include/linux/scatterlist.h

   1 #ifndef _LINUX_SCATTERLIST_H
   2 #define _LINUX_SCATTERLIST_H
   3
   4 #include <asm/scatterlist.h>
   5 #include <linux/mm.h>
   6 #include <linux/string.h>
   7 #include <asm/io.h>
   8
   9 /*
  10  * Notes on SG table design.
  11  *
  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.
  16  *
  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.
  19  *
  20  * If bit 1 is set, then this sg entry is the last element in a list.
  21  *
  22  * See sg_next().
  23  *
  24  */
  25
  26 #define SG_MAGIC        0x87654321
  27
  28 /**
  29  * sg_assign_page - Assign a given page to an SG entry
  30  * @sg:             SG entry
  31  * @page:           The page
  32  *
  33  * Description:
  34  *   Assign page to sg entry. Also see sg_set_page(), the most commonly used
  35  *   variant.
  36  *
  37  **/
  38 static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
  39 {
  40         unsigned long page_link = sg->page_link & 0x3;
  41
  42         /*
  43          * In order for the low bit stealing approach to work, pages
  44          * must be aligned at a 32-bit boundary as a minimum.
  45          */
  46         BUG_ON((unsigned long) page & 0x03);
  47 #ifdef CONFIG_DEBUG_SG
  48         BUG_ON(sg->sg_magic != SG_MAGIC);
  49 #endif
  50         sg->page_link = page_link | (unsigned long) page;
  51 }
  52
  53 /**
  54  * sg_set_page - Set sg entry to point at given page
  55  * @sg:          SG entry
  56  * @page:        The page
  57  * @len:         Length of data
  58  * @offset:      Offset into page
  59  *
  60  * Description:
  61  *   Use this function to set an sg entry pointing at a page, never assign
  62  *   the page directly. We encode sg table information in the lower bits
  63  *   of the page pointer. See sg_page() for looking up the page belonging
  64  *   to an sg entry.
  65  *
  66  **/
  67 static inline void sg_set_page(struct scatterlist *sg, struct page *page,
  68                                unsigned int len, unsigned int offset)
  69 {
  70         sg_assign_page(sg, page);
  71         sg->offset = offset;
  72         sg->length = len;
  73 }
  74
  75 #define sg_page(sg)     ((struct page *) ((sg)->page_link & ~0x3))
  76
  77 /**
  78  * sg_set_buf - Set sg entry to point at given data
  79  * @sg:          SG entry
  80  * @buf:         Data
  81  * @buflen:      Data length
  82  *
  83  **/
  84 static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
  85                               unsigned int buflen)
  86 {
  87         sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
  88 }
  89
  90 /*
  91  * We overload the LSB of the page pointer to indicate whether it's
  92  * a valid sg entry, or whether it points to the start of a new scatterlist.
  93  * Those low bits are there for everyone! (thanks mason :-)
  94  */
  95 #define sg_is_chain(sg)         ((sg)->page_link & 0x01)
  96 #define sg_is_last(sg)          ((sg)->page_link & 0x02)
  97 #define sg_chain_ptr(sg)        \
  98         ((struct scatterlist *) ((sg)->page_link & ~0x03))
  99
 100 /**
 101  * sg_next - return the next scatterlist entry in a list
 102  * @sg:         The current sg entry
 103  *
 104  * Description:
 105  *   Usually the next entry will be @sg@ + 1, but if this sg element is part
 106  *   of a chained scatterlist, it could jump to the start of a new
 107  *   scatterlist array.
 108  *
 109  **/
 110 static inline struct scatterlist *sg_next(struct scatterlist *sg)
 111 {
 112 #ifdef CONFIG_DEBUG_SG
 113         BUG_ON(sg->sg_magic != SG_MAGIC);
 114 #endif
 115         if (sg_is_last(sg))
 116                 return NULL;
 117
 118         sg++;
 119         if (unlikely(sg_is_chain(sg)))
 120                 sg = sg_chain_ptr(sg);
 121
 122         return sg;
 123 }
 124
 125 /*
 126  * Loop over each sg element, following the pointer to a new list if necessary
 127  */
 128 #define for_each_sg(sglist, sg, nr, __i)        \
 129         for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
 130
 131 /**
 132  * sg_last - return the last scatterlist entry in a list
 133  * @sgl:        First entry in the scatterlist
 134  * @nents:      Number of entries in the scatterlist
 135  *
 136  * Description:
 137  *   Should only be used casually, it (currently) scan the entire list
 138  *   to get the last entry.
 139  *
 140  *   Note that the @sgl@ pointer passed in need not be the first one,
 141  *   the important bit is that @nents@ denotes the number of entries that
 142  *   exist from @sgl@.
