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linux
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 */
21static inline __u32 ceph_frag_make(__u32 b, __u32 v)
22{
23 return (b << 24) |
24 (v & (0xffffffu << (24-b)) & 0xffffffu);
25}
26static inline __u32 ceph_frag_bits(__u32 f)
27{
28 return f >> 24;
29}
30static inline __u32 ceph_frag_value(__u32 f)
31{
32 return f & 0xffffffu;
33}
34static inline __u32 ceph_frag_mask(__u32 f)
35{
36 return (0xffffffu << (24-ceph_frag_bits(f))) & 0xffffffu;
37}
38static inline __u32 ceph_frag_mask_shift(__u32 f)
39{
40 return 24 - ceph_frag_bits(f);
41}
42
43static inline bool ceph_frag_contains_value(__u32 f, __u32 v)
44{
45 return (v & ceph_frag_mask(f)) == ceph_frag_value(f);
46}
47
48static 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}
54static inline bool ceph_frag_is_leftmost(__u32 f)
55{
56 return ceph_frag_value(f) == 0;
57}
58static inline bool ceph_frag_is_rightmost(__u32 f)
59{
60 return ceph_frag_value(f) == ceph_frag_mask(f);
61}
62static 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 */
72int ceph_frag_compare(__u32 a, __u32 b);
73
74#endif