Re: Race free attributes in sysfs

[Mark Lord <lkml@rtr.ca>]

Dmitry Torokhov wrote:
> On Sunday 20 May 2007 07:01, Pierre Ossman wrote:
> > Hi Greg,
> >
> > I'm reworking the sysfs stuff in the MMC layer to be a bit more flexible, but
> > there is one thing that has me baffled; how do you add attributes to an object
> > in a race free manner when you have a dynamic set of attributes.
> >
> > I've looked at other parts of the kernel and they all use:
> >
> > 1. Add object.
> > 2. Add attributes.
> >
> > To me, it seems like there's a window between 1 and 2 where the object is in
> > /sys but doesn't have the proper attributes. Life for user space gets very
> > annoying if it has to add artificial delays to avoid this window.
> >
> > So how do I do this properly? Something like this would, from my point of view,
> > be the sane method:
> >
> > 1. Add hidden object.
> > 2. Add attributes.
> > 3. Show object.
>
> 1. dev->uevent_suppress = 1;
> 2. device_register(dev);
> 3. device_create_file(dev, ...);
> 4. dev->uevent_suppress = 0;
> 5. kobject_uevent(&dev->kobj, KOBJ_ADD);

I don't see how that prevents an already-running udevd
from seeing the partially filled in /sys/ entry,
if it were.. say.. already doing a /sys scan,
or even just during initial startup.

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