 143  *
 144  **/
 145 static inline struct scatterlist *sg_last(struct scatterlist *sgl,
 146                                           unsigned int nents)
 147 {
 148 #ifndef ARCH_HAS_SG_CHAIN
 149         struct scatterlist *ret = &sgl[nents - 1];
 150 #else
 151         struct scatterlist *sg, *ret = NULL;
 152         int i;
 153
 154         for_each_sg(sgl, sg, nents, i)
 155                 ret = sg;
 156
 157 #endif
 158 #ifdef CONFIG_DEBUG_SG
 159         BUG_ON(sgl[0].sg_magic != SG_MAGIC);
 160         BUG_ON(!sg_is_last(ret));
 161 #endif
 162         return ret;
 163 }
 164
 165 /**
 166  * sg_chain - Chain two sglists together
 167  * @prv:        First scatterlist
 168  * @prv_nents:  Number of entries in prv
 169  * @sgl:        Second scatterlist
 170  *
 171  * Description:
 172  *   Links @prv@ and @sgl@ together, to form a longer scatterlist.
 173  *
 174  **/
 175 static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
 176                             struct scatterlist *sgl)
 177 {
 178 #ifndef ARCH_HAS_SG_CHAIN
 179         BUG();
 180 #endif
 181         prv[prv_nents - 1].page_link = (unsigned long) sgl | 0x01;
 182 }
 183
 184 /**
 185  * sg_mark_end - Mark the end of the scatterlist
 186  * @sgl:        Scatterlist
 187  * @nents:      Number of entries in sgl
 188  *
 189  * Description:
 190  *   Marks the last entry as the termination point for sg_next()
 191  *
 192  **/
 193 static inline void sg_mark_end(struct scatterlist *sgl, unsigned int nents)
 194 {
 195         sgl[nents - 1].page_link = 0x02;
 196 }
 197
 198 static inline void __sg_mark_end(struct scatterlist *sg)
 199 {
 200         sg->page_link |= 0x02;
 201 }
 202
 203 /**
 204  * sg_init_one - Initialize a single entry sg list
 205  * @sg:          SG entry
 206  * @buf:         Virtual address for IO
 207  * @buflen:      IO length
 208  *
 209  * Notes:
 210  *   This should not be used on a single entry that is part of a larger
 211  *   table. Use sg_init_table() for that.
 212  *
 213  **/
 214 static inline void sg_init_one(struct scatterlist *sg, const void *buf,
 215                                unsigned int buflen)
 216 {
 217         memset(sg, 0, sizeof(*sg));
 218 #ifdef CONFIG_DEBUG_SG
 219         sg->sg_magic = SG_MAGIC;
 220 #endif
 221         sg_mark_end(sg, 1);
 222         sg_set_buf(sg, buf, buflen);
 223 }
 224
 225 /**
 226  * sg_init_table - Initialize SG table
 227  * @sgl:           The SG table
 228  * @nents:         Number of entries in table
 229  *
 230  * Notes:
 231  *   If this is part of a chained sg table, sg_mark_end() should be
 232  *   used only on the last table part.
 233  *
 234  **/
 235 static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
 236 {
 237         memset(sgl, 0, sizeof(*sgl) * nents);
 238         sg_mark_end(sgl, nents);
 239 #ifdef CONFIG_DEBUG_SG
 240         {
 241                 int i;
 242                 for (i = 0; i < nents; i++)
 243                         sgl[i].sg_magic = SG_MAGIC;
 244         }
 245 #endif
 246 }
 247
 248 /**
 249  * sg_phys - Return physical address of an sg entry
 250  * @sg:      SG entry
 251  *
 252  * Description:
 253  *   This calls page_to_phys() on the page in this sg entry, and adds the
 254  *   sg offset. The caller must know that it is legal to call page_to_phys()
 255  *   on the sg page.
 256  *
 257  **/
 258 static inline unsigned long sg_phys(struct scatterlist *sg)
 259 {
 260         return page_to_phys(sg_page(sg)) + sg->offset;
 261 }
 262
 263 /**
 264  * sg_virt - Return virtual address of an sg entry
 265  * @sg:      SG entry
 266  *
 267  * Description:
 268  *   This calls page_address() on the page in this sg entry, and adds the
 269  *   sg offset. The caller must know that the sg page has a valid virtual
 270  *   mapping.
 271  *
 272  **/
 273 static inline void *sg_virt(struct scatterlist *sg)
 274 {
 275         return page_address(sg_page(sg)) + sg->offset;
 276 }
 277
 278 #endif /* _LINUX_SCATTERLIST_H */