4784a46912
with a new implementation that has a mostly reentrant "addchar" routine, supports multiple message buffers in the kernel, and hides the implementation details from callers. The new code uses a kind of sequence number to represend the current read and write positions in the buffer. This approach (suggested mainly by bde) permits the read and write pointers to be maintained separately, which reduces the number of atomic operations that are required. The "mostly reentrant" above refers to the way that while it is now always safe to have any number of concurrent writers, readers could see the message buffer after a writer has advanced the pointers but before it has witten the new character. Discussed on: freebsd-arch
80 lines
3.3 KiB
C
80 lines
3.3 KiB
C
/*
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* Copyright (c) 1981, 1984, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)msgbuf.h 8.1 (Berkeley) 6/2/93
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* $FreeBSD$
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*/
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#ifndef _SYS_MSGBUF_H_
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#define _SYS_MSGBUF_H_
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struct msgbuf {
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char *msg_ptr; /* pointer to buffer */
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#define MSG_MAGIC 0x063062
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u_int msg_magic;
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u_int msg_size; /* size of buffer area */
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u_int msg_wseq; /* write sequence number */
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u_int msg_rseq; /* read sequence number */
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u_int msg_cksum; /* checksum of contents */
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u_int msg_seqmod; /* range for sequence numbers */
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};
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/* Normalise a sequence number or a difference between sequence numbers */
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#define MSGBUF_SEQNORM(mbp, seq) (((seq) + (mbp)->msg_seqmod) % \
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(mbp)->msg_seqmod)
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#define MSGBUF_SEQ_TO_POS(mbp, seq) ((seq) % (mbp)->msg_size)
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/* Subtract sequence numbers, but note that only positive values result. */
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#define MSGBUF_SEQSUB(mbp, seq1, seq2) (MSGBUF_SEQNORM((mbp), (seq1) - (seq2)))
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#ifdef _KERNEL
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extern int msgbuftrigger;
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extern struct msgbuf *msgbufp;
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void msgbufinit(void *ptr, int size);
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void msgbuf_addchar(struct msgbuf *mbp, int c);
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void msgbuf_clear(struct msgbuf *mbp);
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void msgbuf_copy(struct msgbuf *src, struct msgbuf *dst);
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int msgbuf_getbytes(struct msgbuf *mbp, char *buf, int buflen);
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int msgbuf_getchar(struct msgbuf *mbp);
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int msgbuf_getcount(struct msgbuf *mbp);
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void msgbuf_init(struct msgbuf *mbp, void *ptr, int size);
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void msgbuf_reinit(struct msgbuf *mbp, void *ptr, int size);
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int msgbuf_peekbytes(struct msgbuf *mbp, char *buf, int buflen,
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u_int *seqp);
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#if !defined(MSGBUF_SIZE)
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#define MSGBUF_SIZE 32768
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#endif
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#endif
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#endif
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