2 * linux/fs/nfs/direct.c
4 * Copyright (C) 2003 by Chuck Lever <cel@netapp.com>
6 * High-performance uncached I/O for the Linux NFS client
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.
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
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.
29 * Designed by Jeff Kimmel, Chuck Lever, and Trond Myklebust, with
30 * help from Andrew Morton.
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 * 04 May 2005 support O_DIRECT with aio --cel
41 #include <linux/errno.h>
42 #include <linux/sched.h>
43 #include <linux/kernel.h>
44 #include <linux/file.h>
45 #include <linux/pagemap.h>
46 #include <linux/kref.h>
48 #include <linux/nfs_fs.h>
49 #include <linux/nfs_page.h>
50 #include <linux/sunrpc/clnt.h>
52 #include <asm/system.h>
53 #include <asm/uaccess.h>
54 #include <asm/atomic.h>
59 #define NFSDBG_FACILITY NFSDBG_VFS
61 static struct kmem_cache *nfs_direct_cachep;
64 * This represents a set of asynchronous requests that we're waiting on
66 struct nfs_direct_req {
67 struct kref kref; /* release manager */
70 struct nfs_open_context *ctx; /* file open context info */
71 struct kiocb * iocb; /* controlling i/o request */
72 struct inode * inode; /* target file of i/o */
74 /* completion state */
75 atomic_t io_count; /* i/os we're waiting for */
76 spinlock_t lock; /* protect completion state */
77 ssize_t count, /* bytes actually processed */
78 error; /* any reported error */
79 struct completion completion; /* wait for i/o completion */
82 struct list_head rewrite_list; /* saved nfs_write_data structs */
83 struct nfs_write_data * commit_data; /* special write_data for commits */
85 #define NFS_ODIRECT_DO_COMMIT (1) /* an unstable reply was received */
86 #define NFS_ODIRECT_RESCHED_WRITES (2) /* write verification failed */
87 struct nfs_writeverf verf; /* unstable write verifier */
90 static void nfs_direct_write_complete(struct nfs_direct_req *dreq, struct inode *inode);
91 static const struct rpc_call_ops nfs_write_direct_ops;
93 static inline void get_dreq(struct nfs_direct_req *dreq)
95 atomic_inc(&dreq->io_count);
98 static inline int put_dreq(struct nfs_direct_req *dreq)
100 return atomic_dec_and_test(&dreq->io_count);
104 * nfs_direct_IO - NFS address space operation for direct I/O
105 * @rw: direction (read or write)
106 * @iocb: target I/O control block
107 * @iov: array of vectors that define I/O buffer
108 * @pos: offset in file to begin the operation
109 * @nr_segs: size of iovec array
111 * The presence of this routine in the address space ops vector means
112 * the NFS client supports direct I/O. However, we shunt off direct
113 * read and write requests before the VFS gets them, so this method
114 * should never be called.
116 ssize_t nfs_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov, loff_t pos, unsigned long nr_segs)
118 dprintk("NFS: nfs_direct_IO (%s) off/no(%Ld/%lu) EINVAL\n",
119 iocb->ki_filp->f_path.dentry->d_name.name,
120 (long long) pos, nr_segs);
125 static void nfs_direct_dirty_pages(struct page **pages, unsigned int pgbase, size_t count)
132 pages += (pgbase >> PAGE_SHIFT);
133 npages = (count + (pgbase & ~PAGE_MASK) + PAGE_SIZE - 1) >> PAGE_SHIFT;
134 for (i = 0; i < npages; i++) {
135 struct page *page = pages[i];
136 if (!PageCompound(page))
137 set_page_dirty(page);
141 static void nfs_direct_release_pages(struct page **pages, unsigned int npages)
144 for (i = 0; i < npages; i++)
145 page_cache_release(pages[i]);
148 static inline struct nfs_direct_req *nfs_direct_req_alloc(void)
150 struct nfs_direct_req *dreq;
152 dreq = kmem_cache_alloc(nfs_direct_cachep, GFP_KERNEL);
156 kref_init(&dreq->kref);
157 kref_get(&dreq->kref);
158 init_completion(&dreq->completion);
159 INIT_LIST_HEAD(&dreq->rewrite_list);
162 spin_lock_init(&dreq->lock);
163 atomic_set(&dreq->io_count, 0);
171 static void nfs_direct_req_free(struct kref *kref)
173 struct nfs_direct_req *dreq = container_of(kref, struct nfs_direct_req, kref);
175 if (dreq->ctx != NULL)
176 put_nfs_open_context(dreq->ctx);
177 kmem_cache_free(nfs_direct_cachep, dreq);
180 static void nfs_direct_req_release(struct nfs_direct_req *dreq)
182 kref_put(&dreq->kref, nfs_direct_req_free);
186 * Collects and returns the final error value/byte-count.
