linux-kernel - Re: Race free attributes in sysfs

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Date:	Tue, 22 May 2007 11:58:23 -0400
From:	"Kristian Høgsberg" <krh@...planet.net>
To:	"Pierre Ossman" <drzeus-list@...eus.cx>
Cc:	"Kay Sievers" <kay.sievers@...y.org>, "Greg KH" <greg@...ah.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Race free attributes in sysfs

On 5/22/07, Pierre Ossman <drzeus-list@...eus.cx> wrote:
> Kay Sievers wrote:
> > We could change the driver-core to suppress the creation of an attribute
> > if the attribute's show() or store() method returns something like
> > -ENOENT at registration time?
> > The driver would pass _all_ possible attributes of the device at
> > registration time, but the core would only create the attributes which
> > are implemented for this particular device? Would that work for you?
> >
>
> Not sure. Not in an obvious way at least.
>
> It also doesn't feel like "the kernel way". Generally you can
> create/allocate an object, assign attributes to it, then activate it.
> Couldn't it be done so that I can add sysfs stuff to a device after I
> just initialized it? (but before I add it).

I agree here - if it was just possible to do this between create and
add, this discussion would be moot.

> > You can assign any number of attribute groups to the device. If they
> > don't have a group name, they will all be created directly at the device
> > level. Would that work for you?
>
> I've had a look at sysfs groups and the biggest beef I have with those
> is that they're too low level. In order to use them I first need to
> create device attributes, then create an array of pointers to each attr
> member. It would be nice if I could just feed an array of device
> attributes (i.e. I want wrappers).

I did a little helper struct for the firewire subsystem that might be
useful on a more general level.  It's struct fw_attribute_group in
drivers/firewire/fw-device.h and the implementation is
init_fw_attribute_group in drivers/firewire/fw-device.c.  But I agree,
attribute groups require a fair bit of boiler plate code.

cheers,
Kristian
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