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/config.h>
42 #include <linux/errno.h>
43 #include <linux/sched.h>
44 #include <linux/kernel.h>
45 #include <linux/smp_lock.h>
46 #include <linux/file.h>
47 #include <linux/pagemap.h>
48 #include <linux/kref.h>
50 #include <linux/nfs_fs.h>
51 #include <linux/nfs_page.h>
52 #include <linux/sunrpc/clnt.h>
54 #include <asm/system.h>
55 #include <asm/uaccess.h>
56 #include <asm/atomic.h>
60 #define NFSDBG_FACILITY NFSDBG_VFS
62 static kmem_cache_t *nfs_direct_cachep;
65 * This represents a set of asynchronous requests that we're waiting on
67 struct nfs_direct_req {
68 struct kref kref; /* release manager */
71 struct list_head list, /* nfs_read/write_data structs */
72 rewrite_list; /* saved nfs_write_data structs */
73 struct nfs_open_context *ctx; /* file open context info */
74 struct kiocb * iocb; /* controlling i/o request */
75 struct inode * inode; /* target file of i/o */
76 struct page ** pages; /* pages in our buffer */
77 unsigned int npages; /* count of pages */
79 /* completion state */
80 atomic_t io_count; /* i/os we're waiting for */
81 spinlock_t lock; /* protect completion state */
82 ssize_t count, /* bytes actually processed */
83 error; /* any reported error */
84 struct completion completion; /* wait for i/o completion */
87 struct nfs_write_data * commit_data; /* special write_data for commits */
89 #define NFS_ODIRECT_DO_COMMIT (1) /* an unstable reply was received */
90 #define NFS_ODIRECT_RESCHED_WRITES (2) /* write verification failed */
91 struct nfs_writeverf verf; /* unstable write verifier */
94 static void nfs_direct_write_complete(struct nfs_direct_req *dreq, struct inode *inode);
95 static const struct rpc_call_ops nfs_write_direct_ops;
97 static inline void get_dreq(struct nfs_direct_req *dreq)
99 atomic_inc(&dreq->io_count);
102 static inline int put_dreq(struct nfs_direct_req *dreq)
104 return atomic_dec_and_test(&dreq->io_count);
108 * nfs_direct_IO - NFS address space operation for direct I/O
109 * @rw: direction (read or write)
110 * @iocb: target I/O control block
111 * @iov: array of vectors that define I/O buffer
112 * @pos: offset in file to begin the operation
113 * @nr_segs: size of iovec array
115 * The presence of this routine in the address space ops vector means
116 * the NFS client supports direct I/O. However, we shunt off direct
117 * read and write requests before the VFS gets them, so this method
118 * should never be called.
120 ssize_t nfs_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov, loff_t pos, unsigned long nr_segs)
122 dprintk("NFS: nfs_direct_IO (%s) off/no(%Ld/%lu) EINVAL\n",
123 iocb->ki_filp->f_dentry->d_name.name,
124 (long long) pos, nr_segs);
129 static void nfs_direct_dirty_pages(struct page **pages, int npages)
132 for (i = 0; i < npages; i++) {
133 struct page *page = pages[i];
134 if (!PageCompound(page))
135 set_page_dirty_lock(page);
139 static void nfs_direct_release_pages(struct page **pages, int npages)
142 for (i = 0; i < npages; i++)
143 page_cache_release(pages[i]);
146 static inline int nfs_get_user_pages(int rw, unsigned long user_addr, size_t size, struct page ***pages)
148 int result = -ENOMEM;
149 unsigned long page_count;
152 page_count = (user_addr + size + PAGE_SIZE - 1) >> PAGE_SHIFT;
153 page_count -= user_addr >> PAGE_SHIFT;
155 array_size = (page_count * sizeof(struct page *));
156 *pages = kmalloc(array_size, GFP_KERNEL);
158 down_read(¤t->mm->mmap_sem);
159 result = get_user_pages(current, current->mm, user_addr,
160 page_count, (rw == READ), 0,
162 up_read(¤t->mm->mmap_sem);
163 if (result != page_count) {
165 * If we got fewer pages than expected from
166 * get_user_pages(), the user buffer runs off the
167 * end of a mapping; return EFAULT.
