fs/dax.c

   1 /*
   2  * fs/dax.c - Direct Access filesystem code
   3  * Copyright (c) 2013-2014 Intel Corporation
   4  * Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
   5  * Author: Ross Zwisler <ross.zwisler@linux.intel.com>
   6  *
   7  * This program is free software; you can redistribute it and/or modify it
   8  * under the terms and conditions of the GNU General Public License,
   9  * version 2, as published by the Free Software Foundation.
  10  *
  11  * This program is distributed in the hope it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  14  * more details.
  15  */
  16
  17 #include <linux/atomic.h>
  18 #include <linux/blkdev.h>
  19 #include <linux/buffer_head.h>
  20 #include <linux/fs.h>
  21 #include <linux/genhd.h>
  22 #include <linux/highmem.h>
  23 #include <linux/memcontrol.h>
  24 #include <linux/mm.h>
  25 #include <linux/mutex.h>
  26 #include <linux/sched.h>
  27 #include <linux/uio.h>
  28 #include <linux/vmstat.h>
  29
  30 int dax_clear_blocks(struct inode *inode, sector_t block, long size)
  31 {
  32         struct block_device *bdev = inode->i_sb->s_bdev;
  33         sector_t sector = block << (inode->i_blkbits - 9);
  34
  35         might_sleep();
  36         do {
  37                 void *addr;
  38                 unsigned long pfn;
  39                 long count;
  40
  41                 count = bdev_direct_access(bdev, sector, &addr, &pfn, size);
  42                 if (count < 0)
  43                         return count;
  44                 BUG_ON(size < count);
  45                 while (count > 0) {
  46                         unsigned pgsz = PAGE_SIZE - offset_in_page(addr);
  47                         if (pgsz > count)
  48                                 pgsz = count;
  49                         if (pgsz < PAGE_SIZE)
  50                                 memset(addr, 0, pgsz);
  51                         else
  52                                 clear_page(addr);
  53                         addr += pgsz;
  54                         size -= pgsz;
  55                         count -= pgsz;
  56                         BUG_ON(pgsz & 511);
  57                         sector += pgsz / 512;
  58                         cond_resched();
  59                 }
  60         } while (size);
  61
  62         return 0;
  63 }
  64 EXPORT_SYMBOL_GPL(dax_clear_blocks);
  65
  66 static long dax_get_addr(struct buffer_head *bh, void **addr, unsigned blkbits)
  67 {
  68         unsigned long pfn;
  69         sector_t sector = bh->b_blocknr << (blkbits - 9);
  70         return bdev_direct_access(bh->b_bdev, sector, addr, &pfn, bh->b_size);
  71 }
  72
  73 static void dax_new_buf(void *addr, unsigned size, unsigned first, loff_t pos,
  74                         loff_t end)
  75 {
  76         loff_t final = end - pos + first; /* The final byte of the buffer */
  77
  78         if (first > 0)
  79                 memset(addr, 0, first);
  80         if (final < size)
  81                 memset(addr + final, 0, size - final);
  82 }
  83
  84 static bool buffer_written(struct buffer_head *bh)
  85 {
  86         return buffer_mapped(bh) && !buffer_unwritten(bh);
  87 }
  88
  89 /*
  90  * When ext4 encounters a hole, it returns without modifying the buffer_head
  91  * which means that we can't trust b_size.  To cope with this, we set b_state
  92  * to 0 before calling get_block and, if any bit is set, we know we can trust
  93  * b_size.  Unfortunate, really, since ext4 knows precisely how long a hole is
  94  * and would save us time calling get_block repeatedly.
