linux-kernel - Re: [PATCH] virtio-mmio: Devices parameter parsing

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Message-ID: <87sjlooq3m.fsf@rustcorp.com.au>
Date:	Wed, 16 Nov 2011 11:12:05 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Pawel Moll <pawel.moll@....com>, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Cc:	Sasha Levin <levinsasha928@...il.com>,
	Peter Maydell <peter.maydell@...aro.org>,
	Pawel Moll <pawel.moll@....com>
Subject: Re: [PATCH] virtio-mmio: Devices parameter parsing

On Tue, 15 Nov 2011 13:53:05 +0000, Pawel Moll <pawel.moll@....com> wrote:
> +static char *virtio_mmio_cmdline_devices;
> +module_param_named(devices, virtio_mmio_cmdline_devices, charp, 0);

This is the wrong way to do this.

Don't put things in a charp and process it later.  It's lazy.  You
should write parsers for it and call it straight from module_param.

And if you do it that way, multiple devices are simply multiple
arguments.

Like so:

static int virtio_mmio_set(const char *val, const struct kernel_param *kp)
{
        if (!virtio_mmio_cmdline_parent_initialized) {
        	err = device_register(&virtio_mmio_cmdline_parent);
        	if (err)
        		return err;
                virtio_mmio_cmdline_parent_initialized = true;
        }
        
        ... parse here, return -errno on fail, 0 on success.
}

static struct kernel_param_ops param_ops_virtio_mmio = {
        .set = virtio_mmio_set,
        .get = virtio_mmio_get,
};

module_param_cb(device, &param_ops_virtio_mmio, NULL, 0400);

Initialization and error handling is now done for you...

Cheers,
Rusty.
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