include/linux/pagemap.h

   1 #ifndef _LINUX_PAGEMAP_H
   2 #define _LINUX_PAGEMAP_H
   3
   4 /*
   5  * Copyright 1995 Linus Torvalds
   6  */
   7 #include <linux/mm.h>
   8 #include <linux/fs.h>
   9 #include <linux/list.h>
  10 #include <linux/highmem.h>
  11 #include <linux/compiler.h>
  12 #include <asm/uaccess.h>
  13 #include <linux/gfp.h>
  14 #include <linux/bitops.h>
  15 #include <linux/hardirq.h> /* for in_interrupt() */
  16
  17 /*
  18  * Bits in mapping->flags.  The lower __GFP_BITS_SHIFT bits are the page
  19  * allocation mode flags.
  20  */
  21 #define AS_EIO          (__GFP_BITS_SHIFT + 0)  /* IO error on async write */
  22 #define AS_ENOSPC       (__GFP_BITS_SHIFT + 1)  /* ENOSPC on async write */
  23
  24 static inline void mapping_set_error(struct address_space *mapping, int error)
  25 {
  26         if (unlikely(error)) {
  27                 if (error == -ENOSPC)
  28                         set_bit(AS_ENOSPC, &mapping->flags);
  29                 else
  30                         set_bit(AS_EIO, &mapping->flags);
  31         }
  32 }
  33
  34 static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
  35 {
  36         return (__force gfp_t)mapping->flags & __GFP_BITS_MASK;
  37 }
  38
  39 /*
  40  * This is non-atomic.  Only to be used before the mapping is activated.
  41  * Probably needs a barrier...
  42  */
  43 static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
  44 {
  45         m->flags = (m->flags & ~(__force unsigned long)__GFP_BITS_MASK) |
  46                                 (__force unsigned long)mask;
  47 }
  48
  49 /*
  50  * The page cache can done in larger chunks than
  51  * one page, because it allows for more efficient
  52  * throughput (it can then be mapped into user
  53  * space in smaller chunks for same flexibility).
  54  *
  55  * Or rather, it _will_ be done in larger chunks.
  56  */
  57 #define PAGE_CACHE_SHIFT        PAGE_SHIFT
  58 #define PAGE_CACHE_SIZE         PAGE_SIZE
  59 #define PAGE_CACHE_MASK         PAGE_MASK
  60 #define PAGE_CACHE_ALIGN(addr)  (((addr)+PAGE_CACHE_SIZE-1)&PAGE_CACHE_MASK)
  61
  62 #define page_cache_get(page)            get_page(page)
  63 #define page_cache_release(page)        put_page(page)
  64 void release_pages(struct page **pages, int nr, int cold);
  65
  66 /*
  67  * speculatively take a reference to a page.
  68  * If the page is free (_count == 0), then _count is untouched, and 0
  69  * is returned. Otherwise, _count is incremented by 1 and 1 is returned.
  70  *
  71  * This function must be called inside the same rcu_read_lock() section as has
  72  * been used to lookup the page in the pagecache radix-tree (or page table):
  73  * this allows allocators to use a synchronize_rcu() to stabilize _count.
  74  *
  75  * Unless an RCU grace period has passed, the count of all pages coming out
  76  * of the allocator must be considered unstable. page_count may return higher
  77  * than expected, and put_page must be able to do the right thing when the
  78  * page has been finished with, no matter what it is subsequently allocated
  79  * for (because put_page is what is used here to drop an invalid speculative
  80  * reference).
  81  *
  82  * This is the interesting part of the lockless pagecache (and lockless
  83  * get_user_pages) locking protocol, where the lookup-side (eg. find_get_page)
  84  * has the following pattern:
  85  * 1. find page in radix tree
  86  * 2. conditionally increment refcount
  87  * 3. check the page is still in pagecache (if no, goto 1)
  88  *
  89  * Remove-side that cares about stability of _count (eg. reclaim) has the
  90  * following (with tree_lock held for write):
  91  * A. atomically check refcount is correct and set it to 0 (atomic_cmpxchg)
  92  * B. remove page from pagecache
  93  * C. free the page
  94  *
  95  * There are 2 critical interleavings that matter:
  96  * - 2 runs before A: in this case, A sees elevated refcount and bails out
  97  * - A runs before 2: in this case, 2 sees zero refcount and retries;
  98  *   subsequently, B will complete and 1 will find no page, causing the
  99  *   lookup to return NULL.
 100  *
 101  * It is possible that between 1 and 2, the page is removed then the exact same
 102  * page is inserted into the same position in pagecache. That's OK: the
 103  * old find_get_page using tree_lock could equally have run before or after
 104  * such a re-insertion, depending on order that locks are granted.
 105  *
 106  * Lookups racing against pagecache insertion isn't a big problem: either 1
 107  * will find the page or it will not. Likewise, the old find_get_page could run
 108  * either before the insertion or afterwards, depending on timing.
