xref: /openbmc/linux/fs/nfs/direct.c (revision d5cb9783536a41df9f9cba5b0a1d78047ed787f7)
1 /*
2  * linux/fs/nfs/direct.c
3  *
4  * Copyright (C) 2003 by Chuck Lever <cel@netapp.com>
5  *
6  * High-performance uncached I/O for the Linux NFS client
7  *
8  * There are important applications whose performance or correctness
9  * depends on uncached access to file data.  Database clusters
10  * (multiple copies of the same instance running on separate hosts)
11  * implement their own cache coherency protocol that subsumes file
12  * system cache protocols.  Applications that process datasets
13  * considerably larger than the client's memory do not always benefit
14  * from a local cache.  A streaming video server, for instance, has no
15  * need to cache the contents of a file.
16  *
17  * When an application requests uncached I/O, all read and write requests
18  * are made directly to the server; data stored or fetched via these
19  * requests is not cached in the Linux page cache.  The client does not
20  * correct unaligned requests from applications.  All requested bytes are
21  * held on permanent storage before a direct write system call returns to
22  * an application.
23  *
24  * Solaris implements an uncached I/O facility called directio() that
25  * is used for backups and sequential I/O to very large files.  Solaris
26  * also supports uncaching whole NFS partitions with "-o forcedirectio,"
27  * an undocumented mount option.
28  *
29  * Designed by Jeff Kimmel, Chuck Lever, and Trond Myklebust, with
30  * help from Andrew Morton.
31  *
32  * 18 Dec 2001	Initial implementation for 2.4  --cel
33  * 08 Jul 2002	Version for 2.4.19, with bug fixes --trondmy
34  * 08 Jun 2003	Port to 2.5 APIs  --cel
35  * 31 Mar 2004	Handle direct I/O without VFS support  --cel
36  * 15 Sep 2004	Parallel async reads  --cel
37  *
38  */
39 
40 #include <linux/config.h>
41 #include <linux/errno.h>
42 #include <linux/sched.h>
43 #include <linux/kernel.h>
44 #include <linux/smp_lock.h>
45 #include <linux/file.h>
46 #include <linux/pagemap.h>
47 #include <linux/kref.h>
48 
49 #include <linux/nfs_fs.h>
50 #include <linux/nfs_page.h>
51 #include <linux/sunrpc/clnt.h>
52 
53 #include <asm/system.h>
54 #include <asm/uaccess.h>
55 #include <asm/atomic.h>
56 
57 #define NFSDBG_FACILITY		NFSDBG_VFS
58 #define MAX_DIRECTIO_SIZE	(4096UL << PAGE_SHIFT)
59 
60 static kmem_cache_t *nfs_direct_cachep;
61 
62 /*
63  * This represents a set of asynchronous requests that we're waiting on
64  */
65 struct nfs_direct_req {
66 	struct kref		kref;		/* release manager */
67 	struct list_head	list;		/* nfs_read_data structs */
68 	wait_queue_head_t	wait;		/* wait for i/o completion */
69 	struct page **		pages;		/* pages in our buffer */
70 	unsigned int		npages;		/* count of pages */
71 	atomic_t		complete,	/* i/os we're waiting for */
72 				count,		/* bytes actually processed */
73 				error;		/* any reported error */
74 };
75 
76 
77 /**
78  * nfs_get_user_pages - find and set up pages underlying user's buffer
79  * rw: direction (read or write)
80  * user_addr: starting address of this segment of user's buffer
81  * count: size of this segment
82  * @pages: returned array of page struct pointers underlying user's buffer
83  */
84 static inline int
85 nfs_get_user_pages(int rw, unsigned long user_addr, size_t size,
86 		struct page ***pages)
87 {
88 	int result = -ENOMEM;
89 	unsigned long page_count;
90 	size_t array_size;
91 
92 	/* set an arbitrary limit to prevent type overflow */
