SysV IPC msg queue limits

From: Tani Hosokawa (unknown@riverstyx.net)
Date: Mon Jan 17 2000 - 20:58:21 EST


I'm trying to increase the limits for SysV message queues (specifically,
MSGMNB, MSGMNI, and MSGQNUM). I can increase the first two with no problem.

When I try to increase MSGMNB, it fails. I can't even write a single
message without getting EAGAIN. I assume this is because of the msqid_ds
structure: (excerpt below)

/* one msqid structure for each queue on the system */
struct msqid_ds {
...
        unsigned short msg_cbytes; /* current number of bytes on queue */
        ^^^^^^^^^^^^^^
        unsigned short msg_qnum; /* number of messages in queue */
        unsigned short msg_qbytes; /* max number of bytes on queue */
        ^^^^^^^^^^^^^^
...
};

Has anyone else attempted to increase MSGMNB to, say, 256k? I assume this will
break most existing software, since they all rely on a short msg_qbytes and
msg_cbytes for msgctl calls, but this is an application that won't share with
anything else, and I can recompile any apps that need IPC.

I've tried just changing those to unsigned int, but for whatever reason I lost
the ability to send any messages (always returned EAGAIN when IPC_NOWAIT was
set, or just blocked otherwise).

---
tani hosokawa
river styx internet

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