170 nfs_direct_release_pages(*pages, result);
180 static inline struct nfs_direct_req *nfs_direct_req_alloc(void)
182 struct nfs_direct_req *dreq;
184 dreq = kmem_cache_alloc(nfs_direct_cachep, SLAB_KERNEL);
188 kref_init(&dreq->kref);
189 init_completion(&dreq->completion);
190 INIT_LIST_HEAD(&dreq->list);
191 INIT_LIST_HEAD(&dreq->rewrite_list);
194 spin_lock_init(&dreq->lock);
195 atomic_set(&dreq->io_count, 0);
203 static void nfs_direct_req_release(struct kref *kref)
205 struct nfs_direct_req *dreq = container_of(kref, struct nfs_direct_req, kref);
207 if (dreq->ctx != NULL)
208 put_nfs_open_context(dreq->ctx);
209 kmem_cache_free(nfs_direct_cachep, dreq);
213 * Collects and returns the final error value/byte-count.
215 static ssize_t nfs_direct_wait(struct nfs_direct_req *dreq)
217 ssize_t result = -EIOCBQUEUED;
219 /* Async requests don't wait here */
223 result = wait_for_completion_interruptible(&dreq->completion);
226 result = dreq->error;
228 result = dreq->count;
231 kref_put(&dreq->kref, nfs_direct_req_release);
232 return (ssize_t) result;
236 * We must hold a reference to all the pages in this direct read request
237 * until the RPCs complete. This could be long *after* we are woken up in
238 * nfs_direct_wait (for instance, if someone hits ^C on a slow server).
240 * In addition, synchronous I/O uses a stack-allocated iocb. Thus we
241 * can't trust the iocb is still valid here if this is a synchronous
242 * request. If the waiter is woken prematurely, the iocb is long gone.
244 static void nfs_direct_complete(struct nfs_direct_req *dreq)
247 long res = (long) dreq->error;
249 res = (long) dreq->count;
250 aio_complete(dreq->iocb, res, 0);
252 complete_all(&dreq->completion);
254 kref_put(&dreq->kref, nfs_direct_req_release);
258 * Note we also set the number of requests we have in the dreq when we are
259 * done. This prevents races with I/O completion so we will always wait
260 * until all requests have been dispatched and completed.
262 static struct nfs_direct_req *nfs_direct_read_alloc(size_t nbytes, size_t rsize)
264 struct list_head *list;
265 struct nfs_direct_req *dreq;
266 unsigned int rpages = (rsize + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
268 dreq = nfs_direct_req_alloc();
274 struct nfs_read_data *data = nfs_readdata_alloc(rpages);
276 if (unlikely(!data)) {
277 while (!list_empty(list)) {
278 data = list_entry(list->next,
279 struct nfs_read_data, pages);
280 list_del(&data->pages);
281 nfs_readdata_free(data);
283 kref_put(&dreq->kref, nfs_direct_req_release);
287 INIT_LIST_HEAD(&data->pages);
288 list_add(&data->pages, list);
290 data->req = (struct nfs_page *) dreq;
296 kref_get(&dreq->kref);
300 static void nfs_direct_read_result(struct rpc_task *task, void *calldata)
302 struct nfs_read_data *data = calldata;
303 struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;
305 if (nfs_readpage_result(task, data) != 0)
308 spin_lock(&dreq->lock);
310 if (likely(task->tk_status >= 0))
311 dreq->count += data->res.count;
313 dreq->error = task->tk_status;
315 spin_unlock(&dreq->lock);
317 if (put_dreq(dreq)) {
318 nfs_direct_dirty_pages(dreq->pages, dreq->npages);
319 nfs_direct_release_pages(dreq->pages, dreq->npages);
320 nfs_direct_complete(dreq);
324 static const struct rpc_call_ops nfs_read_direct_ops = {
325 .rpc_call_done = nfs_direct_read_result,
326 .rpc_release = nfs_readdata_release,
