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/*
* libpulp - User-space Livepatching Library
*
* Copyright (C) 2021 SUSE Software Solutions GmbH
*
* This file is part of libpulp.
*
* libpulp is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* libpulp is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with libpulp. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef MSGQ_H
#define MSGQ_H
#include <stdarg.h>
/** Define a 2Mb buffer for holding the messages. */
#define MSGQ_BUFFER_MAX (2 * 1024 * 1024)
/** This is the circular message queue datastructure.
*
* It works on a fixed-size buffer and operates maintaining three variables:
*
* - Top.
* - Bottom.
* - Distance.
*
* Take the following illustration as example, after inserting the strings:
*
* - hhhhhhhhhhhhhh.
* - iiiiii
* - jjjjjjj
*
* Which will get the queue in the following state:
*
* hhhhhhhhhhhhhh.iiiiii.jjjjjjj...
* B T
*
* Where 'B' represents the bottom position, 'T' represents the top position,
* and the '.' represents the \0 character.
*
* If we insert the string 'kkkkkkk' next, notice that there is not enough
* space in the buffer for it, so 'T' wraps back to the beginning of the queue,
* overwrite part of the sequence of 'h', increments 'B', and write the message
* in the opened space, which results in the following state:
*
* kkkkkkk.hhhhhh.iiiiii.jjjjjjj...
* T B
*
* resulting in the circular queue behaviour. When reading this queue, the user
* should start reading from the bottom position.
*/
struct msg_queue
{
/** Buffer holding the messages. */
char buffer[MSGQ_BUFFER_MAX];
/** Position pointing to free memory that can be written to. */
int top;
/** Position pointing to the oldest message still in buffer. */
int bottom;
/** Distance betweem top and bottom. Should not be greater than
* MSGQ_BUFFER_MAX. */
int distance;
};
extern struct msg_queue __ulp_msg_queue;
void msgq_push(const char *format, ...);
void msgq_vpush(const char *format, va_list);
#endif /* MSGQ_H */
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