93 	/* XXX: this can probably be as large as INT_MAX */
94 	if (size > MAX_DIRECTIO_SIZE) {
95 		*pages = NULL;
96 		return -EFBIG;
97 	}
98 
99 	page_count = (user_addr + size + PAGE_SIZE - 1) >> PAGE_SHIFT;
100 	page_count -= user_addr >> PAGE_SHIFT;
101 
102 	array_size = (page_count * sizeof(struct page *));
103 	*pages = kmalloc(array_size, GFP_KERNEL);
104 	if (*pages) {
105 		down_read(&current->mm->mmap_sem);
106 		result = get_user_pages(current, current->mm, user_addr,
107 					page_count, (rw == READ), 0,
108 					*pages, NULL);
109 		up_read(&current->mm->mmap_sem);
110 	}
111 	return result;
112 }
113 
114 /**
115  * nfs_free_user_pages - tear down page struct array
116  * @pages: array of page struct pointers underlying target buffer
117  * @npages: number of pages in the array
118  * @do_dirty: dirty the pages as we release them
119  */
120 static void
121 nfs_free_user_pages(struct page **pages, int npages, int do_dirty)
122 {
123 	int i;
124 	for (i = 0; i < npages; i++) {
125 		if (do_dirty)
126 			set_page_dirty_lock(pages[i]);
127 		page_cache_release(pages[i]);
128 	}
129 	kfree(pages);
130 }
131 
132 /**
133  * nfs_direct_req_release - release  nfs_direct_req structure for direct read
134  * @kref: kref object embedded in an nfs_direct_req structure
135  *
136  */
137 static void nfs_direct_req_release(struct kref *kref)
138 {
139 	struct nfs_direct_req *dreq = container_of(kref, struct nfs_direct_req, kref);
140 	kmem_cache_free(nfs_direct_cachep, dreq);
141 }
142 
143 /**
144  * nfs_direct_read_alloc - allocate nfs_read_data structures for direct read
145  * @count: count of bytes for the read request
146  * @rsize: local rsize setting
147  *
148  * Note we also set the number of requests we have in the dreq when we are
149  * done.  This prevents races with I/O completion so we will always wait
150  * until all requests have been dispatched and completed.
151  */
152 static struct nfs_direct_req *nfs_direct_read_alloc(size_t nbytes, unsigned int rsize)
153 {
154 	struct list_head *list;
155 	struct nfs_direct_req *dreq;
156 	unsigned int reads = 0;
157 
158 	dreq = kmem_cache_alloc(nfs_direct_cachep, SLAB_KERNEL);
159 	if (!dreq)
160 		return NULL;
161 
162 	kref_init(&dreq->kref);
163 	init_waitqueue_head(&dreq->wait);
164 	INIT_LIST_HEAD(&dreq->list);
165 	atomic_set(&dreq->count, 0);
166 	atomic_set(&dreq->error, 0);
167 
168 	list = &dreq->list;
169 	for(;;) {
170 		struct nfs_read_data *data = nfs_readdata_alloc();
171 
172 		if (unlikely(!data)) {
173 			while (!list_empty(list)) {
174 				data = list_entry(list->next,
175 						  struct nfs_read_data, pages);
176 				list_del(&data->pages);
177 				nfs_readdata_free(data);
178 			}
179 			kref_put(&dreq->kref, nfs_direct_req_release);
180 			return NULL;
181 		}
182 
183 		INIT_LIST_HEAD(&data->pages);
184 		list_add(&data->pages, list);
185 
186 		data->req = (struct nfs_page *) dreq;
187 		reads++;
188 		if (nbytes <= rsize)
189 			break;
190 		nbytes -= rsize;
191 	}
192 	kref_get(&dreq->kref);
193 	atomic_set(&dreq->complete, reads);
194 	return dreq;
195 }
196 
197 /**
198  * nfs_direct_read_result - handle a read reply for a direct read request
199  * @data: address of NFS READ operation control block
200  * @status: status of this NFS READ operation
201  *
202  * We must hold a reference to all the pages in this direct read request
203  * until the RPCs complete.  This could be long *after* we are woken up in
204  * nfs_direct_read_wait (for instance, if someone hits ^C on a slow server).
