fs/nfs/direct.c

   1 /*
   2  * linux/fs/nfs/direct.c
   3  *
   4  * Copyright (C) 2003 by Chuck Lever <[email protected]>
   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 #define MAX_DIRECTIO_SIZE       (4096UL << PAGE_SHIFT)
  62
  63 static void nfs_free_user_pages(struct page **pages, int npages, int do_dirty);
  64 static kmem_cache_t *nfs_direct_cachep;
  65
  66 /*
  67  * This represents a set of asynchronous requests that we're waiting on
  68  */
  69 struct nfs_direct_req {
  70         struct kref             kref;           /* release manager */
  71         struct list_head        list;           /* nfs_read/write_data structs */
  72         struct file *           filp;           /* file descriptor */
  73         struct kiocb *          iocb;           /* controlling i/o request */
  74         wait_queue_head_t       wait;           /* wait for i/o completion */
  75         struct inode *          inode;          /* target file of i/o */
  76         struct page **          pages;          /* pages in our buffer */
  77         unsigned int            npages;         /* count of pages */
  78         atomic_t                complete,       /* i/os we're waiting for */
  79                                 count,          /* bytes actually processed */
  80                                 error;          /* any reported error */
  81 };
  82
  83
  84 /**
  85  * nfs_direct_IO - NFS address space operation for direct I/O
  86  * @rw: direction (read or write)
  87  * @iocb: target I/O control block
  88  * @iov: array of vectors that define I/O buffer
  89  * @pos: offset in file to begin the operation
  90  * @nr_segs: size of iovec array
  91  *
  92  * The presence of this routine in the address space ops vector means
  93  * the NFS client supports direct I/O.  However, we shunt off direct
  94  * read and write requests before the VFS gets them, so this method
  95  * should never be called.
  96  */
  97 ssize_t nfs_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov, loff_t pos, unsigned long nr_segs)
  98 {
  99         struct dentry *dentry = iocb->ki_filp->f_dentry;
 100
 101         dprintk("NFS: nfs_direct_IO (%s) off/no(%Ld/%lu) EINVAL\n",
 102                         dentry->d_name.name, (long long) pos, nr_segs);
 103
 104         return -EINVAL;
 105 }
 106
 107 static inline int nfs_get_user_pages(int rw, unsigned long user_addr, size_t size, struct page ***pages)
 108 {
 109         int result = -ENOMEM;
 110         unsigned long page_count;
 111         size_t array_size;
 112
 113         /* set an arbitrary limit to prevent type overflow */
 114         if (size > MAX_DIRECTIO_SIZE) {
 115                 *pages = NULL;
 116                 return -EFBIG;
 117         }
 118
 119         page_count = (user_addr + size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 120         page_count -= user_addr >> PAGE_SHIFT;
 121
 122         array_size = (page_count * sizeof(struct page *));
 123         *pages = kmalloc(array_size, GFP_KERNEL);
 124         if (*pages) {
 125                 down_read(&current->mm->mmap_sem);
 126                 result = get_user_pages(current, current->mm, user_addr,
 127                                         page_count, (rw == READ), 0,
 128                                         *pages, NULL);
 129                 up_read(&current->mm->mmap_sem);
 130                 /*
 131                  * If we got fewer pages than expected from get_user_pages(),
 132                  * the user buffer runs off the end of a mapping; return EFAULT.
 133                  */
 134                 if (result >= 0 && result < page_count) {
 135                         nfs_free_user_pages(*pages, result, 0);
 136                         *pages = NULL;
 137                         result = -EFAULT;
 138                 }
 139         }
 140         return result;
 141 }
 142
 143 static void nfs_free_user_pages(struct page **pages, int npages, int do_dirty)
 144 {
 145         int i;
 146         for (i = 0; i < npages; i++) {
 147                 struct page *page = pages[i];
 148                 if (do_dirty && !PageCompound(page))
 149                         set_page_dirty_lock(page);
 150                 page_cache_release(page);
 151         }
 152         kfree(pages);
 153 }
 154
 155 static inline struct nfs_direct_req *nfs_direct_req_alloc(void)
 156 {
 157         struct nfs_direct_req *dreq;
 158
 159         dreq = kmem_cache_alloc(nfs_direct_cachep, SLAB_KERNEL);
 160         if (!dreq)
 161                 return NULL;
 162
 163         kref_init(&dreq->kref);
 164         init_waitqueue_head(&dreq->wait);
 165         INIT_LIST_HEAD(&dreq->list);
 166         dreq->iocb = NULL;
 167         atomic_set(&dreq->count, 0);
 168         atomic_set(&dreq->error, 0);
 169
 170         return dreq;
 171 }
 172
 173 static void nfs_direct_req_release(struct kref *kref)
 174 {
 175         struct nfs_direct_req *dreq = container_of(kref, struct nfs_direct_req, kref);
 176         kmem_cache_free(nfs_direct_cachep, dreq);
 177 }
 178
 179 /*
 180  * Collects and returns the final error value/byte-count.
