patch-2.1.32 linux/fs/nfs/write.c

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diff -u --recursive --new-file v2.1.31/linux/fs/nfs/write.c linux/fs/nfs/write.c
@@ -0,0 +1,823 @@
+/*
+ * 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 understant
+ * it, these are different when doing a swap-out.
+ *
+ * To understand everything that goes one 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>
+ */
+
+#define NFS_NEED_XDR_TYPES
+#include <linux/config.h>
+#include <linux/types.h>
+#include <linux/malloc.h>
+#include <linux/swap.h>
+#include <linux/pagemap.h>
+#include <linux/sunrpc/clnt.h>
+#include <linux/nfs_fs.h>
+#include <asm/uaccess.h>
+
+#define NFSDBG_FACILITY		NFSDBG_PAGECACHE
+
+static void			nfs_wback_lock(struct rpc_task *task);
+static void			nfs_wback_result(struct rpc_task *task);
+
+/*
+ * This struct describes a file region to be written.
+ * It's kind of a pity we have to keep all these lists ourselves, rather
+ * than sticking an extra pointer into struct page.
+ */
+struct nfs_wreq {
+	struct rpc_listitem	wb_list;	/* linked list of req's */
+	struct rpc_task		wb_task;	/* RPC task */
+	struct inode *		wb_inode;	/* inode referenced */
+	struct page *		wb_page;	/* page to be written */
+	unsigned int		wb_offset;	/* offset within page */
+	unsigned int		wb_bytes;	/* dirty range */
+	pid_t			wb_pid;		/* owner process */
+	unsigned short		wb_flags;	/* status flags */
+
+	struct nfs_writeargs *	wb_args;	/* NFS RPC stuff */
+	struct nfs_fattr *	wb_fattr;	/* file attributes */
+};
+#define wb_status		wb_task.tk_status
+
+#define WB_NEXT(req)		((struct nfs_wreq *) ((req)->wb_list.next))
+
+/*
+ * Various flags for wb_flags
+ */
+#define NFS_WRITE_WANTLOCK	0x0001	/* needs to lock page */
+#define NFS_WRITE_LOCKED	0x0002	/* holds lock on page */
+#define NFS_WRITE_CANCELLED	0x0004	/* has been cancelled */
+#define NFS_WRITE_UNCOMMITTED	0x0008	/* written but uncommitted (NFSv3) */
+#define NFS_WRITE_INVALIDATE	0x0010	/* invalidate after write */
+#define NFS_WRITE_INPROGRESS	0x0020	/* RPC call in progress */
+
+#define WB_INPROGRESS(req)	((req)->wb_flags & NFS_WRITE_INPROGRESS)
+#define WB_WANTLOCK(req)	((req)->wb_flags & NFS_WRITE_WANTLOCK)
+#define WB_HAVELOCK(req)	((req)->wb_flags & NFS_WRITE_LOCKED)
+#define WB_CANCELLED(req)	((req)->wb_flags & NFS_WRITE_CANCELLED)
+#define WB_UNCOMMITTED(req)	((req)->wb_flags & NFS_WRITE_UNCOMMITTED)
+#define WB_INVALIDATE(req)	((req)->wb_flags & NFS_WRITE_INVALIDATE)
+
+/*
+ * Cache parameters
+ */
+#define NFS_WRITEBACK_DELAY	(10 * HZ)
+#define NFS_WRITEBACK_MAX	64
+
+/*
+ * Limit number of delayed writes
+ */
+static int			nr_write_requests = 0;
+static struct rpc_wait_queue	write_queue = RPC_INIT_WAITQ("write_chain");
+struct nfs_wreq *		nfs_failed_requests = NULL;
+
+/* Hack for future NFS swap support */
+#ifndef IS_SWAPFILE
+# define IS_SWAPFILE(inode)	(0)
+#endif
+
+/*
+ * Unlock a page after writing it
+ */
+static inline void
+nfs_unlock_page(struct page *page)
+{
+	dprintk("NFS:      unlock %ld\n", page->offset);
+	clear_bit(PG_locked, &page->flags);
+	wake_up(&page->wait);
+
+#ifdef CONFIG_NFS_SWAP
+	/* async swap-out support */
+	if (clear_bit(PG_decr_after, &page->flags))
+		atomic_dec(&page->count);
+	if (clear_bit(PG_swap_unlock_after, &page->flags))
+		swap_after_unlock_page(page->swap_unlock_entry);
+#endif
+}
+
+/*
+ * Transfer a page lock to a write request waiting for it.