  95  */
  96 static bool buffer_size_valid(struct buffer_head *bh)
  97 {
  98         return bh->b_state != 0;
  99 }
 100
 101 static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
 102                       loff_t start, loff_t end, get_block_t get_block,
 103                       struct buffer_head *bh)
 104 {
 105         ssize_t retval = 0;
 106         loff_t pos = start;
 107         loff_t max = start;
 108         loff_t bh_max = start;
 109         void *addr;
 110         bool hole = false;
 111
 112         if (iov_iter_rw(iter) != WRITE)
 113                 end = min(end, i_size_read(inode));
 114
 115         while (pos < end) {
 116                 unsigned len;
 117                 if (pos == max) {
 118                         unsigned blkbits = inode->i_blkbits;
 119                         sector_t block = pos >> blkbits;
 120                         unsigned first = pos - (block << blkbits);
 121                         long size;
 122
 123                         if (pos == bh_max) {
 124                                 bh->b_size = PAGE_ALIGN(end - pos);
 125                                 bh->b_state = 0;
 126                                 retval = get_block(inode, block, bh,
 127                                                    iov_iter_rw(iter) == WRITE);
 128                                 if (retval)
 129                                         break;
 130                                 if (!buffer_size_valid(bh))
 131                                         bh->b_size = 1 << blkbits;
 132                                 bh_max = pos - first + bh->b_size;
 133                         } else {
 134                                 unsigned done = bh->b_size -
 135                                                 (bh_max - (pos - first));
 136                                 bh->b_blocknr += done >> blkbits;
 137                                 bh->b_size -= done;
 138                         }
 139
 140                         hole = iov_iter_rw(iter) != WRITE && !buffer_written(bh);
 141                         if (hole) {
 142                                 addr = NULL;
 143                                 size = bh->b_size - first;
 144                         } else {
 145                                 retval = dax_get_addr(bh, &addr, blkbits);
 146                                 if (retval < 0)
 147                                         break;
 148                                 if (buffer_unwritten(bh) || buffer_new(bh))
 149                                         dax_new_buf(addr, retval, first, pos,
 150                                                                         end);
 151                                 addr += first;
 152                                 size = retval - first;
 153                         }
 154                         max = min(pos + size, end);
 155                 }
 156
 157                 if (iov_iter_rw(iter) == WRITE)
 158                         len = copy_from_iter(addr, max - pos, iter);
 159                 else if (!hole)
 160                         len = copy_to_iter(addr, max - pos, iter);
 161                 else
 162                         len = iov_iter_zero(max - pos, iter);
 163
 164                 if (!len)
 165                         break;
 166
 167                 pos += len;
 168                 addr += len;
 169         }
 170
 171         return (pos == start) ? retval : pos - start;
 172 }
 173
 174 /**
 175  * dax_do_io - Perform I/O to a DAX file
 176  * @iocb: The control block for this I/O
 177  * @inode: The file which the I/O is directed at
 178  * @iter: The addresses to do I/O from or to
 179  * @pos: The file offset where the I/O starts
 180  * @get_block: The filesystem method used to translate file offsets to blocks
 181  * @end_io: A filesystem callback for I/O completion
 182  * @flags: See below
 183  *
 184  * This function uses the same locking scheme as do_blockdev_direct_IO:
 185  * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
 186  * caller for writes.  For reads, we take and release the i_mutex ourselves.
 187  * If DIO_LOCKING is not set, the filesystem takes care of its own locking.
 188  * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
 189  * is in progress.
 190  */
 191 ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
 192                   struct iov_iter *iter, loff_t pos, get_block_t get_block,
 193                   dio_iodone_t end_io, int flags)
 194 {
 195         struct buffer_head bh;
 196         ssize_t retval = -EINVAL;
 197         loff_t end = pos + iov_iter_count(iter);
 198
 199         memset(&bh, 0, sizeof(bh));
 200
 201         if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ) {
 202                 struct address_space *mapping = inode->i_mapping;
 203                 mutex_lock(&inode->i_mutex);
 204                 retval = filemap_write_and_wait_range(mapping, pos, end - 1);
 205                 if (retval) {
 206                         mutex_unlock(&inode->i_mutex);
 207                         goto out;
 208                 }
 209         }
 210
 211         /* Protects against truncate */
 212         inode_dio_begin(inode);
 213
 214         retval = dax_io(inode, iter, pos, end, get_block, &bh);
 215
 216         if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
 217                 mutex_unlock(&inode->i_mutex);
 218
 219         if ((retval > 0) && end_io)
 220                 end_io(iocb, pos, retval, bh.b_private);
 221
 222         inode_dio_end(inode);
 223  out:
 224         return retval;
 225 }
 226 EXPORT_SYMBOL_GPL(dax_do_io);
 227
 228 /*
 229  * The user has performed a load from a hole in the file.  Allocating
 230  * a new page in the file would cause excessive storage usage for
 231  * workloads with sparse files.  We allocate a page cache page instead.
