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
   8 static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
   9                               unsigned int buflen)
  10 {
  11         sg->page = virt_to_page(buf);
  12         sg->offset = offset_in_page(buf);
  13         sg->length = buflen;
  14 }
  15
  16 static inline void sg_init_one(struct scatterlist *sg, const void *buf,
  17                                unsigned int buflen)
  18 {
  19         memset(sg, 0, sizeof(*sg));
  20         sg_set_buf(sg, buf, buflen);
  21 }
  22
  23 /*
  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  */
  44 static 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 }
  53
  54 /*
  55  * Loop over each sg element, following the pointer to a new list if necessary
  56  */
  57 #define for_each_sg(sglist, sg, nr, __i)        \
  58         for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
  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  */
  73 static 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  */
  98 static 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
 107 #endif /* _LINUX_SCATTERLIST_H */