xref: /linux-2.4.37.9/fs/nfs/write.c

/*
 * 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/swap.h>
#include <linux/pagemap.h>
#include <linux/file.h>

#include <linux/sunrpc/clnt.h>
#include <linux/nfs_fs.h>
#include <linux/nfs_mount.h>
#include <linux/nfs_flushd.h>
#include <linux/nfs_page.h>
#include <asm/uaccess.h>
#include <linux/smp_lock.h>

#define NFSDBG_FACILITY		NFSDBG_PAGECACHE

/*
 * Local structures
 *
 * This is the struct where the WRITE/COMMIT arguments go.
 */
struct nfs_write_data {
	struct rpc_task		task;
	struct inode		*inode;
	struct rpc_cred		*cred;
	struct nfs_writeargs	args;		/* argument struct */
	struct nfs_writeres	res;		/* result struct */
	struct nfs_fattr	fattr;
	struct nfs_writeverf	verf;
	struct list_head	pages;		/* Coalesced requests we wish to flush */
	struct page		*pagevec[NFS_WRITE_MAXIOV];
};

/*
 * Local function declarations
 */
static struct nfs_page * nfs_update_request(struct file*, struct inode *,
					    struct page *,
					    unsigned int, unsigned int);
static void	nfs_strategy(struct inode *inode);
static void	nfs_writeback_done(struct rpc_task *);
#ifdef CONFIG_NFS_V3
static void	nfs_commit_done(struct rpc_task *);
#endif

/* Hack for future NFS swap support */
#ifndef IS_SWAPFILE
# define IS_SWAPFILE(inode)	(0)
#endif

static kmem_cache_t *nfs_wdata_cachep;

static __inline__ struct nfs_write_data *nfs_writedata_alloc(void)
{
	struct nfs_write_data	*p;
	p = kmem_cache_alloc(nfs_wdata_cachep, SLAB_NOFS);
	if (p) {
		memset(p, 0, sizeof(*p));
		INIT_LIST_HEAD(&p->pages);
		p->args.pages = p->pagevec;
	}
	return p;
}

static __inline__ void nfs_writedata_free(struct nfs_write_data *p)
{
	kmem_cache_free(nfs_wdata_cachep, p);
}

static void nfs_writedata_release(struct rpc_task *task)
{
	struct nfs_write_data	*wdata = (struct nfs_write_data *)task->tk_calldata;
	nfs_writedata_free(wdata);
}

/*
 * Write a page synchronously.
 * Offset is the data offset within the page.
 */
static int
nfs_writepage_sync(struct file *file, struct inode *inode, struct page *page,
		   unsigned int offset, unsigned int count)
{
	struct rpc_cred	*cred = NULL;
	loff_t		base;
	unsigned int	wsize = NFS_SERVER(inode)->wsize;
	int		result, refresh = 0, written = 0, flags;
	u8		*buffer;
	struct nfs_fattr fattr;
	struct nfs_writeverf verf;


	if (file)
		cred = get_rpccred(nfs_file_cred(file));
	if (!cred)
		cred = get_rpccred(NFS_I(inode)->mm_cred);

	dprintk("NFS:      nfs_writepage_sync(%x/%Ld %d@%Ld)\n",
		inode->i_dev, (long long)NFS_FILEID(inode),
		count, (long long)(page_offset(page) + offset));

	base = page_offset(page) + offset;

	flags = ((IS_SWAPFILE(inode)) ? NFS_RW_SWAP : 0) | NFS_RW_SYNC;

	do {
		if (count < wsize && !IS_SWAPFILE(inode))
			wsize = count;

		result = NFS_PROTO(inode)->write(inode, cred, &fattr, flags,
						 offset, wsize, page, &verf);
		nfs_write_attributes(inode, &fattr);

		if (result < 0) {
			/* Must mark the page invalid after I/O error */
			ClearPageUptodate(page);
			goto io_error;
		}
		if (result != wsize)
			printk("NFS: short write, wsize=%u, result=%d\n",
			wsize, result);
		refresh = 1;
		buffer  += wsize;
		base    += wsize;
	        offset  += wsize;
		written += wsize;
		count   -= wsize;
		/*
		 * If we've extended the file, update the inode
		 * now so we don't invalidate the cache.
		 */
		if (base > inode->i_size)
			inode->i_size = base;
	} while (count);

	if (PageError(page))
		ClearPageError(page);

io_error:
	if (cred)
		put_rpccred(cred);

	return written? written : result;
}

static int
nfs_writepage_async(struct file *file, struct inode *inode, struct page *page,
		    unsigned int offset, unsigned int count)
{
	struct nfs_page	*req;
	loff_t		end;
	int		status;

	req = nfs_update_request(file, inode, page, offset, count);
	status = (IS_ERR(req)) ? PTR_ERR(req) : 0;
	if (status < 0)
		goto out;
	if (!req->wb_cred)
		req->wb_cred = get_rpccred(NFS_I(inode)->mm_cred);
	nfs_unlock_request(req);
	nfs_strategy(inode);
	end = ((loff_t)page->index<<PAGE_CACHE_SHIFT) + (loff_t)(offset + count);
	if (inode->i_size < end)
		inode->i_size = end;

 out:
	return status;
}

/*
 * Write an mmapped page to the server.
 */
int
nfs_writepage(struct page *page)
{
	struct inode *inode = page->mapping->host;
	unsigned long end_index;
	unsigned offset = PAGE_CACHE_SIZE;
	int inode_referenced = 0;
	int err;

