1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * include/linux/buffer_head.h
4 *
5 * Everything to do with buffer_heads.
6 */
7
8#ifndef _LINUX_BUFFER_HEAD_H
9#define _LINUX_BUFFER_HEAD_H
10
11#include <linux/types.h>
12#include <linux/blk_types.h>
13#include <linux/fs.h>
14#include <linux/linkage.h>
15#include <linux/pagemap.h>
16#include <linux/wait.h>
17#include <linux/atomic.h>
18
19enum bh_state_bits {
20 BH_Uptodate, /* Contains valid data */
21 BH_Dirty, /* Is dirty */
22 BH_Lock, /* Is locked */
23 BH_Req, /* Has been submitted for I/O */
24
25 BH_Mapped, /* Has a disk mapping */
26 BH_New, /* Disk mapping was newly created by get_block */
27 BH_Async_Read, /* Is under end_buffer_async_read I/O */
28 BH_Async_Write, /* Is under end_buffer_async_write I/O */
29 BH_Delay, /* Buffer is not yet allocated on disk */
30 BH_Boundary, /* Block is followed by a discontiguity */
31 BH_Write_EIO, /* I/O error on write */
32 BH_Unwritten, /* Buffer is allocated on disk but not written */
33 BH_Quiet, /* Buffer Error Prinks to be quiet */
34 BH_Meta, /* Buffer contains metadata */
35 BH_Prio, /* Buffer should be submitted with REQ_PRIO */
36 BH_Defer_Completion, /* Defer AIO completion to workqueue */
37
38 BH_PrivateStart,/* not a state bit, but the first bit available
39 * for private allocation by other entities
40 */
41};
42
43#define MAX_BUF_PER_PAGE (PAGE_SIZE / 512)
44
45struct page;
46struct buffer_head;
47struct address_space;
48typedef void (bh_end_io_t)(struct buffer_head *bh, int uptodate);
49
50/*
51 * Historically, a buffer_head was used to map a single block
52 * within a page, and of course as the unit of I/O through the
53 * filesystem and block layers. Nowadays the basic I/O unit
54 * is the bio, and buffer_heads are used for extracting block
55 * mappings (via a get_block_t call), for tracking state within
56 * a page (via a page_mapping) and for wrapping bio submission
57 * for backward compatibility reasons (e.g. submit_bh).
58 */
59struct buffer_head {
60 unsigned long b_state; /* buffer state bitmap (see above) */
61 struct buffer_head *b_this_page;/* circular list of page's buffers */
62 union {
63 struct page *b_page; /* the page this bh is mapped to */
64 struct folio *b_folio; /* the folio this bh is mapped to */
65 };
66
67 sector_t b_blocknr; /* start block number */
68 size_t b_size; /* size of mapping */
69 char *b_data; /* pointer to data within the page */
70
71 struct block_device *b_bdev;
72 bh_end_io_t *b_end_io; /* I/O completion */
73 void *b_private; /* reserved for b_end_io */
74 struct list_head b_assoc_buffers; /* associated with another mapping */
75 struct address_space *b_assoc_map; /* mapping this buffer is
76 associated with */
77 atomic_t b_count; /* users using this buffer_head */
78 spinlock_t b_uptodate_lock; /* Used by the first bh in a page, to
79 * serialise IO completion of other
80 * buffers in the page */
81};
82
83/*
84 * macro tricks to expand the set_buffer_foo(), clear_buffer_foo()
85 * and buffer_foo() functions.
86 * To avoid reset buffer flags that are already set, because that causes
87 * a costly cache line transition, check the flag first.
