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Subject: Re: Amancio's tv program with capture!
To: james@miller.cs.uwm.edu (Jim Lowe)
Date: Tue, 23 Jan 96 22:31:55 MET
Cc: hackers@freebsd.org
In-Reply-To: <199601232053.OAA14413@miller.cs.uwm.edu>; from "Jim Lowe" at Jan 23, 96 2:53 pm
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> > > How does one mark the driver/mmapped memory as shared memory
> > > with the current utilities? It isn't real obvious that one can
> > > actually do this without modifiying the shmat system call (or at
> > > least to me).
> > 
> > 
> > 	int	fd;
> > 	caddr_t	mapaddr;
> > 
> > 	if( ( fd = open( DEV_NAME, O_RDWR)) == -1) {
> > 		perror( "open");
> > 		exit( 1);
> > 	}
> > 
> > 	mapaddr =  mmap( 0,			/* map here, 0 = don't care*/
> > 			 DEV_MEM_SIZE,		/* device memory window*/
> > 			 PROT_READ|PROT_WRITE,	/* will be reading/writing*/
> > 			 MAP_HASSEMAPHORE, 	/* (?) prevent caching*/
> > 			 fd,			/* fd for device*/
> > 			 (off_t)0		/* full window*/
> > 			);
> > 

> I know how to mmap.  The question is once you have mapaddr how does
> one attach that to X's shared memory functions through the Xshm 
> utilities?  I don't beleive I have ever head of map_hassemaphore...

Is it possible to mmap() something to the address returned by shmat()?

Something like:

	shmaddr = shmat( shmid, NULL, 0 );
	mapaddr = mmap( shmaddr, ... );

I haven't got a slightest clue about this approach.

/Alby

> 	-Jim