 109  */
 110 static inline int page_cache_get_speculative(struct page *page)
 111 {
 112         VM_BUG_ON(in_interrupt());
 113
 114 #if !defined(CONFIG_SMP) && defined(CONFIG_CLASSIC_RCU)
 115 # ifdef CONFIG_PREEMPT
 116         VM_BUG_ON(!in_atomic());
 117 # endif
 118         /*
 119          * Preempt must be disabled here - we rely on rcu_read_lock doing
 120          * this for us.
 121          *
 122          * Pagecache won't be truncated from interrupt context, so if we have
 123          * found a page in the radix tree here, we have pinned its refcount by
 124          * disabling preempt, and hence no need for the "speculative get" that
 125          * SMP requires.
 126          */
 127         VM_BUG_ON(page_count(page) == 0);
 128         atomic_inc(&page->_count);
 129
 130 #else
 131         if (unlikely(!get_page_unless_zero(page))) {
 132                 /*
 133                  * Either the page has been freed, or will be freed.
 134                  * In either case, retry here and the caller should
 135                  * do the right thing (see comments above).
 136                  */
 137                 return 0;
 138         }
 139 #endif
 140         VM_BUG_ON(PageTail(page));
 141
 142         return 1;
 143 }
 144
 145 static inline int page_freeze_refs(struct page *page, int count)
 146 {
 147         return likely(atomic_cmpxchg(&page->_count, count, 0) == count);
 148 }
 149
 150 static inline void page_unfreeze_refs(struct page *page, int count)
 151 {
 152         VM_BUG_ON(page_count(page) != 0);
 153         VM_BUG_ON(count == 0);
 154
 155         atomic_set(&page->_count, count);
 156 }
 157
 158 #ifdef CONFIG_NUMA
 159 extern struct page *__page_cache_alloc(gfp_t gfp);
 160 #else
 161 static inline struct page *__page_cache_alloc(gfp_t gfp)
 162 {
 163         return alloc_pages(gfp, 0);
 164 }
 165 #endif
 166
 167 static inline struct page *page_cache_alloc(struct address_space *x)
 168 {
 169         return __page_cache_alloc(mapping_gfp_mask(x));
 170 }
 171
 172 static inline struct page *page_cache_alloc_cold(struct address_space *x)
 173 {
 174         return __page_cache_alloc(mapping_gfp_mask(x)|__GFP_COLD);
 175 }
 176
 177 typedef int filler_t(void *, struct page *);
 178
 179 extern struct page * find_get_page(struct address_space *mapping,
 180                                 pgoff_t index);
 181 extern struct page * find_lock_page(struct address_space *mapping,
 182                                 pgoff_t index);
 183 extern struct page * find_or_create_page(struct address_space *mapping,
 184                                 pgoff_t index, gfp_t gfp_mask);
 185 unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
 186                         unsigned int nr_pages, struct page **pages);
 187 unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start,
 188                                unsigned int nr_pages, struct page **pages);
 189 unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
 190                         int tag, unsigned int nr_pages, struct page **pages);
 191
 192 struct page *__grab_cache_page(struct address_space *mapping, pgoff_t index);
 193
 194 /*
 195  * Returns locked page at given index in given cache, creating it if needed.
 196  */
 197 static inline struct page *grab_cache_page(struct address_space *mapping,
 198                                                                 pgoff_t index)
 199 {
 200         return find_or_create_page(mapping, index, mapping_gfp_mask(mapping));
 201 }
 202
 203 extern struct page * grab_cache_page_nowait(struct address_space *mapping,
 204                                 pgoff_t index);
 205 extern struct page * read_cache_page_async(struct address_space *mapping,
 206                                 pgoff_t index, filler_t *filler,
 207                                 void *data);
 208 extern struct page * read_cache_page(struct address_space *mapping,
 209                                 pgoff_t index, filler_t *filler,
 210                                 void *data);
 211 extern int read_cache_pages(struct address_space *mapping,
 212                 struct list_head *pages, filler_t *filler, void *data);
 213
 214 static inline struct page *read_mapping_page_async(
 215                                                 struct address_space *mapping,
 216                                                      pgoff_t index, void *data)
 217 {
 218         filler_t *filler = (filler_t *)mapping->a_ops->readpage;
 219         return read_cache_page_async(mapping, index, filler, data);
 220 }
 221
 222 static inline struct page *read_mapping_page(struct address_space *mapping,
 223                                              pgoff_t index, void *data)
 224 {
 225         filler_t *filler = (filler_t *)mapping->a_ops->readpage;
 226         return read_cache_page(mapping, index, filler, data);
 227 }
 228
 229 int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
 230                                 pgoff_t index, gfp_t gfp_mask);
 231 int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
 232                                 pgoff_t index, gfp_t gfp_mask);
 233 extern void remove_from_page_cache(struct page *page);
 234 extern void __remove_from_page_cache(struct page *page);
 235
 236 /*
 237  * Like add_to_page_cache_locked, but used to add newly allocated pages:
 238  * the page is new, so we can just run SetPageLocked() against it.