+ */
+static inline void
+transfer_page_lock(struct nfs_wreq *req)
+{
+	dprintk("NFS:      transfer_page_lock\n");
+
+	req->wb_flags &= ~NFS_WRITE_WANTLOCK;
+	req->wb_flags |= NFS_WRITE_LOCKED;
+	rpc_wake_up_task(&req->wb_task);
+
+	dprintk("nfs:      wake up task %d (flags %x)\n",
+			req->wb_task.tk_pid, req->wb_flags);
+}
+
+/*
+ * Write a page synchronously.
+ * Offset is the data offset within the page.
+ */
+static int
+nfs_writepage_sync(struct inode *inode, struct page *page,
+				unsigned long offset, unsigned int count)
+{
+	struct nfs_fattr fattr;
+	unsigned int	wsize = NFS_SERVER(inode)->wsize;
+	int		result, refresh = 0, written = 0;
+	u8		*buffer;
+
+	dprintk("NFS:      nfs_writepage_sync(%x/%ld %d@%ld)\n",
+				inode->i_dev, inode->i_ino,
+				count, page->offset + offset);
+
+	buffer = (u8 *) page_address(page) + offset;
+	offset += page->offset;
+
+	do {
+		if (count < wsize && !IS_SWAPFILE(inode))
+			wsize = count;
+
+		result = nfs_proc_write(NFS_SERVER(inode), NFS_FH(inode),
+					offset, wsize, IS_SWAPFILE(inode),
+					buffer, &fattr);
+
+		if (result < 0) {
+			/* Must mark the page invalid after I/O error */
+			clear_bit(PG_uptodate, &page->flags);
+			goto io_error;
+		}
+		refresh = 1;
+		buffer  += wsize;
+		offset  += wsize;
+		written += wsize;
+		count   -= wsize;
+	} while (count);
+
+io_error:
+	if (refresh) {
+		/* See comments in nfs_wback_result */
+		if (fattr.size < inode->i_size)
+			fattr.size = inode->i_size;
+		/* Solaris 2.5 server seems to send garbled
+		 * fattrs occasionally */
+		if (inode->i_ino == fattr.fileid)
+			nfs_refresh_inode(inode, &fattr);
+	}
+
+	nfs_unlock_page(page);
+	return written? written : result;
+}
+
+/*
+ * Append a writeback request to a list
+ */
+static inline void
+append_write_request(struct nfs_wreq **q, struct nfs_wreq *wreq)
+{
+	dprintk("NFS:      append_write_request(%p, %p)\n", q, wreq);
+	rpc_append_list(q, wreq);
+}
+
+/*
+ * Remove a writeback request from a list
+ */
+static inline void
+remove_write_request(struct nfs_wreq **q, struct nfs_wreq *wreq)
+{
+	dprintk("NFS:      remove_write_request(%p, %p)\n", q, wreq);
+	rpc_remove_list(q, wreq);
+}
+
+/*
+ * Find a write request for a given page
+ */
+static inline struct nfs_wreq *
+find_write_request(struct inode *inode, struct page *page)
+{
+	struct nfs_wreq	*head, *req;
+
+	dprintk("NFS:      find_write_request(%x/%ld, %p)\n",
+				inode->i_dev, inode->i_ino, page);
+	if (!(req = head = NFS_WRITEBACK(inode)))
+		return NULL;
+	do {
+		if (req->wb_page == page)
+			return req;
+	} while ((req = WB_NEXT(req)) != head);
+	return NULL;
+}
+
+/*
+ * Find a failed write request by pid
+ */
+static inline struct nfs_wreq *
+find_failed_request(struct inode *inode, pid_t pid)
+{
+	struct nfs_wreq	*head, *req;
+
+	if (!(req = head = nfs_failed_requests))
+		return NULL;
+	do {
+		if (req->wb_inode == inode && req->wb_pid == pid)
+			return req;
+	} while ((req = WB_NEXT(req)) != head);
+	return NULL;
+}
+
+/*
+ * Try to merge adjacent write requests. This works only for requests
+ * issued by the same user.
