include/linux/ceph/ceph_frag.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef FS_CEPH_FRAG_H
   3 #define FS_CEPH_FRAG_H
   4
   5 /*
   6  * "Frags" are a way to describe a subset of a 32-bit number space,
   7  * using a mask and a value to match against that mask.  Any given frag
   8  * (subset of the number space) can be partitioned into 2^n sub-frags.
   9  *
  10  * Frags are encoded into a 32-bit word:
  11  *   8 upper bits = "bits"
  12  *  24 lower bits = "value"
  13  * (We could go to 5+27 bits, but who cares.)
  14  *
  15  * We use the _most_ significant bits of the 24 bit value.  This makes
  16  * values logically sort.
  17  *
  18  * Unfortunately, because the "bits" field is still in the high bits, we
  19  * can't sort encoded frags numerically.  However, it does allow you
  20  * to feed encoded frags as values into frag_contains_value.
  21  */
  22 static inline __u32 ceph_frag_make(__u32 b, __u32 v)
  23 {
  24         return (b << 24) |
  25                 (v & (0xffffffu << (24-b)) & 0xffffffu);
  26 }
  27 static inline __u32 ceph_frag_bits(__u32 f)
  28 {
  29         return f >> 24;
  30 }
  31 static inline __u32 ceph_frag_value(__u32 f)
  32 {
  33         return f & 0xffffffu;
  34 }
  35 static inline __u32 ceph_frag_mask(__u32 f)
  36 {
  37         return (0xffffffu << (24-ceph_frag_bits(f))) & 0xffffffu;
  38 }
  39 static inline __u32 ceph_frag_mask_shift(__u32 f)
  40 {
  41         return 24 - ceph_frag_bits(f);
  42 }
  43
  44 static inline bool ceph_frag_contains_value(__u32 f, __u32 v)
  45 {
  46         return (v & ceph_frag_mask(f)) == ceph_frag_value(f);
  47 }
  48
  49 static inline __u32 ceph_frag_make_child(__u32 f, int by, int i)
  50 {
  51         int newbits = ceph_frag_bits(f) + by;
  52         return ceph_frag_make(newbits,
  53                          ceph_frag_value(f) | (i << (24 - newbits)));
  54 }
  55 static inline bool ceph_frag_is_leftmost(__u32 f)
  56 {
  57         return ceph_frag_value(f) == 0;
  58 }
  59 static inline bool ceph_frag_is_rightmost(__u32 f)
  60 {
  61         return ceph_frag_value(f) == ceph_frag_mask(f);
  62 }
  63 static inline __u32 ceph_frag_next(__u32 f)
  64 {
  65         return ceph_frag_make(ceph_frag_bits(f),
  66                          ceph_frag_value(f) + (0x1000000 >> ceph_frag_bits(f)));
  67 }
  68
  69 /*
  70  * comparator to sort frags logically, as when traversing the
  71  * number space in ascending order...
  72  */
  73 int ceph_frag_compare(__u32 a, __u32 b);
  74
  75 #endif