Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!gatech!ncar!oddjob!uwvax!umn-d-ub!umn-cs!bungia!cimcor!mike
From: mike@cimcor.UUCP (Michael Grenier)
Newsgroups: comp.unix.wizards
Subject: Re: shared memory under SysV
Message-ID: <483@cimcor.UUCP>
Date: 15 May 88 13:35:29 GMT
References: <14379@brl-adm.ARPA>
Organization: Grenier & friends, Forest Lake, MN
Lines: 42
Posted: Sun May 15 08:35:29 1988

From article <14379@brl-adm.ARPA>, by Ed@mead.scrc.symbolics.com (Ed Schwalenberg):
>     Under uPort sysV/AT (a system V, rev. 2 port to IBM AT and clones [swapping,
>     not paging:-) ]) shared memory is supported for, among other things, using
>     the memory-mapped video RAM. 
...
>     much physical memory).  My initial temptation was to assume the
>     documentation was wrong and that a NULL pointer should be returned if
>     shmat fails; however, the doc'n went out of its way to indicate that it
>     should be -1 (presumably -1L) on failure.
> 
>     So, the questions are:
> 	    1) what is the proper return value of shmat on failure;



This is what my graphics package does under Microport Unix V/AT
for the shared memory attach. Using a cast you don't worry if its
long or not.
   
-Mike Grenier    {ihnp4, rutgers, amdahl}!bungia!cimcor!mike

void g_herc_open()
{
	if ((shm_id = shmget ((key_t)Herc_loc, SCREEN_SIZE*2L-1 , 0)) == -1) 
	{
		perror(" gplot:herc_open() - ");
		fprintf(stderr, "Unable to locate shared memory segment \n");
		fprintf(stderr, "Did you execute /etc/shmcreate as found in /etc/rc.d/shm.rc \n");
		fprintf(stderr, "i.e. /etc/shmcreate 0xb0000 b0000 32768\n");
		exit(1);
	};
		
    
    	if ((video_buf = shmat (shm_id, (char *) 0, 0)) == (char *) -1)
    	{
		perror(" gplot:herc_open() - ");
		fprintf(stderr, "Unable to attach shared memory segment \n");
		fprintf(stderr, "Did you execute /etc/shmcreate as found in /etc/rc.d/shm.rc \n");
		exit(1);
	};
	init_io();
}