 181  */
 182 static ssize_t nfs_direct_wait(struct nfs_direct_req *dreq)
 183 {
 184         int result = -EIOCBQUEUED;
 185
 186         /* Async requests don't wait here */
 187         if (dreq->iocb)
 188                 goto out;
 189
 190         result = wait_event_interruptible(dreq->wait,
 191                                         (atomic_read(&dreq->complete) == 0));
 192
 193         if (!result)
 194                 result = atomic_read(&dreq->error);
 195         if (!result)
 196                 result = atomic_read(&dreq->count);
 197
 198 out:
 199         kref_put(&dreq->kref, nfs_direct_req_release);
 200         return (ssize_t) result;
 201 }
 202
 203 /*
 204  * We must hold a reference to all the pages in this direct read request
 205  * until the RPCs complete.  This could be long *after* we are woken up in
 206  * nfs_direct_wait (for instance, if someone hits ^C on a slow server).
 207  *
 208  * In addition, synchronous I/O uses a stack-allocated iocb.  Thus we
 209  * can't trust the iocb is still valid here if this is a synchronous
 210  * request.  If the waiter is woken prematurely, the iocb is long gone.
 211  */
 212 static void nfs_direct_complete(struct nfs_direct_req *dreq)
 213 {
 214         nfs_free_user_pages(dreq->pages, dreq->npages, 1);
 215
 216         if (dreq->iocb) {
 217                 long res = atomic_read(&dreq->error);
 218                 if (!res)
 219                         res = atomic_read(&dreq->count);
 220                 aio_complete(dreq->iocb, res, 0);
 221         } else
 222                 wake_up(&dreq->wait);
 223
 224         kref_put(&dreq->kref, nfs_direct_req_release);
 225 }
 226
 227 /*
 228  * Note we also set the number of requests we have in the dreq when we are
 229  * done.  This prevents races with I/O completion so we will always wait
 230  * until all requests have been dispatched and completed.
 231  */
 232 static struct nfs_direct_req *nfs_direct_read_alloc(size_t nbytes, size_t rsize)
 233 {
 234         struct list_head *list;
 235         struct nfs_direct_req *dreq;
 236         unsigned int reads = 0;
 237         unsigned int rpages = (rsize + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 238
 239         dreq = nfs_direct_req_alloc();
 240         if (!dreq)
 241                 return NULL;
 242
 243         list = &dreq->list;
 244         for(;;) {
 245                 struct nfs_read_data *data = nfs_readdata_alloc(rpages);
 246
 247                 if (unlikely(!data)) {
 248                         while (!list_empty(list)) {
 249                                 data = list_entry(list->next,
 250                                                   struct nfs_read_data, pages);
 251                                 list_del(&data->pages);
 252                                 nfs_readdata_free(data);
 253                         }
 254                         kref_put(&dreq->kref, nfs_direct_req_release);
 255                         return NULL;
 256                 }
 257
 258                 INIT_LIST_HEAD(&data->pages);
 259                 list_add(&data->pages, list);
 260
 261                 data->req = (struct nfs_page *) dreq;
 262                 reads++;
 263                 if (nbytes <= rsize)
 264                         break;
 265                 nbytes -= rsize;
 266         }
 267         kref_get(&dreq->kref);
 268         atomic_set(&dreq->complete, reads);
 269         return dreq;
 270 }
 271
 272 static void nfs_direct_read_result(struct rpc_task *task, void *calldata)
 273 {
 274         struct nfs_read_data *data = calldata;
 275         struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;
 276
 277         if (nfs_readpage_result(task, data) != 0)
 278                 return;
 279         if (likely(task->tk_status >= 0))
 280                 atomic_add(data->res.count, &dreq->count);
 281         else
 282                 atomic_set(&dreq->error, task->tk_status);
 283
 284         if (unlikely(atomic_dec_and_test(&dreq->complete)))
 285                 nfs_direct_complete(dreq);
 286 }
 287
 288 static const struct rpc_call_ops nfs_read_direct_ops = {
 289         .rpc_call_done = nfs_direct_read_result,
 290         .rpc_release = nfs_readdata_release,
 291 };
 292
 293 /*
 294  * For each nfs_read_data struct that was allocated on the list, dispatch
 295  * an NFS READ operation
 296  */
 297 static void nfs_direct_read_schedule(struct nfs_direct_req *dreq, unsigned long user_addr, size_t count, loff_t pos)