330 * For each nfs_read_data struct that was allocated on the list, dispatch
331 * an NFS READ operation
333 static void nfs_direct_read_schedule(struct nfs_direct_req *dreq, unsigned long user_addr, size_t count, loff_t pos)
335 struct nfs_open_context *ctx = dreq->ctx;
336 struct inode *inode = ctx->dentry->d_inode;
337 struct list_head *list = &dreq->list;
338 struct page **pages = dreq->pages;
339 size_t rsize = NFS_SERVER(inode)->rsize;
340 unsigned int curpage, pgbase;
343 pgbase = user_addr & ~PAGE_MASK;
345 struct nfs_read_data *data;
352 BUG_ON(list_empty(list));
353 data = list_entry(list->next, struct nfs_read_data, pages);
354 list_del_init(&data->pages);
357 data->cred = ctx->cred;
358 data->args.fh = NFS_FH(inode);
359 data->args.context = ctx;
360 data->args.offset = pos;
361 data->args.pgbase = pgbase;
362 data->args.pages = &pages[curpage];
363 data->args.count = bytes;
364 data->res.fattr = &data->fattr;
366 data->res.count = bytes;
368 rpc_init_task(&data->task, NFS_CLIENT(inode), RPC_TASK_ASYNC,
369 &nfs_read_direct_ops, data);
370 NFS_PROTO(inode)->read_setup(data);
372 data->task.tk_cookie = (unsigned long) inode;
375 rpc_execute(&data->task);
378 dfprintk(VFS, "NFS: %5u initiated direct read call (req %s/%Ld, %zu bytes @ offset %Lu)\n",
381 (long long)NFS_FILEID(inode),
383 (unsigned long long)data->args.offset);
387 curpage += pgbase >> PAGE_SHIFT;
388 pgbase &= ~PAGE_MASK;
391 } while (count != 0);
392 BUG_ON(!list_empty(list));
395 static ssize_t nfs_direct_read(struct kiocb *iocb, unsigned long user_addr, size_t count, loff_t pos, struct page **pages, unsigned int nr_pages)
399 struct inode *inode = iocb->ki_filp->f_mapping->host;
400 struct rpc_clnt *clnt = NFS_CLIENT(inode);
401 struct nfs_direct_req *dreq;
403 dreq = nfs_direct_read_alloc(count, NFS_SERVER(inode)->rsize);
408 dreq->npages = nr_pages;
410 dreq->ctx = get_nfs_open_context((struct nfs_open_context *)iocb->ki_filp->private_data);
411 if (!is_sync_kiocb(iocb))
414 nfs_add_stats(inode, NFSIOS_DIRECTREADBYTES, count);
415 rpc_clnt_sigmask(clnt, &oldset);
416 nfs_direct_read_schedule(dreq, user_addr, count, pos);
417 result = nfs_direct_wait(dreq);
418 rpc_clnt_sigunmask(clnt, &oldset);
423 static void nfs_direct_free_writedata(struct nfs_direct_req *dreq)
425 list_splice_init(&dreq->rewrite_list, &dreq->list);
426 while (!list_empty(&dreq->list)) {
427 struct nfs_write_data *data = list_entry(dreq->list.next, struct nfs_write_data, pages);
428 list_del(&data->pages);
429 nfs_writedata_release(data);
431 nfs_direct_release_pages(dreq->pages, dreq->npages);
434 #if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
435 static void nfs_direct_write_reschedule(struct nfs_direct_req *dreq)
437 struct inode *inode = dreq->inode;
439 struct nfs_write_data *data;
444 list_for_each(p, &dreq->rewrite_list) {
445 data = list_entry(p, struct nfs_write_data, pages);
452 nfs_fattr_init(&data->fattr);
453 data->res.count = data->args.count;
454 memset(&data->verf, 0, sizeof(data->verf));
457 * Reuse data->task; data->args should not have changed
458 * since the original request was sent.
460 rpc_init_task(&data->task, NFS_CLIENT(inode), RPC_TASK_ASYNC,
461 &nfs_write_direct_ops, data);
462 NFS_PROTO(inode)->write_setup(data, FLUSH_STABLE);
464 data->task.tk_priority = RPC_PRIORITY_NORMAL;
465 data->task.tk_cookie = (unsigned long) inode;
468 * We're called via an RPC callback, so BKL is already held.