 232  * We'll kick it out of the page cache if it's ever written to,
 233  * otherwise it will simply fall out of the page cache under memory
 234  * pressure without ever having been dirtied.
 235  */
 236 static int dax_load_hole(struct address_space *mapping, struct page *page,
 237                                                         struct vm_fault *vmf)
 238 {
 239         unsigned long size;
 240         struct inode *inode = mapping->host;
 241         if (!page)
 242                 page = find_or_create_page(mapping, vmf->pgoff,
 243                                                 GFP_KERNEL | __GFP_ZERO);
 244         if (!page)
 245                 return VM_FAULT_OOM;
 246         /* Recheck i_size under page lock to avoid truncate race */
 247         size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 248         if (vmf->pgoff >= size) {
 249                 unlock_page(page);
 250                 page_cache_release(page);
 251                 return VM_FAULT_SIGBUS;
 252         }
 253
 254         vmf->page = page;
 255         return VM_FAULT_LOCKED;
 256 }
 257
 258 static int copy_user_bh(struct page *to, struct buffer_head *bh,
 259                         unsigned blkbits, unsigned long vaddr)
 260 {
 261         void *vfrom, *vto;
 262         if (dax_get_addr(bh, &vfrom, blkbits) < 0)
 263                 return -EIO;
 264         vto = kmap_atomic(to);
 265         copy_user_page(vto, vfrom, vaddr, to);
 266         kunmap_atomic(vto);
 267         return 0;
 268 }
 269
 270 static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
 271                         struct vm_area_struct *vma, struct vm_fault *vmf)
 272 {
 273         struct address_space *mapping = inode->i_mapping;
 274         sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
 275         unsigned long vaddr = (unsigned long)vmf->virtual_address;
 276         void *addr;
 277         unsigned long pfn;
 278         pgoff_t size;
 279         int error;
 280
 281         i_mmap_lock_read(mapping);
 282
 283         /*
 284          * Check truncate didn't happen while we were allocating a block.
 285          * If it did, this block may or may not be still allocated to the
 286          * file.  We can't tell the filesystem to free it because we can't
 287          * take i_mutex here.  In the worst case, the file still has blocks
 288          * allocated past the end of the file.
 289          */
 290         size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 291         if (unlikely(vmf->pgoff >= size)) {
 292                 error = -EIO;
 293                 goto out;
 294         }
 295
 296         error = bdev_direct_access(bh->b_bdev, sector, &addr, &pfn, bh->b_size);
 297         if (error < 0)
 298                 goto out;
 299         if (error < PAGE_SIZE) {
 300                 error = -EIO;
 301                 goto out;
 302         }
 303
 304         if (buffer_unwritten(bh) || buffer_new(bh))
 305                 clear_page(addr);
 306
 307         error = vm_insert_mixed(vma, vaddr, pfn);
 308
 309  out:
 310         i_mmap_unlock_read(mapping);
 311
 312         if (bh->b_end_io)
 313                 bh->b_end_io(bh, 1);
 314
 315         return error;
 316 }
 317
 318 static int do_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
 319                         get_block_t get_block)
 320 {
 321         struct file *file = vma->vm_file;
 322         struct address_space *mapping = file->f_mapping;
 323         struct inode *inode = mapping->host;
 324         struct page *page;
 325         struct buffer_head bh;
 326         unsigned long vaddr = (unsigned long)vmf->virtual_address;
 327         unsigned blkbits = inode->i_blkbits;
 328         sector_t block;
 329         pgoff_t size;
 330         int error;
 331         int major = 0;
 332
 333         size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 334         if (vmf->pgoff >= size)
 335                 return VM_FAULT_SIGBUS;
 336
 337         memset(&bh, 0, sizeof(bh));
 338         block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);
 339         bh.b_size = PAGE_SIZE;
 340
 341  repeat:
 342         page = find_get_page(mapping, vmf->pgoff);
 343         if (page) {
 344                 if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
 345                         page_cache_release(page);