188 static ssize_t nfs_direct_wait(struct nfs_direct_req *dreq)
190 ssize_t result = -EIOCBQUEUED;
192 /* Async requests don't wait here */
196 result = wait_for_completion_killable(&dreq->completion);
199 result = dreq->error;
201 result = dreq->count;
204 return (ssize_t) result;
208 * Synchronous I/O uses a stack-allocated iocb. Thus we can't trust
209 * the iocb is still valid here if this is a synchronous request.
211 static void nfs_direct_complete(struct nfs_direct_req *dreq)
214 long res = (long) dreq->error;
216 res = (long) dreq->count;
217 aio_complete(dreq->iocb, res, 0);
219 complete_all(&dreq->completion);
221 nfs_direct_req_release(dreq);
225 * We must hold a reference to all the pages in this direct read request
226 * until the RPCs complete. This could be long *after* we are woken up in
227 * nfs_direct_wait (for instance, if someone hits ^C on a slow server).
229 static void nfs_direct_read_result(struct rpc_task *task, void *calldata)
231 struct nfs_read_data *data = calldata;
232 struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;
234 if (nfs_readpage_result(task, data) != 0)
237 spin_lock(&dreq->lock);
238 if (unlikely(task->tk_status < 0)) {
239 dreq->error = task->tk_status;
240 spin_unlock(&dreq->lock);
242 dreq->count += data->res.count;
243 spin_unlock(&dreq->lock);
244 nfs_direct_dirty_pages(data->pagevec,
248 nfs_direct_release_pages(data->pagevec, data->npages);
251 nfs_direct_complete(dreq);
254 static const struct rpc_call_ops nfs_read_direct_ops = {
255 .rpc_call_done = nfs_direct_read_result,
256 .rpc_release = nfs_readdata_release,
260 * For each rsize'd chunk of the user's buffer, dispatch an NFS READ
261 * operation. If nfs_readdata_alloc() or get_user_pages() fails,
262 * bail and stop sending more reads. Read length accounting is
263 * handled automatically by nfs_direct_read_result(). Otherwise, if
264 * no requests have been sent, just return an error.
266 static ssize_t nfs_direct_read_schedule_segment(struct nfs_direct_req *dreq,
267 const struct iovec *iov,
270 struct nfs_open_context *ctx = dreq->ctx;
271 struct inode *inode = ctx->path.dentry->d_inode;
272 unsigned long user_addr = (unsigned long)iov->iov_base;
273 size_t count = iov->iov_len;
274 size_t rsize = NFS_SERVER(inode)->rsize;
280 struct nfs_read_data *data;
283 pgbase = user_addr & ~PAGE_MASK;
284 bytes = min(rsize,count);
287 data = nfs_readdata_alloc(nfs_page_array_len(pgbase, bytes));
291 down_read(¤t->mm->mmap_sem);
292 result = get_user_pages(current, current->mm, user_addr,
293 data->npages, 1, 0, data->pagevec, NULL);
294 up_read(¤t->mm->mmap_sem);
296 nfs_readdata_release(data);
299 if ((unsigned)result < data->npages) {
300 bytes = result * PAGE_SIZE;
301 if (bytes <= pgbase) {
302 nfs_direct_release_pages(data->pagevec, result);
303 nfs_readdata_release(data);
307 data->npages = result;
312 data->req = (struct nfs_page *) dreq;
314 data->cred = ctx->cred;
315 data->args.fh = NFS_FH(inode);