205  */
206 static void nfs_direct_read_result(struct nfs_read_data *data, int status)
207 {
208 	struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;
209 
210 	if (likely(status >= 0))
211 		atomic_add(data->res.count, &dreq->count);
212 	else
213 		atomic_set(&dreq->error, status);
214 
215 	if (unlikely(atomic_dec_and_test(&dreq->complete))) {
216 		nfs_free_user_pages(dreq->pages, dreq->npages, 1);
217 		wake_up(&dreq->wait);
218 		kref_put(&dreq->kref, nfs_direct_req_release);
219 	}
220 }
221 
222 /**
223  * nfs_direct_read_schedule - dispatch NFS READ operations for a direct read
224  * @dreq: address of nfs_direct_req struct for this request
225  * @inode: target inode
226  * @ctx: target file open context
227  * @user_addr: starting address of this segment of user's buffer
228  * @count: size of this segment
229  * @file_offset: offset in file to begin the operation
230  *
231  * For each nfs_read_data struct that was allocated on the list, dispatch
232  * an NFS READ operation
233  */
234 static void nfs_direct_read_schedule(struct nfs_direct_req *dreq,
235 		struct inode *inode, struct nfs_open_context *ctx,
236 		unsigned long user_addr, size_t count, loff_t file_offset)
237 {
238 	struct list_head *list = &dreq->list;
239 	struct page **pages = dreq->pages;
240 	unsigned int curpage, pgbase;
241 	unsigned int rsize = NFS_SERVER(inode)->rsize;
242 
243 	curpage = 0;
244 	pgbase = user_addr & ~PAGE_MASK;
245 	do {
246 		struct nfs_read_data *data;
247 		unsigned int bytes;
248 
249 		bytes = rsize;
250 		if (count < rsize)
251 			bytes = count;
252 
253 		data = list_entry(list->next, struct nfs_read_data, pages);
254 		list_del_init(&data->pages);
255 
256 		data->inode = inode;
257 		data->cred = ctx->cred;
258 		data->args.fh = NFS_FH(inode);
259 		data->args.context = ctx;
260 		data->args.offset = file_offset;
261 		data->args.pgbase = pgbase;
262 		data->args.pages = &pages[curpage];
263 		data->args.count = bytes;
264 		data->res.fattr = &data->fattr;
265 		data->res.eof = 0;
266 		data->res.count = bytes;
267 
268 		NFS_PROTO(inode)->read_setup(data);
269 
270 		data->task.tk_cookie = (unsigned long) inode;
271 		data->task.tk_calldata = data;
272 		data->task.tk_release = nfs_readdata_release;
273 		data->complete = nfs_direct_read_result;
274 
275 		lock_kernel();
276 		rpc_execute(&data->task);
277 		unlock_kernel();
278 
279 		dfprintk(VFS, "NFS: %4d initiated direct read call (req %s/%Ld, %u bytes @ offset %Lu)\n",
280 				data->task.tk_pid,
281 				inode->i_sb->s_id,
282 				(long long)NFS_FILEID(inode),
283 				bytes,
284 				(unsigned long long)data->args.offset);
285 
286 		file_offset += bytes;
287 		pgbase += bytes;
288 		curpage += pgbase >> PAGE_SHIFT;
289 		pgbase &= ~PAGE_MASK;
290 
291 		count -= bytes;
292 	} while (count != 0);
293 }
294 
295 /**
296  * nfs_direct_read_wait - wait for I/O completion for direct reads
297  * @dreq: request on which we are to wait
298  * @intr: whether or not this wait can be interrupted
299  *
300  * Collects and returns the final error value/byte-count.
301  */
302 static ssize_t nfs_direct_read_wait(struct nfs_direct_req *dreq, int intr)
303 {
304 	int result = 0;
305 
306 	if (intr) {
307 		result = wait_event_interruptible(dreq->wait,
308 					(atomic_read(&dreq->complete) == 0));
309 	} else {
310 		wait_event(dreq->wait, (atomic_read(&dreq->complete) == 0));
311 	}
312 
313 	if (!result)
314 		result = atomic_read(&dreq->error);
315 	if (!result)
316 		result = atomic_read(&dreq->count);
317 
318 	kref_put(&dreq->kref, nfs_direct_req_release);
319 	return (ssize_t) result;
320 }
321 
322 /**
323  * nfs_direct_read_seg - Read in one iov segment.  Generate separate
324  *                        read RPCs for each "rsize" bytes.
