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   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  * 04 May 2005  support O_DIRECT with aio  --cel
  38  *
  39  */
  40
  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>
  49
  50 #include <linux/nfs_fs.h>
  51 #include <linux/nfs_page.h>
  52 #include <linux/sunrpc/clnt.h>
  53
  54 #include <asm/system.h>
  55 #include <asm/uaccess.h>
  56 #include <asm/atomic.h>
  57
  58 #include "iostat.h"
  59
  60 #define NFSDBG_FACILITY         NFSDBG_VFS
  61
  62 static void nfs_free_user_pages(struct page **pages, int npages, int do_dirty);
  63 static kmem_cache_t *nfs_direct_cachep;
  64
  65 /*
  66  * This represents a set of asynchronous requests that we're waiting on
  67  */
  68 struct nfs_direct_req {
  69         struct kref             kref;           /* release manager */
  70
  71         /* I/O parameters */
  72         struct list_head        list;           /* nfs_read/write_data structs */
  73         struct file *           filp;           /* file descriptor */
  74         struct kiocb *          iocb;           /* controlling i/o request */
  75         wait_queue_head_t       wait;           /* wait for i/o completion */
  76         struct inode *          inode;          /* target file of i/o */
  77         struct page **          pages;          /* pages in our buffer */
  78         unsigned int            npages;         /* count of pages */
  79
  80         /* completion state */
  81         spinlock_t              lock;           /* protect completion state */
  82         int                     outstanding;    /* i/os we're waiting for */
  83         ssize_t                 count,          /* bytes actually processed */
  84                                 error;          /* any reported error */
  85 };
  86
  87 /**
  88  * nfs_direct_IO - NFS address space operation for direct I/O
  89  * @rw: direction (read or write)
  90  * @iocb: target I/O control block
  91  * @iov: array of vectors that define I/O buffer
  92  * @pos: offset in file to begin the operation
  93  * @nr_segs: size of iovec array
  94  *
  95  * The presence of this routine in the address space ops vector means
  96  * the NFS client supports direct I/O.  However, we shunt off direct
  97  * read and write requests before the VFS gets them, so this method
  98  * should never be called.
  99  */
 100 ssize_t nfs_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov, loff_t pos, unsigned long nr_segs)
 101 {
 102         struct dentry *dentry = iocb->ki_filp->f_dentry;
 103
 104         dprintk("NFS: nfs_direct_IO (%s) off/no(%Ld/%lu) EINVAL\n",
 105                         dentry->d_name.name, (long long) pos, nr_segs);
 106
 107         return -EINVAL;
 108 }
 109
 110 static inline int nfs_get_user_pages(int rw, unsigned long user_addr, size_t size, struct page ***pages)
 111 {
 112         int result = -ENOMEM;
 113         unsigned long page_count;
 114         size_t array_size;
 115
 116         page_count = (user_addr + size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 117         page_count -= user_addr >> PAGE_SHIFT;
 118
 119         array_size = (page_count * sizeof(struct page *));
 120         *pages = kmalloc(array_size, GFP_KERNEL);
 121         if (*pages) {
 122                 down_read(&current->mm->mmap_sem);
 123                 result = get_user_pages(current, current->mm, user_addr,
 124                                         page_count, (rw == READ), 0,
 125                                         *pages, NULL);
 126                 up_read(&current->mm->mmap_sem);
 127                 /*
 128                  * If we got fewer pages than expected from get_user_pages(),
 129                  * the user buffer runs off the end of a mapping; return EFAULT.
 130                  */
 131                 if (result >= 0 && result < page_count) {
 132                         nfs_free_user_pages(*pages, result, 0);
 133                         *pages = NULL;
 134                         result = -EFAULT;
 135                 }
 136         }
 137         return result;
 138 }
 139
 140 static void nfs_free_user_pages(struct page **pages, int npages, int do_dirty)
 141 {
 142         int i;
 143         for (i = 0; i < npages; i++) {
 144                 struct page *page = pages[i];
 145                 if (do_dirty && !PageCompound(page))
 146                         set_page_dirty_lock(page);
 147                 page_cache_release(page);
 148         }
 149         kfree(pages);
 150 }
 151
 152 static inline struct nfs_direct_req *nfs_direct_req_alloc(void)
 153 {
 154         struct nfs_direct_req *dreq;
 155
 156         dreq = kmem_cache_alloc(nfs_direct_cachep, SLAB_KERNEL);
 157         if (!dreq)
 158                 return NULL;
 159
 160         kref_init(&dreq->kref);
 161         init_waitqueue_head(&dreq->wait);
 162         INIT_LIST_HEAD(&dreq->list);
 163         dreq->iocb = NULL;
 164         spin_lock_init(&dreq->lock);
 165         dreq->outstanding = 0;
 166         dreq->count = 0;
 167         dreq->error = 0;
 168
 169         return dreq;
 170 }
 171
 172 static void nfs_direct_req_release(struct kref *kref)
 173 {
 174         struct nfs_direct_req *dreq = container_of(kref, struct nfs_direct_req, kref);
 175         kmem_cache_free(nfs_direct_cachep, dreq);
 176 }
 177
 178 /*
 179  * Collects and returns the final error value/byte-count.
