75 lines
1.9 KiB
C
75 lines
1.9 KiB
C
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#ifndef FS_CEPH_FRAG_H
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#define FS_CEPH_FRAG_H
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/*
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* "Frags" are a way to describe a subset of a 32-bit number space,
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* using a mask and a value to match against that mask. Any given frag
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* (subset of the number space) can be partitioned into 2^n sub-frags.
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*
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* Frags are encoded into a 32-bit word:
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* 8 upper bits = "bits"
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* 24 lower bits = "value"
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* (We could go to 5+27 bits, but who cares.)
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*
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* We use the _most_ significant bits of the 24 bit value. This makes
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* values logically sort.
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*
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* Unfortunately, because the "bits" field is still in the high bits, we
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* can't sort encoded frags numerically. However, it does allow you
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* to feed encoded frags as values into frag_contains_value.
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*/
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static inline __u32 ceph_frag_make(__u32 b, __u32 v)
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{
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return (b << 24) |
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(v & (0xffffffu << (24-b)) & 0xffffffu);
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}
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static inline __u32 ceph_frag_bits(__u32 f)
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{
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return f >> 24;
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}
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static inline __u32 ceph_frag_value(__u32 f)
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{
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return f & 0xffffffu;
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}
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static inline __u32 ceph_frag_mask(__u32 f)
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{
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return (0xffffffu << (24-ceph_frag_bits(f))) & 0xffffffu;
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}
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static inline __u32 ceph_frag_mask_shift(__u32 f)
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{
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return 24 - ceph_frag_bits(f);
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}
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static inline bool ceph_frag_contains_value(__u32 f, __u32 v)
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{
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return (v & ceph_frag_mask(f)) == ceph_frag_value(f);
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}
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static inline __u32 ceph_frag_make_child(__u32 f, int by, int i)
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{
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int newbits = ceph_frag_bits(f) + by;
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return ceph_frag_make(newbits,
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ceph_frag_value(f) | (i << (24 - newbits)));
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}
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static inline bool ceph_frag_is_leftmost(__u32 f)
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{
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return ceph_frag_value(f) == 0;
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}
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static inline bool ceph_frag_is_rightmost(__u32 f)
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{
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return ceph_frag_value(f) == ceph_frag_mask(f);
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}
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static inline __u32 ceph_frag_next(__u32 f)
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{
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return ceph_frag_make(ceph_frag_bits(f),
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ceph_frag_value(f) + (0x1000000 >> ceph_frag_bits(f)));
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}
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/*
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* comparator to sort frags logically, as when traversing the
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* number space in ascending order...
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*/
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int ceph_frag_compare(__u32 a, __u32 b);
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#endif
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