325  * @inode: target inode
326  * @ctx: target file open context
327  * @user_addr: starting address of this segment of user's buffer
328  * @count: size of this segment
329  * @file_offset: offset in file to begin the operation
330  * @pages: array of addresses of page structs defining user's buffer
331  * @nr_pages: number of pages in the array
332  *
333  */
334 static ssize_t nfs_direct_read_seg(struct inode *inode,
335 		struct nfs_open_context *ctx, unsigned long user_addr,
336 		size_t count, loff_t file_offset, struct page **pages,
337 		unsigned int nr_pages)
338 {
339 	ssize_t result;
340 	sigset_t oldset;
341 	struct rpc_clnt *clnt = NFS_CLIENT(inode);
342 	struct nfs_direct_req *dreq;
343 
344 	dreq = nfs_direct_read_alloc(count, NFS_SERVER(inode)->rsize);
345 	if (!dreq)
346 		return -ENOMEM;
347 
348 	dreq->pages = pages;
349 	dreq->npages = nr_pages;
350 
351 	rpc_clnt_sigmask(clnt, &oldset);
352 	nfs_direct_read_schedule(dreq, inode, ctx, user_addr, count,
353 				 file_offset);
354 	result = nfs_direct_read_wait(dreq, clnt->cl_intr);
355 	rpc_clnt_sigunmask(clnt, &oldset);
356 
357 	return result;
358 }
359 
360 /**
361  * nfs_direct_read - For each iov segment, map the user's buffer
362  *                   then generate read RPCs.
363  * @inode: target inode
364  * @ctx: target file open context
365  * @iov: array of vectors that define I/O buffer
366  * file_offset: offset in file to begin the operation
367  * nr_segs: size of iovec array
368  *
369  * We've already pushed out any non-direct writes so that this read
370  * will see them when we read from the server.
371  */
372 static ssize_t
373 nfs_direct_read(struct inode *inode, struct nfs_open_context *ctx,
374 		const struct iovec *iov, loff_t file_offset,
375 		unsigned long nr_segs)
376 {
377 	ssize_t tot_bytes = 0;
378 	unsigned long seg = 0;
379 
380 	while ((seg < nr_segs) && (tot_bytes >= 0)) {
381 		ssize_t result;
382 		int page_count;
383 		struct page **pages;
384 		const struct iovec *vec = &iov[seg++];
385 		unsigned long user_addr = (unsigned long) vec->iov_base;
386 		size_t size = vec->iov_len;
387 
388                 page_count = nfs_get_user_pages(READ, user_addr, size, &pages);
389                 if (page_count < 0) {
390                         nfs_free_user_pages(pages, 0, 0);
391 			if (tot_bytes > 0)
392 				break;
393                         return page_count;
394                 }
395 
396 		result = nfs_direct_read_seg(inode, ctx, user_addr, size,
397 				file_offset, pages, page_count);
398 
399 		if (result <= 0) {
400 			if (tot_bytes > 0)
401 				break;
402 			return result;
403 		}
404 		tot_bytes += result;
405 		file_offset += result;
406 		if (result < size)
407 			break;
408 	}
409 
410 	return tot_bytes;
411 }
412 
413 /**
414  * nfs_direct_write_seg - Write out one iov segment.  Generate separate
415  *                        write RPCs for each "wsize" bytes, then commit.
416  * @inode: target inode
417  * @ctx: target file open context
418  * user_addr: starting address of this segment of user's buffer
419  * count: size of this segment
420  * file_offset: offset in file to begin the operation
421  * @pages: array of addresses of page structs defining user's buffer
422  * nr_pages: size of pages array
423  */
424 static ssize_t nfs_direct_write_seg(struct inode *inode,
425 		struct nfs_open_context *ctx, unsigned long user_addr,