 180  */
 181 static ssize_t nfs_direct_wait(struct nfs_direct_req *dreq)
 182 {
 183         ssize_t result = -EIOCBQUEUED;
 184
 185         /* Async requests don't wait here */
 186         if (dreq->iocb)
 187                 goto out;
 188
 189         result = wait_event_interruptible(dreq->wait, (dreq->outstanding == 0));
 190
 191         if (!result)
 192                 result = dreq->error;
 193         if (!result)
 194                 result = dreq->count;
 195
 196 out:
 197         kref_put(&dreq->kref, nfs_direct_req_release);
 198         return (ssize_t) result;
 199 }
 200
 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_wait (for instance, if someone hits ^C on a slow server).
 205  *
 206  * In addition, synchronous I/O uses a stack-allocated iocb.  Thus we
 207  * can't trust the iocb is still valid here if this is a synchronous
 208  * request.  If the waiter is woken prematurely, the iocb is long gone.
 209  */
 210 static void nfs_direct_complete(struct nfs_direct_req *dreq)
 211 {
 212         nfs_free_user_pages(dreq->pages, dreq->npages, 1);
 213
 214         if (dreq->iocb) {
 215                 long res = (long) dreq->error;
 216                 if (!res)
 217                         res = (long) dreq->count;
 218                 aio_complete(dreq->iocb, res, 0);
 219         } else
 220                 wake_up(&dreq->wait);
 221
 222         kref_put(&dreq->kref, nfs_direct_req_release);
 223 }
 224
 225 /*
 226  * Note we also set the number of requests we have in the dreq when we are
 227  * done.  This prevents races with I/O completion so we will always wait
 228  * until all requests have been dispatched and completed.
 229  */
 230 static struct nfs_direct_req *nfs_direct_read_alloc(size_t nbytes, size_t rsize)
 231 {
 232         struct list_head *list;
 233         struct nfs_direct_req *dreq;
 234         unsigned int rpages = (rsize + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 235
 236         dreq = nfs_direct_req_alloc();
 237         if (!dreq)
 238                 return NULL;
 239
 240         list = &dreq->list;
 241         for(;;) {
 242                 struct nfs_read_data *data = nfs_readdata_alloc(rpages);
 243
 244                 if (unlikely(!data)) {
 245                         while (!list_empty(list)) {
 246                                 data = list_entry(list->next,
 247                                                   struct nfs_read_data, pages);
 248                                 list_del(&data->pages);
 249                                 nfs_readdata_free(data);
 250                         }
 251                         kref_put(&dreq->kref, nfs_direct_req_release);
 252                         return NULL;
 253                 }
 254
 255                 INIT_LIST_HEAD(&data->pages);
 256                 list_add(&data->pages, list);
 257
 258                 data->req = (struct nfs_page *) dreq;
 259                 dreq->outstanding++;
 260                 if (nbytes <= rsize)
 261                         break;
 262                 nbytes -= rsize;
 263         }
 264         kref_get(&dreq->kref);
 265         return dreq;
 266 }
 267
 268 static void nfs_direct_read_result(struct rpc_task *task, void *calldata)
 269 {
 270         struct nfs_read_data *data = calldata;
 271         struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;
 272
 273         if (nfs_readpage_result(task, data) != 0)
 274                 return;
 275
 276         spin_lock(&dreq->lock);
 277
 278         if (likely(task->tk_status >= 0))
 279                 dreq->count += data->res.count;
 280         else
 281                 dreq->error = task->tk_status;
 282
 283         if (--dreq->outstanding) {
 284                 spin_unlock(&dreq->lock);
 285                 return;
 286         }
 287
 288         spin_unlock(&dreq->lock);
 289         nfs_direct_complete(dreq);
 290 }
 291
 292 static const struct rpc_call_ops nfs_read_direct_ops = {
 293         .rpc_call_done = nfs_direct_read_result,
 294         .rpc_release = nfs_readdata_release,
 295 };
 296
 297 /*
 298  * For each nfs_read_data struct that was allocated on the list, dispatch
 299  * an NFS READ operation
 300  */
 301 static void nfs_direct_read_schedule(struct nfs_direct_req *dreq, unsigned long user_addr, size_t count, loff_t pos)
 302 {
 303         struct file *file = dreq->filp;
 304         struct inode *inode = file->f_mapping->host;
 305         struct nfs_open_context *ctx = (struct nfs_open_context *)
 306                                                         file->private_data;
 307         struct list_head *list = &dreq->list;
 308         struct page **pages = dreq->pages;