	/*
	 * Note: We need to ensure that we have a reference to the inode
	 *       if we are to do asynchronous writes. If not, waiting
	 *       in nfs_wait_on_request() may deadlock with clear_inode().
	 *
	 *       If igrab() fails here, then it is in any case safe to
	 *       call nfs_wb_page(), since there will be no pending writes.
	 */
	if (igrab(inode) != 0)
		inode_referenced = 1;
	end_index = inode->i_size >> PAGE_CACHE_SHIFT;

	/* Ensure we've flushed out any previous writes */
	nfs_wb_page(inode,page);

	/* easy case */
	if (page->index < end_index)
		goto do_it;
	/* things got complicated... */
	offset = inode->i_size & (PAGE_CACHE_SIZE-1);

	/* OK, are we completely out? */
	err = -EIO;
	if (page->index >= end_index+1 || !offset)
		goto out;
do_it:
	lock_kernel();
	if (NFS_SERVER(inode)->wsize >= PAGE_CACHE_SIZE && !IS_SYNC(inode) &&
			inode_referenced) {
		err = nfs_writepage_async(NULL, inode, page, 0, offset);
		if (err >= 0)
			err = 0;
	} else {
		err = nfs_writepage_sync(NULL, inode, page, 0, offset);
		if (err == offset)
			err = 0;
	}
	unlock_kernel();
out:
	UnlockPage(page);
	if (inode_referenced)
		iput(inode);
	return err;
}

/*
 * Check whether the file range we want to write to is locked by
 * us.
 */
static int
region_locked(struct inode *inode, struct nfs_page *req)
{
	struct file_lock	*fl;
	loff_t			rqstart, rqend;

	/* Don't optimize writes if we don't use NLM */
	if (NFS_SERVER(inode)->flags & NFS_MOUNT_NONLM)
		return 0;

	rqstart = page_offset(req->wb_page) + req->wb_offset;
	rqend = rqstart + req->wb_bytes;
	for (fl = inode->i_flock; fl; fl = fl->fl_next) {
		if (fl->fl_owner == current->files && (fl->fl_flags & FL_POSIX)
		    && fl->fl_type == F_WRLCK
		    && fl->fl_start <= rqstart && rqend <= fl->fl_end) {
			return 1;
		}
	}

	return 0;
}

/*
 * Insert a write request into an inode
 * Note: we sort the list in order to be able to optimize nfs_find_request()
 *	 & co. for the 'write append' case. For 2.5 we may want to consider
 *	 some form of hashing so as to perform well on random writes.
 */
static inline void
nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
{
	struct list_head *pos, *head;
	unsigned long pg_idx = page_index(req->wb_page);

	if (!list_empty(&req->wb_hash))
		return;
	if (!NFS_WBACK_BUSY(req))
		printk(KERN_ERR "NFS: unlocked request attempted hashed!\n");
	head = &inode->u.nfs_i.writeback;
	if (list_empty(head))
		igrab(inode);
	list_for_each_prev(pos, head) {
		struct nfs_page *entry = nfs_inode_wb_entry(pos);
		if (page_index(entry->wb_page) < pg_idx)
			break;
	}
	inode->u.nfs_i.npages++;
	list_add(&req->wb_hash, pos);
	req->wb_count++;
}

/*
 * Insert a write request into an inode
 */
static inline void
nfs_inode_remove_request(struct nfs_page *req)
{
	struct inode *inode;
	spin_lock(&nfs_wreq_lock);
	if (list_empty(&req->wb_hash)) {
		spin_unlock(&nfs_wreq_lock);
		return;
	}
	if (!NFS_WBACK_BUSY(req))
		printk(KERN_ERR "NFS: unlocked request attempted unhashed!\n");
	inode = req->wb_inode;
	list_del(&req->wb_hash);
	INIT_LIST_HEAD(&req->wb_hash);
	inode->u.nfs_i.npages--;
	if ((inode->u.nfs_i.npages == 0) != list_empty(&inode->u.nfs_i.writeback))
		printk(KERN_ERR "NFS: desynchronized value of nfs_i.npages.\n");
	if (list_empty(&inode->u.nfs_i.writeback)) {
		spin_unlock(&nfs_wreq_lock);
		iput(inode);
	} else
		spin_unlock(&nfs_wreq_lock);
	nfs_clear_request(req);
	nfs_release_request(req);
}

