linux-kernel - Re: [PATCH] debugfs: Revamp debugfs_create_{u,x,s}{8,16,32,64} to support signed integers

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Date:	Sun, 16 Dec 2007 18:19:53 +0100
From:	Mattias Nissler <mattias.nissler@....de>
To:	Greg KH <greg@...ah.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] debugfs: Revamp debugfs_create_{u,x,s}{8,16,32,64} to
	support signed integers

On Sun, 2007-12-16 at 09:05 -0800, Greg KH wrote:
> On Sun, Dec 16, 2007 at 05:37:59PM +0100, Mattias Nissler wrote:
> > This makes debugfs use its own file_operations for the value accessor files
> > created by debugfs_create_XXX. Having that, we can also have proper versions
> > for signed integers.
> 
> Why not tweak the "SIMPLE_ATTRIBUTE" code to support this instead?  That
> way debugfs and all other filesystems could also use these attributes?

I expected that question ;-) Actually, I had a version that did this.
But it ended up being ugly, cause SIMPLE_ATTRIBUTEs expect to access the
values via get/set functions using u64. Here is what I did and why I
didn't like it:

* I made the set/get function interface more generic (as it is in the
debugfs patch), i.e. getting passed the buf, so they have to
decode/encode whatever they like into the buf instead of working with
u64
* This means either all code using SIMPLE_ATTRIBUTES must be changed, or
I need to add another wrapper macro that produces suitable get/set
functions from the u64 versions it gets passed.
* Changing all SIMPLE_ATTRIBUTE users is not what I want, cause moving
the csnprintf()/strtoull() calls out of the SIMPLE_ATTRIBUTE code means
it becomes less simple to use it, right?
* The wrapper is actually possible, but it suffers from cases where
somebody passes NULL for a get or set function (which is actually
expected, compare the code in libfs.c) It is possible to hack around
this, but it's ugly.

Then I thought, well, SIMPLE_ATTRIBUTEs are made to work with a set/get
function pair. But debugfs expects a pointer to an actual variable
anyway, so just bypass the SIMPLE_ATTRIBUTE code and make debugfs use
it's own file_operations (most of them shamelessly stolen from the
SIMPLE_ATTRIBUTE code, I admit).

Mattias

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