buffer_head.h

  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	BH_Migrate,     /* Buffer is being migrated (norefs) */
 38
 39	BH_PrivateStart,/* not a state bit, but the first bit available
 40			 * for private allocation by other entities
 41			 */
 42};
 43
 44#define MAX_BUF_PER_PAGE (PAGE_SIZE / 512)
 45
 46struct page;
 47struct buffer_head;
 48struct address_space;
 49typedef void (bh_end_io_t)(struct buffer_head *bh, int uptodate);
 50
 51/*
 52 * Historically, a buffer_head was used to map a single block
 53 * within a page, and of course as the unit of I/O through the
 54 * filesystem and block layers.  Nowadays the basic I/O unit
 55 * is the bio, and buffer_heads are used for extracting block
 56 * mappings (via a get_block_t call), for tracking state within
 57 * a folio (via a folio_mapping) and for wrapping bio submission
 58 * for backward compatibility reasons (e.g. submit_bh).
 59 */
 60struct buffer_head {
 61	unsigned long b_state;		/* buffer state bitmap (see above) */
 62	struct buffer_head *b_this_page;/* circular list of page's buffers */
 63	union {
 64		struct page *b_page;	/* the page this bh is mapped to */
 65		struct folio *b_folio;	/* the folio this bh is mapped to */
 66	};
 67
 68	sector_t b_blocknr;		/* start block number */
 69	size_t b_size;			/* size of mapping */
 70	char *b_data;			/* pointer to data within the page */
 71
 72	struct block_device *b_bdev;
 73	bh_end_io_t *b_end_io;		/* I/O completion */
 74 	void *b_private;		/* reserved for b_end_io */
 75	struct list_head b_assoc_buffers; /* associated with another mapping */
 76	struct address_space *b_assoc_map;	/* mapping this buffer is
 77						   associated with */
 78	atomic_t b_count;		/* users using this buffer_head */
 79	spinlock_t b_uptodate_lock;	/* Used by the first bh in a page, to
 80					 * serialise IO completion of other
 81					 * buffers in the page */
 82};
 83
 84/*
 85 * macro tricks to expand the set_buffer_foo(), clear_buffer_foo()
 86 * and buffer_foo() functions.
 87 * To avoid reset buffer flags that are already set, because that causes
 88 * a costly cache line transition, check the flag first.
 89 */
 90#define BUFFER_FNS(bit, name)						\
 91static __always_inline void set_buffer_##name(struct buffer_head *bh)	\
 92{									\
 93	if (!test_bit(BH_##bit, &(bh)->b_state))			\
 94		set_bit(BH_##bit, &(bh)->b_state);			\
 95}									\
 96static __always_inline void clear_buffer_##name(struct buffer_head *bh)	\
 97{									\
 98	clear_bit(BH_##bit, &(bh)->b_state);				\
 99}									\
100static __always_inline int buffer_##name(const struct buffer_head *bh)	\
101{									\
102	return test_bit(BH_##bit, &(bh)->b_state);			\
103}
104
105/*
106 * test_set_buffer_foo() and test_clear_buffer_foo()
107 */
108#define TAS_BUFFER_FNS(bit, name)					\
109static __always_inline int test_set_buffer_##name(struct buffer_head *bh) \
110{									\
111	return test_and_set_bit(BH_##bit, &(bh)->b_state);		\
112}									\
113static __always_inline int test_clear_buffer_##name(struct buffer_head *bh) \
114{									\
115	return test_and_clear_bit(BH_##bit, &(bh)->b_state);		\
116}									\
117
118/*
119 * Emit the buffer bitops functions.   Note that there are also functions
120 * of the form "mark_buffer_foo()".  These are higher-level functions which
121 * do something in addition to setting a b_state bit.
122 */
123BUFFER_FNS(Dirty, dirty)
124TAS_BUFFER_FNS(Dirty, dirty)
125BUFFER_FNS(Lock, locked)
126BUFFER_FNS(Req, req)
127TAS_BUFFER_FNS(Req, req)
128BUFFER_FNS(Mapped, mapped)
129BUFFER_FNS(New, new)
130BUFFER_FNS(Async_Read, async_read)
131BUFFER_FNS(Async_Write, async_write)
132BUFFER_FNS(Delay, delay)
133BUFFER_FNS(Boundary, boundary)
134BUFFER_FNS(Write_EIO, write_io_error)
135BUFFER_FNS(Unwritten, unwritten)
136BUFFER_FNS(Meta, meta)
137BUFFER_FNS(Prio, prio)
138BUFFER_FNS(Defer_Completion, defer_completion)
139
140static __always_inline void set_buffer_uptodate(struct buffer_head *bh)
141{
142	/*
143	 * If somebody else already set this uptodate, they will
144	 * have done the memory barrier, and a reader will thus
145	 * see *some* valid buffer state.