316 data->args.context = ctx;
317 data->args.offset = pos;
318 data->args.pgbase = pgbase;
319 data->args.pages = data->pagevec;
320 data->args.count = bytes;
321 data->res.fattr = &data->fattr;
323 data->res.count = bytes;
325 rpc_init_task(&data->task, NFS_CLIENT(inode), RPC_TASK_ASYNC,
326 &nfs_read_direct_ops, data);
327 NFS_PROTO(inode)->read_setup(data);
329 data->task.tk_cookie = (unsigned long) inode;
331 rpc_execute(&data->task);
333 dprintk("NFS: %5u initiated direct read call "
334 "(req %s/%Ld, %zu bytes @ offset %Lu)\n",
337 (long long)NFS_FILEID(inode),
339 (unsigned long long)data->args.offset);
344 /* FIXME: Remove this unnecessary math from final patch */
346 pgbase &= ~PAGE_MASK;
347 BUG_ON(pgbase != (user_addr & ~PAGE_MASK));
350 } while (count != 0);
354 return result < 0 ? (ssize_t) result : -EFAULT;
357 static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
358 const struct iovec *iov,
359 unsigned long nr_segs,
362 ssize_t result = -EINVAL;
363 size_t requested_bytes = 0;
368 for (seg = 0; seg < nr_segs; seg++) {
369 const struct iovec *vec = &iov[seg];
370 result = nfs_direct_read_schedule_segment(dreq, vec, pos);
373 requested_bytes += result;
374 if ((size_t)result < vec->iov_len)
380 nfs_direct_complete(dreq);
382 if (requested_bytes != 0)
390 static ssize_t nfs_direct_read(struct kiocb *iocb, const struct iovec *iov,
391 unsigned long nr_segs, loff_t pos)
394 struct inode *inode = iocb->ki_filp->f_mapping->host;
395 struct nfs_direct_req *dreq;
397 dreq = nfs_direct_req_alloc();
402 dreq->ctx = get_nfs_open_context(nfs_file_open_context(iocb->ki_filp));
403 if (!is_sync_kiocb(iocb))
406 result = nfs_direct_read_schedule_iovec(dreq, iov, nr_segs, pos);
408 result = nfs_direct_wait(dreq);
409 nfs_direct_req_release(dreq);
414 static void nfs_direct_free_writedata(struct nfs_direct_req *dreq)
416 while (!list_empty(&dreq->rewrite_list)) {
417 struct nfs_write_data *data = list_entry(dreq->rewrite_list.next, struct nfs_write_data, pages);
418 list_del(&data->pages);
419 nfs_direct_release_pages(data->pagevec, data->npages);
420 nfs_writedata_release(data);
424 #if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
425 static void nfs_direct_write_reschedule(struct nfs_direct_req *dreq)
427 struct inode *inode = dreq->inode;
429 struct nfs_write_data *data;
434 list_for_each(p, &dreq->rewrite_list) {
435 data = list_entry(p, struct nfs_write_data, pages);
442 nfs_fattr_init(&data->fattr);
443 data->res.count = data->args.count;
444 memset(&data->verf, 0, sizeof(data->verf));
447 * Reuse data->task; data->args should not have changed
448 * since the original request was sent.
450 rpc_init_task(&data->task, NFS_CLIENT(inode), RPC_TASK_ASYNC,
451 &nfs_write_direct_ops, data);
452 NFS_PROTO(inode)->write_setup(data, FLUSH_STABLE);
454 data->task.tk_priority = RPC_PRIORITY_NORMAL;
455 data->task.tk_cookie = (unsigned long) inode;
458 * We're called via an RPC callback, so BKL is already held.
