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git.proxmox.com Git - mirror_ubuntu-zesty-kernel.git/blob - include/linux/scatterlist.h
1 #ifndef _LINUX_SCATTERLIST_H
2 #define _LINUX_SCATTERLIST_H
5 #include <asm/scatterlist.h>
7 #include <linux/string.h>
11 * Notes on SG table design.
13 * Architectures must provide an unsigned long page_link field in the
14 * scatterlist struct. We use that to place the page pointer AND encode
15 * information about the sg table as well. The two lower bits are reserved
16 * for this information.
18 * If bit 0 is set, then the page_link contains a pointer to the next sg
19 * table list. Otherwise the next entry is at sg + 1.
21 * If bit 1 is set, then this sg entry is the last element in a list.
27 #define SG_MAGIC 0x87654321
30 * We overload the LSB of the page pointer to indicate whether it's
31 * a valid sg entry, or whether it points to the start of a new scatterlist.
32 * Those low bits are there for everyone! (thanks mason :-)
34 #define sg_is_chain(sg) ((sg)->page_link & 0x01)
35 #define sg_is_last(sg) ((sg)->page_link & 0x02)
36 #define sg_chain_ptr(sg) \
37 ((struct scatterlist *) ((sg)->page_link & ~0x03))
40 * sg_assign_page - Assign a given page to an SG entry
45 * Assign page to sg entry. Also see sg_set_page(), the most commonly used
49 static inline void sg_assign_page(struct scatterlist
*sg
, struct page
*page
)
51 unsigned long page_link
= sg
->page_link
& 0x3;
54 * In order for the low bit stealing approach to work, pages
55 * must be aligned at a 32-bit boundary as a minimum.
57 BUG_ON((unsigned long) page
& 0x03);
58 #ifdef CONFIG_DEBUG_SG
59 BUG_ON(sg
->sg_magic
!= SG_MAGIC
);
60 BUG_ON(sg_is_chain(sg
));
62 sg
->page_link
= page_link
| (unsigned long) page
;
66 * sg_set_page - Set sg entry to point at given page
69 * @len: Length of data
70 * @offset: Offset into page
73 * Use this function to set an sg entry pointing at a page, never assign
74 * the page directly. We encode sg table information in the lower bits
75 * of the page pointer. See sg_page() for looking up the page belonging
79 static inline void sg_set_page(struct scatterlist
*sg
, struct page
*page
,
80 unsigned int len
, unsigned int offset
)
82 sg_assign_page(sg
, page
);
87 static inline struct page
*sg_page(struct scatterlist
*sg
)
89 #ifdef CONFIG_DEBUG_SG
90 BUG_ON(sg
->sg_magic
!= SG_MAGIC
);
91 BUG_ON(sg_is_chain(sg
));
93 return (struct page
*)((sg
)->page_link
& ~0x3);
97 * sg_set_buf - Set sg entry to point at given data
100 * @buflen: Data length
103 static inline void sg_set_buf(struct scatterlist
*sg
, const void *buf
,
106 sg_set_page(sg
, virt_to_page(buf
), buflen
, offset_in_page(buf
));
110 * sg_next - return the next scatterlist entry in a list
111 * @sg: The current sg entry
114 * Usually the next entry will be @sg@ + 1, but if this sg element is part
115 * of a chained scatterlist, it could jump to the start of a new
119 static inline struct scatterlist
*sg_next(struct scatterlist
*sg
)
121 #ifdef CONFIG_DEBUG_SG
122 BUG_ON(sg
->sg_magic
!= SG_MAGIC
);
128 if (unlikely(sg_is_chain(sg
)))
129 sg
= sg_chain_ptr(sg
);
135 * Loop over each sg element, following the pointer to a new list if necessary
137 #define for_each_sg(sglist, sg, nr, __i) \
138 for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
141 * sg_last - return the last scatterlist entry in a list
142 * @sgl: First entry in the scatterlist
143 * @nents: Number of entries in the scatterlist
146 * Should only be used casually, it (currently) scan the entire list
147 * to get the last entry.
