Date: Mon, 21 Jul 1997 18:19:49 -0500 (CDT) From: jpt@msc.edu (Joseph Thomas) To: freebsd-hackers@FreeBSD.ORG Subject: Cloned devices??? Message-ID: <199707212319.SAA06830@uh.msc.edu>
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I'm looking for a way to do what the 'clone' device in
SunOS/streams allows the driver to do. Any pointers/ideas?
(Okay - let's see if I can explain this and make it understandable.)
Basically, I have an application which would like to
have several unique opens to a device without the application
having to poll minor numbers. With the clone device, an open
call to a known major/minor will cause the xxx_open() routine
to find an unused minor device and return makedev(major,unique minor).
A couple of advantages of this include a) user always opens one device,
b) you don't clutter up your /dev directory with every possible
major/minor pair.
Example:
/dev has node clone, major M, minor 0.
application does:
for ( i = 0; i < 3; i++ )
fd[i] = open ( "/dev/clone", O_RDWR );
where fd[0] would actually point to a device with major M, minor 1,
fd[1] would point to major M, minor 2,
and fd[2] would point to major M, minor 3.
what I'd like to avoid is:
/dev/clone00 major M, minor 0
/dev/clone01 major M, minor 1
/dev/clone02 major M, minor 2
/dev/clone03 major M, minor 3
.
.
.
/dev/cloneNN major M, minor NN
and application:
for ( i = 0; i < 3; i++ )
for ( j = 0; j < NN; j++ ) {
sprintf ( name, "/dev/clone%2d", j );
if ( ( fd[i] = open ( name, O_RDWR ) ) > 0 )
break;
}
Does this make sense?
--
Joseph Thomas E/Mail: jpt@msc.edu
Minnesota Supercomputer Center, Inc. jpt@magic.net
1200 Washington Ave So. Tel: +1 612 337 3558
Minneapolis, MN 55415-1227 FAX: +1 612 337 3400
An elephant is a mouse with an operating system.
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