+ */
+static inline int
+update_write_request(struct nfs_wreq *req, unsigned first, unsigned bytes)
+{
+	unsigned	rqfirst = req->wb_offset,
+			rqlast = rqfirst + req->wb_bytes,
+			last = first + bytes;
+
+	dprintk("nfs:      trying to update write request %p\n", req);
+
+	/* Check the credentials associated with this write request.
+	 * If the buffer is owned by the same user, we can happily
+	 * add our data without risking server permission problems.
+	 * Note that I'm not messing around with RPC root override creds
+	 * here, because they're used by swap requests only which
+	 * always write out full pages. */
+	if (!rpcauth_matchcred(&req->wb_task, req->wb_task.tk_cred)) {
+		dprintk("NFS:      update failed (cred mismatch)\n");
+		return 0;
+	}
+
+	if (first < rqfirst)
+		rqfirst = first;
+	if (rqlast < last)
+		rqlast = last;
+	req->wb_offset = rqfirst;
+	req->wb_bytes  = rqlast - rqfirst;
+
+	return 1;
+}
+
+/*
+ * Create and initialize a writeback request
+ */
+static inline struct nfs_wreq *
+create_write_request(struct inode *inode, struct page *page,
+				unsigned offset, unsigned bytes)
+{
+	struct nfs_wreq *wreq;
+	struct rpc_clnt	*clnt = NFS_CLIENT(inode);
+	struct rpc_task	*task;
+
+	dprintk("NFS:      create_write_request(%x/%ld, %ld+%d)\n",
+				inode->i_dev, inode->i_ino,
+				page->offset + offset, bytes);
+
+	/* FIXME: Enforce hard limit on number of concurrent writes? */
+
+	wreq = (struct nfs_wreq *) kmalloc(sizeof(*wreq), GFP_USER);
+	if (!wreq)
+		return NULL;
+	memset(wreq, 0, sizeof(*wreq));
+
+	task = &wreq->wb_task;
+	rpc_init_task(task, clnt, nfs_wback_result, 0);
+	task->tk_calldata = wreq;
+	task->tk_action = nfs_wback_lock;
+
+	rpcauth_lookupcred(task);	/* Obtain user creds */
+	if (task->tk_status < 0) {
+		rpc_release_task(task);
+		kfree(wreq);
+		return NULL;
+	}
+
+	/* Put the task on inode's writeback request list. */
+	wreq->wb_inode  = inode;
+	wreq->wb_pid    = current->pid;
+	wreq->wb_page   = page;
+	wreq->wb_offset = offset;
+	wreq->wb_bytes  = bytes;
+	inode->i_count++;
+	page->count++;
+
+	append_write_request(&NFS_WRITEBACK(inode), wreq);
+
+	if (nr_write_requests++ > NFS_WRITEBACK_MAX*3/4)
+		rpc_wake_up_next(&write_queue);
+
+	return wreq;
+}
+
+/*
+ * Schedule a writeback RPC call.
+ * If the server is congested, don't add to our backlog of queued
+ * requests but call it synchronously.
+ * The function returns true if the page has been unlocked as the
+ * consequence of a synchronous write call.
+ *
+ * FIXME: Here we could walk the inode's lock list to see whether the
+ * page we're currently writing to has been write-locked by the caller.
+ * If it is, we could schedule an async write request with a long
+ * delay in order to avoid writing back the page until the lock is
+ * released.