146	 *
147	 * Any other serialization (with IO errors or whatever that
148	 * might clear the bit) has to come from other state (eg BH_Lock).
149	 */
150	if (test_bit(BH_Uptodate, &bh->b_state))
151		return;
152
153	/*
154	 * make it consistent with folio_mark_uptodate
155	 * pairs with smp_load_acquire in buffer_uptodate
156	 */
157	smp_mb__before_atomic();
158	set_bit(BH_Uptodate, &bh->b_state);
159}
160
161static __always_inline void clear_buffer_uptodate(struct buffer_head *bh)
162{
163	clear_bit(BH_Uptodate, &bh->b_state);
164}
165
166static __always_inline int buffer_uptodate(const struct buffer_head *bh)
167{
168	/*
169	 * make it consistent with folio_test_uptodate
170	 * pairs with smp_mb__before_atomic in set_buffer_uptodate
171	 */
172	return test_bit_acquire(BH_Uptodate, &bh->b_state);
173}
174
175static inline unsigned long bh_offset(const struct buffer_head *bh)
176{
177	return (unsigned long)(bh)->b_data & (page_size(bh->b_page) - 1);
178}
179
180/* If we *know* page->private refers to buffer_heads */
181#define page_buffers(page)					\
182	({							\
183		BUG_ON(!PagePrivate(page));			\
184		((struct buffer_head *)page_private(page));	\
185	})
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);
203struct buffer_head *create_empty_buffers(struct folio *folio,
204		unsigned long blocksize, unsigned long b_state);
205void end_buffer_read_sync(struct buffer_head *bh, int uptodate);
206void end_buffer_write_sync(struct buffer_head *bh, int uptodate);
207
208/* Things to do with buffers at mapping->private_list */
209void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode);
210int generic_buffers_fsync_noflush(struct file *file, loff_t start, loff_t end,
211				  bool datasync);
212int generic_buffers_fsync(struct file *file, loff_t start, loff_t end,
213			  bool datasync);
214void clean_bdev_aliases(struct block_device *bdev, sector_t block,
215			sector_t len);
216static inline void clean_bdev_bh_alias(struct buffer_head *bh)
217{
218	clean_bdev_aliases(bh->b_bdev, bh->b_blocknr, 1);
219}
220
221void mark_buffer_async_write(struct buffer_head *bh);
222void __wait_on_buffer(struct buffer_head *);
223wait_queue_head_t *bh_waitq_head(struct buffer_head *bh);
224struct buffer_head *__find_get_block(struct block_device *bdev, sector_t block,
225			unsigned size);
226struct buffer_head *__find_get_block_nonatomic(struct block_device *bdev,
227			sector_t block, 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_folio(struct folio *folio, struct writeback_control *wbc,
256		void *get_block);
257int __block_write_full_folio(struct inode *inode, struct folio *folio,
258		get_block_t *get_block, struct writeback_control *wbc);
259int block_read_full_folio(struct folio *, get_block_t *);
260bool block_is_partially_uptodate(struct folio *, size_t from, size_t count);
261int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
262		struct folio **foliop, get_block_t *get_block);
263int __block_write_begin(struct folio *folio, loff_t pos, unsigned len,
264		get_block_t *get_block);
265int block_write_end(loff_t pos, unsigned len, unsigned copied, struct folio *);
266int generic_write_end(const struct kiocb *, struct address_space *,
267				loff_t, unsigned len, unsigned copied,
268				struct folio *, void *);
269void folio_zero_new_buffers(struct folio *folio, size_t from, size_t to);
270int cont_write_begin(const struct kiocb *, struct address_space *, loff_t,
271			unsigned, struct folio **, void **,
272			get_block_t *, loff_t *);
273int generic_cont_expand_simple(struct inode *inode, loff_t size);
274void block_commit_write(struct folio *folio, size_t from, size_t to);
275int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
276				get_block_t get_block);
277sector_t generic_block_bmap(struct address_space *, sector_t, get_block_t *);
278int block_truncate_page(struct address_space *, loff_t, get_block_t *);
279
280#ifdef CONFIG_MIGRATION
281extern int buffer_migrate_folio(struct address_space *,
282		struct folio *dst, struct folio *src, enum migrate_mode);
283extern int buffer_migrate_folio_norefs(struct address_space *,
284		struct folio *dst, struct folio *src, enum migrate_mode);
285#else
286#define buffer_migrate_folio NULL
287#define buffer_migrate_folio_norefs NULL
288#endif
289
290/*
291 * inline definitions
292 */
293
294static inline void get_bh(struct buffer_head *bh)
295{
296        atomic_inc(&bh->b_count);
297}
298
299static inline void put_bh(struct buffer_head *bh)
300{
301        smp_mb__before_atomic();
302        atomic_dec(&bh->b_count);
303}
304
305/**
306 * brelse - Release a buffer.
