linux-kernel - Re: [PATCH] kobject: make sure kobj->ktype is set before kobject

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Date:	Thu, 29 Nov 2007 18:17:47 +0100
From:	Kay Sievers <kay.sievers@...y.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Cornelia Huck <cornelia.huck@...ibm.com>, Greg KH <greg@...ah.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Jonathan Corbet <corbet@....net>,
	Randy Dunlap <randy.dunlap@...cle.com>
Subject: Re: [PATCH] kobject: make sure kobj->ktype is set before
	kobject_init

On Thu, 2007-11-29 at 12:06 -0500, Alan Stern wrote:
> On Thu, 29 Nov 2007, Kay Sievers wrote:
> 
> > > In fact, if we were designing the kobject API from scratch, I'd suggest 
> > > making the ktype value an argument to kobject_init() so that it 
> > > _couldn't_ be omitted.
> > 
> > Sounds fine, maybe we should also pass the name along, so it will be
> > obvious what happens here:
> >   int kobject_init(struct kobject *kobj, struct kobj_type *type, const char *fmt, ...)
> 
> I don't know...  Normally *_init() routines can't fail, but this could.  
> Then things like device_register() would run into trouble: The caller 
> wouldn't know whether a failure occurred before or after the 
> kobject_init() call, so it wouldn't know what sort of cleanup action 
> was needed: kfree() or device_put().

But wouldn't device_register() do the kobject cleanup for you when it
fails? Why would a caller of device_register() care about the state of
the kobject?

> > Oh, if you want to rewind on error and have an initialized but still
> > unregistered kobject, and just want to free the allocated name by
> > calling kobject_cleanup() or kobject_put() you might not expect, that
> > your whole object that embeds the kobject will be gone. Just something
> > we need to document ...
> 
> When that sort of thing happens, the unwinding should be done by the   
> code responsible for whole object.  For example, if device_add() fails
> then the caller should go on to call device_put() rather than
> kfree(dev).
> 
> That's how you would expect things to work in most cases.  There aren't
> many bare kobjects in the kernel.
> 
> I agree that documenting this behavior would be good.

Ok, fine. Hope we will collect all that information in the end. :)

Kay

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