+ */
+static inline int
+schedule_write_request(struct nfs_wreq *req, int sync)
+{
+	struct rpc_task	*task = &req->wb_task;
+	struct inode	*inode = req->wb_inode;
+
+	if (NFS_CONGESTED(inode) || nr_write_requests >= NFS_WRITEBACK_MAX)
+		sync = 1;
+
+	if (sync) {
+		dprintk("NFS: %4d schedule_write_request (sync)\n",
+					task->tk_pid);
+		/* Page is already locked */
+		req->wb_flags |= NFS_WRITE_LOCKED;
+		rpc_execute(task);
+	} else {
+		dprintk("NFS: %4d schedule_write_request (async)\n",
+					task->tk_pid);
+		task->tk_flags |= RPC_TASK_ASYNC;
+		task->tk_timeout = NFS_WRITEBACK_DELAY;
+		rpc_sleep_on(&write_queue, task, NULL, NULL);
+	}
+
+	return sync == 0;
+}
+
+/*
+ * Wait for request to complete
+ * This is almost a copy of __wait_on_page
+ */
+static inline int
+wait_on_write_request(struct nfs_wreq *req)
+{
+	struct wait_queue	wait = { current, NULL };
+	struct page		*page = req->wb_page;
+
+	add_wait_queue(&page->wait, &wait);
+	page->count++;
+repeat:
+	current->state = TASK_INTERRUPTIBLE;
+	if (PageLocked(page)) {
+		schedule();
+		goto repeat;
+	}
+	remove_wait_queue(&page->wait, &wait);
+	current->state = TASK_RUNNING;
+	atomic_dec(&page->count);
+	return signalled()? -ERESTARTSYS : 0;
+}
+
+/*
+ * Write a page to the server. This will be used for NFS swapping only
+ * (for now), and we currently do this synchronously only.
+ */
+int
+nfs_writepage(struct inode *inode, struct page *page)
+{
+	return nfs_writepage_sync(inode, page, 0, PAGE_SIZE);
+}
+
+/*
+ * Update and possibly write a cached page of an NFS file.
+ * The page is already locked when we get here.
+ *
+ * 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 inode *inode, struct page *page, const char *buffer,
+			unsigned long offset, unsigned int count, int sync)
+{
+	struct nfs_wreq	*req;
+	int		status = 0, page_locked = 1;
+	u8		*page_addr;
+
+	dprintk("NFS:      nfs_updatepage(%x/%ld %d@%ld, sync=%d)\n",
+				inode->i_dev, inode->i_ino,
+				count, page->offset+offset, sync);
+
+	page_addr = (u8 *) page_address(page);
+
+	/* If wsize is smaller than page size, update and write
+	 * page synchronously.
+	 */
+	if (NFS_SERVER(inode)->wsize < PAGE_SIZE) {
+		copy_from_user(page_addr + offset, buffer, count);
+		return nfs_writepage_sync(inode, page, offset, count);
+	}
+
+	/*
+	 * Try to find a corresponding request on the writeback queue.
+	 * If there is one, we can be sure that this request is not
+	 * yet being processed, because we hold a lock on the page.
+	 *
+	 * If the request was created by us, update it. Otherwise,
+	 * transfer the page lock and flush out the dirty page now.
+	 * After returning, generic_file_write will wait on the
+	 * page and retry the update.
+	 */
+	if ((req = find_write_request(inode, page)) != NULL) {
+		if (update_write_request(req, offset, count)) {
+			copy_from_user(page_addr + offset, buffer, count);
+			goto updated;
+		}
+		dprintk("NFS:      wake up conflicting write request.\n");
+		transfer_page_lock(req);
+		return 0;
+	}
+
+	/* Create the write request. */
+	if (!(req = create_write_request(inode, page, offset, count))) {
+		status = -ENOBUFS;
+		goto done;
+	}
+
+	/* Copy data to page buffer. */
+	copy_from_user(page_addr + offset, buffer, count);
+
+	/* Schedule request */
+	page_locked = schedule_write_request(req, sync);
+
+updated:
+	/*
+	 * If we wrote up to the end of the chunk, transmit request now.