88 */
89#define BUFFER_FNS(bit, name) \
90static __always_inline void set_buffer_##name(struct buffer_head *bh) \
91{ \
92 if (!test_bit(BH_##bit, &(bh)->b_state)) \
93 set_bit(BH_##bit, &(bh)->b_state); \
94} \
95static __always_inline void clear_buffer_##name(struct buffer_head *bh) \
96{ \
97 clear_bit(BH_##bit, &(bh)->b_state); \
98} \
99static __always_inline int buffer_##name(const struct buffer_head *bh) \
100{ \
101 return test_bit(BH_##bit, &(bh)->b_state); \
102}
103
104/*
105 * test_set_buffer_foo() and test_clear_buffer_foo()
106 */
107#define TAS_BUFFER_FNS(bit, name) \
108static __always_inline int test_set_buffer_##name(struct buffer_head *bh) \
109{ \
110 return test_and_set_bit(BH_##bit, &(bh)->b_state); \
111} \
112static __always_inline int test_clear_buffer_##name(struct buffer_head *bh) \
113{ \
114 return test_and_clear_bit(BH_##bit, &(bh)->b_state); \
115} \
116
117/*
118 * Emit the buffer bitops functions. Note that there are also functions
119 * of the form "mark_buffer_foo()". These are higher-level functions which
120 * do something in addition to setting a b_state bit.
121 */
122BUFFER_FNS(Dirty, dirty)
123TAS_BUFFER_FNS(Dirty, dirty)
124BUFFER_FNS(Lock, locked)
125BUFFER_FNS(Req, req)
126TAS_BUFFER_FNS(Req, req)
127BUFFER_FNS(Mapped, mapped)
128BUFFER_FNS(New, new)
129BUFFER_FNS(Async_Read, async_read)
130BUFFER_FNS(Async_Write, async_write)
131BUFFER_FNS(Delay, delay)
132BUFFER_FNS(Boundary, boundary)
133BUFFER_FNS(Write_EIO, write_io_error)
134BUFFER_FNS(Unwritten, unwritten)
135BUFFER_FNS(Meta, meta)
136BUFFER_FNS(Prio, prio)
137BUFFER_FNS(Defer_Completion, defer_completion)
138
139static __always_inline void set_buffer_uptodate(struct buffer_head *bh)
140{
141 /*
142 * If somebody else already set this uptodate, they will
143 * have done the memory barrier, and a reader will thus
144 * see *some* valid buffer state.
145 *
146 * Any other serialization (with IO errors or whatever that
147 * might clear the bit) has to come from other state (eg BH_Lock).
148 */
149 if (test_bit(BH_Uptodate, &bh->b_state))
150 return;
151
152 /*
153 * make it consistent with folio_mark_uptodate
154 * pairs with smp_load_acquire in buffer_uptodate
155 */
156 smp_mb__before_atomic();
157 set_bit(nr: BH_Uptodate, addr: &bh->b_state);
158}
159
160static __always_inline void clear_buffer_uptodate(struct buffer_head *bh)
161{
162 clear_bit(nr: BH_Uptodate, addr: &bh->b_state);
163}
164
165static __always_inline int buffer_uptodate(const struct buffer_head *bh)
166{
167 /*
168 * make it consistent with folio_test_uptodate
169 * pairs with smp_mb__before_atomic in set_buffer_uptodate
170 */
171 return test_bit_acquire(BH_Uptodate, &bh->b_state);
172}
173
174static inline unsigned long bh_offset(const struct buffer_head *bh)
175{
176 return (unsigned long)(bh)->b_data & (page_size(page: bh->b_page) - 1);
177}
178
179/* If we *know* page->private refers to buffer_heads */
180#define page_buffers(page) \
181 ({ \
182 BUG_ON(!PagePrivate(page)); \
183 ((struct buffer_head *)page_private(page)); \
184 })
185#define page_has_buffers(page) PagePrivate(page)
186#define folio_buffers(folio) folio_get_private(folio)
187
188void buffer_check_dirty_writeback(struct folio *folio,
189 bool *dirty, bool *writeback);
190
191/*
192 * Declarations
193 */
194
195void mark_buffer_dirty(struct buffer_head *bh);
196void mark_buffer_write_io_error(struct buffer_head *bh);
197void touch_buffer(struct buffer_head *bh);
198void folio_set_bh(struct buffer_head *bh, struct folio *folio,
199 unsigned long offset);
200struct buffer_head *folio_alloc_buffers(struct folio *folio, unsigned long size,
201 gfp_t gfp);
202struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
203 bool retry);
204struct buffer_head *create_empty_buffers(struct folio *folio,
205 unsigned long blocksize, unsigned long b_state);
206void end_buffer_read_sync(struct buffer_head *bh, int uptodate);
207void end_buffer_write_sync(struct buffer_head *bh, int uptodate);
208void end_buffer_async_write(struct buffer_head *bh, int uptodate);
209
210/* Things to do with buffers at mapping->private_list */
211void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode);
212int generic_buffers_fsync_noflush(struct file *file, loff_t start, loff_t end,
213 bool datasync);
214int generic_buffers_fsync(struct file *file, loff_t start, loff_t end,
215 bool datasync);
216void clean_bdev_aliases(struct block_device *bdev, sector_t block,
217 sector_t len);
218static inline void clean_bdev_bh_alias(struct buffer_head *bh)
219{
220 clean_bdev_aliases(bdev: bh->b_bdev, block: bh->b_blocknr, len: 1);
221}
222
223void mark_buffer_async_write(struct buffer_head *bh);
224void __wait_on_buffer(struct buffer_head *);
225wait_queue_head_t *bh_waitq_head(struct buffer_head *bh);
226struct buffer_head *__find_get_block(struct block_device *bdev, sector_t block,
227 unsigned size);
228struct buffer_head *bdev_getblk(struct block_device *bdev, sector_t block,
229 unsigned size, gfp_t gfp);
230void __brelse(struct buffer_head *);
231void __bforget(struct buffer_head *);
232void __breadahead(struct block_device *, sector_t block, unsigned int size);
233struct buffer_head *__bread_gfp(struct block_device *,
234 sector_t block, unsigned size, gfp_t gfp);
235struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
236void free_buffer_head(struct buffer_head * bh);
237void unlock_buffer(struct buffer_head *bh);
238void __lock_buffer(struct buffer_head *bh);
239int sync_dirty_buffer(struct buffer_head *bh);
240int __sync_dirty_buffer(struct buffer_head *bh, blk_opf_t op_flags);
241void write_dirty_buffer(struct buffer_head *bh, blk_opf_t op_flags);
242void submit_bh(blk_opf_t, struct buffer_head *);
243void write_boundary_block(struct block_device *bdev,
244 sector_t bblock, unsigned blocksize);
245int bh_uptodate_or_lock(struct buffer_head *bh);
246int __bh_read(struct buffer_head *bh, blk_opf_t op_flags, bool wait);
247void __bh_read_batch(int nr, struct buffer_head *bhs[],
248 blk_opf_t op_flags, bool force_lock);
249
250/*
251 * Generic address_space_operations implementations for buffer_head-backed
252 * address_spaces.
253 */
254void block_invalidate_folio(struct folio *folio, size_t offset, size_t length);
255int block_write_full_page(struct page *page, get_block_t *get_block,
256 struct writeback_control *wbc);
257int __block_write_full_folio(struct inode *inode, struct folio *folio,
258 get_block_t *get_block, struct writeback_control *wbc,
259 bh_end_io_t *handler);
260int block_read_full_folio(struct folio *, get_block_t *);
261bool block_is_partially_uptodate(struct folio *, size_t from, size_t count);
262int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
263 struct page **pagep, get_block_t *get_block);
264int __block_write_begin(struct page *page, loff_t pos, unsigned len,
265 get_block_t *get_block);
266int block_write_end(struct file *, struct address_space *,
267 loff_t, unsigned, unsigned,
268 struct page *, void *);
269int generic_write_end(struct file *, struct address_space *,
270 loff_t, unsigned, unsigned,
271 struct page *, void *);
272void folio_zero_new_buffers(struct folio *folio, size_t from, size_t to);
273void clean_page_buffers(struct page *page);
274int cont_write_begin(struct file *, struct address_space *, loff_t,
275 unsigned, struct page **, void **,
276 get_block_t *, loff_t *);
