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	Fri, 1 Aug 1997 12:23:48 -0700 (PDT)
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To: Terry Lambert <terry@lambert.org>
cc: msmith@atrad.adelaide.edu.au (Michael Smith), luigi@labinfo.iet.unipi.it,
        hackers@FreeBSD.ORG
Subject: Re: device close behaviour - a question 
In-reply-to: Your message of "Fri, 01 Aug 1997 10:40:34 PDT."
             <199708011740.KAA09486@phaeton.artisoft.com> 
Date: Fri, 01 Aug 1997 12:23:48 -0700
From: Amancio Hasty <hasty@rah.star-gate.com>
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Hi,

Curious, shouldn't the responsibility of managing the behavior of
open/close fall on the device driver . After all the driver should
dictate whether it can manage multiple open instances. As for determining
whether there are multiple opens on a device we can create an ioctl
which returns the number of opens . Ideally, it should return instances
of the states for each open. 

	Amancio
>From The Desk Of Terry Lambert :
> > > I am having a problem related to the having multiple (actually,
> > > 2) open descriptors on the same character device. More specifically,
> > > I notice that only the last close does actually invoke the device
> > > close routine.
> > 
> > Heh.  This one is tricky.
> 
> Poul-Henning was talking about this before on the -current list.
> 
> In general, I believe everyone agreed that it was desirable to
> differentiate between "close" and "last close" to provide for
> "per open instance" private data on devices.
> 
> There is an issue on open, as well, since a device may be
> instanced once, but have multiple references created for it
> (Mike's inheritance of fd's on fork() or on exec() without
> the close-on-exec flag set via fcntl() is one example of this).
> 
> The issue is that there is not a semantic seperation between
> reference instance vs. device instance at open time, so a close
> differentiation is less than useful.  Both corrections would
> need to occur simultaneously for either one to be useful alone.
> 
> 
> > You cannot ever guarantee any fixed number of openers on a device.
> 
> O_EXCL or function equivalent.
> 
> 
> 					Terry Lambert
> 					terry@lambert.org
> ---
> Any opinions in this posting are my own and not those of my present
> or previous employers.
>