 346                         return VM_FAULT_RETRY;
 347                 }
 348                 if (unlikely(page->mapping != mapping)) {
 349                         unlock_page(page);
 350                         page_cache_release(page);
 351                         goto repeat;
 352                 }
 353                 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 354                 if (unlikely(vmf->pgoff >= size)) {
 355                         /*
 356                          * We have a struct page covering a hole in the file
 357                          * from a read fault and we've raced with a truncate
 358                          */
 359                         error = -EIO;
 360                         goto unlock_page;
 361                 }
 362         }
 363
 364         error = get_block(inode, block, &bh, 0);
 365         if (!error && (bh.b_size < PAGE_SIZE))
 366                 error = -EIO;           /* fs corruption? */
 367         if (error)
 368                 goto unlock_page;
 369
 370         if (!buffer_mapped(&bh) && !buffer_unwritten(&bh) && !vmf->cow_page) {
 371                 if (vmf->flags & FAULT_FLAG_WRITE) {
 372                         error = get_block(inode, block, &bh, 1);
 373                         count_vm_event(PGMAJFAULT);
 374                         mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
 375                         major = VM_FAULT_MAJOR;
 376                         if (!error && (bh.b_size < PAGE_SIZE))
 377                                 error = -EIO;
 378                         if (error)
 379                                 goto unlock_page;
 380                 } else {
 381                         return dax_load_hole(mapping, page, vmf);
 382                 }
 383         }
 384
 385         if (vmf->cow_page) {
 386                 struct page *new_page = vmf->cow_page;
 387                 if (buffer_written(&bh))
 388                         error = copy_user_bh(new_page, &bh, blkbits, vaddr);
 389                 else
 390                         clear_user_highpage(new_page, vaddr);
 391                 if (error)
 392                         goto unlock_page;
 393                 vmf->page = page;
 394                 if (!page) {
 395                         i_mmap_lock_read(mapping);
 396                         /* Check we didn't race with truncate */
 397                         size = (i_size_read(inode) + PAGE_SIZE - 1) >>
 398                                                                 PAGE_SHIFT;
 399                         if (vmf->pgoff >= size) {
 400                                 i_mmap_unlock_read(mapping);
 401                                 error = -EIO;
 402                                 goto out;
 403                         }
 404                 }
 405                 return VM_FAULT_LOCKED;
 406         }
 407
 408         /* Check we didn't race with a read fault installing a new page */
 409         if (!page && major)
 410                 page = find_lock_page(mapping, vmf->pgoff);
 411
 412         if (page) {
 413                 unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
 414                                                         PAGE_CACHE_SIZE, 0);
 415                 delete_from_page_cache(page);
 416                 unlock_page(page);
 417                 page_cache_release(page);
 418         }
 419
 420         error = dax_insert_mapping(inode, &bh, vma, vmf);
 421
 422  out:
 423         if (error == -ENOMEM)
 424                 return VM_FAULT_OOM | major;
 425         /* -EBUSY is fine, somebody else faulted on the same PTE */
 426         if ((error < 0) && (error != -EBUSY))
 427                 return VM_FAULT_SIGBUS | major;
 428         return VM_FAULT_NOPAGE | major;
 429
 430  unlock_page:
 431         if (page) {
 432                 unlock_page(page);
 433                 page_cache_release(page);
 434         }
 435         goto out;
 436 }
 437
 438 /**
 439  * dax_fault - handle a page fault on a DAX file
 440  * @vma: The virtual memory area where the fault occurred
 441  * @vmf: The description of the fault
 442  * @get_block: The filesystem method used to translate file offsets to blocks
 443  *
 444  * When a page fault occurs, filesystems may call this helper in their
 445  * fault handler for DAX files.