 298 {
 299         struct file *file = dreq->filp;
 300         struct inode *inode = file->f_mapping->host;
 301         struct nfs_open_context *ctx = (struct nfs_open_context *)
 302                                                         file->private_data;
 303         struct list_head *list = &dreq->list;
 304         struct page **pages = dreq->pages;
 305         size_t rsize = NFS_SERVER(inode)->rsize;
 306         unsigned int curpage, pgbase;
 307
 308         curpage = 0;
 309         pgbase = user_addr & ~PAGE_MASK;
 310         do {
 311                 struct nfs_read_data *data;
 312                 size_t bytes;
 313
 314                 bytes = rsize;
 315                 if (count < rsize)
 316                         bytes = count;
 317
 318                 data = list_entry(list->next, struct nfs_read_data, pages);
 319                 list_del_init(&data->pages);
 320
 321                 data->inode = inode;
 322                 data->cred = ctx->cred;
 323                 data->args.fh = NFS_FH(inode);
 324                 data->args.context = ctx;
 325                 data->args.offset = pos;
 326                 data->args.pgbase = pgbase;
 327                 data->args.pages = &pages[curpage];
 328                 data->args.count = bytes;
 329                 data->res.fattr = &data->fattr;
 330                 data->res.eof = 0;
 331                 data->res.count = bytes;
 332
 333                 rpc_init_task(&data->task, NFS_CLIENT(inode), RPC_TASK_ASYNC,
 334                                 &nfs_read_direct_ops, data);
 335                 NFS_PROTO(inode)->read_setup(data);
 336
 337                 data->task.tk_cookie = (unsigned long) inode;
 338
 339                 lock_kernel();
 340                 rpc_execute(&data->task);
 341                 unlock_kernel();
 342
 343                 dfprintk(VFS, "NFS: %4d initiated direct read call (req %s/%Ld, %u bytes @ offset %Lu)\n",
 344                                 data->task.tk_pid,
 345                                 inode->i_sb->s_id,
 346                                 (long long)NFS_FILEID(inode),
 347                                 bytes,
 348                                 (unsigned long long)data->args.offset);
 349
 350                 pos += bytes;
 351                 pgbase += bytes;
 352                 curpage += pgbase >> PAGE_SHIFT;
 353                 pgbase &= ~PAGE_MASK;
 354
 355                 count -= bytes;
 356         } while (count != 0);
 357 }
 358
 359 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)
 360 {
 361         ssize_t result;
 362         sigset_t oldset;
 363         struct inode *inode = iocb->ki_filp->f_mapping->host;
 364         struct rpc_clnt *clnt = NFS_CLIENT(inode);
 365         struct nfs_direct_req *dreq;
 366
 367         dreq = nfs_direct_read_alloc(count, NFS_SERVER(inode)->rsize);
 368         if (!dreq)
 369                 return -ENOMEM;
 370
 371         dreq->pages = pages;
 372         dreq->npages = nr_pages;
 373         dreq->inode = inode;
 374         dreq->filp = iocb->ki_filp;
 375         if (!is_sync_kiocb(iocb))
 376                 dreq->iocb = iocb;
 377
 378         nfs_add_stats(inode, NFSIOS_DIRECTREADBYTES, count);
 379         rpc_clnt_sigmask(clnt, &oldset);
 380         nfs_direct_read_schedule(dreq, user_addr, count, pos);
 381         result = nfs_direct_wait(dreq);
 382         rpc_clnt_sigunmask(clnt, &oldset);
 383
 384         return result;
 385 }
 386
 387 static struct nfs_direct_req *nfs_direct_write_alloc(size_t nbytes, size_t wsize)
 388 {
 389         struct list_head *list;
 390         struct nfs_direct_req *dreq;
 391         unsigned int writes = 0;
 392         unsigned int wpages = (wsize + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 393
 394         dreq = nfs_direct_req_alloc();
 395         if (!dreq)
 396                 return NULL;
 397
 398         list = &dreq->list;
 399         for(;;) {
 400                 struct nfs_write_data *data = nfs_writedata_alloc(wpages);
 401
 402                 if (unlikely(!data)) {
 403                         while (!list_empty(list)) {
 404                                 data = list_entry(list->next,
 405                                                   struct nfs_write_data, pages);
 406                                 list_del(&data->pages);
 407                                 nfs_writedata_free(data);
 408                         }
