FreeBSD-5.3/sys/kern/subr_msgbuf.c
/*
* Copyright (c) 2003 Ian Dowse. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD: src/sys/kern/subr_msgbuf.c,v 1.2 2003/09/05 11:12:00 phk Exp $
*/
/*
* Generic message buffer support routines.
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/msgbuf.h>
/* Read/write sequence numbers are modulo a multiple of the buffer size. */
#define SEQMOD(size) ((size) * 16)
static u_int msgbuf_cksum(struct msgbuf *mbp);
/*
* Initialize a message buffer of the specified size at the specified
* location. This also zeros the buffer area.
*/
void
msgbuf_init(struct msgbuf *mbp, void *ptr, int size)
{
mbp->msg_ptr = ptr;
mbp->msg_size = size;
mbp->msg_seqmod = SEQMOD(size);
msgbuf_clear(mbp);
mbp->msg_magic = MSG_MAGIC;
}
/*
* Reinitialize a message buffer, retaining its previous contents if
* the size and checksum are correct. If the old contents cannot be
* recovered, the message buffer is cleared.
*/
void
msgbuf_reinit(struct msgbuf *mbp, void *ptr, int size)
{
u_int cksum;
if (mbp->msg_magic != MSG_MAGIC || mbp->msg_size != size) {
msgbuf_init(mbp, ptr, size);
return;
}
mbp->msg_seqmod = SEQMOD(size);
mbp->msg_wseq = MSGBUF_SEQNORM(mbp, mbp->msg_wseq);
mbp->msg_rseq = MSGBUF_SEQNORM(mbp, mbp->msg_rseq);
mbp->msg_ptr = ptr;
cksum = msgbuf_cksum(mbp);
if (cksum != mbp->msg_cksum) {
if (bootverbose) {
printf("msgbuf cksum mismatch (read %x, calc %x)\n",
mbp->msg_cksum, cksum);
printf("Old msgbuf not recovered\n");
}
msgbuf_clear(mbp);
}
}
/*
* Clear the message buffer.
*/
void
msgbuf_clear(struct msgbuf *mbp)
{
bzero(mbp->msg_ptr, mbp->msg_size);
mbp->msg_wseq = 0;
mbp->msg_rseq = 0;
mbp->msg_cksum = 0;
}
/*
* Get a count of the number of unread characters in the message buffer.
*/
int
msgbuf_getcount(struct msgbuf *mbp)
{
u_int len;
len = MSGBUF_SEQSUB(mbp, mbp->msg_wseq, mbp->msg_rseq);
if (len > mbp->msg_size)
len = mbp->msg_size;
return (len);
}
/*
* Append a character to a message buffer. This function can be
* considered fully reentrant so long as the number of concurrent
* callers is less than the number of characters in the buffer.
* However, the message buffer is only guaranteed to be consistent
* for reading when there are no callers in this function.
*/
void
msgbuf_addchar(struct msgbuf *mbp, int c)
{
u_int new_seq, pos, seq;
do {
seq = mbp->msg_wseq;
new_seq = MSGBUF_SEQNORM(mbp, seq + 1);
} while (atomic_cmpset_rel_int(&mbp->msg_wseq, seq, new_seq) == 0);
pos = MSGBUF_SEQ_TO_POS(mbp, seq);
atomic_add_int(&mbp->msg_cksum, (u_int)(u_char)c -
(u_int)(u_char)mbp->msg_ptr[pos]);
mbp->msg_ptr[pos] = c;
}
/*
* Read and mark as read a character from a message buffer.
* Returns the character, or -1 if no characters are available.
*/
int
msgbuf_getchar(struct msgbuf *mbp)
{
u_int len, wseq;
int c;
wseq = mbp->msg_wseq;
len = MSGBUF_SEQSUB(mbp, wseq, mbp->msg_rseq);
if (len == 0)
return (-1);
if (len > mbp->msg_size)
mbp->msg_rseq = MSGBUF_SEQNORM(mbp, wseq - mbp->msg_size);
c = (u_char)mbp->msg_ptr[MSGBUF_SEQ_TO_POS(mbp, mbp->msg_rseq)];
mbp->msg_rseq = MSGBUF_SEQNORM(mbp, mbp->msg_rseq + 1);
return (c);
}
/*
* Read and mark as read a number of characters from a message buffer.
* Returns the number of characters that were placed in `buf'.
*/
int
msgbuf_getbytes(struct msgbuf *mbp, char *buf, int buflen)
{
u_int len, pos, wseq;
wseq = mbp->msg_wseq;
len = MSGBUF_SEQSUB(mbp, wseq, mbp->msg_rseq);
if (len == 0)
return (0);
if (len > mbp->msg_size) {
mbp->msg_rseq = MSGBUF_SEQNORM(mbp, wseq - mbp->msg_size);
len = mbp->msg_size;
}
pos = MSGBUF_SEQ_TO_POS(mbp, mbp->msg_rseq);
len = min(len, mbp->msg_size - pos);
len = min(len, (u_int)buflen);
bcopy(&mbp->msg_ptr[pos], buf, len);
mbp->msg_rseq = MSGBUF_SEQNORM(mbp, mbp->msg_rseq + len);
return (len);
}
/*
* Peek at the full contents of a message buffer without marking any
* data as read. `seqp' should point to an unsigned integer that
* msgbuf_peekbytes() can use to retain state between calls so that
* the whole message buffer can be read in multiple short reads.
* To initialise this variable to the start of the message buffer,
* call msgbuf_peekbytes() with a NULL `buf' parameter.
*
* Returns the number of characters that were placed in `buf'.
*/
int
msgbuf_peekbytes(struct msgbuf *mbp, char *buf, int buflen, u_int *seqp)
{
u_int len, pos, wseq;
if (buf == NULL) {
/* Just initialise *seqp. */
*seqp = MSGBUF_SEQNORM(mbp, mbp->msg_wseq - mbp->msg_size);
return (0);
}
wseq = mbp->msg_wseq;
len = MSGBUF_SEQSUB(mbp, wseq, *seqp);
if (len == 0)
return (0);
if (len > mbp->msg_size) {
*seqp = MSGBUF_SEQNORM(mbp, wseq - mbp->msg_size);
len = mbp->msg_size;
}
pos = MSGBUF_SEQ_TO_POS(mbp, *seqp);
len = min(len, mbp->msg_size - pos);
len = min(len, (u_int)buflen);
bcopy(&mbp->msg_ptr[MSGBUF_SEQ_TO_POS(mbp, *seqp)], buf, len);
*seqp = MSGBUF_SEQNORM(mbp, *seqp + len);
return (len);
}
/*
* Compute the checksum for the complete message buffer contents.
*/
static u_int
msgbuf_cksum(struct msgbuf *mbp)
{
u_int i, sum;
sum = 0;
for (i = 0; i < mbp->msg_size; i++)
sum += (u_char)mbp->msg_ptr[i];
return (sum);
}
/*
* Copy from one message buffer to another.
*/
void
msgbuf_copy(struct msgbuf *src, struct msgbuf *dst)
{
int c;
while ((c = msgbuf_getchar(src)) >= 0)
msgbuf_addchar(dst, c);
}