+	 * We should be a bit more intelligent about detecting whether a
+	 * process accesses the file sequentially or not.
+	 */
+	if (page_locked && (offset + count >= PAGE_SIZE || sync))
+		req->wb_flags |= NFS_WRITE_WANTLOCK;
+
+	/* If the page was written synchronously, return any error that
+	 * may have happened; otherwise return the write count. */
+	if (page_locked || (status = nfs_write_error(inode)) >= 0)
+		status = count;
+
+done:
+	/* Unlock page and wake up anyone sleeping on it */
+	if (page_locked) {
+		if (req && WB_WANTLOCK(req)) {
+			transfer_page_lock(req);
+			/* rpc_execute(&req->wb_task); */
+			if (sync) {
+				wait_on_write_request(req);
+				if ((count = nfs_write_error(inode)) < 0)
+					status = count;
+			}
+		} else
+			nfs_unlock_page(page);
+	}
+
+	dprintk("NFS:      nfs_updatepage returns %d (isize %ld)\n",
+						status, inode->i_size);
+	return status;
+}
+
+/*
+ * Flush out a dirty page.
+ */ 
+static inline void
+nfs_flush_request(struct nfs_wreq *req)
+{
+	struct page	*page = req->wb_page;
+
+	dprintk("NFS:      nfs_flush_request(%x/%ld, @%ld)\n",
+				page->inode->i_dev, page->inode->i_ino,
+				page->offset);
+
+	req->wb_flags |= NFS_WRITE_WANTLOCK;
+	if (!set_bit(PG_locked, &page->flags)) {
+		transfer_page_lock(req);
+	} else {
+		printk(KERN_WARNING "NFS oops in %s: can't lock page!\n",
+					__FUNCTION__);
+		rpc_wake_up_task(&req->wb_task);
+	}
+}
+
+/*
+ * Flush writeback requests. See nfs_flush_dirty_pages for details.
+ */
+static struct nfs_wreq *
+nfs_flush_pages(struct inode *inode, pid_t pid, off_t offset, off_t len,
+						int invalidate)
+{
+	struct nfs_wreq *head, *req, *last = NULL;
+	off_t		rqoffset, rqend, end;
+
+	end = len? offset + len : 0x7fffffffUL;
+
+	req = head = NFS_WRITEBACK(inode);
+	while (req != NULL) {
+		dprintk("NFS: %4d nfs_flush inspect %x/%ld @%ld fl %x\n",
+				req->wb_task.tk_pid,
+				req->wb_inode->i_dev, req->wb_inode->i_ino,
+				req->wb_page->offset, req->wb_flags);
+		if (!WB_INPROGRESS(req)) {
+			rqoffset = req->wb_page->offset + req->wb_offset;
+			rqend    = rqoffset + req->wb_bytes;
+
+			if (rqoffset < end && offset < rqend
+			 && (pid == 0 || req->wb_pid == pid)) {
+				if (!WB_HAVELOCK(req))
+					nfs_flush_request(req);
+				last = req;
+			}
+		}
+		if (invalidate)
+			req->wb_flags |= NFS_WRITE_INVALIDATE;
+		if ((req = WB_NEXT(req)) == head)
+			break;
+	}
+
+	return last;
+}
+
+/*
+ * Cancel all writeback requests, both pending and in process.
+ */
+static void
+nfs_cancel_dirty(struct inode *inode, pid_t pid)
+{
+	struct nfs_wreq *head, *req;
+
+	req = head = NFS_WRITEBACK(inode);
+	while (req != NULL) {
+		if (req->wb_pid == pid) {
+			req->wb_flags |= NFS_WRITE_CANCELLED;
+			rpc_exit(&req->wb_task, 0);
+		}
+		if ((req = WB_NEXT(req)) == head)
+			break;
+	}
+}
+
+/*
+ * Flush out all dirty pages belonging to a certain user process and
+ * maybe wait for the RPC calls to complete.