460 rpc_execute(&data->task);
462 dprintk("NFS: %5u rescheduled direct write call (req %s/%Ld, %u bytes @ offset %Lu)\n",
465 (long long)NFS_FILEID(inode),
467 (unsigned long long)data->args.offset);
471 nfs_direct_write_complete(dreq, inode);
474 static void nfs_direct_commit_result(struct rpc_task *task, void *calldata)
476 struct nfs_write_data *data = calldata;
477 struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;
479 /* Call the NFS version-specific code */
480 if (NFS_PROTO(data->inode)->commit_done(task, data) != 0)
482 if (unlikely(task->tk_status < 0)) {
483 dprintk("NFS: %5u commit failed with error %d.\n",
484 task->tk_pid, task->tk_status);
485 dreq->flags = NFS_ODIRECT_RESCHED_WRITES;
486 } else if (memcmp(&dreq->verf, &data->verf, sizeof(data->verf))) {
487 dprintk("NFS: %5u commit verify failed\n", task->tk_pid);
488 dreq->flags = NFS_ODIRECT_RESCHED_WRITES;
491 dprintk("NFS: %5u commit returned %d\n", task->tk_pid, task->tk_status);
492 nfs_direct_write_complete(dreq, data->inode);
495 static const struct rpc_call_ops nfs_commit_direct_ops = {
496 .rpc_call_done = nfs_direct_commit_result,
497 .rpc_release = nfs_commit_release,
500 static void nfs_direct_commit_schedule(struct nfs_direct_req *dreq)
502 struct nfs_write_data *data = dreq->commit_data;
504 data->inode = dreq->inode;
505 data->cred = dreq->ctx->cred;
507 data->args.fh = NFS_FH(data->inode);
508 data->args.offset = 0;
509 data->args.count = 0;
511 data->res.fattr = &data->fattr;
512 data->res.verf = &data->verf;
514 rpc_init_task(&data->task, NFS_CLIENT(dreq->inode), RPC_TASK_ASYNC,
515 &nfs_commit_direct_ops, data);
516 NFS_PROTO(data->inode)->commit_setup(data, 0);
518 data->task.tk_priority = RPC_PRIORITY_NORMAL;
519 data->task.tk_cookie = (unsigned long)data->inode;
520 /* Note: task.tk_ops->rpc_release will free dreq->commit_data */
521 dreq->commit_data = NULL;
523 dprintk("NFS: %5u initiated commit call\n", data->task.tk_pid);
525 rpc_execute(&data->task);
528 static void nfs_direct_write_complete(struct nfs_direct_req *dreq, struct inode *inode)
530 int flags = dreq->flags;
534 case NFS_ODIRECT_DO_COMMIT:
535 nfs_direct_commit_schedule(dreq);
537 case NFS_ODIRECT_RESCHED_WRITES:
538 nfs_direct_write_reschedule(dreq);
541 if (dreq->commit_data != NULL)
542 nfs_commit_free(dreq->commit_data);
543 nfs_direct_free_writedata(dreq);
544 nfs_zap_mapping(inode, inode->i_mapping);
545 nfs_direct_complete(dreq);
549 static void nfs_alloc_commit_data(struct nfs_direct_req *dreq)
551 dreq->commit_data = nfs_commit_alloc();
552 if (dreq->commit_data != NULL)
553 dreq->commit_data->req = (struct nfs_page *) dreq;
556 static inline void nfs_alloc_commit_data(struct nfs_direct_req *dreq)
558 dreq->commit_data = NULL;
561 static void nfs_direct_write_complete(struct nfs_direct_req *dreq, struct inode *inode)
563 nfs_direct_free_writedata(dreq);
564 nfs_zap_mapping(inode, inode->i_mapping);
565 nfs_direct_complete(dreq);
569 static void nfs_direct_write_result(struct rpc_task *task, void *calldata)
571 struct nfs_write_data *data = calldata;
572 struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;
573 int status = task->tk_status;
575 if (nfs_writeback_done(task, data) != 0)
578 spin_lock(&dreq->lock);
580 if (unlikely(status < 0)) {
581 /* An error has occurred, so we should not commit */
583 dreq->error = status;
585 if (unlikely(dreq->error != 0))
588 dreq->count += data->res.count;
590 if (data->res.verf->committed != NFS_FILE_SYNC) {
591 switch (dreq->flags) {
593 memcpy(&dreq->verf, &data->verf, sizeof(dreq->verf));
594 dreq->flags = NFS_ODIRECT_DO_COMMIT;
596 case NFS_ODIRECT_DO_COMMIT:
597 if (memcmp(&dreq->verf, &data->verf, sizeof(dreq->verf))) {
598 dprintk("NFS: %5u write verify failed\n", task->tk_pid);
599 dreq->flags = NFS_ODIRECT_RESCHED_WRITES;
604 spin_unlock(&dreq->lock);
608 * NB: Return the value of the first error return code. Subsequent
609 * errors after the first one are ignored.
