1 #ifndef _LINUX_SCATTERLIST_H
2 #define _LINUX_SCATTERLIST_H
4 #include <asm/scatterlist.h>
6 #include <linux/string.h>
10 * Notes on SG table design.
12 * Architectures must provide an unsigned long page_link field in the
13 * scatterlist struct. We use that to place the page pointer AND encode
14 * information about the sg table as well. The two lower bits are reserved
15 * for this information.
17 * If bit 0 is set, then the page_link contains a pointer to the next sg
18 * table list. Otherwise the next entry is at sg + 1.
20 * If bit 1 is set, then this sg entry is the last element in a list.
27 * sg_set_page - Set sg entry to point at given page
32 * Use this function to set an sg entry pointing at a page, never assign
33 * the page directly. We encode sg table information in the lower bits
34 * of the page pointer. See sg_page() for looking up the page belonging
38 static inline void sg_set_page(struct scatterlist *sg, struct page *page)
40 unsigned long page_link = sg->page_link & 0x3;
42 sg->page_link = page_link | (unsigned long) page;
45 #define sg_page(sg) ((struct page *) ((sg)->page_link & ~0x3))
48 * sg_set_buf - Set sg entry to point at given data
51 * @buflen: Data length
54 static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
57 sg_set_page(sg, virt_to_page(buf));
58 sg->offset = offset_in_page(buf);
63 * We overload the LSB of the page pointer to indicate whether it's
64 * a valid sg entry, or whether it points to the start of a new scatterlist.
65 * Those low bits are there for everyone! (thanks mason :-)
67 #define sg_is_chain(sg) ((sg)->page_link & 0x01)
68 #define sg_is_last(sg) ((sg)->page_link & 0x02)
69 #define sg_chain_ptr(sg) \
70 ((struct scatterlist *) ((sg)->page_link & ~0x03))
73 * sg_next - return the next scatterlist entry in a list
74 * @sg: The current sg entry
77 * Usually the next entry will be @sg@ + 1, but if this sg element is part
78 * of a chained scatterlist, it could jump to the start of a new
82 static inline struct scatterlist *sg_next(struct scatterlist *sg)
88 if (unlikely(sg_is_chain(sg)))
89 sg = sg_chain_ptr(sg);
95 * Loop over each sg element, following the pointer to a new list if necessary
97 #define for_each_sg(sglist, sg, nr, __i) \
98 for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
101 * sg_last - return the last scatterlist entry in a list
102 * @sgl: First entry in the scatterlist
103 * @nents: Number of entries in the scatterlist
106 * Should only be used casually, it (currently) scan the entire list
107 * to get the last entry.
109 * Note that the @sgl@ pointer passed in need not be the first one,
110 * the important bit is that @nents@ denotes the number of entries that
114 static inline struct scatterlist *sg_last(struct scatterlist *sgl,
117 #ifndef ARCH_HAS_SG_CHAIN
118 struct scatterlist *ret = &sgl[nents - 1];
120 struct scatterlist *sg, *ret = NULL;
123 for_each_sg(sgl, sg, nents, i)
131 * sg_chain - Chain two sglists together
132 * @prv: First scatterlist
133 * @prv_nents: Number of entries in prv
134 * @sgl: Second scatterlist
137 * Links @prv@ and @sgl@ together, to form a longer scatterlist.
140 static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
141 struct scatterlist *sgl)
143 #ifndef ARCH_HAS_SG_CHAIN
146 prv[prv_nents - 1].page_link = (unsigned long) sgl | 0x01;
150 * sg_mark_end - Mark the end of the scatterlist
152 * @nents: Number of entries in sgl
155 * Marks the last entry as the termination point for sg_next()
158 static inline void sg_mark_end(struct scatterlist *sgl, unsigned int nents)
160 sgl[nents - 1].page_link = 0x02;
163 static inline void __sg_mark_end(struct scatterlist *sg)
165 sg->page_link |= 0x02;
169 * sg_init_one - Initialize a single entry sg list
171 * @buf: Virtual address for IO
175 * This should not be used on a single entry that is part of a larger
176 * table. Use sg_init_table() for that.
179 static inline void sg_init_one(struct scatterlist *sg, const void *buf,
182 memset(sg, 0, sizeof(*sg));
184 sg_set_buf(sg, buf, buflen);
188 * sg_init_table - Initialize SG table
190 * @nents: Number of entries in table
193 * If this is part of a chained sg table, sg_mark_end() should be
194 * used only on the last table part.
197 static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
199 memset(sgl, 0, sizeof(*sgl) * nents);
200 sg_mark_end(sgl, nents);
204 * sg_phys - Return physical address of an sg entry
208 * This calls page_to_phys() on the page in this sg entry, and adds the
209 * sg offset. The caller must know that it is legal to call page_to_phys()
213 static inline unsigned long sg_phys(struct scatterlist *sg)
215 return page_to_phys(sg_page(sg)) + sg->offset;
219 * sg_virt - Return virtual address of an sg entry
223 * This calls page_address() on the page in this sg entry, and adds the
224 * sg offset. The caller must know that the sg page has a valid virtual
228 static inline void *sg_virt(struct scatterlist *sg)
230 return page_address(sg_page(sg)) + sg->offset;
233 #endif /* _LINUX_SCATTERLIST_H */