linux/include/linux/scatterlist.h
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   1#ifndef _LINUX_SCATTERLIST_H
   2#define _LINUX_SCATTERLIST_H
   3
   4#include <linux/string.h>
   5#include <linux/bug.h>
   6#include <linux/mm.h>
   7
   8#include <asm/types.h>
   9#include <asm/scatterlist.h>
  10#include <asm/io.h>
  11
  12struct sg_table {
  13        struct scatterlist *sgl;        /* the list */
  14        unsigned int nents;             /* number of mapped entries */
  15        unsigned int orig_nents;        /* original size of list */
  16};
  17
  18/*
  19 * Notes on SG table design.
  20 *
  21 * Architectures must provide an unsigned long page_link field in the
  22 * scatterlist struct. We use that to place the page pointer AND encode
  23 * information about the sg table as well. The two lower bits are reserved
  24 * for this information.
  25 *
  26 * If bit 0 is set, then the page_link contains a pointer to the next sg
  27 * table list. Otherwise the next entry is at sg + 1.
  28 *
  29 * If bit 1 is set, then this sg entry is the last element in a list.
  30 *
  31 * See sg_next().
  32 *
  33 */
  34
  35#define SG_MAGIC        0x87654321
  36
  37/*
  38 * We overload the LSB of the page pointer to indicate whether it's
  39 * a valid sg entry, or whether it points to the start of a new scatterlist.
  40 * Those low bits are there for everyone! (thanks mason :-)
  41 */
  42#define sg_is_chain(sg)         ((sg)->page_link & 0x01)
  43#define sg_is_last(sg)          ((sg)->page_link & 0x02)
  44#define sg_chain_ptr(sg)        \
  45        ((struct scatterlist *) ((sg)->page_link & ~0x03))
  46
  47/**
  48 * sg_assign_page - Assign a given page to an SG entry
  49 * @sg:             SG entry
  50 * @page:           The page
  51 *
  52 * Description:
  53 *   Assign page to sg entry. Also see sg_set_page(), the most commonly used
  54 *   variant.
  55 *
  56 **/
  57static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
  58{
  59        unsigned long page_link = sg->page_link & 0x3;
  60
  61        /*
  62         * In order for the low bit stealing approach to work, pages
  63         * must be aligned at a 32-bit boundary as a minimum.
  64         */
  65        BUG_ON((unsigned long) page & 0x03);
  66#ifdef CONFIG_DEBUG_SG
  67        BUG_ON(sg->sg_magic != SG_MAGIC);
  68        BUG_ON(sg_is_chain(sg));
  69#endif
  70        sg->page_link = page_link | (unsigned long) page;
  71}
  72
  73/**
  74 * sg_set_page - Set sg entry to point at given page
  75 * @sg:          SG entry
  76 * @page:        The page
  77 * @len:         Length of data
  78 * @offset:      Offset into page
  79 *
  80 * Description:
  81 *   Use this function to set an sg entry pointing at a page, never assign
  82 *   the page directly. We encode sg table information in the lower bits
  83 *   of the page pointer. See sg_page() for looking up the page belonging
  84 *   to an sg entry.
  85 *
  86 **/
  87static inline void sg_set_page(struct scatterlist *sg, struct page *page,
  88                               unsigned int len, unsigned int offset)
  89{
  90        sg_assign_page(sg, page);
  91        sg->offset = offset;
  92        sg->length = len;
  93}
  94
  95static inline struct page *sg_page(struct scatterlist *sg)
  96{
  97#ifdef CONFIG_DEBUG_SG
  98        BUG_ON(sg->sg_magic != SG_MAGIC);
  99        BUG_ON(sg_is_chain(sg));
 100#endif
 101        return (struct page *)((sg)->page_link & ~0x3);
 102}
 103
 104/**
 105 * sg_set_buf - Set sg entry to point at given data
 106 * @sg:          SG entry
 107 * @buf:         Data
 108 * @buflen:      Data length
 109 *
 110 **/
 111static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
 112                              unsigned int buflen)
 113{
 114        sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
 115}
 116
 117/*
 118 * Loop over each sg element, following the pointer to a new list if necessary
 119 */
 120#define for_each_sg(sglist, sg, nr, __i)        \
 121        for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
 122
 123/**
 124 * sg_chain - Chain two sglists together
 125 * @prv:        First scatterlist
 126 * @prv_nents:  Number of entries in prv
 127 * @sgl:        Second scatterlist
 128 *
 129 * Description:
 130 *   Links @prv@ and @sgl@ together, to form a longer scatterlist.
 131 *
 132 **/
 133static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
 134                            struct scatterlist *sgl)
 135{
 136#ifndef ARCH_HAS_SG_CHAIN
 137        BUG();
 138#endif
 139
 140        /*
 141         * offset and length are unused for chain entry.  Clear them.
 142         */
 143        prv[prv_nents - 1].offset = 0;
 144        prv[prv_nents - 1].length = 0;
 145
 146        /*
 147         * Set lowest bit to indicate a link pointer, and make sure to clear
 148         * the termination bit if it happens to be set.
