diff options
Diffstat (limited to 'iov.h')
| -rw-r--r-- | iov.h | 76 |
1 files changed, 76 insertions, 0 deletions
@@ -28,4 +28,80 @@ size_t iov_from_buf(const struct iovec *iov, size_t iov_cnt, size_t iov_to_buf(const struct iovec *iov, size_t iov_cnt, size_t offset, void *buf, size_t bytes); size_t iov_size(const struct iovec *iov, size_t iov_cnt); + +/* + * DOC: Theory of Operation, struct iov_tail + * + * Sometimes a single logical network frame is split across multiple buffers, + * represented by an IO vector (struct iovec[]). We often want to process this + * one header / network layer at a time. So, it's useful to maintain a "tail" + * of the vector representing the parts we haven't yet extracted. + * + * The headers we extract need not line up with buffer boundaries (though we do + * assume they're contiguous within a single buffer for now). So, we could + * represent that tail as another struct iovec[], but that would mean copying + * the whole array of struct iovecs, just so we can adjust the offset and length + * on the first one. + * + * So, instead represent the tail as pointer into an existing struct iovec[], + * with an explicit offset for where the "tail" starts within it. If we extract + * enough headers that some buffers of the original vector no longer contain + * part of the tail, we (lazily) advance our struct iovec * to the first buffer + * we still need, and adjust the vector length and offset to match. + */ + +/** + * struct iov_tail - An IO vector which may have some headers logically removed + * @iov: IO vector + * @cnt: Number of entries in @iov + * @off: Current offset in @iov + */ +struct iov_tail { + const struct iovec *iov; + size_t cnt, off; +}; + +/** + * IOV_TAIL() - Create a new IOV tail + * @iov_: IO vector to create tail from + * @cnt_: Length of the IO vector at @iov_ + * @off_: Byte offset in the IO vector where the tail begins + */ +#define IOV_TAIL(iov_, cnt_, off_) \ + (struct iov_tail){ .iov = (iov_), .cnt = (cnt_), .off = (off_) } + +bool iov_tail_prune(struct iov_tail *tail); +size_t iov_tail_size(struct iov_tail *tail); +void *iov_peek_header_(struct iov_tail *tail, size_t len, size_t align); +void *iov_remove_header_(struct iov_tail *tail, size_t len, size_t align); + +/** + * IOV_PEEK_HEADER() - Get typed pointer to a header from an IOV tail + * @tail_: IOV tail to get header from + * @type_: Data type of the header + * + * @tail_ may be pruned, but will represent the same bytes as before. + * + * Returns: Pointer of type (@type_ *) located at the start of @tail_, NULL if + * we can't get a contiguous and aligned pointer. + */ +#define IOV_PEEK_HEADER(tail_, type_) \ + ((type_ *)(iov_peek_header_((tail_), \ + sizeof(type_), __alignof__(type_)))) + +/** + * IOV_REMOVE_HEADER() - Remove and return typed header from an IOV tail + * @tail_: IOV tail to remove header from (modified) + * @type_: Data type of the header to remove + * + * On success, @tail_ is updated so that it longer includes the bytes of the + * returned header. + * + * Returns: Pointer of type (@type_ *) located at the old start of @tail_, NULL + * if we can't get a contiguous and aligned pointer. + */ +#define IOV_REMOVE_HEADER(tail_, type_) \ + ((type_ *)(iov_remove_header_((tail_), \ + sizeof(type_), __alignof__(type_)))) + #endif /* IOVEC_H */ |