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105 lines
4.3 KiB
C
105 lines
4.3 KiB
C
#ifndef _HAPROXY_NCBUF_T_H
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#define _HAPROXY_NCBUF_T_H
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/* **** public documentation ****
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*
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* <ncbuf> stands for non-contiguous circular buffer. This type can be used to
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* store data in a non-linear way with gaps between them. The buffer is
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* circular and so data may wrapped.
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*
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* The API of <ncbuf> is split in two parts. Please refer to the public API
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* declared in this header file which should cover all the needs.
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*
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* To minimize the memory footprint, size of data and gaps are inserted in the
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* gaps themselves. This way <ncbuf> does not need to maintain a separate list
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* of data offsets in a dedicated structure. However, this put some limitations
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* on the buffer usage that the user need to know.
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*
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* First, a space will always be reserved in the allocated buffer area to store
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* the size of the first data block. Use ncb_size(buf) to retrieve the usable
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* size of the allocated buffer excluding the reserved space.
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*
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* Second, add and deletion operations are constraint and may be impossible if
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* a minimal gap size between data is not respected. A caller must always
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* inspect the return values of these functions. To limit these errors and
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* improve the buffer performance, <ncbuf> should be reserved for use-cases
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* where the number of formed gaps is kept minimal and evenly spread.
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*/
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/* **** internal documentation ****
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*
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* This section is useful to users who need to understand how ncbuf are
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* implemented.
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*
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* Public and internal functions all shared a common abstraction of the buffer.
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* The buffer content is represented as a list of blocks, alternating between
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* DATA and GAP blocks. This simplifies the buffer examination loop and
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* insertion/deletion. Note that this list of blocks is not stored in the
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* buffer structure.
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*
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* The buffer is considered to always start with a DATA block. The size of this
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* block is stored just before <head> which is the pointer for offset 0. This
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* space will always be reserved for this usage. It can be accessed through
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* ncb_int_head(buf). If the buffer has no data at head, the reserved space
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* will simply contains the value 0, and will be follow by a gap.
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*
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* A gap always contains the size of the gap itself and the size of the next
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* data block. Here is a small representation of a gap stored at offset <x>
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* before a data block at offset <y>.
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*
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* x y
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* ------------------------------------------------------------
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* xxxxxx| GAP-SZ | DATA-SZ | | xxxxxxxxxxxxx...
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* ------------------------------------------------------------
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* | -------- GAP-SZ -------------- > | --- DATA-SZ --->
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*
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* This means that a gap must be at least big enough to store two sizes.
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* However, there is an optimization when the last block of the buffer is a
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* gap. In this case, there is no minimal size for this block. If the gap is
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* too small, the two sizes won't be stored in it. This block is considered
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* to be a reduced gap. The block API will detect such a gap if stored at an
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* offset near the end of the buffer.
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*
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*/
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#include <inttypes.h>
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/* ncb_sz_t is the basic type used in ncbuf to represent data and gap sizes.
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* Use a bigger type to extend the maximum data size supported in the buffer.
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* On the other hand, this also increases the minimal gap size which can
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* cause more rejection for add/delete operations.
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*/
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typedef uint32_t ncb_sz_t;
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/* reserved size before head used to store first data block size */
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#define NCB_RESERVED_SZ (sizeof(ncb_sz_t))
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/* A gap contains its size and the size of the data following it. */
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#define NCB_GAP_MIN_SZ (sizeof(ncb_sz_t) * 2)
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#define NCB_GAP_SZ_OFF 0
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#define NCB_GAP_SZ_DATA_OFF (sizeof(ncb_sz_t))
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#define NCBUF_NULL ((struct ncbuf){ })
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struct ncbuf {
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char *area;
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ncb_sz_t size;
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ncb_sz_t head;
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};
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enum ncb_ret {
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NCB_RET_OK = 0, /* no error */
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NCB_RET_GAP_SIZE, /* operation would create a too small gap */
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NCB_RET_DATA_REJ, /* operation would overwrite data with different one */
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};
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/* Define how insert is conducted in regards with already stored data. */
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enum ncb_add_mode {
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NCB_ADD_PRESERVE, /* keep the already stored data and only insert in gaps */
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NCB_ADD_OVERWRT, /* overwrite old data with new ones */
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NCB_ADD_COMPARE, /* compare before insert : if new data are different do not proceed */
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};
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#endif /* _HAPROXY_NCBUF_T_H */
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