 446  */
 447 int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
 448                         get_block_t get_block)
 449 {
 450         int result;
 451         struct super_block *sb = file_inode(vma->vm_file)->i_sb;
 452
 453         if (vmf->flags & FAULT_FLAG_WRITE) {
 454                 sb_start_pagefault(sb);
 455                 file_update_time(vma->vm_file);
 456         }
 457         result = do_dax_fault(vma, vmf, get_block);
 458         if (vmf->flags & FAULT_FLAG_WRITE)
 459                 sb_end_pagefault(sb);
 460
 461         return result;
 462 }
 463 EXPORT_SYMBOL_GPL(dax_fault);
 464
 465 /**
 466  * dax_pfn_mkwrite - handle first write to DAX page
 467  * @vma: The virtual memory area where the fault occurred
 468  * @vmf: The description of the fault
 469  *
 470  */
 471 int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 472 {
 473         struct super_block *sb = file_inode(vma->vm_file)->i_sb;
 474
 475         sb_start_pagefault(sb);
 476         file_update_time(vma->vm_file);
 477         sb_end_pagefault(sb);
 478         return VM_FAULT_NOPAGE;
 479 }
 480 EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
 481
 482 /**
 483  * dax_zero_page_range - zero a range within a page of a DAX file
 484  * @inode: The file being truncated
 485  * @from: The file offset that is being truncated to
 486  * @length: The number of bytes to zero
 487  * @get_block: The filesystem method used to translate file offsets to blocks
 488  *
 489  * This function can be called by a filesystem when it is zeroing part of a
 490  * page in a DAX file.  This is intended for hole-punch operations.  If
 491  * you are truncating a file, the helper function dax_truncate_page() may be
 492  * more convenient.
 493  *
 494  * We work in terms of PAGE_CACHE_SIZE here for commonality with
 495  * block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem
 496  * took care of disposing of the unnecessary blocks.  Even if the filesystem
 497  * block size is smaller than PAGE_SIZE, we have to zero the rest of the page
 498  * since the file might be mmapped.
 499  */
 500 int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
 501                                                         get_block_t get_block)
 502 {
 503         struct buffer_head bh;
 504         pgoff_t index = from >> PAGE_CACHE_SHIFT;
 505         unsigned offset = from & (PAGE_CACHE_SIZE-1);
 506         int err;
 507
 508         /* Block boundary? Nothing to do */
 509         if (!length)
 510                 return 0;
 511         BUG_ON((offset + length) > PAGE_CACHE_SIZE);
 512
 513         memset(&bh, 0, sizeof(bh));
 514         bh.b_size = PAGE_CACHE_SIZE;
 515         err = get_block(inode, index, &bh, 0);
 516         if (err < 0)
 517                 return err;
 518         if (buffer_written(&bh)) {
 519                 void *addr;
 520                 err = dax_get_addr(&bh, &addr, inode->i_blkbits);
 521                 if (err < 0)
 522                         return err;
 523                 memset(addr + offset, 0, length);
 524         }
 525
 526         return 0;
 527 }
 528 EXPORT_SYMBOL_GPL(dax_zero_page_range);
 529
 530 /**
 531  * dax_truncate_page - handle a partial page being truncated in a DAX file
 532  * @inode: The file being truncated
 533  * @from: The file offset that is being truncated to
 534  * @get_block: The filesystem method used to translate file offsets to blocks
 535  *
 536  * Similar to block_truncate_page(), this function can be called by a
 537  * filesystem when it is truncating a DAX file to handle the partial page.
 538  *
 539  * We work in terms of PAGE_CACHE_SIZE here for commonality with
 540  * block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem
 541  * took care of disposing of the unnecessary blocks.  Even if the filesystem
 542  * block size is smaller than PAGE_SIZE, we have to zero the rest of the page
 543  * since the file might be mmapped.
 544  */
 545 int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
 546 {
 547         unsigned length = PAGE_CACHE_ALIGN(from) - from;
 548         return dax_zero_page_range(inode, from, length, get_block);
 549 }
 550 EXPORT_SYMBOL_GPL(dax_truncate_page);