17e33d2ef9
gwbuf struct dcb struct This int field will hold the last command executed or sent to backend. It will be 0 for most cases, setting it with a different value could help route differently the data from backend to client or some custom error messages.
99 lines
3.6 KiB
C
99 lines
3.6 KiB
C
#ifndef _BUFFER_H
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#define _BUFFER_H
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/*
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* This file is distributed as part of the SkySQL Gateway. It is free
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* software: you can redistribute it and/or modify it under the terms of the
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* GNU General Public License as published by the Free Software Foundation,
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* version 2.
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*
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* This program is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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* FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
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* details.
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*
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* You should have received a copy of the GNU General Public License along with
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* this program; if not, write to the Free Software Foundation, Inc., 51
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* Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Copyright SkySQL Ab 2013
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*/
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/**
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* @file buffer.h Definitions relating the gateway buffer manipulation facilities.
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*
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* These are used to store all data coming in form or going out to the client and the
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* backend structures.
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*
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* The buffers are designed to be used in linked lists and such that they may be passed
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* from one side of the gateway to another without the need to copy data. It may be the case
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* that not all of the data in the buffer is valid, to this end a start and end pointer are
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* included that point to the first valid byte in the buffer and the first byte after the
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* last valid byte. This allows data to be consumed from either end of the buffer whilst
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* still allowing for the copy free semantics of the buffering system.
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*
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* @verbatim
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* Revision History
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*
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* Date Who Description
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* 10/06/2013 Mark Riddoch Initial implementation
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* 11/07/2013 Mark Riddoch Addition of reference count in the gwbuf
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* 16/07/2013 Massimiliano Pinto Added command type for the queue
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*
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* @endverbatim
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*/
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/**
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* A structure to encapsualte the data in a form that the data itself can be
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* shared between multiple GWBUF's without the need to make multiple copies
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* but still maintain separate data pointers.
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*/
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typedef struct {
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unsigned char *data; /**< Physical memory that was allocated */
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int refcount; /**< Reference count on the buffer */
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} SHARED_BUF;
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/**
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* The buffer structure used by the descriptor control blocks.
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*
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* Linked lists of buffers are created as data is read from a descriptor
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* or written to a descriptor. The use of linked lists of buffers with
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* flexible data pointers is designed to minimise the need for data to
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* be copied within the gateway.
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*/
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typedef struct gwbuf {
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struct gwbuf *next; /**< Next buffer in a linked chain of buffers */
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void *start; /**< Start of the valid data */
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void *end; /**< First byte after the valid data */
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SHARED_BUF *sbuf; /**< The shared buffer with the real data */
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int command; /**< The command type for the queue */
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} GWBUF;
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/*
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* Macros to access the data in the buffers
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*/
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#define GWBUF_DATA(b) ((b)->start) /**< First valid, uncomsumed
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* byte in the buffer
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*/
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#define GWBUF_LENGTH(b) ((b)->end - (b)->start) /**< Number of bytes in the
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* individual buffer
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*/
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#define GWBUF_EMPTY(b) ((b)->start == (b)->end) /**< True if all bytes in the
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* buffer have been consumed
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*/
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#define GWBUF_CONSUME(b, bytes) (b)->start += bytes /**< Consume a number of bytes
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* in the buffer
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*/
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/*
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* Function prototypes for the API to maniplate the buffers
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*/
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extern GWBUF *gwbuf_alloc(unsigned int size);
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extern void gwbuf_free(GWBUF *buf);
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extern GWBUF *gwbuf_clone(GWBUF *buf);
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extern GWBUF *gwbuf_append(GWBUF *head, GWBUF *tail);
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extern GWBUF *gwbuf_consume(GWBUF *head, unsigned int length);
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extern unsigned int gwbuf_length(GWBUF *head);
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#endif
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