libceph: add start en/decoding block helpers
Add ceph_start_encoding() and ceph_start_decoding(), the equivalent of ENCODE_START and DECODE_START in the userspace ceph code. This is based on a patch from Mike Christie <michaelc@cs.wisc.edu>. Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
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@ -218,6 +218,60 @@ static inline void ceph_encode_string(void **p, void *end,
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*p += len;
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}
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/*
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* version and length starting block encoders/decoders
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*/
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/* current code version (u8) + compat code version (u8) + len of struct (u32) */
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#define CEPH_ENCODING_START_BLK_LEN 6
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/**
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* ceph_start_encoding - start encoding block
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* @struct_v: current (code) version of the encoding
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* @struct_compat: oldest code version that can decode it
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* @struct_len: length of struct encoding
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*/
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static inline void ceph_start_encoding(void **p, u8 struct_v, u8 struct_compat,
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u32 struct_len)
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{
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ceph_encode_8(p, struct_v);
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ceph_encode_8(p, struct_compat);
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ceph_encode_32(p, struct_len);
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}
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/**
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* ceph_start_decoding - start decoding block
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* @v: current version of the encoding that the code supports
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* @name: name of the struct (free-form)
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* @struct_v: out param for the encoding version
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* @struct_len: out param for the length of struct encoding
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*
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* Validates the length of struct encoding, so unsafe ceph_decode_*
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* variants can be used for decoding.
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*/
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static inline int ceph_start_decoding(void **p, void *end, u8 v,
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const char *name, u8 *struct_v,
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u32 *struct_len)
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{
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u8 struct_compat;
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ceph_decode_need(p, end, CEPH_ENCODING_START_BLK_LEN, bad);
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*struct_v = ceph_decode_8(p);
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struct_compat = ceph_decode_8(p);
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if (v < struct_compat) {
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pr_warn("got struct_v %d struct_compat %d > %d of %s\n",
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*struct_v, struct_compat, v, name);
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return -EINVAL;
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}
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*struct_len = ceph_decode_32(p);
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ceph_decode_need(p, end, *struct_len, bad);
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return 0;
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bad:
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return -ERANGE;
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}
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#define ceph_encode_need(p, end, n, bad) \
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do { \
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if (!likely(ceph_has_room(p, end, n))) \
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