307 * @bh: The buffer to release.
308 *
309 * Decrement a buffer_head's reference count.  If @bh is NULL, this
310 * function is a no-op.
311 *
312 * If all buffers on a folio have zero reference count, are clean
313 * and unlocked, and if the folio is unlocked and not under writeback
314 * then try_to_free_buffers() may strip the buffers from the folio in
315 * preparation for freeing it (sometimes, rarely, buffers are removed
316 * from a folio but it ends up not being freed, and buffers may later
317 * be reattached).
318 *
319 * Context: Any context.
320 */
321static inline void brelse(struct buffer_head *bh)
322{
323	if (bh)
324		__brelse(bh);
325}
326
327/**
328 * bforget - Discard any dirty data in a buffer.
329 * @bh: The buffer to forget.
330 *
331 * Call this function instead of brelse() if the data written to a buffer
332 * no longer needs to be written back.  It will clear the buffer's dirty
333 * flag so writeback of this buffer will be skipped.
334 *
335 * Context: Any context.
336 */
337static inline void bforget(struct buffer_head *bh)
338{
339	if (bh)
340		__bforget(bh);
341}
342
343static inline struct buffer_head *
344sb_bread(struct super_block *sb, sector_t block)
345{
346	return __bread_gfp(sb->s_bdev, block, sb->s_blocksize, __GFP_MOVABLE);
347}
348
349static inline struct buffer_head *
350sb_bread_unmovable(struct super_block *sb, sector_t block)
351{
352	return __bread_gfp(sb->s_bdev, block, sb->s_blocksize, 0);
353}
354
355static inline void
356sb_breadahead(struct super_block *sb, sector_t block)
357{
358	__breadahead(sb->s_bdev, block, sb->s_blocksize);
359}
360
361static inline struct buffer_head *getblk_unmovable(struct block_device *bdev,
362		sector_t block, unsigned size)
363{
364	gfp_t gfp;
365
366	gfp = mapping_gfp_constraint(bdev->bd_mapping, ~__GFP_FS);
367	gfp |= __GFP_NOFAIL;
368
369	return bdev_getblk(bdev, block, size, gfp);
370}
371
372static inline struct buffer_head *__getblk(struct block_device *bdev,
373		sector_t block, unsigned size)
374{
375	gfp_t gfp;
376
377	gfp = mapping_gfp_constraint(bdev->bd_mapping, ~__GFP_FS);
378	gfp |= __GFP_MOVABLE | __GFP_NOFAIL;
379
380	return bdev_getblk(bdev, block, size, gfp);
381}
382
383static inline struct buffer_head *sb_getblk(struct super_block *sb,
384		sector_t block)
385{
386	return __getblk(sb->s_bdev, block, sb->s_blocksize);
387}
388
389static inline struct buffer_head *sb_getblk_gfp(struct super_block *sb,
390		sector_t block, gfp_t gfp)
391{
392	return bdev_getblk(sb->s_bdev, block, sb->s_blocksize, gfp);
393}
394
395static inline struct buffer_head *
396sb_find_get_block(struct super_block *sb, sector_t block)
397{
398	return __find_get_block(sb->s_bdev, block, sb->s_blocksize);
399}
400
401static inline struct buffer_head *
402sb_find_get_block_nonatomic(struct super_block *sb, sector_t block)
403{
404	return __find_get_block_nonatomic(sb->s_bdev, block, sb->s_blocksize);
405}
406
407static inline void
408map_bh(struct buffer_head *bh, struct super_block *sb, sector_t block)
409{
410	set_buffer_mapped(bh);
411	bh->b_bdev = sb->s_bdev;
412	bh->b_blocknr = block;
413	bh->b_size = sb->s_blocksize;
414}
415
416static inline void wait_on_buffer(struct buffer_head *bh)
417{
418	might_sleep();
419	if (buffer_locked(bh))
420		__wait_on_buffer(bh);
421}
422
423static inline int trylock_buffer(struct buffer_head *bh)
424{
425	return likely(!test_and_set_bit_lock(BH_Lock, &bh->b_state));
426}
427
428static inline void lock_buffer(struct buffer_head *bh)
429{
430	might_sleep();
431	if (!trylock_buffer(bh))
432		__lock_buffer(bh);
433}
434
435static inline void bh_readahead(struct buffer_head *bh, blk_opf_t op_flags)
436{
437	if (!buffer_uptodate(bh) && trylock_buffer(bh)) {
