Date: Mon, 5 Aug 2002 14:47:02 -0500 (CDT)
From: Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de>
To: Patrick Mochel <mochel@osdl.org>
cc: linux-kernel@vger.kernel.org
Subject: Re: driverfs API Updates
In-Reply-To: <Pine.LNX.4.44.0208051216090.1241-100000@cherise.pdx.osdl.net>
Message-ID: <Pine.LNX.4.44.0208051438430.2694-100000@chaos.physics.uiowa.edu>
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On Mon, 5 Aug 2002, Patrick Mochel wrote:

> [1]: The reason for the macro is because the driverfs internals
> have changed enough to be able to support attributes of any type. In
> order to do this in a type-safe manner, we have a generic object type
> (struct attribute) that we use. We pass this to an intermediate layer
> that does a container_of() on that object to obtain the specific
> attribute type. 

Of course that means that it's not really type-safe, since it has no way 
to check whether the object is embedded in the right type of struct, right 
;) (But I think that's okay, C doesn't have provisions for real 
inheritance)

> This means the specific attribute types have an embedded struct
> attribute in them, making the initializers kinda ugly. I played with
> anonymous structs and unions to have something that could
> theoretically work, but they apparently don't like named
> initializers. 

Have you considered just putting in the embedded part via some macro - 
I think that's what NTFS does for compilers which don't support unnamed 
structs.

Basically

#define EMB_ATTRIBUTE \
	int emb1;
	int emb2

struct my_attribute {
	EMB_ATTRIBUTE
	int my1;
	int my2;
};

That'll work with named initializers just fine, so the users don't have to 
deal with ugly DEVICE_ATTR macros, where one forgets if parameter #3 was 
show or store ;) - It follows the common way of hiding away unavoidable 
ugliness in some header.

> [2]: I wanted to consolidate the first two parameters, but I couldn't
> find a way to stringify ##name (or un-stringify "strname"). Is that
> even possible? 

Why would stringify (include/linux/stringify.h) not work? However, Al Viro 
may get mad at you for generating ungreppable symbols either way ;-)

--Kai


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