 409                         kref_put(&dreq->kref, nfs_direct_req_release);
 410                         return NULL;
 411                 }
 412
 413                 INIT_LIST_HEAD(&data->pages);
 414                 list_add(&data->pages, list);
 415
 416                 data->req = (struct nfs_page *) dreq;
 417                 writes++;
 418                 if (nbytes <= wsize)
 419                         break;
 420                 nbytes -= wsize;
 421         }
 422         kref_get(&dreq->kref);
 423         atomic_set(&dreq->complete, writes);
 424         return dreq;
 425 }
 426
 427 static void nfs_direct_write_result(struct rpc_task *task, void *calldata)
 428 {
 429         struct nfs_write_data *data = calldata;
 430         struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;
 431         int status = task->tk_status;
 432
 433         if (nfs_writeback_done(task, data) != 0)
 434                 return;
 435         /* If the server fell back to an UNSTABLE write, it's an error. */
 436         if (unlikely(data->res.verf->committed != NFS_FILE_SYNC))
 437                 status = -EIO;
 438
 439         if (likely(status >= 0))
 440                 atomic_add(data->res.count, &dreq->count);
 441         else
 442                 atomic_set(&dreq->error, status);
 443
 444         if (unlikely(atomic_dec_and_test(&dreq->complete))) {
 445                 nfs_end_data_update(data->inode);
 446                 nfs_direct_complete(dreq);
 447         }
 448 }
 449
 450 static const struct rpc_call_ops nfs_write_direct_ops = {
 451         .rpc_call_done = nfs_direct_write_result,
 452         .rpc_release = nfs_writedata_release,
 453 };
 454
 455 /*
 456  * For each nfs_write_data struct that was allocated on the list, dispatch
 457  * an NFS WRITE operation
 458  *
 459  * XXX: For now, support only FILE_SYNC writes.  Later we may add
 460  *      support for UNSTABLE + COMMIT.
 461  */
 462 static void nfs_direct_write_schedule(struct nfs_direct_req *dreq, unsigned long user_addr, size_t count, loff_t pos)
 463 {
 464         struct file *file = dreq->filp;
 465         struct inode *inode = file->f_mapping->host;
 466         struct nfs_open_context *ctx = (struct nfs_open_context *)
 467                                                         file->private_data;
 468         struct list_head *list = &dreq->list;
 469         struct page **pages = dreq->pages;
 470         size_t wsize = NFS_SERVER(inode)->wsize;
 471         unsigned int curpage, pgbase;
 472
 473         curpage = 0;
 474         pgbase = user_addr & ~PAGE_MASK;
 475         do {
 476                 struct nfs_write_data *data;
 477                 size_t bytes;
 478
 479                 bytes = wsize;
 480                 if (count < wsize)
 481                         bytes = count;
 482
 483                 data = list_entry(list->next, struct nfs_write_data, pages);
 484                 list_del_init(&data->pages);
 485
 486                 data->inode = inode;
 487                 data->cred = ctx->cred;
 488                 data->args.fh = NFS_FH(inode);
 489                 data->args.context = ctx;
 490                 data->args.offset = pos;
 491                 data->args.pgbase = pgbase;
 492                 data->args.pages = &pages[curpage];
 493                 data->args.count = bytes;
 494                 data->res.fattr = &data->fattr;
 495                 data->res.count = bytes;
 496                 data->res.verf = &data->verf;
 497
 498                 rpc_init_task(&data->task, NFS_CLIENT(inode), RPC_TASK_ASYNC,
 499                                 &nfs_write_direct_ops, data);
 500                 NFS_PROTO(inode)->write_setup(data, FLUSH_STABLE);
 501
 502                 data->task.tk_priority = RPC_PRIORITY_NORMAL;
 503                 data->task.tk_cookie = (unsigned long) inode;
 504
 505                 lock_kernel();
 506                 rpc_execute(&data->task);
 507                 unlock_kernel();
 508
 509                 dfprintk(VFS, "NFS: %4d initiated direct write call (req %s/%Ld, %u bytes @ offset %Lu)\n",
 510                                 data->task.tk_pid,
 511                                 inode->i_sb->s_id,
 512                                 (long long)NFS_FILEID(inode),
 513                                 bytes,
 514                                 (unsigned long long)data->args.offset);
 515
 516                 pos += bytes;
 517                 pgbase += bytes;
