include/linux/ceph/ceph_frag.h

   1 #ifndef FS_CEPH_FRAG_H
   2 #define FS_CEPH_FRAG_H
   3
   4 /*
   5  * "Frags" are a way to describe a subset of a 32-bit number space,
   6  * using a mask and a value to match against that mask.  Any given frag
   7  * (subset of the number space) can be partitioned into 2^n sub-frags.
   8  *
   9  * Frags are encoded into a 32-bit word:
  10  *   8 upper bits = "bits"
  11  *  24 lower bits = "value"
  12  * (We could go to 5+27 bits, but who cares.)
  13  *
  14  * We use the _most_ significant bits of the 24 bit value.  This makes
  15  * values logically sort.
  16  *
  17  * Unfortunately, because the "bits" field is still in the high bits, we
  18  * can't sort encoded frags numerically.  However, it does allow you
  19  * to feed encoded frags as values into frag_contains_value.
  20  */
  21 static inline __u32 ceph_frag_make(__u32 b, __u32 v)
  22 {
  23         return (b << 24) |
  24                 (v & (0xffffffu << (24-b)) & 0xffffffu);
  25 }
  26 static inline __u32 ceph_frag_bits(__u32 f)
  27 {
  28         return f >> 24;
  29 }
  30 static inline __u32 ceph_frag_value(__u32 f)
  31 {
  32         return f & 0xffffffu;
  33 }
  34 static inline __u32 ceph_frag_mask(__u32 f)
  35 {
  36         return (0xffffffu << (24-ceph_frag_bits(f))) & 0xffffffu;
  37 }
  38 static inline __u32 ceph_frag_mask_shift(__u32 f)
  39 {
  40         return 24 - ceph_frag_bits(f);
  41 }
  42
  43 static inline bool ceph_frag_contains_value(__u32 f, __u32 v)
  44 {
  45         return (v & ceph_frag_mask(f)) == ceph_frag_value(f);
  46 }
  47
  48 static inline __u32 ceph_frag_make_child(__u32 f, int by, int i)
  49 {
  50         int newbits = ceph_frag_bits(f) + by;
  51         return ceph_frag_make(newbits,
  52                          ceph_frag_value(f) | (i << (24 - newbits)));
  53 }
  54 static inline bool ceph_frag_is_leftmost(__u32 f)
  55 {
  56         return ceph_frag_value(f) == 0;
  57 }
  58 static inline bool ceph_frag_is_rightmost(__u32 f)
  59 {
  60         return ceph_frag_value(f) == ceph_frag_mask(f);
  61 }
  62 static inline __u32 ceph_frag_next(__u32 f)
  63 {
  64         return ceph_frag_make(ceph_frag_bits(f),
  65                          ceph_frag_value(f) + (0x1000000 >> ceph_frag_bits(f)));
  66 }
  67
  68 /*
  69  * comparator to sort frags logically, as when traversing the
  70  * number space in ascending order...
  71  */
  72 int ceph_frag_compare(__u32 a, __u32 b);
  73
  74 #endif