/*
 * Find a request
 */
static inline struct nfs_page *
_nfs_find_request(struct inode *inode, struct page *page)
{
	struct list_head	*head, *pos;
	unsigned long pg_idx = page_index(page);

	head = &inode->u.nfs_i.writeback;
	list_for_each_prev(pos, head) {
		struct nfs_page *req = nfs_inode_wb_entry(pos);
		unsigned long found_idx = page_index(req->wb_page);

		if (pg_idx < found_idx)
			continue;
		if (pg_idx != found_idx)
			break;
		req->wb_count++;
		return req;
	}
	return NULL;
}

static struct nfs_page *
nfs_find_request(struct inode *inode, struct page *page)
{
	struct nfs_page		*req;

	spin_lock(&nfs_wreq_lock);
	req = _nfs_find_request(inode, page);
	spin_unlock(&nfs_wreq_lock);
	return req;
}

/*
 * Add a request to the inode's dirty list.
 */
static inline void
nfs_mark_request_dirty(struct nfs_page *req)
{
	struct inode *inode = req->wb_inode;

	spin_lock(&nfs_wreq_lock);
	nfs_list_add_request(req, &inode->u.nfs_i.dirty);
	inode->u.nfs_i.ndirty++;
	__nfs_del_lru(req);
	__nfs_add_lru(&NFS_SERVER(inode)->lru_dirty, req);
	spin_unlock(&nfs_wreq_lock);
	mark_inode_dirty(inode);
}

/*
 * Check if a request is dirty
 */
static inline int
nfs_dirty_request(struct nfs_page *req)
{
	struct inode *inode = req->wb_inode;
	return !list_empty(&req->wb_list) && req->wb_list_head == &inode->u.nfs_i.dirty;
}

#ifdef CONFIG_NFS_V3
/*
 * Add a request to the inode's commit list.
 */
static inline void
nfs_mark_request_commit(struct nfs_page *req)
{
	struct inode *inode = req->wb_inode;

	spin_lock(&nfs_wreq_lock);
	nfs_list_add_request(req, &inode->u.nfs_i.commit);
	inode->u.nfs_i.ncommit++;
	__nfs_del_lru(req);
	__nfs_add_lru(&NFS_SERVER(inode)->lru_commit, req);
	spin_unlock(&nfs_wreq_lock);
	mark_inode_dirty(inode);
}
#endif

/*
 * Wait for a request to complete.
 *
 * Interruptible by signals only if mounted with intr flag.
 */
static int
nfs_wait_on_requests(struct inode *inode, unsigned long idx_start, unsigned int npages)
{
	struct list_head	*p, *head;
	unsigned long		idx_end;
	unsigned int		res = 0;
	int			error;

	if (npages == 0)
		idx_end = ~0;
	else
		idx_end = idx_start + npages - 1;

	head = &inode->u.nfs_i.writeback;
 restart:
	spin_lock(&nfs_wreq_lock);
	list_for_each_prev(p, head) {
		unsigned long pg_idx;
		struct nfs_page *req = nfs_inode_wb_entry(p);

		pg_idx = page_index(req->wb_page);
		if (pg_idx < idx_start)
			break;
		if (pg_idx > idx_end)
			continue;

		if (!NFS_WBACK_BUSY(req))
			continue;
		req->wb_count++;
		spin_unlock(&nfs_wreq_lock);
		error = nfs_wait_on_request(req);
		nfs_release_request(req);
		if (error < 0)
			return error;
		res++;
		goto restart;
	}
	spin_unlock(&nfs_wreq_lock);
	return res;
}

/**
 * nfs_scan_lru_dirty_timeout - Scan LRU list for timed out dirty requests
 * @server: NFS superblock data
 * @dst: destination list
 *
 * Moves a maximum of 'wpages' requests from the NFS dirty page LRU list.
 * The elements are checked to ensure that they form a contiguous set
 * of pages, and that they originated from the same file.
 */
int
nfs_scan_lru_dirty_timeout(struct nfs_server *server, struct list_head *dst)
{
	struct inode *inode;
	int npages;

	npages = nfs_scan_lru_timeout(&server->lru_dirty, dst, server->wpages);
	if (npages) {
		inode = nfs_list_entry(dst->next)->wb_inode;
		inode->u.nfs_i.ndirty -= npages;
	}
	return npages;
}

/**
 * nfs_scan_lru_dirty - Scan LRU list for dirty requests
 * @server: NFS superblock data
 * @dst: destination list
 *
 * Moves a maximum of 'wpages' requests from the NFS dirty page LRU list.
 * The elements are checked to ensure that they form a contiguous set
 * of pages, and that they originated from the same file.
 */
int
nfs_scan_lru_dirty(struct nfs_server *server, struct list_head *dst)
{
	struct inode *inode;
	int npages;

	npages = nfs_scan_lru(&server->lru_dirty, dst, server->wpages);
	if (npages) {
		inode = nfs_list_entry(dst->next)->wb_inode;
		inode->u.nfs_i.ndirty -= npages;
	}
	return npages;
}

