linux-kernel - Re: [PATCH] PNP: handle sysfs errors

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Date:	Wed, 11 Oct 2006 15:45:01 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	ambx1@....rr.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PNP: handle sysfs errors

On Wed, 11 Oct 2006 17:51:09 -0400
Jeff Garzik <jeff@...zik.org> wrote:

> +	int rc = device_create_file(&dev->dev,&dev_attr_options);
> +	if (rc) goto err;
> +	rc = device_create_file(&dev->dev,&dev_attr_resources);
> +	if (rc) goto err_opt;
> +	rc = device_create_file(&dev->dev,&dev_attr_id);
> +	if (rc) goto err_res;
> +
>  	return 0;
> +
> +err_res:
> +	device_remove_file(&dev->dev,&dev_attr_resources);
> +err_opt:
> +	device_remove_file(&dev->dev,&dev_attr_options);
> +err:
> +	return rc;

That's a common pattern, isn't it?

I wonder if we could create some sort of automatic-unwinding engine:

int pnp_interface_attach_device(struct pnp_dev *dev)
{
	struct unwind_engine *u = NULL;
	int err;

	u = UNWINDABLE(u, err, device_create_file(&dev->dev,&dev_attr_options),
			device_remove_file, &dev->dev, &dev_attr_options);
	u = UNWINDABLE(u, err, device_create_file(&dev->dev,&dev_attr_id)
			device_remove_file, &dev->dev, &dev_attr_options);
	u = UNWINDABLE(u, err, device_create_file(&dev->dev,&dev_attr_id),
			device_remove_file, &dev->dev, &dev_attr_id);
	err = unwind(err, u);
	return err;
}

and, umm,

#define UNWINDABLE(u, err, expr, undo_fn, arg1, arg2)
	if (err == 0) {
		err = (expr);
		if (err == 0)
			u = add_unwind(u, undo_fn, arg1, arg2);
	}
	u;

int unwind(int err, struct unwind_engine *u)
{
	if (err == 0)
		return 0;
	for (all entries in u in opposite order) {
		u->fn(u->arg0, u>arg1);
		kfree(u);
	}
	return err;
}


I dunno - probably too crappy to live, but it'd encourage/help people to
dtrt.
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