426 		size_t count, loff_t file_offset, struct page **pages,
427 		int nr_pages)
428 {
429 	const unsigned int wsize = NFS_SERVER(inode)->wsize;
430 	size_t request;
431 	int curpage, need_commit;
432 	ssize_t result, tot_bytes;
433 	struct nfs_writeverf first_verf;
434 	struct nfs_write_data *wdata;
435 
436 	wdata = nfs_writedata_alloc();
437 	if (!wdata)
438 		return -ENOMEM;
439 
440 	wdata->inode = inode;
441 	wdata->cred = ctx->cred;
442 	wdata->args.fh = NFS_FH(inode);
443 	wdata->args.context = ctx;
444 	wdata->args.stable = NFS_UNSTABLE;
445 	if (IS_SYNC(inode) || NFS_PROTO(inode)->version == 2 || count <= wsize)
446 		wdata->args.stable = NFS_FILE_SYNC;
447 	wdata->res.fattr = &wdata->fattr;
448 	wdata->res.verf = &wdata->verf;
449 
450 	nfs_begin_data_update(inode);
451 retry:
452 	need_commit = 0;
453 	tot_bytes = 0;
454 	curpage = 0;
455 	request = count;
456 	wdata->args.pgbase = user_addr & ~PAGE_MASK;
457 	wdata->args.offset = file_offset;
458 	do {
459 		wdata->args.count = request;
460 		if (wdata->args.count > wsize)
461 			wdata->args.count = wsize;
462 		wdata->args.pages = &pages[curpage];
463 
464 		dprintk("NFS: direct write: c=%u o=%Ld ua=%lu, pb=%u, cp=%u\n",
465 			wdata->args.count, (long long) wdata->args.offset,
466 			user_addr + tot_bytes, wdata->args.pgbase, curpage);
467 
468 		lock_kernel();
469 		result = NFS_PROTO(inode)->write(wdata);
470 		unlock_kernel();
471 
472 		if (result <= 0) {
473 			if (tot_bytes > 0)
474 				break;
475 			goto out;
476 		}
477 
478 		if (tot_bytes == 0)
479 			memcpy(&first_verf.verifier, &wdata->verf.verifier,
480 						sizeof(first_verf.verifier));
481 		if (wdata->verf.committed != NFS_FILE_SYNC) {
482 			need_commit = 1;
483 			if (memcmp(&first_verf.verifier, &wdata->verf.verifier,
484 					sizeof(first_verf.verifier)));
485 				goto sync_retry;
486 		}
487 
488 		tot_bytes += result;
489 
490 		/* in case of a short write: stop now, let the app recover */
491 		if (result < wdata->args.count)
492 			break;
493 
494 		wdata->args.offset += result;
495 		wdata->args.pgbase += result;
496 		curpage += wdata->args.pgbase >> PAGE_SHIFT;
497 		wdata->args.pgbase &= ~PAGE_MASK;
498 		request -= result;
499 	} while (request != 0);
500 
501 	/*
502 	 * Commit data written so far, even in the event of an error
503 	 */
504 	if (need_commit) {
505 		wdata->args.count = tot_bytes;
506 		wdata->args.offset = file_offset;
507 
508 		lock_kernel();
509 		result = NFS_PROTO(inode)->commit(wdata);
510 		unlock_kernel();
511 
512 		if (result < 0 || memcmp(&first_verf.verifier,
513 					 &wdata->verf.verifier,
514 					 sizeof(first_verf.verifier)) != 0)
515 			goto sync_retry;
516 	}
517 	result = tot_bytes;
518 
519 out:
520 	nfs_end_data_update(inode);
521 	nfs_writedata_free(wdata);
522 	return result;
523 
524 sync_retry:
525 	wdata->args.stable = NFS_FILE_SYNC;
526 	goto retry;
527 }
528 
529 /**
530  * nfs_direct_write - For each iov segment, map the user's buffer
531  *                    then generate write and commit RPCs.
532  * @inode: target inode
533  * @ctx: target file open context
534  * @iov: array of vectors that define I/O buffer
535  * file_offset: offset in file to begin the operation
536  * nr_segs: size of iovec array
537  *
538  * Upon return, generic_file_direct_IO invalidates any cached pages
539  * that non-direct readers might access, so they will pick up these
540  * writes immediately.