/*
 * nfs_scan_dirty - Scan an inode for dirty requests
 * @inode: NFS inode to scan
 * @dst: destination list
 * @idx_start: lower bound of page->index to scan.
 * @npages: idx_start + npages sets the upper bound to scan.
 *
 * Moves requests from the inode's dirty page list.
 * The requests are *not* checked to ensure that they form a contiguous set.
 */
static int
nfs_scan_dirty(struct inode *inode, struct list_head *dst, unsigned long idx_start, unsigned int npages)
{
	int	res;
	res = nfs_scan_list(&inode->u.nfs_i.dirty, dst, idx_start, npages);
	inode->u.nfs_i.ndirty -= res;
	if ((inode->u.nfs_i.ndirty == 0) != list_empty(&inode->u.nfs_i.dirty))
		printk(KERN_ERR "NFS: desynchronized value of nfs_i.ndirty.\n");
	return res;
}

#ifdef CONFIG_NFS_V3
/**
 * nfs_scan_lru_commit_timeout - Scan LRU list for timed out commit requests
 * @server: NFS superblock data
 * @dst: destination list
 *
 * Finds the first a timed out request in the NFS commit LRU list and moves it
 * to the list dst. If such an element is found, we move all other commit
 * requests that apply to the same inode.
 * The assumption is that doing everything in a single commit-to-disk is
 * the cheaper alternative.
 */
int
nfs_scan_lru_commit_timeout(struct nfs_server *server, struct list_head *dst)
{
	struct inode *inode;
	int npages;

	npages = nfs_scan_lru_timeout(&server->lru_commit, dst, 1);
	if (npages) {
		inode = nfs_list_entry(dst->next)->wb_inode;
		npages += nfs_scan_list(&inode->u.nfs_i.commit, dst, 0, 0);
		inode->u.nfs_i.ncommit -= npages;
	}
	return npages;
}


/**
 * nfs_scan_lru_commit_timeout - Scan LRU list for timed out commit requests
 * @server: NFS superblock data
 * @dst: destination list
 *
 * Finds the first request in the NFS commit LRU list and moves it
 * to the list dst. If such an element is found, we move all other commit
 * requests that apply to the same inode.
 * The assumption is that doing everything in a single commit-to-disk is
 * the cheaper alternative.
 */
int
nfs_scan_lru_commit(struct nfs_server *server, struct list_head *dst)
{
	struct inode *inode;
	int npages;

	npages = nfs_scan_lru(&server->lru_commit, dst, 1);
	if (npages) {
		inode = nfs_list_entry(dst->next)->wb_inode;
		npages += nfs_scan_list(&inode->u.nfs_i.commit, dst, 0, 0);
		inode->u.nfs_i.ncommit -= npages;
	}
	return npages;
}

/*
 * nfs_scan_commit - Scan an inode for commit requests
 * @inode: NFS inode to scan
 * @dst: destination list
 * @idx_start: lower bound of page->index to scan.
 * @npages: idx_start + npages sets the upper bound to scan.
 *
 * Moves requests from the inode's 'commit' request list.
 * The requests are *not* checked to ensure that they form a contiguous set.
 */
static int
nfs_scan_commit(struct inode *inode, struct list_head *dst, unsigned long idx_start, unsigned int npages)
{
	int	res;
	res = nfs_scan_list(&inode->u.nfs_i.commit, dst, idx_start, npages);
	inode->u.nfs_i.ncommit -= res;
	if ((inode->u.nfs_i.ncommit == 0) != list_empty(&inode->u.nfs_i.commit))
		printk(KERN_ERR "NFS: desynchronized value of nfs_i.ncommit.\n");
	return res;
}
#endif


/*
 * Try to update any existing write request, or create one if there is none.
 * In order to match, the request's credentials must match those of
 * the calling process.
 *
 * Note: Should always be called with the Page Lock held!
 */
static struct nfs_page *
nfs_update_request(struct file* file, struct inode *inode, struct page *page,
		   unsigned int offset, unsigned int bytes)
{
	struct nfs_page		*req, *new = NULL;
	unsigned long		rqend, end;

	end = offset + bytes;

	for (;;) {
		/* Loop over all inode entries and see if we find
		 * A request for the page we wish to update
		 */
		spin_lock(&nfs_wreq_lock);
		req = _nfs_find_request(inode, page);
		if (req) {
			if (!nfs_lock_request_dontget(req)) {
				int error;
				spin_unlock(&nfs_wreq_lock);
				error = nfs_wait_on_request(req);
				nfs_release_request(req);
				if (error < 0)
					return ERR_PTR(error);
				continue;
			}
			spin_unlock(&nfs_wreq_lock);
			if (new)
				nfs_release_request(new);
			break;
		}

		if (new) {
			nfs_lock_request_dontget(new);
			nfs_inode_add_request(inode, new);
			spin_unlock(&nfs_wreq_lock);
			nfs_mark_request_dirty(new);
			return new;
		}
		spin_unlock(&nfs_wreq_lock);

		new = nfs_create_request(nfs_file_cred(file), inode, page, offset, bytes);
		if (IS_ERR(new))
			return new;
		if (file) {
			new->wb_file = file;
			get_file(file);
		}
		/* If the region is locked, adjust the timeout */
		if (region_locked(inode, new))
			new->wb_timeout = jiffies + NFS_WRITEBACK_LOCKDELAY;
		else
			new->wb_timeout = jiffies + NFS_WRITEBACK_DELAY;
	}

