From owner-freebsd-questions  Mon Sep 13 19:34:13 1999
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Date: Mon, 13 Sep 1999 19:34:05 -0700 (PDT)
From: Bill Fenner <fenner@research.att.com>
Message-Id: <199909140234.TAA00595@mango.attlabs.att.com>
To: freebsd-questions@freebsd.org
Subject: Why can't I set MSGBUF_SIZE?
Cc: fenner@research.att.com
Sender: owner-freebsd-questions@FreeBSD.ORG
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Ok, I'm going completely insane here.

mango% grep MSGBUF /sys/i386/conf/MANGO
options         "MSGBUF_SIZE=81920"
mango% cat /sys/compile/MANGO/opt_msgbuf.h
#define MSGBUF_SIZE 81920

/sys/i386/i386/machdep.c:

int bill_is_going_crazy = MSGBUF_SIZE;
#if MSGBUF_SIZE != 81920
#error "It didn't work!"
#endif

...
        msgbufinit(msgbufp, MSGBUF_SIZE);


kgdb:
(kgdb) p bill_is_going_crazy 
$1 = 81920

so clearly, both because the compilation succeeded and because the
kernel variable is set to what I think it should be, MSGBUF_SIZE
was 81920 at compile time.  However,

(kgdb) x/x msgbufp
0xc0416fec:     0x00063062
(kgdb) 
0xc0416ff0:     0x00001fec

msg_magic is set to MSG_MAGIC, which is all well and good.  msg_size,
however, is 8172 (8192 - sizeof(struct msgbuf)), what you would
expect if MSGBUF_SIZE was 8192 (the default if not overridden -- but
it's clear from the variable bill_is_going_crazy that the override
succeeded).

Someone, please tell me what I'm missing!

Thanks,
  Bill


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