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 75