Return to msg CVS log

Up to [MW Coherent from dump] / coherent / a / usr / man / COHERENT

coherent

msg                       Device Driver                       msg




Message device driver


The file  /dev/msg is an interface to  the message device driver.
It is  assigned major device 25  (minor device 0) and  can be ac-
cessed as a character-special device.

All messaging operations  are performed through the COHERENT sys-
tem call  ioctl.  Each of the  operations msgctl, msgget, msgsnd,
and msgrcv  is performed with an integer  array as its parameter.
The first  element of the array is reserved  for the return value
(default,  -1).  Subsequent  elements  represent arguments.   The
call to  ioctl passes  MSGCTL, MSGGET,  MSGSND, or MSGRCV  as the
second argument,  and an array  of parameters as  the third argu-
ment.  The first argument is an open file descriptor to /dev/msg.

Prior to accessing the devices, a entry must be created in direc-
tory /dev, as follows:


/etc/mknod /dev/msg c 25 0
/bin/chmod 444 /dev/msg


***** Notes *****

The total space allocated for  message text (NNMMSSGG * NNMMSSCC) must be
less than 64 kilobytes.

Allocation of too many message queues (NNMMSSQQIIDD) or messages (NNMMSSGG)
can exhaust  kernel data space,  thus preventing the  system from
running.  Recommended safe limits are NNMMSSQQIIDD=16 and NNMMSSGG=100.

Private message queues are not supported.  Message queues must be
removed manually when no longer required.  Queue identifiers con-
sist of  a scaled slot number plus a  slot usage sequence number.
Using the system call msgctl with the option IPC_STAT will obtain
information on the specified slot, even when it returns an error.

To remove  all message  queues, compile  and run the  following C
code:


msgget( 0, 0 );    /* must do first */



for ( qid = 0x100; qid < 0x4000; qid += 0x100 ) {
        struct msqid_ds msb;
        msb.msg_perm.seq = 0;
        msgctl( qid, IPC_STAT, &msb );





COHERENT Lexicon                                           Page 1




msg                       Device Driver                       msg




        if ( msb.msg_perm.seq > 0 )
                msgctl (msb.msg_perm.seq, IPC_RMID, 0 );
}


To load msg use the command drvld.

***** Files *****

/usr/include/sys/ipc.h
/usr/include/sys/msg.h
/dev/msg

***** See Also *****

device drivers, drvld, msgctl(), msgget(), msgop()








































COHERENT Lexicon                                           Page 2

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.