 309         size_t rsize = NFS_SERVER(inode)->rsize;
 310         unsigned int curpage, pgbase;
 311
 312         curpage = 0;
 313         pgbase = user_addr & ~PAGE_MASK;
 314         do {
 315                 struct nfs_read_data *data;
 316                 size_t bytes;
 317
 318                 bytes = rsize;
 319                 if (count < rsize)
 320                         bytes = count;
 321
 322                 data = list_entry(list->next, struct nfs_read_data, pages);
 323                 list_del_init(&data->pages);
 324
 325                 data->inode = inode;
 326                 data->cred = ctx->cred;
 327                 data->args.fh = NFS_FH(inode);
 328                 data->args.context = ctx;
 329                 data->args.offset = pos;
 330                 data->args.pgbase = pgbase;
 331                 data->args.pages = &pages[curpage];
 332                 data->args.count = bytes;
 333                 data->res.fattr = &data->fattr;
 334                 data->res.eof = 0;
 335                 data->res.count = bytes;
 336
 337                 rpc_init_task(&data->task, NFS_CLIENT(inode), RPC_TASK_ASYNC,
 338                                 &nfs_read_direct_ops, data);
 339                 NFS_PROTO(inode)->read_setup(data);
 340
 341                 data->task.tk_cookie = (unsigned long) inode;
 342
 343                 lock_kernel();
 344                 rpc_execute(&data->task);
 345                 unlock_kernel();
 346
 347                 dfprintk(VFS, "NFS: %4d initiated direct read call (req %s/%Ld, %u bytes @ offset %Lu)\n",
 348                                 data->task.tk_pid,
 349                                 inode->i_sb->s_id,
 350                                 (long long)NFS_FILEID(inode),
 351                                 bytes,
 352                                 (unsigned long long)data->args.offset);
 353
 354                 pos += bytes;
 355                 pgbase += bytes;
 356                 curpage += pgbase >> PAGE_SHIFT;
 357                 pgbase &= ~PAGE_MASK;
 358
 359                 count -= bytes;
 360         } while (count != 0);
 361 }
 362
 363 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)
 364 {
 365         ssize_t result;
 366         sigset_t oldset;
 367         struct inode *inode = iocb->ki_filp->f_mapping->host;
 368         struct rpc_clnt *clnt = NFS_CLIENT(inode);
 369         struct nfs_direct_req *dreq;
 370
 371         dreq = nfs_direct_read_alloc(count, NFS_SERVER(inode)->rsize);
 372         if (!dreq)
 373                 return -ENOMEM;
 374
 375         dreq->pages = pages;
 376         dreq->npages = nr_pages;
 377         dreq->inode = inode;
 378         dreq->filp = iocb->ki_filp;
 379         if (!is_sync_kiocb(iocb))
 380                 dreq->iocb = iocb;
 381
 382         nfs_add_stats(inode, NFSIOS_DIRECTREADBYTES, count);
 383         rpc_clnt_sigmask(clnt, &oldset);
 384         nfs_direct_read_schedule(dreq, user_addr, count, pos);
 385         result = nfs_direct_wait(dreq);
 386         rpc_clnt_sigunmask(clnt, &oldset);
 387
 388         return result;
 389 }
 390
 391 static struct nfs_direct_req *nfs_direct_write_alloc(size_t nbytes, size_t wsize)
 392 {
 393         struct list_head *list;
 394         struct nfs_direct_req *dreq;
 395         unsigned int wpages = (wsize + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 396
 397         dreq = nfs_direct_req_alloc();
 398         if (!dreq)
 399                 return NULL;
 400
 401         list = &dreq->list;
 402         for(;;) {
 403                 struct nfs_write_data *data = nfs_writedata_alloc(wpages);
 404
 405                 if (unlikely(!data)) {
 406                         while (!list_empty(list)) {
 407                                 data = list_entry(list->next,
 408                                                   struct nfs_write_data, pages);
 409                                 list_del(&data->pages);
 410                                 nfs_writedata_free(data);
 411                         }
 412                         kref_put(&dreq->kref, nfs_direct_req_release);
 413                         return NULL;
 414                 }
 415
 416                 INIT_LIST_HEAD(&data->pages);
 417                 list_add(&data->pages, list);
 418
 419                 data->req = (struct nfs_page *) dreq;
 420                 dreq->outstanding++;
 421                 if (nbytes <= wsize)
 422                         break;
 423                 nbytes -= wsize;
 424         }
 425         kref_get(&dreq->kref);
 426         return dreq;
 427 }
 428
 429 /*
 430  * NB: Return the value of the first error return code.  Subsequent
 431  *     errors after the first one are ignored.
