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1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3  * bvec iterator
4  *
5  * Copyright (C) 2001 Ming Lei <ming.lei@canonical.com>
6  */
7 #ifndef __LINUX_BVEC_ITER_H
8 #define __LINUX_BVEC_ITER_H
9 
10 #include <linux/bug.h>
11 #include <linux/errno.h>
12 #include <linux/limits.h>
13 #include <linux/minmax.h>
14 #include <linux/mm.h>
15 #include <linux/types.h>
16 
17 struct page;
18 
19 /**
20  * struct bio_vec - a contiguous range of physical memory addresses
21  * @bv_page:   First page associated with the address range.
22  * @bv_len:    Number of bytes in the address range.
23  * @bv_offset: Start of the address range relative to the start of @bv_page.
24  *
25  * The following holds for a bvec if n * PAGE_SIZE < bv_offset + bv_len:
26  *
27  *   nth_page(@bv_page, n) == @bv_page + n
28  *
29  * This holds because page_is_mergeable() checks the above property.
30  */
31 struct bio_vec {
32 	struct page	*bv_page;
33 	unsigned int	bv_len;
34 	unsigned int	bv_offset;
35 };
36 
37 struct bvec_iter {
38 	sector_t		bi_sector;	/* device address in 512 byte
39 						   sectors */
40 	unsigned int		bi_size;	/* residual I/O count */
41 
42 	unsigned int		bi_idx;		/* current index into bvl_vec */
43 
44 	unsigned int            bi_bvec_done;	/* number of bytes completed in
45 						   current bvec */
46 };
47 
48 struct bvec_iter_all {
49 	struct bio_vec	bv;
50 	int		idx;
51 	unsigned	done;
52 };
53 
54 /*
55  * various member access, note that bio_data should of course not be used
56  * on highmem page vectors
57  */
58 #define __bvec_iter_bvec(bvec, iter)	(&(bvec)[(iter).bi_idx])
59 
60 /* multi-page (mp_bvec) helpers */
61 #define mp_bvec_iter_page(bvec, iter)				\
62 	(__bvec_iter_bvec((bvec), (iter))->bv_page)
63 
64 #define mp_bvec_iter_len(bvec, iter)				\
65 	min((iter).bi_size,					\
66 	    __bvec_iter_bvec((bvec), (iter))->bv_len - (iter).bi_bvec_done)
67 
68 #define mp_bvec_iter_offset(bvec, iter)				\
69 	(__bvec_iter_bvec((bvec), (iter))->bv_offset + (iter).bi_bvec_done)
70 
71 #define mp_bvec_iter_page_idx(bvec, iter)			\
72 	(mp_bvec_iter_offset((bvec), (iter)) / PAGE_SIZE)
73 
74 #define mp_bvec_iter_bvec(bvec, iter)				\
75 ((struct bio_vec) {						\
76 	.bv_page	= mp_bvec_iter_page((bvec), (iter)),	\
77 	.bv_len		= mp_bvec_iter_len((bvec), (iter)),	\
78 	.bv_offset	= mp_bvec_iter_offset((bvec), (iter)),	\
79 })
80 
81 /* For building single-page bvec in flight */
82  #define bvec_iter_offset(bvec, iter)				\
83 	(mp_bvec_iter_offset((bvec), (iter)) % PAGE_SIZE)
84 
85 #define bvec_iter_len(bvec, iter)				\
86 	min_t(unsigned, mp_bvec_iter_len((bvec), (iter)),		\
87 	      PAGE_SIZE - bvec_iter_offset((bvec), (iter)))
88 
89 #define bvec_iter_page(bvec, iter)				\
90 	(mp_bvec_iter_page((bvec), (iter)) +			\
91 	 mp_bvec_iter_page_idx((bvec), (iter)))
92 
93 #define bvec_iter_bvec(bvec, iter)				\
94 ((struct bio_vec) {						\
95 	.bv_page	= bvec_iter_page((bvec), (iter)),	\
96 	.bv_len		= bvec_iter_len((bvec), (iter)),	\
97 	.bv_offset	= bvec_iter_offset((bvec), (iter)),	\
98 })
99 
bvec_iter_advance(const struct bio_vec * bv,struct bvec_iter * iter,unsigned bytes)100 static inline bool bvec_iter_advance(const struct bio_vec *bv,
101 		struct bvec_iter *iter, unsigned bytes)
102 {
103 	unsigned int idx = iter->bi_idx;
104 
105 	if (WARN_ONCE(bytes > iter->bi_size,
106 		     "Attempted to advance past end of bvec iter\n")) {
107 		iter->bi_size = 0;
108 		return false;
109 	}
110 
111 	iter->bi_size -= bytes;
112 	bytes += iter->bi_bvec_done;
113 
114 	while (bytes && bytes >= bv[idx].bv_len) {
115 		bytes -= bv[idx].bv_len;
116 		idx++;
117 	}
118 
119 	iter->bi_idx = idx;
120 	iter->bi_bvec_done = bytes;
121 	return true;
122 }
123 
bvec_iter_skip_zero_bvec(struct bvec_iter * iter)124 static inline void bvec_iter_skip_zero_bvec(struct bvec_iter *iter)
125 {
126 	iter->bi_bvec_done = 0;
127 	iter->bi_idx++;
128 }
129 
130 #define for_each_bvec(bvl, bio_vec, iter, start)			\
131 	for (iter = (start);						\
132 	     (iter).bi_size &&						\
133 		((bvl = bvec_iter_bvec((bio_vec), (iter))), 1);	\
134 	     (bvl).bv_len ? (void)bvec_iter_advance((bio_vec), &(iter),	\
135 		     (bvl).bv_len) : bvec_iter_skip_zero_bvec(&(iter)))
136 
137 /* for iterating one bio from start to end */
138 #define BVEC_ITER_ALL_INIT (struct bvec_iter)				\
139 {									\
140 	.bi_sector	= 0,						\
141 	.bi_size	= UINT_MAX,					\
142 	.bi_idx		= 0,						\
143 	.bi_bvec_done	= 0,						\
144 }
145 
bvec_init_iter_all(struct bvec_iter_all * iter_all)146 static inline struct bio_vec *bvec_init_iter_all(struct bvec_iter_all *iter_all)
147 {
148 	iter_all->done = 0;
149 	iter_all->idx = 0;
150 
151 	return &iter_all->bv;
152 }
153 
bvec_advance(const struct bio_vec * bvec,struct bvec_iter_all * iter_all)154 static inline void bvec_advance(const struct bio_vec *bvec,
155 				struct bvec_iter_all *iter_all)
156 {
157 	struct bio_vec *bv = &iter_all->bv;
158 
159 	if (iter_all->done) {
160 		bv->bv_page++;
161 		bv->bv_offset = 0;
162 	} else {
163 		bv->bv_page = bvec->bv_page + (bvec->bv_offset >> PAGE_SHIFT);
164 		bv->bv_offset = bvec->bv_offset & ~PAGE_MASK;
165 	}
166 	bv->bv_len = min_t(unsigned int, PAGE_SIZE - bv->bv_offset,
167 			   bvec->bv_len - iter_all->done);
168 	iter_all->done += bv->bv_len;
169 
170 	if (iter_all->done == bvec->bv_len) {
171 		iter_all->idx++;
172 		iter_all->done = 0;
173 	}
174 }
175 
176 #endif /* __LINUX_BVEC_ITER_H */
177