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-rw-r--r--include/linux/scatterlist.h79
1 files changed, 77 insertions, 2 deletions
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index bed5ab4d756a..2dc7464cce52 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -20,8 +20,36 @@ static inline void sg_init_one(struct scatterlist *sg, const void *buf,
20 sg_set_buf(sg, buf, buflen); 20 sg_set_buf(sg, buf, buflen);
21} 21}
22 22
23#define sg_next(sg) ((sg) + 1) 23/*
24#define sg_last(sg, nents) (&(sg[(nents) - 1])) 24 * We overload the LSB of the page pointer to indicate whether it's
25 * a valid sg entry, or whether it points to the start of a new scatterlist.
26 * Those low bits are there for everyone! (thanks mason :-)
27 */
28#define sg_is_chain(sg) ((unsigned long) (sg)->page & 0x01)
29#define sg_chain_ptr(sg) \
30 ((struct scatterlist *) ((unsigned long) (sg)->page & ~0x01))
31
32/**
33 * sg_next - return the next scatterlist entry in a list
34 * @sg: The current sg entry
35 *
36 * Usually the next entry will be @sg@ + 1, but if this sg element is part
37 * of a chained scatterlist, it could jump to the start of a new
38 * scatterlist array.
39 *
40 * Note that the caller must ensure that there are further entries after
41 * the current entry, this function will NOT return NULL for an end-of-list.
42 *
43 */
44static inline struct scatterlist *sg_next(struct scatterlist *sg)
45{
46 sg++;
47
48 if (unlikely(sg_is_chain(sg)))
49 sg = sg_chain_ptr(sg);
50
51 return sg;
52}
25 53
26/* 54/*
27 * Loop over each sg element, following the pointer to a new list if necessary 55 * Loop over each sg element, following the pointer to a new list if necessary
@@ -29,4 +57,51 @@ static inline void sg_init_one(struct scatterlist *sg, const void *buf,
29#define for_each_sg(sglist, sg, nr, __i) \ 57#define for_each_sg(sglist, sg, nr, __i) \
30 for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg)) 58 for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
31 59
60/**
61 * sg_last - return the last scatterlist entry in a list
62 * @sgl: First entry in the scatterlist
63 * @nents: Number of entries in the scatterlist
64 *
65 * Should only be used casually, it (currently) scan the entire list
66 * to get the last entry.
67 *
68 * Note that the @sgl@ pointer passed in need not be the first one,
69 * the important bit is that @nents@ denotes the number of entries that
70 * exist from @sgl@.
71 *
72 */
73static inline struct scatterlist *sg_last(struct scatterlist *sgl,
74 unsigned int nents)
75{
76#ifndef ARCH_HAS_SG_CHAIN
77 struct scatterlist *ret = &sgl[nents - 1];
78#else
79 struct scatterlist *sg, *ret = NULL;
80 int i;
81
82 for_each_sg(sgl, sg, nents, i)
83 ret = sg;
84
85#endif
86 return ret;
87}
88
89/**
90 * sg_chain - Chain two sglists together
91 * @prv: First scatterlist
92 * @prv_nents: Number of entries in prv
93 * @sgl: Second scatterlist
94 *
95 * Links @prv@ and @sgl@ together, to form a longer scatterlist.
96 *
97 */
98static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
99 struct scatterlist *sgl)
100{
101#ifndef ARCH_HAS_SG_CHAIN
102 BUG();
103#endif
104 prv[prv_nents - 1].page = (struct page *) ((unsigned long) sgl | 0x01);
105}
106
32#endif /* _LINUX_SCATTERLIST_H */ 107#endif /* _LINUX_SCATTERLIST_H */