470 rpc_execute(&data->task);
472 dprintk("NFS: %5u rescheduled direct write call (req %s/%Ld, %u bytes @ offset %Lu)\n",
475 (long long)NFS_FILEID(inode),
477 (unsigned long long)data->args.offset);
481 nfs_direct_write_complete(dreq, inode);
484 static void nfs_direct_commit_result(struct rpc_task *task, void *calldata)
486 struct nfs_write_data *data = calldata;
487 struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;
489 /* Call the NFS version-specific code */
490 if (NFS_PROTO(data->inode)->commit_done(task, data) != 0)
492 if (unlikely(task->tk_status < 0)) {
493 dreq->error = task->tk_status;
494 dreq->flags = NFS_ODIRECT_RESCHED_WRITES;
496 if (memcmp(&dreq->verf, &data->verf, sizeof(data->verf))) {
497 dprintk("NFS: %5u commit verify failed\n", task->tk_pid);
498 dreq->flags = NFS_ODIRECT_RESCHED_WRITES;
501 dprintk("NFS: %5u commit returned %d\n", task->tk_pid, task->tk_status);
502 nfs_direct_write_complete(dreq, data->inode);
505 static const struct rpc_call_ops nfs_commit_direct_ops = {
506 .rpc_call_done = nfs_direct_commit_result,
507 .rpc_release = nfs_commit_release,
510 static void nfs_direct_commit_schedule(struct nfs_direct_req *dreq)
512 struct nfs_write_data *data = dreq->commit_data;
514 data->inode = dreq->inode;
515 data->cred = dreq->ctx->cred;
517 data->args.fh = NFS_FH(data->inode);
518 data->args.offset = 0;
519 data->args.count = 0;
521 data->res.fattr = &data->fattr;
522 data->res.verf = &data->verf;
524 rpc_init_task(&data->task, NFS_CLIENT(dreq->inode), RPC_TASK_ASYNC,
525 &nfs_commit_direct_ops, data);
526 NFS_PROTO(data->inode)->commit_setup(data, 0);
528 data->task.tk_priority = RPC_PRIORITY_NORMAL;
529 data->task.tk_cookie = (unsigned long)data->inode;
530 /* Note: task.tk_ops->rpc_release will free dreq->commit_data */
531 dreq->commit_data = NULL;
533 dprintk("NFS: %5u initiated commit call\n", data->task.tk_pid);
536 rpc_execute(&data->task);
540 static void nfs_direct_write_complete(struct nfs_direct_req *dreq, struct inode *inode)
542 int flags = dreq->flags;
546 case NFS_ODIRECT_DO_COMMIT:
547 nfs_direct_commit_schedule(dreq);
549 case NFS_ODIRECT_RESCHED_WRITES:
550 nfs_direct_write_reschedule(dreq);
553 nfs_end_data_update(inode);
554 if (dreq->commit_data != NULL)
555 nfs_commit_free(dreq->commit_data);
556 nfs_direct_free_writedata(dreq);
557 nfs_direct_complete(dreq);
561 static void nfs_alloc_commit_data(struct nfs_direct_req *dreq)
563 dreq->commit_data = nfs_commit_alloc(0);
564 if (dreq->commit_data != NULL)
565 dreq->commit_data->req = (struct nfs_page *) dreq;
568 static inline void nfs_alloc_commit_data(struct nfs_direct_req *dreq)
570 dreq->commit_data = NULL;
573 static void nfs_direct_write_complete(struct nfs_direct_req *dreq, struct inode *inode)
575 nfs_end_data_update(inode);
576 nfs_direct_free_writedata(dreq);
577 nfs_direct_complete(dreq);
581 static struct nfs_direct_req *nfs_direct_write_alloc(size_t nbytes, size_t wsize)
583 struct list_head *list;
584 struct nfs_direct_req *dreq;
585 unsigned int wpages = (wsize + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
587 dreq = nfs_direct_req_alloc();
593 struct nfs_write_data *data = nfs_writedata_alloc(wpages);
595 if (unlikely(!data)) {
596 while (!list_empty(list)) {
597 data = list_entry(list->next,
598 struct nfs_write_data, pages);
599 list_del(&data->pages);
600 nfs_writedata_free(data);
602 kref_put(&dreq->kref, nfs_direct_req_release);
606 INIT_LIST_HEAD(&data->pages);
607 list_add(&data->pages, list);
609 data->req = (struct nfs_page *) dreq;
616 nfs_alloc_commit_data(dreq);
618 kref_get(&dreq->kref);
622 static void nfs_direct_write_result(struct rpc_task *task, void *calldata)
624 struct nfs_write_data *data = calldata;
625 struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;
626 int status = task->tk_status;
628 if (nfs_writeback_done(task, data) != 0)
631 spin_lock(&dreq->lock);
633 if (likely(status >= 0))
634 dreq->count += data->res.count;
636 dreq->error = task->tk_status;
638 if (data->res.verf->committed != NFS_FILE_SYNC) {
639 switch (dreq->flags) {
641 memcpy(&dreq->verf, &data->verf, sizeof(dreq->verf));
642 dreq->flags = NFS_ODIRECT_DO_COMMIT;
644 case NFS_ODIRECT_DO_COMMIT:
645 if (memcmp(&dreq->verf, &data->verf, sizeof(dreq->verf))) {
646 dprintk("NFS: %5u write verify failed\n", task->tk_pid);
647 dreq->flags = NFS_ODIRECT_RESCHED_WRITES;
652 spin_unlock(&dreq->lock);
656 * NB: Return the value of the first error return code. Subsequent
657 * errors after the first one are ignored.