	/* We have a request for our page.
	 * If the creds don't match, or the
	 * page addresses don't match,
	 * tell the caller to wait on the conflicting
	 * request.
	 */
	rqend = req->wb_offset + req->wb_bytes;
	if (req->wb_file != file
	    || req->wb_page != page
	    || !nfs_dirty_request(req)
	    || offset > rqend || end < req->wb_offset) {
		nfs_unlock_request(req);
		return ERR_PTR(-EBUSY);
	}

	/* Okay, the request matches. Update the region */
	if (offset < req->wb_offset) {
		req->wb_offset = offset;
		req->wb_bytes = rqend - req->wb_offset;
	}

	if (end > rqend)
		req->wb_bytes = end - req->wb_offset;

	return req;
}

/*
 * This is the strategy routine for NFS.
 * It is called by nfs_updatepage whenever the user wrote up to the end
 * of a page.
 *
 * We always try to submit a set of requests in parallel so that the
 * server's write code can gather writes. This is mainly for the benefit
 * of NFSv2.
 *
 * We never submit more requests than we think the remote can handle.
 * For UDP sockets, we make sure we don't exceed the congestion window;
 * for TCP, we limit the number of requests to 8.
 *
 * NFS_STRATEGY_PAGES gives the minimum number of requests for NFSv2 that
 * should be sent out in one go. This is for the benefit of NFSv2 servers
 * that perform write gathering.
 *
 * FIXME: Different servers may have different sweet spots.
 * Record the average congestion window in server struct?
 */
#define NFS_STRATEGY_PAGES      8
static void
nfs_strategy(struct inode *inode)
{
	unsigned int	dirty, wpages;

	dirty  = inode->u.nfs_i.ndirty;
	wpages = NFS_SERVER(inode)->wpages;
#ifdef CONFIG_NFS_V3
	if (NFS_PROTO(inode)->version == 2) {
		if (dirty >= NFS_STRATEGY_PAGES * wpages)
			nfs_flush_file(inode, 0, 0, 0);
	} else if (dirty >= wpages)
		nfs_flush_file(inode, 0, 0, 0);
#else
	if (dirty >= NFS_STRATEGY_PAGES * wpages)
		nfs_flush_file(inode, 0, 0, 0);
#endif
}

int
nfs_flush_incompatible(struct file *file, struct page *page)
{
	struct rpc_cred	*cred = nfs_file_cred(file);
	struct inode	*inode = page->mapping->host;
	struct nfs_page	*req;
	int		status = 0;
	/*
	 * Look for a request corresponding to this page. If there
	 * is one, and it belongs to another file, we flush it out
	 * before we try to copy anything into the page. Do this
	 * due to the lack of an ACCESS-type call in NFSv2.
	 * Also do the same if we find a request from an existing
	 * dropped page.
	 */
	req = nfs_find_request(inode,page);
	if (req) {
		if (req->wb_file != file || req->wb_cred != cred || req->wb_page != page)
			status = nfs_wb_page(inode, page);
		nfs_release_request(req);
	}
	return (status < 0) ? status : 0;
}

/*
 * Update and possibly write a cached page of an NFS file.
 *
 * XXX: Keep an eye on generic_file_read to make sure it doesn't do bad
 * things with a page scheduled for an RPC call (e.g. invalidate it).
 */
int
nfs_updatepage(struct file *file, struct page *page, unsigned int offset, unsigned int count)
{
	struct dentry	*dentry = file->f_dentry;
	struct inode	*inode = page->mapping->host;
	struct nfs_page	*req;
	loff_t		end;
	int		status = 0;

	dprintk("NFS:      nfs_updatepage(%s/%s %d@%Ld)\n",
		dentry->d_parent->d_name.name, dentry->d_name.name,
		count, (long long)(page_offset(page) +offset));

	/*
	 * If wsize is smaller than page size, update and write
	 * page synchronously.
	 */
	if (NFS_SERVER(inode)->wsize < PAGE_CACHE_SIZE || IS_SYNC(inode)) {
		status = nfs_writepage_sync(file, inode, page, offset, count);
		if (status > 0) {
			if (offset == 0 && status == PAGE_CACHE_SIZE)
				SetPageUptodate(page);
			return 0;
		}
		return status;
	}

	/*
	 * Try to find an NFS request corresponding to this page
	 * and update it.
	 * If the existing request cannot be updated, we must flush
	 * it out now.
	 */
	do {
		req = nfs_update_request(file, inode, page, offset, count);
		status = (IS_ERR(req)) ? PTR_ERR(req) : 0;
		if (status != -EBUSY)
			break;
		/* Request could not be updated. Flush it out and try again */
		status = nfs_wb_page(inode, page);
	} while (status >= 0);
	if (status < 0)
		goto done;

	status = 0;
	end = ((loff_t)page->index<<PAGE_CACHE_SHIFT) + (loff_t)(offset + count);
	if (inode->i_size < end)
		inode->i_size = end;

