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ceph_frag.h
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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 int ceph_frag_contains_value(__u32 f, __u32 v)
44 {
45  return (v & ceph_frag_mask(f)) == ceph_frag_value(f);
46 }
47 static inline int ceph_frag_contains_frag(__u32 f, __u32 sub)
48 {
49  /* is sub as specific as us, and contained by us? */
50  return ceph_frag_bits(sub) >= ceph_frag_bits(f) &&
51  (ceph_frag_value(sub) & ceph_frag_mask(f)) == ceph_frag_value(f);
52 }
53 
54 static inline __u32 ceph_frag_parent(__u32 f)
55 {
56  return ceph_frag_make(ceph_frag_bits(f) - 1,
57  ceph_frag_value(f) & (ceph_frag_mask(f) << 1));
58 }
59 static inline int ceph_frag_is_left_child(__u32 f)
60 {
61  return ceph_frag_bits(f) > 0 &&
62  (ceph_frag_value(f) & (0x1000000 >> ceph_frag_bits(f))) == 0;
63 }
64 static inline int ceph_frag_is_right_child(__u32 f)
65 {
66  return ceph_frag_bits(f) > 0 &&
67  (ceph_frag_value(f) & (0x1000000 >> ceph_frag_bits(f))) == 1;
68 }
69 static inline __u32 ceph_frag_sibling(__u32 f)
70 {
71  return ceph_frag_make(ceph_frag_bits(f),
72  ceph_frag_value(f) ^ (0x1000000 >> ceph_frag_bits(f)));
73 }
74 static inline __u32 ceph_frag_left_child(__u32 f)
75 {
76  return ceph_frag_make(ceph_frag_bits(f)+1, ceph_frag_value(f));
77 }
78 static inline __u32 ceph_frag_right_child(__u32 f)
79 {
80  return ceph_frag_make(ceph_frag_bits(f)+1,
81  ceph_frag_value(f) | (0x1000000 >> (1+ceph_frag_bits(f))));
82 }
83 static inline __u32 ceph_frag_make_child(__u32 f, int by, int i)
84 {
85  int newbits = ceph_frag_bits(f) + by;
86  return ceph_frag_make(newbits,
87  ceph_frag_value(f) | (i << (24 - newbits)));
88 }
89 static inline int ceph_frag_is_leftmost(__u32 f)
90 {
91  return ceph_frag_value(f) == 0;
92 }
93 static inline int ceph_frag_is_rightmost(__u32 f)
94 {
95  return ceph_frag_value(f) == ceph_frag_mask(f);
96 }
97 static inline __u32 ceph_frag_next(__u32 f)
98 {
99  return ceph_frag_make(ceph_frag_bits(f),
100  ceph_frag_value(f) + (0x1000000 >> ceph_frag_bits(f)));
101 }
102 
103 /*
104  * comparator to sort frags logically, as when traversing the
105  * number space in ascending order...
106  */
108 
109 #endif