 432  */
 433 static void nfs_direct_write_result(struct rpc_task *task, void *calldata)
 434 {
 435         struct nfs_write_data *data = calldata;
 436         struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;
 437         int status = task->tk_status;
 438
 439         if (nfs_writeback_done(task, data) != 0)
 440                 return;
 441         /* If the server fell back to an UNSTABLE write, it's an error. */
 442         if (unlikely(data->res.verf->committed != NFS_FILE_SYNC))
 443                 status = -EIO;
 444
 445         spin_lock(&dreq->lock);
 446
 447         if (likely(status >= 0))
 448                 dreq->count += data->res.count;
 449         else
 450                 dreq->error = status;
 451
 452         if (--dreq->outstanding) {
 453                 spin_unlock(&dreq->lock);
 454                 return;
 455         }
 456
 457         spin_unlock(&dreq->lock);
 458
 459         nfs_end_data_update(data->inode);
 460         nfs_direct_complete(dreq);
 461 }
 462
 463 static const struct rpc_call_ops nfs_write_direct_ops = {
 464         .rpc_call_done = nfs_direct_write_result,
 465         .rpc_release = nfs_writedata_release,
 466 };
 467
 468 /*
 469  * For each nfs_write_data struct that was allocated on the list, dispatch
 470  * an NFS WRITE operation
 471  *
 472  * XXX: For now, support only FILE_SYNC writes.  Later we may add
 473  *      support for UNSTABLE + COMMIT.
 474  */
 475 static void nfs_direct_write_schedule(struct nfs_direct_req *dreq, unsigned long user_addr, size_t count, loff_t pos)
 476 {
 477         struct file *file = dreq->filp;
 478         struct inode *inode = file->f_mapping->host;
 479         struct nfs_open_context *ctx = (struct nfs_open_context *)
 480                                                         file->private_data;
 481         struct list_head *list = &dreq->list;
 482         struct page **pages = dreq->pages;
 483         size_t wsize = NFS_SERVER(inode)->wsize;
 484         unsigned int curpage, pgbase;
 485
 486         curpage = 0;
 487         pgbase = user_addr & ~PAGE_MASK;
 488         do {
 489                 struct nfs_write_data *data;
 490                 size_t bytes;
 491
 492                 bytes = wsize;
 493                 if (count < wsize)
 494                         bytes = count;
 495
 496                 data = list_entry(list->next, struct nfs_write_data, pages);
 497                 list_del_init(&data->pages);
 498
 499                 data->inode = inode;
 500                 data->cred = ctx->cred;
 501                 data->args.fh = NFS_FH(inode);
 502                 data->args.context = ctx;
 503                 data->args.offset = pos;
 504                 data->args.pgbase = pgbase;
 505                 data->args.pages = &pages[curpage];
 506                 data->args.count = bytes;
 507                 data->res.fattr = &data->fattr;
 508                 data->res.count = bytes;
 509                 data->res.verf = &data->verf;
 510
 511                 rpc_init_task(&data->task, NFS_CLIENT(inode), RPC_TASK_ASYNC,
 512                                 &nfs_write_direct_ops, data);
 513                 NFS_PROTO(inode)->write_setup(data, FLUSH_STABLE);
 514
 515                 data->task.tk_priority = RPC_PRIORITY_NORMAL;
 516                 data->task.tk_cookie = (unsigned long) inode;
 517
 518                 lock_kernel();
 519                 rpc_execute(&data->task);
 520                 unlock_kernel();
 521
 522                 dfprintk(VFS, "NFS: %4d initiated direct write call (req %s/%Ld, %u bytes @ offset %Lu)\n",
 523                                 data->task.tk_pid,
 524                                 inode->i_sb->s_id,
 525                                 (long long)NFS_FILEID(inode),
 526                                 bytes,
 527                                 (unsigned long long)data->args.offset);
 528
 529                 pos += bytes;
 530                 pgbase += bytes;
 531                 curpage += pgbase >> PAGE_SHIFT;
 532                 pgbase &= ~PAGE_MASK;
 533
 534                 count -= bytes;
 535         } while (count != 0);
 536 }
 537
 538 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)
 539 {