+ *
+ * Another purpose of this function is sync()ing a file range before a
+ * write lock is released. This is what offset and length are for, even if
+ * this isn't used by the nlm module yet.
+ */
+int
+nfs_flush_dirty_pages(struct inode *inode, off_t offset, off_t len)
+{
+	struct nfs_wreq *last = NULL;
+
+	dprintk("NFS:      flush_dirty_pages(%x/%ld for pid %d %ld/%ld)\n",
+				inode->i_dev, inode->i_ino, current->pid,
+				offset, len);
+
+	if (signalled())
+		nfs_cancel_dirty(inode, current->pid);
+
+	while (!signalled()) {
+		/* Flush all pending writes for this pid and file region */
+		last = nfs_flush_pages(inode, current->pid, offset, len, 0);
+		if (last == NULL)
+			break;
+		wait_on_write_request(last);
+	}
+
+	return signalled()? -ERESTARTSYS : 0;
+}
+
+/*
+ * Flush out any pending write requests and flag that they be discarded
+ * after the write is complete.
+ *
+ * This function is called from nfs_revalidate_inode just before it calls
+ * invalidate_inode_pages. After nfs_flush_pages returns, we can be sure
+ * that all dirty pages are locked, so that invalidate_inode_pages does
+ * not throw away any dirty pages.
+ */
+void
+nfs_invalidate_pages(struct inode *inode)
+{
+	dprintk("NFS:      nfs_invalidate_pages(%x/%ld)\n",
+				inode->i_dev, inode->i_ino);
+
+	nfs_flush_pages(inode, 0, 0, 0, 1);
+}
+
+/*
+ * Cancel any pending write requests after a given offset
+ * (called from nfs_notify_change).
+ */
+int
+nfs_truncate_dirty_pages(struct inode *inode, unsigned long offset)
+{
+	struct nfs_wreq *req, *head;
+	unsigned long	rqoffset;
+
+	dprintk("NFS:      truncate_dirty_pages(%x/%ld, %ld)\n",
+				inode->i_dev, inode->i_ino, offset);
+
+	req = head = NFS_WRITEBACK(inode);
+	while (req != NULL) {
+		rqoffset = req->wb_page->offset + req->wb_offset;
+
+		if (rqoffset >= offset) {
+			req->wb_flags |= NFS_WRITE_CANCELLED;
+			rpc_exit(&req->wb_task, 0);
+		} else if (rqoffset + req->wb_bytes >= offset) {
+			req->wb_bytes = offset - rqoffset;
+		}
+		if ((req = WB_NEXT(req)) == head)
+			break;
+	}
+
+	return 0;
+}
+
+/*
+ * Check if a previous write operation returned an error
+ */
+int
+nfs_check_error(struct inode *inode)
+{
+	struct nfs_wreq	*req;
+	int		status = 0;
+
+	dprintk("nfs:      checking for write error inode %04x/%ld\n",
+			inode->i_dev, inode->i_ino);
+
+	if (!(req = find_failed_request(inode, current->pid)))
+		return 0;
+
+	dprintk("nfs: write error %d inode %04x/%ld\n",
+			req->wb_task.tk_status, inode->i_dev, inode->i_ino);
+
+	status = req->wb_task.tk_status;
+	remove_write_request(&nfs_failed_requests, req);
+	iput(req->wb_inode);
+	kfree(req);
+	return status;
+}
+
+/*
+ * The following procedures make up the writeback finite state machinery:
+ *
+ * 1.	Try to lock the page if not yet locked by us,
+ *	set up the RPC call info, and pass to the call FSM.