 149         */
 150        prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
 151}
 152
 153/**
 154 * sg_mark_end - Mark the end of the scatterlist
 155 * @sg:          SG entryScatterlist
 156 *
 157 * Description:
 158 *   Marks the passed in sg entry as the termination point for the sg
 159 *   table. A call to sg_next() on this entry will return NULL.
 160 *
 161 **/
 162static inline void sg_mark_end(struct scatterlist *sg)
 163{
 164#ifdef CONFIG_DEBUG_SG
 165        BUG_ON(sg->sg_magic != SG_MAGIC);
 166#endif
 167        /*
 168         * Set termination bit, clear potential chain bit
 169         */
 170        sg->page_link |= 0x02;
 171        sg->page_link &= ~0x01;
 172}
 173
 174/**
 175 * sg_phys - Return physical address of an sg entry
 176 * @sg:      SG entry
 177 *
 178 * Description:
 179 *   This calls page_to_phys() on the page in this sg entry, and adds the
 180 *   sg offset. The caller must know that it is legal to call page_to_phys()
 181 *   on the sg page.
 182 *
 183 **/
 184static inline dma_addr_t sg_phys(struct scatterlist *sg)
 185{
 186        return page_to_phys(sg_page(sg)) + sg->offset;
 187}
 188
 189/**
 190 * sg_virt - Return virtual address of an sg entry
 191 * @sg:      SG entry
 192 *
 193 * Description:
 194 *   This calls page_address() on the page in this sg entry, and adds the
 195 *   sg offset. The caller must know that the sg page has a valid virtual
 196 *   mapping.
 197 *
 198 **/
 199static inline void *sg_virt(struct scatterlist *sg)
 200{
 201        return page_address(sg_page(sg)) + sg->offset;
 202}
 203
 204struct scatterlist *sg_next(struct scatterlist *);
 205struct scatterlist *sg_last(struct scatterlist *s, unsigned int);
 206void sg_init_table(struct scatterlist *, unsigned int);
 207void sg_init_one(struct scatterlist *, const void *, unsigned int);
 208
 209typedef struct scatterlist *(sg_alloc_fn)(unsigned int, gfp_t);
 210typedef void (sg_free_fn)(struct scatterlist *, unsigned int);
 211
 212void __sg_free_table(struct sg_table *, unsigned int, sg_free_fn *);
 213void sg_free_table(struct sg_table *);
 214int __sg_alloc_table(struct sg_table *, unsigned int, unsigned int, gfp_t,
 215                     sg_alloc_fn *);
 216int sg_alloc_table(struct sg_table *, unsigned int, gfp_t);
 217int sg_alloc_table_from_pages(struct sg_table *sgt,
 218        struct page **pages, unsigned int n_pages,
 219        unsigned long offset, unsigned long size,
 220        gfp_t gfp_mask);
 221
 222size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
 223                           void *buf, size_t buflen);
 224size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
 225                         void *buf, size_t buflen);
 226
 227/*
 228 * Maximum number of entries that will be allocated in one piece, if
 229 * a list larger than this is required then chaining will be utilized.
 230 */
 231#define SG_MAX_SINGLE_ALLOC             (PAGE_SIZE / sizeof(struct scatterlist))
 232
 233
 234/*
 235 * Mapping sg iterator
 236 *
 237 * Iterates over sg entries mapping page-by-page.  On each successful
 238 * iteration, @miter->page points to the mapped page and
 239 * @miter->length bytes of data can be accessed at @miter->addr.  As
 240 * long as an interation is enclosed between start and stop, the user
 241 * is free to choose control structure and when to stop.
 242 *
 243 * @miter->consumed is set to @miter->length on each iteration.  It
 244 * can be adjusted if the user can't consume all the bytes in one go.
 245 * Also, a stopped iteration can be resumed by calling next on it.
 246 * This is useful when iteration needs to release all resources and
 247 * continue later (e.g. at the next interrupt).
 248 */
 249
 250#define SG_MITER_ATOMIC         (1 << 0)         /* use kmap_atomic */
 251#define SG_MITER_TO_SG          (1 << 1)        /* flush back to phys on unmap */
 252#define SG_MITER_FROM_SG        (1 << 2)        /* nop */
 253
 254struct sg_mapping_iter {
 255        /* the following three fields can be accessed directly */
 256        struct page             *page;          /* currently mapped page */
 257        void                    *addr;          /* pointer to the mapped area */
 258        size_t                  length;         /* length of the mapped area */
 259        size_t                  consumed;       /* number of consumed bytes */
 260
 261        /* these are internal states, keep away */
 262        struct scatterlist      *__sg;          /* current entry */
 263        unsigned int            __nents;        /* nr of remaining entries */
 264        unsigned int            __offset;       /* offset within sg */
 265        unsigned int            __flags;
 266};
 267
 268void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
 269                    unsigned int nents, unsigned int flags);
 270bool sg_miter_next(struct sg_mapping_iter *miter);
 271void sg_miter_stop(struct sg_mapping_iter *miter);
 272
 273#endif /* _LINUX_SCATTERLIST_H */
 274
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