 239  */
 240 static inline int add_to_page_cache(struct page *page,
 241                 struct address_space *mapping, pgoff_t offset, gfp_t gfp_mask)
 242 {
 243         int error;
 244
 245         SetPageLocked(page);
 246         error = add_to_page_cache_locked(page, mapping, offset, gfp_mask);
 247         if (unlikely(error))
 248                 ClearPageLocked(page);
 249         return error;
 250 }
 251
 252 /*
 253  * Return byte-offset into filesystem object for page.
 254  */
 255 static inline loff_t page_offset(struct page *page)
 256 {
 257         return ((loff_t)page->index) << PAGE_CACHE_SHIFT;
 258 }
 259
 260 static inline pgoff_t linear_page_index(struct vm_area_struct *vma,
 261                                         unsigned long address)
 262 {
 263         pgoff_t pgoff = (address - vma->vm_start) >> PAGE_SHIFT;
 264         pgoff += vma->vm_pgoff;
 265         return pgoff >> (PAGE_CACHE_SHIFT - PAGE_SHIFT);
 266 }
 267
 268 extern void __lock_page(struct page *page);
 269 extern int __lock_page_killable(struct page *page);
 270 extern void __lock_page_nosync(struct page *page);
 271 extern void unlock_page(struct page *page);
 272
 273 /*
 274  * lock_page may only be called if we have the page's inode pinned.
 275  */
 276 static inline void lock_page(struct page *page)
 277 {
 278         might_sleep();
 279         if (TestSetPageLocked(page))
 280                 __lock_page(page);
 281 }
 282
 283 /*
 284  * lock_page_killable is like lock_page but can be interrupted by fatal
 285  * signals.  It returns 0 if it locked the page and -EINTR if it was
 286  * killed while waiting.
 287  */
 288 static inline int lock_page_killable(struct page *page)
 289 {
 290         might_sleep();
 291         if (TestSetPageLocked(page))
 292                 return __lock_page_killable(page);
 293         return 0;
 294 }
 295
 296 /*
 297  * lock_page_nosync should only be used if we can't pin the page's inode.
 298  * Doesn't play quite so well with block device plugging.
 299  */
 300 static inline void lock_page_nosync(struct page *page)
 301 {
 302         might_sleep();
 303         if (TestSetPageLocked(page))
 304                 __lock_page_nosync(page);
 305 }
 306
 307 /*
 308  * This is exported only for wait_on_page_locked/wait_on_page_writeback.
 309  * Never use this directly!
 310  */
 311 extern void wait_on_page_bit(struct page *page, int bit_nr);
 312
 313 /*
 314  * Wait for a page to be unlocked.
 315  *
 316  * This must be called with the caller "holding" the page,
 317  * ie with increased "page->count" so that the page won't
 318  * go away during the wait..
 319  */
 320 static inline void wait_on_page_locked(struct page *page)
 321 {
 322         if (PageLocked(page))
 323                 wait_on_page_bit(page, PG_locked);
 324 }
 325
 326 /*
 327  * Wait for a page to complete writeback
 328  */
 329 static inline void wait_on_page_writeback(struct page *page)
 330 {
 331         if (PageWriteback(page))
 332                 wait_on_page_bit(page, PG_writeback);
 333 }
 334
 335 extern void end_page_writeback(struct page *page);
 336
 337 /*
 338  * Fault a userspace page into pagetables.  Return non-zero on a fault.
 339  *
 340  * This assumes that two userspace pages are always sufficient.  That's
 341  * not true if PAGE_CACHE_SIZE > PAGE_SIZE.
 342  */
 343 static inline int fault_in_pages_writeable(char __user *uaddr, int size)
 344 {
 345         int ret;
 346
 347         if (unlikely(size == 0))
 348                 return 0;
 349
 350         /*
 351          * Writing zeroes into userspace here is OK, because we know that if
 352          * the zero gets there, we'll be overwriting it.
 353          */
 354         ret = __put_user(0, uaddr);
 355         if (ret == 0) {
 356                 char __user *end = uaddr + size - 1;
 357
 358                 /*
 359                  * If the page was already mapped, this will get a cache miss
 360                  * for sure, so try to avoid doing it.
 361                  */
 362                 if (((unsigned long)uaddr & PAGE_MASK) !=
 363                                 ((unsigned long)end & PAGE_MASK))
 364                         ret = __put_user(0, end);
 365         }
 366         return ret;
 367 }
 368
 369 static inline int fault_in_pages_readable(const char __user *uaddr, int size)
 370 {
 371         volatile char c;
 372         int ret;
 373
 374         if (unlikely(size == 0))
 375                 return 0;
 376
 377         ret = __get_user(c, uaddr);
 378         if (ret == 0) {
 379                 const char __user *end = uaddr + size - 1;
 380
 381                 if (((unsigned long)uaddr & PAGE_MASK) !=
 382                                 ((unsigned long)end & PAGE_MASK))
 383                         ret = __get_user(c, end);
 384         }
 385         return ret;
 386 }
 387
 388 #endif /* _LINUX_PAGEMAP_H */