	/* If we wrote past the end of the page.
	 * Call the strategy routine so it can send out a bunch
	 * of requests.
	 */
	if (req->wb_offset == 0 && req->wb_bytes == PAGE_CACHE_SIZE) {
		SetPageUptodate(page);
		nfs_unlock_request(req);
		nfs_strategy(inode);
	} else
		nfs_unlock_request(req);
done:
        dprintk("NFS:      nfs_updatepage returns %d (isize %Ld)\n",
                                                status, (long long)inode->i_size);
	if (status < 0)
		ClearPageUptodate(page);
	return status;
}

/*
 * Set up the argument/result storage required for the RPC call.
 */
static void
nfs_write_rpcsetup(struct list_head *head, struct nfs_write_data *data)
{
	struct nfs_page		*req;
	struct page		**pages;
	unsigned int		count;

	/* Set up the RPC argument and reply structs
	 * NB: take care not to mess about with data->commit et al. */

	pages = data->args.pages;
	count = 0;
	while (!list_empty(head)) {
		struct nfs_page *req = nfs_list_entry(head->next);
		nfs_list_remove_request(req);
		nfs_list_add_request(req, &data->pages);
		*pages++ = req->wb_page;
		count += req->wb_bytes;
	}
	req = nfs_list_entry(data->pages.next);
	data->inode = req->wb_inode;
	data->cred = req->wb_cred;
	data->args.fh     = NFS_FH(req->wb_inode);
	data->args.offset = page_offset(req->wb_page) + req->wb_offset;
	data->args.pgbase = req->wb_offset;
	data->args.count  = count;
	data->res.fattr   = &data->fattr;
	data->res.count   = count;
	data->res.verf    = &data->verf;
}


/*
 * Create an RPC task for the given write request and kick it.
 * The page must have been locked by the caller.
 *
 * It may happen that the page we're passed is not marked dirty.
 * This is the case if nfs_updatepage detects a conflicting request
 * that has been written but not committed.
 */
static int
nfs_flush_one(struct list_head *head, struct inode *inode, int how)
{
	struct rpc_clnt 	*clnt = NFS_CLIENT(inode);
	struct nfs_write_data	*data;
	struct rpc_task		*task;
	struct rpc_message	msg;
	int                     flags,
				nfsvers = NFS_PROTO(inode)->version,
				async = !(how & FLUSH_SYNC),
				stable = (how & FLUSH_STABLE);
	sigset_t		oldset;


	data = nfs_writedata_alloc();
	if (!data)
		goto out_bad;
	task = &data->task;

	/* Set the initial flags for the task.  */
	flags = (async) ? RPC_TASK_ASYNC : 0;

	/* Set up the argument struct */
	nfs_write_rpcsetup(head, data);
	if (nfsvers < 3)
		data->args.stable = NFS_FILE_SYNC;
	else if (stable) {
		if (!inode->u.nfs_i.ncommit)
			data->args.stable = NFS_FILE_SYNC;
		else
			data->args.stable = NFS_DATA_SYNC;
	} else
		data->args.stable = NFS_UNSTABLE;

	/* Finalize the task. */
	rpc_init_task(task, clnt, nfs_writeback_done, flags);
	task->tk_calldata = data;
	/* Release requests */
	task->tk_release = nfs_writedata_release;

#ifdef CONFIG_NFS_V3
	msg.rpc_proc = (nfsvers == 3) ? NFS3PROC_WRITE : NFSPROC_WRITE;
#else
	msg.rpc_proc = NFSPROC_WRITE;
#endif
	msg.rpc_argp = &data->args;
	msg.rpc_resp = &data->res;
	msg.rpc_cred = data->cred;

	dprintk("NFS: %4d initiated write call (req %x/%Ld count %u)\n",
		task->tk_pid,
		inode->i_dev,
		(long long)NFS_FILEID(inode),
		data->args.count);

	rpc_clnt_sigmask(clnt, &oldset);
	rpc_call_setup(task, &msg, 0);
	lock_kernel();
	rpc_execute(task);
	unlock_kernel();
	rpc_clnt_sigunmask(clnt, &oldset);
	return 0;
 out_bad:
	while (!list_empty(head)) {
		struct nfs_page *req = nfs_list_entry(head->next);
		nfs_list_remove_request(req);
		nfs_mark_request_dirty(req);
		nfs_unlock_request(req);
	}
	return -ENOMEM;
}

int
nfs_flush_list(struct list_head *head, int wpages, int how)
{
	LIST_HEAD(one_request);
	struct nfs_page		*req;
	int			error = 0;
	unsigned int		pages = 0;

	while (!list_empty(head)) {
		pages += nfs_coalesce_requests(head, &one_request, wpages);
		req = nfs_list_entry(one_request.next);
		error = nfs_flush_one(&one_request, req->wb_inode, how);
		if (error < 0)
			break;
	}
	if (error >= 0)
		return pages;

	while (!list_empty(head)) {
		req = nfs_list_entry(head->next);
		nfs_list_remove_request(req);
		nfs_mark_request_dirty(req);
		nfs_unlock_request(req);
	}
	return error;
}


