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