611 static void nfs_direct_write_release(void *calldata)
613 struct nfs_write_data *data = calldata;
614 struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;
617 nfs_direct_write_complete(dreq, data->inode);
620 static const struct rpc_call_ops nfs_write_direct_ops = {
621 .rpc_call_done = nfs_direct_write_result,
622 .rpc_release = nfs_direct_write_release,
626 * For each wsize'd chunk of the user's buffer, dispatch an NFS WRITE
627 * operation. If nfs_writedata_alloc() or get_user_pages() fails,
628 * bail and stop sending more writes. Write length accounting is
629 * handled automatically by nfs_direct_write_result(). Otherwise, if
630 * no requests have been sent, just return an error.
632 static ssize_t nfs_direct_write_schedule_segment(struct nfs_direct_req *dreq,
633 const struct iovec *iov,
634 loff_t pos, int sync)
636 struct nfs_open_context *ctx = dreq->ctx;
637 struct inode *inode = ctx->path.dentry->d_inode;
638 unsigned long user_addr = (unsigned long)iov->iov_base;
639 size_t count = iov->iov_len;
640 size_t wsize = NFS_SERVER(inode)->wsize;
646 struct nfs_write_data *data;
649 pgbase = user_addr & ~PAGE_MASK;
650 bytes = min(wsize,count);
653 data = nfs_writedata_alloc(nfs_page_array_len(pgbase, bytes));
657 down_read(¤t->mm->mmap_sem);
658 result = get_user_pages(current, current->mm, user_addr,
659 data->npages, 0, 0, data->pagevec, NULL);
660 up_read(¤t->mm->mmap_sem);
662 nfs_writedata_release(data);
665 if ((unsigned)result < data->npages) {
666 bytes = result * PAGE_SIZE;
667 if (bytes <= pgbase) {
668 nfs_direct_release_pages(data->pagevec, result);
669 nfs_writedata_release(data);
673 data->npages = result;
678 list_move_tail(&data->pages, &dreq->rewrite_list);
680 data->req = (struct nfs_page *) dreq;
682 data->cred = ctx->cred;
683 data->args.fh = NFS_FH(inode);
684 data->args.context = ctx;
685 data->args.offset = pos;
686 data->args.pgbase = pgbase;
687 data->args.pages = data->pagevec;
688 data->args.count = bytes;
689 data->res.fattr = &data->fattr;
690 data->res.count = bytes;
691 data->res.verf = &data->verf;
693 rpc_init_task(&data->task, NFS_CLIENT(inode), RPC_TASK_ASYNC,
694 &nfs_write_direct_ops, data);
695 NFS_PROTO(inode)->write_setup(data, sync);
697 data->task.tk_priority = RPC_PRIORITY_NORMAL;
698 data->task.tk_cookie = (unsigned long) inode;
700 rpc_execute(&data->task);
702 dprintk("NFS: %5u initiated direct write call "
703 "(req %s/%Ld, %zu bytes @ offset %Lu)\n",
706 (long long)NFS_FILEID(inode),
708 (unsigned long long)data->args.offset);
714 /* FIXME: Remove this useless math from the final patch */
716 pgbase &= ~PAGE_MASK;
717 BUG_ON(pgbase != (user_addr & ~PAGE_MASK));
720 } while (count != 0);
724 return result < 0 ? (ssize_t) result : -EFAULT;
727 static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
728 const struct iovec *iov,
729 unsigned long nr_segs,
730 loff_t pos, int sync)
733 size_t requested_bytes = 0;
738 for (seg = 0; seg < nr_segs; seg++) {
739 const struct iovec *vec = &iov[seg];
740 result = nfs_direct_write_schedule_segment(dreq, vec,
744 requested_bytes += result;
745 if ((size_t)result < vec->iov_len)
751 nfs_direct_write_complete(dreq, dreq->inode);
753 if (requested_bytes != 0)
761 static ssize_t nfs_direct_write(struct kiocb *iocb, const struct iovec *iov,
762 unsigned long nr_segs, loff_t pos,
766 struct inode *inode = iocb->ki_filp->f_mapping->host;
767 struct nfs_direct_req *dreq;
768 size_t wsize = NFS_SERVER(inode)->wsize;
771 dreq = nfs_direct_req_alloc();
774 nfs_alloc_commit_data(dreq);
776 if (dreq->commit_data == NULL || count < wsize)
780 dreq->ctx = get_nfs_open_context(nfs_file_open_context(iocb->ki_filp));
781 if (!is_sync_kiocb(iocb))
784 result = nfs_direct_write_schedule_iovec(dreq, iov, nr_segs, pos, sync);
786 result = nfs_direct_wait(dreq);
787 nfs_direct_req_release(dreq);
793 * nfs_file_direct_read - file direct read operation for NFS files
794 * @iocb: target I/O control block
795 * @iov: vector of user buffers into which to read data
796 * @nr_segs: size of iov vector
797 * @pos: byte offset in file where reading starts
799 * We use this function for direct reads instead of calling
800 * generic_file_aio_read() in order to avoid gfar's check to see if
801 * the request starts before the end of the file. For that check
802 * to work, we must generate a GETATTR before each direct read, and
803 * even then there is a window between the GETATTR and the subsequent
804 * READ where the file size could change. Our preference is simply
805 * to do all reads the application wants, and the server will take
806 * care of managing the end of file boundary.