149 * Note that the @sgl@ pointer passed in need not be the first one,
150 * the important bit is that @nents@ denotes the number of entries that
154 static inline struct scatterlist
*sg_last(struct scatterlist
*sgl
,
157 #ifndef ARCH_HAS_SG_CHAIN
158 struct scatterlist
*ret
= &sgl
[nents
- 1];
160 struct scatterlist
*sg
, *ret
= NULL
;
163 for_each_sg(sgl
, sg
, nents
, i
)
167 #ifdef CONFIG_DEBUG_SG
168 BUG_ON(sgl
[0].sg_magic
!= SG_MAGIC
);
169 BUG_ON(!sg_is_last(ret
));
175 * sg_chain - Chain two sglists together
176 * @prv: First scatterlist
177 * @prv_nents: Number of entries in prv
178 * @sgl: Second scatterlist
181 * Links @prv@ and @sgl@ together, to form a longer scatterlist.
184 static inline void sg_chain(struct scatterlist
*prv
, unsigned int prv_nents
,
185 struct scatterlist
*sgl
)
187 #ifndef ARCH_HAS_SG_CHAIN
192 * offset and length are unused for chain entry. Clear them.
194 prv
[prv_nents
- 1].offset
= 0;
195 prv
[prv_nents
- 1].length
= 0;
198 * Set lowest bit to indicate a link pointer, and make sure to clear
199 * the termination bit if it happens to be set.
201 prv
[prv_nents
- 1].page_link
= ((unsigned long) sgl
| 0x01) & ~0x02;
205 * sg_mark_end - Mark the end of the scatterlist
206 * @sg: SG entryScatterlist
209 * Marks the passed in sg entry as the termination point for the sg
210 * table. A call to sg_next() on this entry will return NULL.
213 static inline void sg_mark_end(struct scatterlist
*sg
)
215 #ifdef CONFIG_DEBUG_SG
216 BUG_ON(sg
->sg_magic
!= SG_MAGIC
);
219 * Set termination bit, clear potential chain bit
221 sg
->page_link
|= 0x02;
222 sg
->page_link
&= ~0x01;
226 * sg_init_table - Initialize SG table
228 * @nents: Number of entries in table
231 * If this is part of a chained sg table, sg_mark_end() should be
232 * used only on the last table part.
235 static inline void sg_init_table(struct scatterlist
*sgl
, unsigned int nents
)
237 memset(sgl
, 0, sizeof(*sgl
) * nents
);
238 #ifdef CONFIG_DEBUG_SG
241 for (i
= 0; i
< nents
; i
++)
242 sgl
[i
].sg_magic
= SG_MAGIC
;
245 sg_mark_end(&sgl
[nents
- 1]);
249 * sg_init_one - Initialize a single entry sg list
251 * @buf: Virtual address for IO
255 * This should not be used on a single entry that is part of a larger
256 * table. Use sg_init_table() for that.
259 static inline void sg_init_one(struct scatterlist
*sg
, const void *buf
,
262 sg_init_table(sg
, 1);
263 sg_set_buf(sg
, buf
, buflen
);
267 * sg_phys - Return physical address of an sg entry
271 * This calls page_to_phys() on the page in this sg entry, and adds the
272 * sg offset. The caller must know that it is legal to call page_to_phys()
276 static inline dma_addr_t
sg_phys(struct scatterlist
*sg
)
278 return page_to_phys(sg_page(sg
)) + sg
->offset
;
282 * sg_virt - Return virtual address of an sg entry
286 * This calls page_address() on the page in this sg entry, and adds the
287 * sg offset. The caller must know that the sg page has a valid virtual
291 static inline void *sg_virt(struct scatterlist
*sg
)
293 return page_address(sg_page(sg
)) + sg
->offset
;
296 #endif /* _LINUX_SCATTERLIST_H */