438		if (!buffer_uptodate(bh))
439			__bh_read(bh, op_flags, false);
440		else
441			unlock_buffer(bh);
442	}
443}
444
445static inline void bh_read_nowait(struct buffer_head *bh, blk_opf_t op_flags)
446{
447	if (!bh_uptodate_or_lock(bh))
448		__bh_read(bh, op_flags, false);
449}
450
451/* Returns 1 if buffer uptodated, 0 on success, and -EIO on error. */
452static inline int bh_read(struct buffer_head *bh, blk_opf_t op_flags)
453{
454	if (bh_uptodate_or_lock(bh))
455		return 1;
456	return __bh_read(bh, op_flags, true);
457}
458
459static inline void bh_read_batch(int nr, struct buffer_head *bhs[])
460{
461	__bh_read_batch(nr, bhs, 0, true);
462}
463
464static inline void bh_readahead_batch(int nr, struct buffer_head *bhs[],
465				      blk_opf_t op_flags)
466{
467	__bh_read_batch(nr, bhs, op_flags, false);
468}
469
470/**
471 * __bread() - Read a block.
472 * @bdev: The block device to read from.
473 * @block: Block number in units of block size.
474 * @size: The block size of this device in bytes.
475 *
476 * Read a specified block, and return the buffer head that refers
477 * to it.  The memory is allocated from the movable area so that it can
478 * be migrated.  The returned buffer head has its refcount increased.
479 * The caller should call brelse() when it has finished with the buffer.
480 *
481 * Context: May sleep waiting for I/O.
482 * Return: NULL if the block was unreadable.
483 */
484static inline struct buffer_head *__bread(struct block_device *bdev,
485		sector_t block, unsigned size)
486{
487	return __bread_gfp(bdev, block, size, __GFP_MOVABLE);
488}
489
490/**
491 * get_nth_bh - Get a reference on the n'th buffer after this one.
492 * @bh: The buffer to start counting from.
493 * @count: How many buffers to skip.
494 *
495 * This is primarily useful for finding the nth buffer in a folio; in
496 * that case you pass the head buffer and the byte offset in the folio
497 * divided by the block size.  It can be used for other purposes, but
498 * it will wrap at the end of the folio rather than returning NULL or
499 * proceeding to the next folio for you.
500 *
501 * Return: The requested buffer with an elevated refcount.
502 */
503static inline __must_check
504struct buffer_head *get_nth_bh(struct buffer_head *bh, unsigned int count)
505{
506	while (count--)
507		bh = bh->b_this_page;
508	get_bh(bh);
509	return bh;
510}
511
512bool block_dirty_folio(struct address_space *mapping, struct folio *folio);
513
514#ifdef CONFIG_BUFFER_HEAD
515
516void buffer_init(void);
517bool try_to_free_buffers(struct folio *folio);
518int inode_has_buffers(struct inode *inode);
519void invalidate_inode_buffers(struct inode *inode);
520int remove_inode_buffers(struct inode *inode);
521int sync_mapping_buffers(struct address_space *mapping);
522void invalidate_bh_lrus(void);
523void invalidate_bh_lrus_cpu(void);
524bool has_bh_in_lru(int cpu, void *dummy);
525extern int buffer_heads_over_limit;
526
527#else /* CONFIG_BUFFER_HEAD */
528
529static inline void buffer_init(void) {}
530static inline bool try_to_free_buffers(struct folio *folio) { return true; }
531static inline int inode_has_buffers(struct inode *inode) { return 0; }
532static inline void invalidate_inode_buffers(struct inode *inode) {}
533static inline int remove_inode_buffers(struct inode *inode) { return 1; }
534static inline int sync_mapping_buffers(struct address_space *mapping) { return 0; }
535static inline void invalidate_bh_lrus(void) {}
536static inline void invalidate_bh_lrus_cpu(void) {}
537static inline bool has_bh_in_lru(int cpu, void *dummy) { return false; }
538#define buffer_heads_over_limit 0
539
540#endif /* CONFIG_BUFFER_HEAD */
541#endif /* _LINUX_BUFFER_HEAD_H */