From: d...@gcom.com (David Grothe)
Subject: Clone Drivers
Date: 1998/09/25
Message-ID: <360BEEFC.868BAC27@gcom.com>#1/1
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Hello all,
I am in the process of making Linux STREAMS (LiS) compatible with kernel
version 2.1.120 and beyond. "Thanks" to Linus for putting the hooks
into the kernel source.
I am writing to you concerning the concept of "clone driver" as it is
understood by STREAMS and by SVR4 Unix systems. The SVR4 meaning of a
"clone driver" is that the character special device (only) driver's open
routine is allowed to change the minor device number associated with the
"device" being opened. This allows drivers to implement pools of
devices under a single /dev entry. Each open gets an available minor
device from the pool.
I am going to have to re-implement this for LiS 2.1.xx because my 2.0.xx
implementation does not carry forward to the 2.1.xx kernels.
Now comes the question: I am going to have to write pretty much the
same piece of code either under the covers of LiS or as an addition to
the sys_open routine. If I do the former then the feature will be
available to LiS STREAMS drivers only. If I do the latter, and you
accept the code into the kernel, then the feature will be available to
any character special device driver.
Please let me know if you want me to add this feature to sys_open.
Otherwise I will just put it inside LiS.
Thanks,
Dave
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From: m...@roan.co.uk (Mike Jagdis)
Subject: Re: Clone Drivers
Date: 1998/09/28
Message-ID: <Pine.LNX.3.91.980928125927.5653A-100000@toaster.roan.co.uk>#1/1
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On Fri, 25 Sep 1998, David Grothe wrote:
> Now comes the question: I am going to have to write pretty much the
> same piece of code either under the covers of LiS or as an addition to
> the sys_open routine. If I do the former then the feature will be
> available to LiS STREAMS drivers only. If I do the latter, and you
> accept the code into the kernel, then the feature will be available to
> any character special device driver.
Have you considered making a separate clone device driver? The
major number is used to identify the clone device. When opened
it uses the node's minor number as the real major number, allocates
an unused minor and punts the open to the constructed device.
iBCS does something similar when opening file names representing
AF_UNIX sockets, TLI/XTI transport providers etc.
Mike
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