659 static void nfs_direct_write_release(void *calldata)
661 struct nfs_write_data *data = calldata;
662 struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;
665 nfs_direct_write_complete(dreq, data->inode);
668 static const struct rpc_call_ops nfs_write_direct_ops = {
669 .rpc_call_done = nfs_direct_write_result,
670 .rpc_release = nfs_direct_write_release,
674 * For each nfs_write_data struct that was allocated on the list, dispatch
675 * an NFS WRITE operation
677 static void nfs_direct_write_schedule(struct nfs_direct_req *dreq, unsigned long user_addr, size_t count, loff_t pos, int sync)
679 struct nfs_open_context *ctx = dreq->ctx;
680 struct inode *inode = ctx->dentry->d_inode;
681 struct list_head *list = &dreq->list;
682 struct page **pages = dreq->pages;
683 size_t wsize = NFS_SERVER(inode)->wsize;
684 unsigned int curpage, pgbase;
687 pgbase = user_addr & ~PAGE_MASK;
689 struct nfs_write_data *data;
696 BUG_ON(list_empty(list));
697 data = list_entry(list->next, struct nfs_write_data, pages);
698 list_move_tail(&data->pages, &dreq->rewrite_list);
701 data->cred = ctx->cred;
702 data->args.fh = NFS_FH(inode);
703 data->args.context = ctx;
704 data->args.offset = pos;
705 data->args.pgbase = pgbase;
706 data->args.pages = &pages[curpage];
707 data->args.count = bytes;
708 data->res.fattr = &data->fattr;
709 data->res.count = bytes;
710 data->res.verf = &data->verf;
712 rpc_init_task(&data->task, NFS_CLIENT(inode), RPC_TASK_ASYNC,
713 &nfs_write_direct_ops, data);
714 NFS_PROTO(inode)->write_setup(data, sync);
716 data->task.tk_priority = RPC_PRIORITY_NORMAL;
717 data->task.tk_cookie = (unsigned long) inode;
720 rpc_execute(&data->task);
723 dfprintk(VFS, "NFS: %5u initiated direct write call (req %s/%Ld, %zu bytes @ offset %Lu)\n",
726 (long long)NFS_FILEID(inode),
728 (unsigned long long)data->args.offset);
732 curpage += pgbase >> PAGE_SHIFT;
733 pgbase &= ~PAGE_MASK;
736 } while (count != 0);
737 BUG_ON(!list_empty(list));
740 static ssize_t nfs_direct_write(struct kiocb *iocb, unsigned long user_addr, size_t count, loff_t pos, struct page **pages, int nr_pages)
744 struct inode *inode = iocb->ki_filp->f_mapping->host;
745 struct rpc_clnt *clnt = NFS_CLIENT(inode);
746 struct nfs_direct_req *dreq;
747 size_t wsize = NFS_SERVER(inode)->wsize;
750 dreq = nfs_direct_write_alloc(count, wsize);
753 if (dreq->commit_data == NULL || count < wsize)
757 dreq->npages = nr_pages;
759 dreq->ctx = get_nfs_open_context((struct nfs_open_context *)iocb->ki_filp->private_data);
760 if (!is_sync_kiocb(iocb))
763 nfs_add_stats(inode, NFSIOS_DIRECTWRITTENBYTES, count);
765 nfs_begin_data_update(inode);
767 rpc_clnt_sigmask(clnt, &oldset);
768 nfs_direct_write_schedule(dreq, user_addr, count, pos, sync);
769 result = nfs_direct_wait(dreq);
770 rpc_clnt_sigunmask(clnt, &oldset);
776 * nfs_file_direct_read - file direct read operation for NFS files
777 * @iocb: target I/O control block
778 * @buf: user's buffer into which to read data
779 * @count: number of bytes to read
780 * @pos: byte offset in file where reading starts
782 * We use this function for direct reads instead of calling
783 * generic_file_aio_read() in order to avoid gfar's check to see if
784 * the request starts before the end of the file. For that check
785 * to work, we must generate a GETATTR before each direct read, and
786 * even then there is a window between the GETATTR and the subsequent
787 * READ where the file size could change. Our preference is simply
788 * to do all reads the application wants, and the server will take
789 * care of managing the end of file boundary.