 518                 curpage += pgbase >> PAGE_SHIFT;
 519                 pgbase &= ~PAGE_MASK;
 520
 521                 count -= bytes;
 522         } while (count != 0);
 523 }
 524
 525 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)
 526 {
 527         ssize_t result;
 528         sigset_t oldset;
 529         struct inode *inode = iocb->ki_filp->f_mapping->host;
 530         struct rpc_clnt *clnt = NFS_CLIENT(inode);
 531         struct nfs_direct_req *dreq;
 532
 533         dreq = nfs_direct_write_alloc(count, NFS_SERVER(inode)->wsize);
 534         if (!dreq)
 535                 return -ENOMEM;
 536
 537         dreq->pages = pages;
 538         dreq->npages = nr_pages;
 539         dreq->inode = inode;
 540         dreq->filp = iocb->ki_filp;
 541         if (!is_sync_kiocb(iocb))
 542                 dreq->iocb = iocb;
 543
 544         nfs_add_stats(inode, NFSIOS_DIRECTWRITTENBYTES, count);
 545
 546         nfs_begin_data_update(inode);
 547
 548         rpc_clnt_sigmask(clnt, &oldset);
 549         nfs_direct_write_schedule(dreq, user_addr, count, pos);
 550         result = nfs_direct_wait(dreq);
 551         rpc_clnt_sigunmask(clnt, &oldset);
 552
 553         return result;
 554 }
 555
 556 /**
 557  * nfs_file_direct_read - file direct read operation for NFS files
 558  * @iocb: target I/O control block
 559  * @buf: user's buffer into which to read data
 560  * @count: number of bytes to read
 561  * @pos: byte offset in file where reading starts
 562  *
 563  * We use this function for direct reads instead of calling
 564  * generic_file_aio_read() in order to avoid gfar's check to see if
 565  * the request starts before the end of the file.  For that check
 566  * to work, we must generate a GETATTR before each direct read, and
 567  * even then there is a window between the GETATTR and the subsequent
 568  * READ where the file size could change.  Our preference is simply
 569  * to do all reads the application wants, and the server will take
 570  * care of managing the end of file boundary.
 571  *
 572  * This function also eliminates unnecessarily updating the file's
 573  * atime locally, as the NFS server sets the file's atime, and this
 574  * client must read the updated atime from the server back into its
 575  * cache.
 576  */
 577 ssize_t nfs_file_direct_read(struct kiocb *iocb, char __user *buf, size_t count, loff_t pos)
 578 {
 579         ssize_t retval = -EINVAL;
 580         int page_count;
 581         struct page **pages;
 582         struct file *file = iocb->ki_filp;
 583         struct address_space *mapping = file->f_mapping;
 584
 585         dprintk("nfs: direct read(%s/%s, %lu@%Ld)\n",
 586                 file->f_dentry->d_parent->d_name.name,
 587                 file->f_dentry->d_name.name,
 588                 (unsigned long) count, (long long) pos);
 589
 590         if (count < 0)
 591                 goto out;
 592         retval = -EFAULT;
 593         if (!access_ok(VERIFY_WRITE, buf, count))
 594                 goto out;
 595         retval = 0;
 596         if (!count)
 597                 goto out;
 598
 599         retval = nfs_sync_mapping(mapping);
 600         if (retval)
 601                 goto out;
 602
 603         page_count = nfs_get_user_pages(READ, (unsigned long) buf,
 604                                                 count, &pages);
 605         if (page_count < 0) {
 606                 nfs_free_user_pages(pages, 0, 0);
 607                 retval = page_count;
 608                 goto out;
 609         }
 610
 611         retval = nfs_direct_read(iocb, (unsigned long) buf, count, pos,
 612                                                 pages, page_count);
 613         if (retval > 0)
 614                 iocb->ki_pos = pos + retval;
 615
 616 out:
 617         return retval;
 618 }
 619
 620 /**
 621  * nfs_file_direct_write - file direct write operation for NFS files
 622  * @iocb: target I/O control block
 623  * @buf: user's buffer from which to write data
 624  * @count: number of bytes to write
 625  * @pos: byte offset in file where writing starts
 626  *
 627  * We use this function for direct writes instead of calling
 628  * generic_file_aio_write() in order to avoid taking the inode
 629  * semaphore and updating the i_size.  The NFS server will set
 630  * the new i_size and this client must read the updated size
 631  * back into its cache.  We let the server do generic write
 632  * parameter checking and report problems.
