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To: freebsd-hackers@freebsd.org
Subject: shmget(2) broken in 2.0.5?
Date: Wed, 12 Jul 95 16:58:43 -0400
From: "Shawn M. Carey" <smcarey@mailbox.syr.edu>
Sender: hackers-owner@freebsd.org
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Hello,

	I have recenlty started porting a pair of apps that use shared
memory for IPC over to FreeBSD 2.0.5.  Note that these apps worked very
well under 1.1.5 (with the addition of a homemade ftok()), but under 2.0.5
shmget() seems to be trying to allocate more shared RAM when you ask it
for an ID by specfying an already existing key.  Here's that call from the
parent process that allocates the shared RAM:

(gdb) p *ShmKey
$1 = 5944
(gdb) p *Size1
$2 = 262176

      ShmID = shmget(*ShmKey, *Size1, 0x1ff|IPC_CREAT|IPC_EXCL);

(gdb) p ShmID
$3 = 851968

Coincidentally, if I try to do "ipcs -m" at this point, ipcs seg faults.
But if I do a plain "ipcs", it reports the memory as follows:

bandit.290% ipcs
Message Queues:
T     ID     KEY        MODE       OWNER    GROUP

Shared Memory:
T     ID     KEY        MODE       OWNER    GROUP
m 851968       5944 --rwarwarwa  s_carey rtaiprop

Semaphores:
T     ID     KEY        MODE       OWNER    GROUP

The child gets the key passed to it via argv[], and from that it figures
out what the ID is:

(gdb) p *ShmKey
$1 = 5944
(gdb) p *Size1
$2 = 262176

      ShmID = shmget(*ShmKey, *Size1, 0x1ff);

(gdb) p ShmID
$3 = -1


Maybe I'm doing something wrong here?  My experience with SysV IPC is
admittedly lacking.  This used to work with 1.1.5, and continues to
work on other platforms (DG/UX), so I suspect I've found a bug.  Has
anyone else ran into this?

Thanks,
-Shawn Carey