791 * This function also eliminates unnecessarily updating the file's
792 * atime locally, as the NFS server sets the file's atime, and this
793 * client must read the updated atime from the server back into its
796 ssize_t nfs_file_direct_read(struct kiocb *iocb, char __user *buf, size_t count, loff_t pos)
798 ssize_t retval = -EINVAL;
801 struct file *file = iocb->ki_filp;
802 struct address_space *mapping = file->f_mapping;
804 dprintk("nfs: direct read(%s/%s, %lu@%Ld)\n",
805 file->f_dentry->d_parent->d_name.name,
806 file->f_dentry->d_name.name,
807 (unsigned long) count, (long long) pos);
812 if (!access_ok(VERIFY_WRITE, buf, count))
818 retval = nfs_sync_mapping(mapping);
822 retval = nfs_get_user_pages(READ, (unsigned long) buf,
828 retval = nfs_direct_read(iocb, (unsigned long) buf, count, pos,
831 iocb->ki_pos = pos + retval;
838 * nfs_file_direct_write - file direct write operation for NFS files
839 * @iocb: target I/O control block
840 * @buf: user's buffer from which to write data
841 * @count: number of bytes to write
842 * @pos: byte offset in file where writing starts
844 * We use this function for direct writes instead of calling
845 * generic_file_aio_write() in order to avoid taking the inode
846 * semaphore and updating the i_size. The NFS server will set
847 * the new i_size and this client must read the updated size
848 * back into its cache. We let the server do generic write
849 * parameter checking and report problems.
851 * We also avoid an unnecessary invocation of generic_osync_inode(),
852 * as it is fairly meaningless to sync the metadata of an NFS file.
854 * We eliminate local atime updates, see direct read above.
856 * We avoid unnecessary page cache invalidations for normal cached
857 * readers of this file.
859 * Note that O_APPEND is not supported for NFS direct writes, as there
860 * is no atomic O_APPEND write facility in the NFS protocol.
862 ssize_t nfs_file_direct_write(struct kiocb *iocb, const char __user *buf, size_t count, loff_t pos)
867 struct file *file = iocb->ki_filp;
868 struct address_space *mapping = file->f_mapping;
870 dfprintk(VFS, "nfs: direct write(%s/%s, %lu@%Ld)\n",
871 file->f_dentry->d_parent->d_name.name,
872 file->f_dentry->d_name.name,
873 (unsigned long) count, (long long) pos);
875 retval = generic_write_checks(file, &pos, &count, 0);
880 if ((ssize_t) count < 0)
887 if (!access_ok(VERIFY_READ, buf, count))
890 retval = nfs_sync_mapping(mapping);
894 retval = nfs_get_user_pages(WRITE, (unsigned long) buf,
900 retval = nfs_direct_write(iocb, (unsigned long) buf, count,
901 pos, pages, page_count);
904 * XXX: nfs_end_data_update() already ensures this file's
905 * cached data is subsequently invalidated. Do we really
906 * need to call invalidate_inode_pages2() again here?
908 * For aio writes, this invalidation will almost certainly
909 * occur before the writes complete. Kind of racey.
911 if (mapping->nrpages)
912 invalidate_inode_pages2(mapping);
915 iocb->ki_pos = pos + retval;
922 * nfs_init_directcache - create a slab cache for nfs_direct_req structures
925 int __init nfs_init_directcache(void)
927 nfs_direct_cachep = kmem_cache_create("nfs_direct_cache",
928 sizeof(struct nfs_direct_req),
929 0, (SLAB_RECLAIM_ACCOUNT|
932 if (nfs_direct_cachep == NULL)
939 * nfs_destroy_directcache - destroy the slab cache for nfs_direct_req structures
942 void __exit nfs_destroy_directcache(void)
944 if (kmem_cache_destroy(nfs_direct_cachep))
945 printk(KERN_INFO "nfs_direct_cache: not all structures were freed\n");