Date: Wed, 08 Nov 2000 16:45:51 -0800 From: bruno schwander <bschwand@dvart.com> To: Terry Lambert <tlambert@primenet.com> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: close call in a device ? Message-ID: <3A09F3BF.B028E0F8@dvart.com> References: <200011082033.NAA25455@usr08.primenet.com>
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Terry Lambert wrote:
> > > when a process closes the device, I do not get a "close" call for each
> > > process closing the device. I instead get a close only on the last
> > > process closing the device.
> >
> > devices in a similar way as the one is used for scanning pty's).
>
> To add to this, the close calls can be forces; there is a flag
> in the device structure wich can force notification. I'm not
> sure what it does over a fork(), though: I think you really want
> open notification.
>
You mean that when I register my device/kernel module, I can explicitely
request that all close calls will notify my module ? That is exactly what I
need.
What do you mean by open notification ? I do get all "open" calls to my
device, just not all the "close"
> The main problem with per process resources is that the VFS that
> implements devices, specfs, doesn't own its own vnodes.
Could you develop a little ? I don't know about VFS, specfs and vnodes...
What I did is make a module that defines a struct cdevsw with the open/read/
etc callbacks, then I register my calls for various devices entries with
make_dev(), and at the end used the DEV_MODULE() macro to declare it to the
system. I modeled that after the example in /usr/src/share/examples/kld of
FreeBSD 4
Is there a different driver/module architecture ?
> This is actually the primary reason that VMWARE can only run
> one instance at a time of a virtual machine: there is no way
> to have per open instance resources, which are not shared.
>
> If you were to use the TFS flag (grep for TFS in the headers,
> that's a substring), you could make specfs own its own vnodes.
>
Where should I look for this ? I looked into /usr/src/ and only some
references to NTFS and TFS filesystems turned up ?
Would I have to roll out a custom filesystem to have this running ?
> The way you would handle your problem then is by returning a
> different instance of the device, with a different instance of
> per process attached storage. It's pretty simple to do this:
> just return a different vnode for the next open of the same
> device, instead of the same vnode with an additional reference.
this is really confusing me... in the example I had, the only thing I return
from my open routine is an int telling success or errors happened... any
pointers for the vnode stuff ? if it could apply to what I am trying to do ?
Am I basing my driver on the wrong stuff ?
> NB: If you are trying to do this for VMWARE or some other binary
> code, there's no way that the pty opening soloution suggested in
> the previous posting will be able to work for you, since the code
Yes, I came to that conclusion too.
> will expect a particular behaviour. Right now, FreeBSD doesn't
> support this behaviour (cloning devices), but as pointed out
> above, it's not hard to implement, it's mostly just labor
> intensive.
>
> Terry Lambert
> terry@lambert.org
> ---
> Any opinions in this posting are my own and not those of my present
> or previous employers.
--
###########################################################################
Bruno Schwander
Senior Software Engineer
Worldgate Communications, Inc
email: bschwand@dvart.com
############################################################################
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