808 * This function also eliminates unnecessarily updating the file's
809 * atime locally, as the NFS server sets the file's atime, and this
810 * client must read the updated atime from the server back into its
813 ssize_t nfs_file_direct_read(struct kiocb *iocb, const struct iovec *iov,
814 unsigned long nr_segs, loff_t pos)
816 ssize_t retval = -EINVAL;
817 struct file *file = iocb->ki_filp;
818 struct address_space *mapping = file->f_mapping;
821 count = iov_length(iov, nr_segs);
822 nfs_add_stats(mapping->host, NFSIOS_DIRECTREADBYTES, count);
824 dprintk("nfs: direct read(%s/%s, %zd@%Ld)\n",
825 file->f_path.dentry->d_parent->d_name.name,
826 file->f_path.dentry->d_name.name,
827 count, (long long) pos);
833 retval = nfs_sync_mapping(mapping);
837 retval = nfs_direct_read(iocb, iov, nr_segs, pos);
839 iocb->ki_pos = pos + retval;
846 * nfs_file_direct_write - file direct write operation for NFS files
847 * @iocb: target I/O control block
848 * @iov: vector of user buffers from which to write data
849 * @nr_segs: size of iov vector
850 * @pos: byte offset in file where writing starts
852 * We use this function for direct writes instead of calling
853 * generic_file_aio_write() in order to avoid taking the inode
854 * semaphore and updating the i_size. The NFS server will set
855 * the new i_size and this client must read the updated size
856 * back into its cache. We let the server do generic write
857 * parameter checking and report problems.
859 * We also avoid an unnecessary invocation of generic_osync_inode(),
860 * as it is fairly meaningless to sync the metadata of an NFS file.
862 * We eliminate local atime updates, see direct read above.
864 * We avoid unnecessary page cache invalidations for normal cached
865 * readers of this file.
867 * Note that O_APPEND is not supported for NFS direct writes, as there
868 * is no atomic O_APPEND write facility in the NFS protocol.
870 ssize_t nfs_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
871 unsigned long nr_segs, loff_t pos)
873 ssize_t retval = -EINVAL;
874 struct file *file = iocb->ki_filp;
875 struct address_space *mapping = file->f_mapping;
878 count = iov_length(iov, nr_segs);
879 nfs_add_stats(mapping->host, NFSIOS_DIRECTWRITTENBYTES, count);
881 dfprintk(VFS, "nfs: direct write(%s/%s, %zd@%Ld)\n",
882 file->f_path.dentry->d_parent->d_name.name,
883 file->f_path.dentry->d_name.name,
884 count, (long long) pos);
886 retval = generic_write_checks(file, &pos, &count, 0);
890 goto out; /* return 0 */
893 if ((ssize_t) count < 0)
899 retval = nfs_sync_mapping(mapping);
903 retval = nfs_direct_write(iocb, iov, nr_segs, pos, count);
906 iocb->ki_pos = pos + retval;
913 * nfs_init_directcache - create a slab cache for nfs_direct_req structures
916 int __init nfs_init_directcache(void)
918 nfs_direct_cachep = kmem_cache_create("nfs_direct_cache",
919 sizeof(struct nfs_direct_req),
920 0, (SLAB_RECLAIM_ACCOUNT|
923 if (nfs_direct_cachep == NULL)
930 * nfs_destroy_directcache - destroy the slab cache for nfs_direct_req structures
933 void nfs_destroy_directcache(void)
935 kmem_cache_destroy(nfs_direct_cachep);