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Date: Mon, 19 Feb 2001 16:53:40 +0100 (CET)
From: Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz>
To: Jeff Garzik <jgarzik@mandrakesoft.com>
cc: David Howells <dhowells@cambridge.redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [LONG RANT] Re: Linux stifles innovation... 
In-Reply-To: <Pine.LNX.3.96.1010219085405.17842F-100000@mandrakesoft.mandrakesoft.com>
Message-ID: <Pine.LNX.3.96.1010219162217.20451A-100000@artax.karlin.mff.cuni.cz>
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> > I suspect part of the problem with commercial driver support on Linux is that
> > the Linux driver API (such as it is) is relatively poorly documented
> 
> In-kernel documentation, agreed.
> 
> _Linux Device Drivers_ is a good reference for 2.2 and below.

And do implementators of generic kernel functions and developers of device
drivers respect it? And how can they respect it if it's a commercial book?

> > and seems
> > to change almost on a week-by-week basis anyway. I've done my share of chasing
> > the current kernel revision with drivers that aren't part of the kernel tree:
> > by the time you update the driver to work with the current kernel revision,
> > there's a new one out, and the driver doesn't compile with it.
> 
> This is entirely in your imagination.  Driver APIs are stable across the
> stable series of kernels: 2.0.0 through 2.0.38, 2.2.0 through 2.2.18,
> 2.4.0 through whatever.

No true. Do you remember for example the mark_buffer_dirty change in some
2.2.x that triggered ext2 directory corruption? (mark_buffer_dirty was
changed so that it could block). 

Another example of bug that comes from the lack of specification is
calling of get_free_pages by non-running processes that caused lockups on
all kernels < 2.2.15. And it is still not cleaned up - see tcp_recvmsg(). 

Having documentation could prevent this kind of bugs. You don't need too
long texts, just a brief description: "this function may be called from
process/bh/interrupt context, it may/may not block, it may/may not be
called in TASK_[UN]INTERURPTIBLE state, it may take these locks."

With documentation developers would be able to change implementation of
kernel functions without the need to recheck all drivers that use them. 

Saying "code is the specification" is not good.

Mikulas

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