541  */
542 static ssize_t nfs_direct_write(struct inode *inode,
543 		struct nfs_open_context *ctx, const struct iovec *iov,
544 		loff_t file_offset, unsigned long nr_segs)
545 {
546 	ssize_t tot_bytes = 0;
547 	unsigned long seg = 0;
548 
549 	while ((seg < nr_segs) && (tot_bytes >= 0)) {
550 		ssize_t result;
551 		int page_count;
552 		struct page **pages;
553 		const struct iovec *vec = &iov[seg++];
554 		unsigned long user_addr = (unsigned long) vec->iov_base;
555 		size_t size = vec->iov_len;
556 
557                 page_count = nfs_get_user_pages(WRITE, user_addr, size, &pages);
558                 if (page_count < 0) {
559                         nfs_free_user_pages(pages, 0, 0);
560 			if (tot_bytes > 0)
561 				break;
562                         return page_count;
563                 }
564 
565 		result = nfs_direct_write_seg(inode, ctx, user_addr, size,
566 				file_offset, pages, page_count);
567 		nfs_free_user_pages(pages, page_count, 0);
568 
569 		if (result <= 0) {
570 			if (tot_bytes > 0)
571 				break;
572 			return result;
573 		}
574 		tot_bytes += result;
575 		file_offset += result;
576 		if (result < size)
577 			break;
578 	}
579 	return tot_bytes;
580 }
581 
582 /**
583  * nfs_direct_IO - NFS address space operation for direct I/O
584  * rw: direction (read or write)
585  * @iocb: target I/O control block
586  * @iov: array of vectors that define I/O buffer
587  * file_offset: offset in file to begin the operation
588  * nr_segs: size of iovec array
589  *
590  */
591 ssize_t
592 nfs_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
593 		loff_t file_offset, unsigned long nr_segs)
594 {
595 	ssize_t result = -EINVAL;
596 	struct file *file = iocb->ki_filp;
597 	struct nfs_open_context *ctx;
598 	struct dentry *dentry = file->f_dentry;
599 	struct inode *inode = dentry->d_inode;
600 
601 	/*
602 	 * No support for async yet
603 	 */
604 	if (!is_sync_kiocb(iocb))
605 		return result;
606 
607 	ctx = (struct nfs_open_context *)file->private_data;
608 	switch (rw) {
609 	case READ:
610 		dprintk("NFS: direct_IO(read) (%s) off/no(%Lu/%lu)\n",
611 				dentry->d_name.name, file_offset, nr_segs);
612 
613 		result = nfs_direct_read(inode, ctx, iov,
614 						file_offset, nr_segs);
615 		break;
616 	case WRITE:
617 		dprintk("NFS: direct_IO(write) (%s) off/no(%Lu/%lu)\n",
618 				dentry->d_name.name, file_offset, nr_segs);
619 
620 		result = nfs_direct_write(inode, ctx, iov,
621 						file_offset, nr_segs);
622 		break;
623 	default:
624 		break;
625 	}
626 	return result;
627 }
628 
629 /**
630  * nfs_file_direct_read - file direct read operation for NFS files
631  * @iocb: target I/O control block
632  * @buf: user's buffer into which to read data
633  * count: number of bytes to read
634  * pos: byte offset in file where reading starts
635  *
636  * We use this function for direct reads instead of calling
637  * generic_file_aio_read() in order to avoid gfar's check to see if
638  * the request starts before the end of the file.  For that check
639  * to work, we must generate a GETATTR before each direct read, and
640  * even then there is a window between the GETATTR and the subsequent
641  * READ where the file size could change.  So our preference is simply
642  * to do all reads the application wants, and the server will take
643  * care of managing the end of file boundary.
644  *
645  * This function also eliminates unnecessarily updating the file's
646  * atime locally, as the NFS server sets the file's atime, and this
647  * client must read the updated atime from the server back into its
648  * cache.
649  */
650 ssize_t
651 nfs_file_direct_read(struct kiocb *iocb, char __user *buf, size_t count, loff_t pos)
652 {
653 	ssize_t retval = -EINVAL;
654 	loff_t *ppos = &iocb->ki_pos;
655 	struct file *file = iocb->ki_filp;
656 	struct nfs_open_context *ctx =
657 			(struct nfs_open_context *) file->private_data;
658 	struct address_space *mapping = file->f_mapping;
659 	struct inode *inode = mapping->host;
660 	struct iovec iov = {
661 		.iov_base = buf,
662 		.iov_len = count,
663 	};
664 
665 	dprintk("nfs: direct read(%s/%s, %lu@%lu)\n",
666 		file->f_dentry->d_parent->d_name.name,
667 		file->f_dentry->d_name.name,
668 		(unsigned long) count, (unsigned long) pos);
669 
670 	if (!is_sync_kiocb(iocb))
671 		goto out;
672 	if (count < 0)
673 		goto out;
674 	retval = -EFAULT;
675 	if (!access_ok(VERIFY_WRITE, iov.iov_base, iov.iov_len))
676 		goto out;
677 	retval = 0;
678 	if (!count)
679 		goto out;
680 
681 	if (mapping->nrpages) {
682 		retval = filemap_fdatawrite(mapping);
683 		if (retval == 0)
684 			retval = nfs_wb_all(inode);
685 		if (retval == 0)
686 			retval = filemap_fdatawait(mapping);
687 		if (retval)
688 			goto out;
689 	}
690 
691 	retval = nfs_direct_read(inode, ctx, &iov, pos, 1);
692 	if (retval > 0)
693 		*ppos = pos + retval;
694 
695 out:
696 	return retval;
697 }
698 
699 /**
700  * nfs_file_direct_write - file direct write operation for NFS files
701  * @iocb: target I/O control block
702  * @buf: user's buffer from which to write data
703  * count: number of bytes to write
704  * pos: byte offset in file where writing starts
705  *
706  * We use this function for direct writes instead of calling
707  * generic_file_aio_write() in order to avoid taking the inode
708  * semaphore and updating the i_size.  The NFS server will set
709  * the new i_size and this client must read the updated size
710  * back into its cache.  We let the server do generic write
711  * parameter checking and report problems.
