode. As far as I understand
* it, these are different when doing a swap-out.
*
* To understand everything that goes on here and in the NFS read code,
* one should be aware that a page is locked in exactly one of the following
* cases:
*
* - A write request is in progress.
* - A user process is in generic_file_write/nfs_update_page
* - A user process is in generic_file_read
*
* Also note that because of the way pages are invalidated in
* nfs_revalidate_inode, the following assertions hold:
*
* - If a page is dirty, there will be no read requests (a page will
* not be re-read unless invalidated by nfs_revalidate_inode).
* - If the page is not uptodate, there will be no pending write
* requests, and no process will be in nfs_update_page.
*
* FIXME: Interaction with the vmscan routines is not optimal yet.
* Either vmscan must be made nfs-savvy, or we need a different page
* reclaim concept that supports something like FS-independent
* buffer_heads with a b_ops-> field.
*
* Copyright (C) 1996, 1997, Olaf Kirch <okir@monad.swb.de>
*/
#include <linux/config.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/file.h>
#include <linux/mpage.h>
#include <linux/writeback.h>
#include <linux/sunrpc/clnt.h>
#include <linux/nfs_fs.h>
#include <linux/nfs_mount.h>
#include <linux/nfs_page.h>
#include <asm/uaccess.h>
#include <linux/smp_lock.h>
#include "delegation.h"
#define NFSDBG_FACILITY NFSDBG_PAGECACHE
#define MIN_POOL_WRITE (32)
#define MIN_POOL_COMMIT (4)
/*
* Local function declarations
*/
static struct nfs_page * nfs_update_request(struct nfs_open_context*,
struct inode *,
struct page *,
unsigned int, unsigned int);
static void nfs_writeback_done_partial(struct nfs_write_data *, int);
static void nfs_writeback_done_full(struct nfs_write_data *, int);
static int nfs_wait_on_write_congestion(struct address_space *, int<