 633  *
 634  * We also avoid an unnecessary invocation of generic_osync_inode(),
 635  * as it is fairly meaningless to sync the metadata of an NFS file.
 636  *
 637  * We eliminate local atime updates, see direct read above.
 638  *
 639  * We avoid unnecessary page cache invalidations for normal cached
 640  * readers of this file.
 641  *
 642  * Note that O_APPEND is not supported for NFS direct writes, as there
 643  * is no atomic O_APPEND write facility in the NFS protocol.
 644  */
 645 ssize_t nfs_file_direct_write(struct kiocb *iocb, const char __user *buf, size_t count, loff_t pos)
 646 {
 647         ssize_t retval;
 648         int page_count;
 649         struct page **pages;
 650         struct file *file = iocb->ki_filp;
 651         struct address_space *mapping = file->f_mapping;
 652
 653         dfprintk(VFS, "nfs: direct write(%s/%s, %lu@%Ld)\n",
 654                 file->f_dentry->d_parent->d_name.name,
 655                 file->f_dentry->d_name.name,
 656                 (unsigned long) count, (long long) pos);
 657
 658         retval = generic_write_checks(file, &pos, &count, 0);
 659         if (retval)
 660                 goto out;
 661
 662         retval = -EINVAL;
 663         if ((ssize_t) count < 0)
 664                 goto out;
 665         retval = 0;
 666         if (!count)
 667                 goto out;
 668
 669         retval = -EFAULT;
 670         if (!access_ok(VERIFY_READ, buf, count))
 671                 goto out;
 672
 673         retval = nfs_sync_mapping(mapping);
 674         if (retval)
 675                 goto out;
 676
 677         page_count = nfs_get_user_pages(WRITE, (unsigned long) buf,
 678                                                 count, &pages);
 679         if (page_count < 0) {
 680                 nfs_free_user_pages(pages, 0, 0);
 681                 retval = page_count;
 682                 goto out;
 683         }
 684
 685         retval = nfs_direct_write(iocb, (unsigned long) buf, count,
 686                                         pos, pages, page_count);
 687
 688         /*
 689          * XXX: nfs_end_data_update() already ensures this file's
 690          *      cached data is subsequently invalidated.  Do we really
 691          *      need to call invalidate_inode_pages2() again here?
 692          *
 693          *      For aio writes, this invalidation will almost certainly
 694          *      occur before the writes complete.  Kind of racey.
 695          */
 696         if (mapping->nrpages)
 697                 invalidate_inode_pages2(mapping);
 698
 699         if (retval > 0)
 700                 iocb->ki_pos = pos + retval;
 701
 702 out:
 703         return retval;
 704 }
 705
 706 /**
 707  * nfs_init_directcache - create a slab cache for nfs_direct_req structures
 708  *
 709  */
 710 int nfs_init_directcache(void)
 711 {
 712         nfs_direct_cachep = kmem_cache_create("nfs_direct_cache",
 713                                                 sizeof(struct nfs_direct_req),
 714                                                 0, SLAB_RECLAIM_ACCOUNT,
 715                                                 NULL, NULL);
 716         if (nfs_direct_cachep == NULL)
 717                 return -ENOMEM;
 718
 719         return 0;
 720 }
 721
 722 /**
 723  * nfs_init_directcache - destroy the slab cache for nfs_direct_req structures
 724  *
 725  */
 726 void nfs_destroy_directcache(void)
 727 {
 728         if (kmem_cache_destroy(nfs_direct_cachep))
 729                 printk(KERN_INFO "nfs_direct_cache: not all structures were freed\n");
 730 }