 540         ssize_t result;
 541         sigset_t oldset;
 542         struct inode *inode = iocb->ki_filp->f_mapping->host;
 543         struct rpc_clnt *clnt = NFS_CLIENT(inode);
 544         struct nfs_direct_req *dreq;
 545
 546         dreq = nfs_direct_write_alloc(count, NFS_SERVER(inode)->wsize);
 547         if (!dreq)
 548                 return -ENOMEM;
 549
 550         dreq->pages = pages;
 551         dreq->npages = nr_pages;
 552         dreq->inode = inode;
 553         dreq->filp = iocb->ki_filp;
 554         if (!is_sync_kiocb(iocb))
 555                 dreq->iocb = iocb;
 556
 557         nfs_add_stats(inode, NFSIOS_DIRECTWRITTENBYTES, count);
 558
 559         nfs_begin_data_update(inode);
 560
 561         rpc_clnt_sigmask(clnt, &oldset);
 562         nfs_direct_write_schedule(dreq, user_addr, count, pos);
 563         result = nfs_direct_wait(dreq);
 564         rpc_clnt_sigunmask(clnt, &oldset);
 565
 566         return result;
 567 }
 568
 569 /**
 570  * nfs_file_direct_read - file direct read operation for NFS files
 571  * @iocb: target I/O control block
 572  * @buf: user's buffer into which to read data
 573  * @count: number of bytes to read
 574  * @pos: byte offset in file where reading starts
 575  *
 576  * We use this function for direct reads instead of calling
 577  * generic_file_aio_read() in order to avoid gfar's check to see if
 578  * the request starts before the end of the file.  For that check
 579  * to work, we must generate a GETATTR before each direct read, and
 580  * even then there is a window between the GETATTR and the subsequent
 581  * READ where the file size could change.  Our preference is simply
 582  * to do all reads the application wants, and the server will take
 583  * care of managing the end of file boundary.
 584  *
 585  * This function also eliminates unnecessarily updating the file's
 586  * atime locally, as the NFS server sets the file's atime, and this
 587  * client must read the updated atime from the server back into its
 588  * cache.
 589  */
 590 ssize_t nfs_file_direct_read(struct kiocb *iocb, char __user *buf, size_t count, loff_t pos)
 591 {
 592         ssize_t retval = -EINVAL;
 593         int page_count;
 594         struct page **pages;
 595         struct file *file = iocb->ki_filp;
 596         struct address_space *mapping = file->f_mapping;
 597
 598         dprintk("nfs: direct read(%s/%s, %lu@%Ld)\n",
 599                 file->f_dentry->d_parent->d_name.name,
 600                 file->f_dentry->d_name.name,
 601                 (unsigned long) count, (long long) pos);
 602
 603         if (count < 0)
 604                 goto out;
 605         retval = -EFAULT;
 606         if (!access_ok(VERIFY_WRITE, buf, count))
 607                 goto out;
 608         retval = 0;
 609         if (!count)
 610                 goto out;
 611
 612         retval = nfs_sync_mapping(mapping);
 613         if (retval)
 614                 goto out;
 615
 616         page_count = nfs_get_user_pages(READ, (unsigned long) buf,
 617                                                 count, &pages);
 618         if (page_count < 0) {
 619                 nfs_free_user_pages(pages, 0, 0);
 620                 retval = page_count;
 621                 goto out;
 622         }
 623
 624         retval = nfs_direct_read(iocb, (unsigned long) buf, count, pos,
 625                                                 pages, page_count);
 626         if (retval > 0)
 627                 iocb->ki_pos = pos + retval;
 628
 629 out:
 630         return retval;
 631 }
 632
 633 /**
 634  * nfs_file_direct_write - file direct write operation for NFS files
 635  * @iocb: target I/O control block
 636  * @buf: user's buffer from which to write data
 637  * @count: number of bytes to write
 638  * @pos: byte offset in file where writing starts
 639  *
 640  * We use this function for direct writes instead of calling
 641  * generic_file_aio_write() in order to avoid taking the inode
 642  * semaphore and updating the i_size.  The NFS server will set
 643  * the new i_size and this client must read the updated size
 644  * back into its cache.  We let the server do generic write
 645  * parameter checking and report problems.