+ */
+static void
+nfs_wback_lock(struct rpc_task *task)
+{
+	struct nfs_wreq	*req = (struct nfs_wreq *) task->tk_calldata;
+	struct page	*page = req->wb_page;
+	struct inode	*inode = req->wb_inode;
+
+	dprintk("NFS: %4d nfs_wback_lock (status %d flags %x)\n",
+			task->tk_pid, task->tk_status, req->wb_flags);
+
+	if (!WB_HAVELOCK(req))
+		req->wb_flags |= NFS_WRITE_WANTLOCK;
+
+	if (WB_WANTLOCK(req) && set_bit(PG_locked, &page->flags)) {
+		dprintk("NFS:      page already locked in writeback_lock!\n");
+		task->tk_timeout = 2 * HZ;
+		rpc_sleep_on(&write_queue, task, NULL, NULL);
+		return;
+	}
+	task->tk_status = 0;
+	req->wb_flags &= ~NFS_WRITE_WANTLOCK;
+	req->wb_flags |=  NFS_WRITE_LOCKED;
+
+	if (req->wb_args == 0) {
+		size_t	size = sizeof(struct nfs_writeargs)
+			     + sizeof(struct nfs_fattr);
+		void	*ptr;
+
+		if (!(ptr = kmalloc(size, GFP_KERNEL))) {
+			task->tk_timeout = HZ;
+			rpc_sleep_on(&write_queue, task, NULL, NULL);
+			return;
+		}
+		req->wb_args = (struct nfs_writeargs *) ptr;
+		req->wb_fattr = (struct nfs_fattr *) (req->wb_args + 1);
+	}
+
+	/* Setup the task struct for a writeback call */
+	req->wb_args->fh = NFS_FH(inode);
+	req->wb_args->offset = page->offset + req->wb_offset;
+	req->wb_args->count  = req->wb_bytes;
+	req->wb_args->buffer = (void *) (page_address(page) + req->wb_offset);
+
+	rpc_call_setup(task, NFSPROC_WRITE, req->wb_args, req->wb_fattr, 0);
+
+	req->wb_flags |= NFS_WRITE_INPROGRESS;
+}
+
+/*
+ * 2.	Collect the result
+ */
+static void
+nfs_wback_result(struct rpc_task *task)
+{
+	struct nfs_wreq *req = (struct nfs_wreq *) task->tk_calldata;
+	struct inode	*inode;
+	struct page	*page;
+	int		status;
+
+	dprintk("NFS: %4d nfs_wback_result (status %d)\n",
+				task->tk_pid, task->tk_status);
+
+	inode  = req->wb_inode;
+	page   = req->wb_page;
+	status = task->tk_status;
+
+	/* Remove request from writeback list and wake up tasks
+	 * sleeping on it. */
+	remove_write_request(&NFS_WRITEBACK(inode), req);
+
+	if (status < 0) {
+		/*
+		 * An error occurred. Report the error back to the
+		 * application by adding the failed request to the
+		 * inode's error list.
+		 */
+		if (find_failed_request(inode, req->wb_pid)) {
+			status = 0;
+		} else {
+			dprintk("NFS: %4d saving write failure code\n",
+						task->tk_pid);
+			append_write_request(&nfs_failed_requests, req);
+			inode->i_count++;
+		}
+		clear_bit(PG_uptodate, &page->flags);
+	} else if (!WB_CANCELLED(req)) {
+		/* Update attributes as result of writeback. 
+		 * Beware: when UDP replies arrive out of order, we
+		 * may end up overwriting a previous, bigger file size.
+		 */
+		if (req->wb_fattr->size < inode->i_size)
+			req->wb_fattr->size = inode->i_size;
+		/* possible Solaris 2.5 server bug workaround */
+		if (inode->i_ino == req->wb_fattr->fileid)
+			nfs_refresh_inode(inode, req->wb_fattr);
+	}
+
+	rpc_release_task(task);
+
+	if (WB_INVALIDATE(req))
+		clear_bit(PG_uptodate, &page->flags);
+	if (WB_HAVELOCK(req))
+		nfs_unlock_page(page);
+
+	if (req->wb_args) {
+		kfree(req->wb_args);
+		req->wb_args = 0;
+	}
+	if (status >= 0)
+		kfree(req);
+
+	free_page(page_address(page));
+	iput(inode);
+	nr_write_requests--;
+}
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