/*
 * This function is called when the WRITE call is complete.
 */
static void
nfs_writeback_done(struct rpc_task *task)
{
	struct nfs_write_data	*data = (struct nfs_write_data *) task->tk_calldata;
	struct nfs_writeargs	*argp = &data->args;
	struct nfs_writeres	*resp = &data->res;
	struct inode		*inode = data->inode;
	struct nfs_page		*req;
	struct page		*page;

	dprintk("NFS: %4d nfs_writeback_done (status %d)\n",
		task->tk_pid, task->tk_status);

	if (nfs_async_handle_jukebox(task))
		return;

	/* We can't handle that yet but we check for it nevertheless */
	if (resp->count < argp->count && task->tk_status >= 0) {
		static unsigned long    complain;
		if (time_before(complain, jiffies)) {
			printk(KERN_WARNING
			       "NFS: Server wrote less than requested.\n");
			complain = jiffies + 300 * HZ;
		}
		/* Can't do anything about it right now except throw
		 * an error. */
		task->tk_status = -EIO;
	}
#ifdef CONFIG_NFS_V3
	if (resp->verf->committed < argp->stable && task->tk_status >= 0) {
		/* We tried a write call, but the server did not
		 * commit data to stable storage even though we
		 * requested it.
		 * Note: There is a known bug in Tru64 < 5.0 in which
		 *	 the server reports NFS_DATA_SYNC, but performs
		 *	 NFS_FILE_SYNC. We therefore implement this checking
		 *	 as a dprintk() in order to avoid filling syslog.
		 */
		static unsigned long    complain;

		if (time_before(complain, jiffies)) {
			dprintk("NFS: faulty NFSv3 server %s:"
				" (committed = %d) != (stable = %d)\n",
				NFS_SERVER(inode)->hostname,
				resp->verf->committed, argp->stable);
			complain = jiffies + 300 * HZ;
		}
	}
#endif

	/*
	 * Update attributes as result of writeback.
	 * FIXME: There is an inherent race with invalidate_inode_pages and
	 *	  writebacks since the page->count is kept > 1 for as long
	 *	  as the page has a write request pending.
	 */
	nfs_write_attributes(inode, resp->fattr);
	while (!list_empty(&data->pages)) {
		req = nfs_list_entry(data->pages.next);
		nfs_list_remove_request(req);
		page = req->wb_page;

		dprintk("NFS: write (%x/%Ld %d@%Ld)",
			req->wb_inode->i_dev,
			(long long)NFS_FILEID(req->wb_inode),
			req->wb_bytes,
			(long long)(page_offset(page) + req->wb_offset));

		if (task->tk_status < 0) {
			ClearPageUptodate(page);
			SetPageError(page);
			if (req->wb_file)
				req->wb_file->f_error = task->tk_status;
			nfs_inode_remove_request(req);
			dprintk(", error = %d\n", task->tk_status);
			goto next;
		}

#ifdef CONFIG_NFS_V3
		if (argp->stable != NFS_UNSTABLE || resp->verf->committed == NFS_FILE_SYNC) {
			nfs_inode_remove_request(req);
			dprintk(" OK\n");
			goto next;
		}
		memcpy(&req->wb_verf, resp->verf, sizeof(req->wb_verf));
		req->wb_timeout = jiffies + NFS_COMMIT_DELAY;
		nfs_mark_request_commit(req);
		dprintk(" marked for commit\n");
#else
		nfs_inode_remove_request(req);
#endif
	next:
		nfs_unlock_request(req);
	}
}


#ifdef CONFIG_NFS_V3
/*
 * Set up the argument/result storage required for the RPC call.
 */
static void
nfs_commit_rpcsetup(struct list_head *head, struct nfs_write_data *data)
{
	struct nfs_page		*first, *last;
	struct inode		*inode;
	loff_t			start, end, len;

	/* Set up the RPC argument and reply structs
	 * NB: take care not to mess about with data->commit et al. */

	list_splice(head, &data->pages);
	INIT_LIST_HEAD(head);
	first = nfs_list_entry(data->pages.next);
	last = nfs_list_entry(data->pages.prev);
	inode = first->wb_inode;

	/*
	 * Determine the offset range of requests in the COMMIT call.
	 * We rely on the fact that data->pages is an ordered list...
	 */
	start = page_offset(first->wb_page) + first->wb_offset;
	end = page_offset(last->wb_page) + (last->wb_offset + last->wb_bytes);
	len = end - start;
	/* If 'len' is not a 32-bit quantity, pass '0' in the COMMIT call */
	if (end >= inode->i_size || len < 0 || len > (~((u32)0) >> 1))
		len = 0;

	data->inode	  = inode;
	data->cred	  = first->wb_cred;
	data->args.fh     = NFS_FH(inode);
	data->args.offset = start;
	data->res.count   = data->args.count = (u32)len;
	data->res.fattr   = &data->fattr;
	data->res.verf    = &data->verf;
}

/*
 * Commit dirty pages
 */
int
nfs_commit_list(struct list_head *head, int how)
{
	struct rpc_message	msg;
	struct rpc_clnt		*clnt;
	struct nfs_write_data	*data;
	struct rpc_task         *task;
	struct nfs_page         *req;
	int                     flags,
				async = !(how & FLUSH_SYNC);
	sigset_t		oldset;

	data = nfs_writedata_alloc();

	if (!data)
		goto out_bad;
	task = &data->task;

	flags = (async) ? RPC_TASK_ASYNC : 0;