277int generic_cont_expand_simple(struct inode *inode, loff_t size);
278void block_commit_write(struct page *page, unsigned int from, unsigned int to);
279int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
280 get_block_t get_block);
281sector_t generic_block_bmap(struct address_space *, sector_t, get_block_t *);
282int block_truncate_page(struct address_space *, loff_t, get_block_t *);
283
284#ifdef CONFIG_MIGRATION
285extern int buffer_migrate_folio(struct address_space *,
286 struct folio *dst, struct folio *src, enum migrate_mode);
287extern int buffer_migrate_folio_norefs(struct address_space *,
288 struct folio *dst, struct folio *src, enum migrate_mode);
289#else
290#define buffer_migrate_folio NULL
291#define buffer_migrate_folio_norefs NULL
292#endif
293
294/*
295 * inline definitions
296 */
297
298static inline void get_bh(struct buffer_head *bh)
299{
300 atomic_inc(v: &bh->b_count);
301}
302
303static inline void put_bh(struct buffer_head *bh)
304{
305 smp_mb__before_atomic();
306 atomic_dec(v: &bh->b_count);
307}
308
309static inline void brelse(struct buffer_head *bh)
310{
311 if (bh)
312 __brelse(bh);
313}
314
315static inline void bforget(struct buffer_head *bh)
316{
317 if (bh)
318 __bforget(bh);
319}
320
321static inline struct buffer_head *
322sb_bread(struct super_block *sb, sector_t block)
323{
324 return __bread_gfp(sb->s_bdev, block, size: sb->s_blocksize, __GFP_MOVABLE);
325}
326
327static inline struct buffer_head *
328sb_bread_unmovable(struct super_block *sb, sector_t block)
329{
330 return __bread_gfp(sb->s_bdev, block, size: sb->s_blocksize, gfp: 0);
331}
332
333static inline void
334sb_breadahead(struct super_block *sb, sector_t block)
335{
336 __breadahead(sb->s_bdev, block, size: sb->s_blocksize);
337}
338
339static inline struct buffer_head *getblk_unmovable(struct block_device *bdev,
340 sector_t block, unsigned size)
341{
342 gfp_t gfp;
343
344 gfp = mapping_gfp_constraint(mapping: bdev->bd_inode->i_mapping, gfp_mask: ~__GFP_FS);
345 gfp |= __GFP_NOFAIL;
346
347 return bdev_getblk(bdev, block, size, gfp);
348}
349
350static inline struct buffer_head *__getblk(struct block_device *bdev,
351 sector_t block, unsigned size)
352{
353 gfp_t gfp;
354
355 gfp = mapping_gfp_constraint(mapping: bdev->bd_inode->i_mapping, gfp_mask: ~__GFP_FS);
356 gfp |= __GFP_MOVABLE | __GFP_NOFAIL;
357
358 return bdev_getblk(bdev, block, size, gfp);
359}
360
361static inline struct buffer_head *sb_getblk(struct super_block *sb,
362 sector_t block)
363{
364 return __getblk(bdev: sb->s_bdev, block, size: sb->s_blocksize);
365}
366
367static inline struct buffer_head *sb_getblk_gfp(struct super_block *sb,
368 sector_t block, gfp_t gfp)
369{
370 return bdev_getblk(bdev: sb->s_bdev, block, size: sb->s_blocksize, gfp);
371}
372
373static inline struct buffer_head *
374sb_find_get_block(struct super_block *sb, sector_t block)
375{
376 return __find_get_block(bdev: sb->s_bdev, block, size: sb->s_blocksize);
377}
378
379static inline void
380map_bh(struct buffer_head *bh, struct super_block *sb, sector_t block)
381{
382 set_buffer_mapped(bh);
383 bh->b_bdev = sb->s_bdev;
384 bh->b_blocknr = block;
385 bh->b_size = sb->s_blocksize;
386}
387
388static inline void wait_on_buffer(struct buffer_head *bh)
389{
390 might_sleep();
391 if (buffer_locked(bh))
392 __wait_on_buffer(bh);
393}
394
395static inline int trylock_buffer(struct buffer_head *bh)
396{
397 return likely(!test_and_set_bit_lock(BH_Lock, &bh->b_state));
398}
399
400static inline void lock_buffer(struct buffer_head *bh)
401{
402 might_sleep();
403 if (!trylock_buffer(bh))
404 __lock_buffer(bh);
405}
406
407static inline void bh_readahead(struct buffer_head *bh, blk_opf_t op_flags)