 646  *
 647  * We also avoid an unnecessary invocation of generic_osync_inode(),
 648  * as it is fairly meaningless to sync the metadata of an NFS file.
 649  *
 650  * We eliminate local atime updates, see direct read above.
 651  *
 652  * We avoid unnecessary page cache invalidations for normal cached
 653  * readers of this file.
 654  *
 655  * Note that O_APPEND is not supported for NFS direct writes, as there
 656  * is no atomic O_APPEND write facility in the NFS protocol.
 657  */
 658 ssize_t nfs_file_direct_write(struct kiocb *iocb, const char __user *buf, size_t count, loff_t pos)
 659 {
 660         ssize_t retval;
 661         int page_count;
 662         struct page **pages;
 663         struct file *file = iocb->ki_filp;
 664         struct address_space *mapping = file->f_mapping;
 665
 666         dfprintk(VFS, "nfs: direct write(%s/%s, %lu@%Ld)\n",
 667                 file->f_dentry->d_parent->d_name.name,
 668                 file->f_dentry->d_name.name,
 669                 (unsigned long) count, (long long) pos);
 670
 671         retval = generic_write_checks(file, &pos, &count, 0);
 672         if (retval)
 673                 goto out;
 674
 675         retval = -EINVAL;
 676         if ((ssize_t) count < 0)
 677                 goto out;
 678         retval = 0;
 679         if (!count)
 680                 goto out;
 681
 682         retval = -EFAULT;
 683         if (!access_ok(VERIFY_READ, buf, count))
 684                 goto out;
 685
 686         retval = nfs_sync_mapping(mapping);
 687         if (retval)
 688                 goto out;
 689
 690         page_count = nfs_get_user_pages(WRITE, (unsigned long) buf,
 691                                                 count, &pages);
 692         if (page_count < 0) {
 693                 nfs_free_user_pages(pages, 0, 0);
 694                 retval = page_count;
 695                 goto out;
 696         }
 697
 698         retval = nfs_direct_write(iocb, (unsigned long) buf, count,
 699                                         pos, pages, page_count);
 700
 701         /*
 702          * XXX: nfs_end_data_update() already ensures this file's
 703          *      cached data is subsequently invalidated.  Do we really
 704          *      need to call invalidate_inode_pages2() again here?
 705          *
 706          *      For aio writes, this invalidation will almost certainly
 707          *      occur before the writes complete.  Kind of racey.
 708          */
 709         if (mapping->nrpages)
 710                 invalidate_inode_pages2(mapping);
 711
 712         if (retval > 0)
 713                 iocb->ki_pos = pos + retval;
 714
 715 out:
 716         return retval;
 717 }
 718
 719 /**
 720  * nfs_init_directcache - create a slab cache for nfs_direct_req structures
 721  *
 722  */
 723 int nfs_init_directcache(void)
 724 {
 725         nfs_direct_cachep = kmem_cache_create("nfs_direct_cache",
 726                                                 sizeof(struct nfs_direct_req),
 727                                                 0, SLAB_RECLAIM_ACCOUNT,
 728                                                 NULL, NULL);
 729         if (nfs_direct_cachep == NULL)
 730                 return -ENOMEM;
 731
 732         return 0;
 733 }
 734
 735 /**
 736  * nfs_init_directcache - destroy the slab cache for nfs_direct_req structures
 737  *
 738  */
 739 void nfs_destroy_directcache(void)
 740 {
 741         if (kmem_cache_destroy(nfs_direct_cachep))
 742                 printk(KERN_INFO "nfs_direct_cache: not all structures were freed\n");
 743 }