linux-kernel - Re: [PATCH v3 1/6] ACPI: dock: convert sysfs attributes to an attribute

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Date:	Mon, 19 Oct 2009 10:56:17 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Alex Chiang <achiang@...com>
Cc:	lenb@...nel.org, shaohua.li@...el.com,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v3 1/6] ACPI: dock: convert sysfs attributes to an
	attribute_group

On Mon, Oct 19, 2009 at 11:21:38AM -0600, Alex Chiang wrote:
> Hi Dmitry,
> 
> * Dmitry Torokhov <dmitry.torokhov@...il.com>:
> > On Fri, Oct 16, 2009 at 03:14:59PM -0600, Alex Chiang wrote:
> > > As suggested by Dmitry Torokhov, convert the individual sysfs
> > > attributes into an attribute group.
> > > 
> > > This change eliminates quite a bit of copy/paste code in the
> > > error handling paths.
> > > 
> > 
> > Looks much better, one more suggestion though:
> > 
> > > +err_unregister:
> > > +	printk(KERN_ERR "%s encountered error %d\n", __func__, ret);
> > 
> > If you want to print error this it should probably go down, right before
> > "return ret".
> 
> This is true for this patch, 1/6... but by the end of the series,
> the problem has resolved itself.
> 
> I agree that it's sloppy to have this bit of inconsistency in the
> middle of the patch series, but I'm reluctant to spin the entire
> series again, for sake of a printk.
> 
> > > +	sysfs_remove_group(&dock_device->dev.kobj, &dock_attribute_group);
> > 
> > It begs another label right here. There are cases when yo0u already
> > registered the platform device but haven't added the sysfs group, right?
> 
> This isn't quite true. In this patch, 1/6, our sequence goes:
> 
> 	platform_device_register_simple()
> 	platform_device_add_data()
> 	/* twiddle some state in the platform device, no error paths though */
> 	sysfs_create_group()
> 
> Arguably, the platform_device_add_data() call could fail with
> -ENOMEM, but the code today doesn't deal with that error
> condition, and I didn't touch the platform_device_add_data()
> line.
> 
> So really, there are no other exit paths between registering the
> platform device and adding the sysfs group.
>

If sysfs_create_group() fails you will go to err_unregister: which will
try to remove the non-existing group. While the current sysfs code is
relsilient against such errors it may not be so in the future. It is
better to have a separate label and bypass sysfs_remove_group() if
sysfs_create_group() returned error.

> By the end of the patch series, I combine the _register_simple()
> call with the _add_data() call and the final sequence looks like
> this:
> 
> 	if (platform_device_register_data() == error)
> 		return error;
> 
> 	/* twiddle local state in platform device */
> 
> 	if (sysfs_create_group())
> 		goto err_unregister;
> 
> 	/* other stuff */
> 
> 	err_unregister:
> 		printk(KERN_ERR "%s encountered error %d\n", __func__, ret);
> 		sysfs_remove_group(&dd->dev.kobj, &dock_attribute_group);
> 		platform_device_unregister(dd);
> 		return ret;
> 

-- 
Dmitry
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