408{
409 if (!buffer_uptodate(bh) && trylock_buffer(bh)) {
410 if (!buffer_uptodate(bh))
411 __bh_read(bh, op_flags, wait: false);
412 else
413 unlock_buffer(bh);
414 }
415}
416
417static inline void bh_read_nowait(struct buffer_head *bh, blk_opf_t op_flags)
418{
419 if (!bh_uptodate_or_lock(bh))
420 __bh_read(bh, op_flags, wait: false);
421}
422
423/* Returns 1 if buffer uptodated, 0 on success, and -EIO on error. */
424static inline int bh_read(struct buffer_head *bh, blk_opf_t op_flags)
425{
426 if (bh_uptodate_or_lock(bh))
427 return 1;
428 return __bh_read(bh, op_flags, wait: true);
429}
430
431static inline void bh_read_batch(int nr, struct buffer_head *bhs[])
432{
433 __bh_read_batch(nr, bhs, op_flags: 0, force_lock: true);
434}
435
436static inline void bh_readahead_batch(int nr, struct buffer_head *bhs[],
437 blk_opf_t op_flags)
438{
439 __bh_read_batch(nr, bhs, op_flags, force_lock: false);
440}
441
442/**
443 * __bread() - reads a specified block and returns the bh
444 * @bdev: the block_device to read from
445 * @block: number of block
446 * @size: size (in bytes) to read
447 *
448 * Reads a specified block, and returns buffer head that contains it.
449 * The page cache is allocated from movable area so that it can be migrated.
450 * It returns NULL if the block was unreadable.
451 */
452static inline struct buffer_head *
453__bread(struct block_device *bdev, sector_t block, unsigned size)
454{
455 return __bread_gfp(bdev, block, size, __GFP_MOVABLE);
456}
457
458/**
459 * get_nth_bh - Get a reference on the n'th buffer after this one.
460 * @bh: The buffer to start counting from.
461 * @count: How many buffers to skip.
462 *
463 * This is primarily useful for finding the nth buffer in a folio; in
464 * that case you pass the head buffer and the byte offset in the folio
465 * divided by the block size. It can be used for other purposes, but
466 * it will wrap at the end of the folio rather than returning NULL or
467 * proceeding to the next folio for you.
468 *
469 * Return: The requested buffer with an elevated refcount.
470 */
471static inline __must_check
472struct buffer_head *get_nth_bh(struct buffer_head *bh, unsigned int count)
473{
474 while (count--)
475 bh = bh->b_this_page;
476 get_bh(bh);
477 return bh;
478}
479
480bool block_dirty_folio(struct address_space *mapping, struct folio *folio);
481
482#ifdef CONFIG_BUFFER_HEAD
483
484void buffer_init(void);
485bool try_to_free_buffers(struct folio *folio);
486int inode_has_buffers(struct inode *inode);
487void invalidate_inode_buffers(struct inode *inode);
488int remove_inode_buffers(struct inode *inode);
489int sync_mapping_buffers(struct address_space *mapping);
490void invalidate_bh_lrus(void);
491void invalidate_bh_lrus_cpu(void);
492bool has_bh_in_lru(int cpu, void *dummy);
493extern int buffer_heads_over_limit;
494
495#else /* CONFIG_BUFFER_HEAD */
496
497static inline void buffer_init(void) {}
498static inline bool try_to_free_buffers(struct folio *folio) { return true; }
499static inline int inode_has_buffers(struct inode *inode) { return 0; }
500static inline void invalidate_inode_buffers(struct inode *inode) {}
501static inline int remove_inode_buffers(struct inode *inode) { return 1; }
502static inline int sync_mapping_buffers(struct address_space *mapping) { return 0; }
503static inline void invalidate_bh_lrus(void) {}
504static inline void invalidate_bh_lrus_cpu(void) {}
505static inline bool has_bh_in_lru(int cpu, void *dummy) { return false; }
506#define buffer_heads_over_limit 0
507
508#endif /* CONFIG_BUFFER_HEAD */
509#endif /* _LINUX_BUFFER_HEAD_H */
510

source code of linux/include/linux/buffer_head.h