netdev - Re: [PATCH net-next] sockopt: Make SO

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Message-ID: <1350942738.8609.1375.camel@edumazet-glaptop>
Date:	Mon, 22 Oct 2012 23:52:18 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Brian Haley <brian.haley@...com>
Cc:	Pavel Emelyanov <xemul@...allels.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next] sockopt: Make SO_BINDTODEVICE readable

On Mon, 2012-10-22 at 17:47 -0400, Brian Haley wrote:
> On 10/22/2012 05:37 PM, Eric Dumazet wrote:
> > On Mon, 2012-10-22 at 17:20 -0400, Brian Haley wrote:
> > 
> >> 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.






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