netdev - Re: [patch net-next-2.6 1/2] net: allow to change carrier via sysfs

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Date:	Tue, 30 Aug 2011 16:14:22 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Jiri Pirko <jpirko@...hat.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net,
	eric.dumazet@...il.com, shemminger@...tta.com
Subject: Re: [patch net-next-2.6 1/2] net: allow to change carrier via sysfs

On Tue, 2011-08-30 at 16:46 +0200, Jiri Pirko wrote:
> Allow to write to "carrier" attribute. Devices may implement ndo_change_carrier
> callback to allow changing carrier from userspace.
[...]
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index 56e42ab..c8f2ca4 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -126,6 +126,30 @@ static ssize_t show_broadcast(struct device *dev,
>  	return -EINVAL;
>  }
>  
> +static ssize_t store_carrier(struct device *dev, struct device_attribute *attr,
> +			     const char *buf, size_t len)
> +{
> +	struct net_device *netdev = to_net_dev(dev);
> +	ssize_t ret;
> +	int new_value;
> +
> +	if (!capable(CAP_NET_ADMIN))
> +		return -EPERM;
> +
> +	if (!netif_running(netdev))
> +		return -EINVAL;

Not sure that's the right error code.

> +	if (sscanf(buf, "%d", &new_value) != 1)
> +		return -EINVAL;

kstrtoint()

(Or maybe we should have kstrobool().)

> +	if (!rtnl_trylock())
> +		return restart_syscall();
[...]

This is consistent with other attributes, but it seems like a really bad
practice as it will generally result in the process busy-waiting on the
RTNL lock!  I think it would be better to add and use an
rtnl_lock_interruptible().

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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