Re: [PATCH net-next] sockopt: Make SO_BINDTODEVICE readable

On Mon, 2012-10-22 at 23:52 +0200, Eric Dumazet wrote:

On Mon, 2012-10-22 at 17:47 -0400, Brian Haley wrote:

quoted

On 10/22/2012 05:37 PM, Eric Dumazet wrote:

quoted

On Mon, 2012-10-22 at 17:20 -0400, Brian Haley wrote:

quoted

It's not much different from what's there:

	setsockopt("foo");

	rename foo -> bar

	index = getsockopt();
	if_indextoname(index) -> "bar"

I more raised the issue since you pass a 'char *' to setsockopt() but an 'int *'
to getsockopt(), I don't think any other value is non-symmetrical like this.

-Brian

I meant another cpu can be changing dev->name[] content while the
strcpy() is done, and you get a mangled devname, like "for" or "bao"
instead of "foo" or "bar"

Even when holding the rcu_read_lock()?  I'd have to hold the rtnl lock there?

Yes, rcu_read_lock() only makes sure the device doesnt disappear.

But its name can be changed.

You could use a seqcount_t, so that readers dont have to lock rtnl.

But do we really want to return a name here, I am not yet convinced.

If setsockopt() takes a name then it makes no sense that getsockopt()
would return an index.  Perhaps an SO_BINDTOIFINDEX would be useful, but
let's not make SO_BINDTODEVICE mean two different things.

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.