	/* Set up the argument struct */
	nfs_commit_rpcsetup(head, data);
	req = nfs_list_entry(data->pages.next);
	clnt = NFS_CLIENT(req->wb_inode);

	rpc_init_task(task, clnt, nfs_commit_done, flags);
	task->tk_calldata = data;
	/* Release requests */
	task->tk_release = nfs_writedata_release;

	msg.rpc_proc = NFS3PROC_COMMIT;
	msg.rpc_argp = &data->args;
	msg.rpc_resp = &data->res;
	msg.rpc_cred = data->cred;

	dprintk("NFS: %4d initiated commit call\n", task->tk_pid);
	rpc_clnt_sigmask(clnt, &oldset);
	rpc_call_setup(task, &msg, 0);
	lock_kernel();
	rpc_execute(task);
	unlock_kernel();
	rpc_clnt_sigunmask(clnt, &oldset);
	return 0;
 out_bad:
	while (!list_empty(head)) {
		req = nfs_list_entry(head->next);
		nfs_list_remove_request(req);
		nfs_mark_request_commit(req);
		nfs_unlock_request(req);
	}
	return -ENOMEM;
}

/*
 * COMMIT call returned
 */
static void
nfs_commit_done(struct rpc_task *task)
{
	struct nfs_write_data	*data = (struct nfs_write_data *)task->tk_calldata;
	struct nfs_writeres	*resp = &data->res;
	struct nfs_page		*req;
	struct inode		*inode = data->inode;

        dprintk("NFS: %4d nfs_commit_done (status %d)\n",
                                task->tk_pid, task->tk_status);

	if (nfs_async_handle_jukebox(task))
		return;

	nfs_write_attributes(inode, resp->fattr);
	while (!list_empty(&data->pages)) {
		req = nfs_list_entry(data->pages.next);
		nfs_list_remove_request(req);

		dprintk("NFS: commit (%x/%Ld %d@%Ld)",
			req->wb_inode->i_dev,
			(long long)NFS_FILEID(req->wb_inode),
			req->wb_bytes,
			(long long)(page_offset(req->wb_page) + req->wb_offset));
		if (task->tk_status < 0) {
			if (req->wb_file)
				req->wb_file->f_error = task->tk_status;
			nfs_inode_remove_request(req);
			dprintk(", error = %d\n", task->tk_status);
			goto next;
		}

		/* Okay, COMMIT succeeded, apparently. Check the verifier
		 * returned by the server against all stored verfs. */
		if (!memcmp(req->wb_verf.verifier, data->verf.verifier, sizeof(data->verf.verifier))) {
			/* We have a match */
			nfs_inode_remove_request(req);
			dprintk(" OK\n");
			goto next;
		}
		/* We have a mismatch. Write the page again */
		dprintk(" mismatch\n");
		nfs_mark_request_dirty(req);
	next:
		nfs_unlock_request(req);
	}
}
#endif

int nfs_flush_file(struct inode *inode, unsigned long idx_start,
		   unsigned int npages, int how)
{
	LIST_HEAD(head);
	int			res,
				error = 0;

	spin_lock(&nfs_wreq_lock);
	res = nfs_scan_dirty(inode, &head, idx_start, npages);
	spin_unlock(&nfs_wreq_lock);
	if (res)
		error = nfs_flush_list(&head, NFS_SERVER(inode)->wpages, how);
	if (error < 0)
		return error;
	return res;
}

#ifdef CONFIG_NFS_V3
int nfs_commit_file(struct inode *inode, int how)
{
	LIST_HEAD(head);
	int			res,
				error = 0;

	spin_lock(&nfs_wreq_lock);
	res = nfs_scan_commit(inode, &head, 0, 0);
	spin_unlock(&nfs_wreq_lock);
	if (res)
		error = nfs_commit_list(&head, how);
	if (error < 0)
		return error;
	return res;
}
#endif

int nfs_sync_file(struct inode *inode, unsigned long idx_start,
		  unsigned int npages, int how)
{
	int	error,
		wait;

	wait = how & FLUSH_WAIT;
	how &= ~FLUSH_WAIT;

	do {
		error = 0;
		if (wait)
			error = nfs_wait_on_requests(inode, idx_start, npages);
		if (error == 0)
			error = nfs_flush_file(inode, idx_start, npages, how);
#ifdef CONFIG_NFS_V3
		if (error == 0)
			error = nfs_commit_file(inode, how);
#endif
	} while (error > 0);
	return error;
}

int nfs_init_writepagecache(void)
{
	nfs_wdata_cachep = kmem_cache_create("nfs_write_data",
					     sizeof(struct nfs_write_data),
					     0, SLAB_HWCACHE_ALIGN,
					     NULL, NULL);
	if (nfs_wdata_cachep == NULL)
		return -ENOMEM;

	return 0;
}

void nfs_destroy_writepagecache(void)
{
	if (kmem_cache_destroy(nfs_wdata_cachep))
		printk(KERN_INFO "nfs_write_data: not all structures were freed\n");
}