712  *
713  * We also avoid an unnecessary invocation of generic_osync_inode(),
714  * as it is fairly meaningless to sync the metadata of an NFS file.
715  *
716  * We eliminate local atime updates, see direct read above.
717  *
718  * We avoid unnecessary page cache invalidations for normal cached
719  * readers of this file.
720  *
721  * Note that O_APPEND is not supported for NFS direct writes, as there
722  * is no atomic O_APPEND write facility in the NFS protocol.
723  */
724 ssize_t
725 nfs_file_direct_write(struct kiocb *iocb, const char __user *buf, size_t count, loff_t pos)
726 {
727 	ssize_t retval = -EINVAL;
728 	loff_t *ppos = &iocb->ki_pos;
729 	unsigned long limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
730 	struct file *file = iocb->ki_filp;
731 	struct nfs_open_context *ctx =
732 			(struct nfs_open_context *) file->private_data;
733 	struct address_space *mapping = file->f_mapping;
734 	struct inode *inode = mapping->host;
735 	struct iovec iov = {
736 		.iov_base = (char __user *)buf,
737 		.iov_len = count,
738 	};
739 
740 	dfprintk(VFS, "nfs: direct write(%s/%s(%ld), %lu@%lu)\n",
741 		file->f_dentry->d_parent->d_name.name,
742 		file->f_dentry->d_name.name, inode->i_ino,
743 		(unsigned long) count, (unsigned long) pos);
744 
745 	if (!is_sync_kiocb(iocb))
746 		goto out;
747 	if (count < 0)
748 		goto out;
749         if (pos < 0)
750 		goto out;
751 	retval = -EFAULT;
752 	if (!access_ok(VERIFY_READ, iov.iov_base, iov.iov_len))
753 		goto out;
754 	retval = -EFBIG;
755 	if (limit != RLIM_INFINITY) {
756 		if (pos >= limit) {
757 			send_sig(SIGXFSZ, current, 0);
758 			goto out;
759 		}
760 		if (count > limit - (unsigned long) pos)
761 			count = limit - (unsigned long) pos;
762 	}
763 	retval = 0;
764 	if (!count)
765 		goto out;
766 
767 	if (mapping->nrpages) {
768 		retval = filemap_fdatawrite(mapping);
769 		if (retval == 0)
770 			retval = nfs_wb_all(inode);
771 		if (retval == 0)
772 			retval = filemap_fdatawait(mapping);
773 		if (retval)
774 			goto out;
775 	}
776 
777 	retval = nfs_direct_write(inode, ctx, &iov, pos, 1);
778 	if (mapping->nrpages)
779 		invalidate_inode_pages2(mapping);
780 	if (retval > 0)
781 		*ppos = pos + retval;
782 
783 out:
784 	return retval;
785 }
786 
787 int nfs_init_directcache(void)
788 {
789 	nfs_direct_cachep = kmem_cache_create("nfs_direct_cache",
790 						sizeof(struct nfs_direct_req),
791 						0, SLAB_RECLAIM_ACCOUNT,
792 						NULL, NULL);
793 	if (nfs_direct_cachep == NULL)
794 		return -ENOMEM;
795 
796 	return 0;
797 }
798 
799 void nfs_destroy_directcache(void)
800 {
801 	if (kmem_cache_destroy(nfs_direct_cachep))
802 		printk(KERN_INFO "nfs_direct_cache: not all structures were freed\n");
803 }
804