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

[Pavel Emelyanov <xemul@parallels.com>]

On 10/22/2012 04:43 AM, David Miller wrote:
> From: Pavel Emelyanov <xemul@parallels.com>
> Date: Fri, 19 Oct 2012 13:55:56 +0400
> 
>> The SO_BINDTODEVICE option is the only SOL_SOCKET one that can be set, but
>> cannot be get via sockopt API. The only way we can find the device id a
>> socket is bound to is via sock-diag interface. But the diag works only on
>> hashed sockets, while the opt in question can be set for yet unhashed one.
>>
>> That said, in order to know what device a socket is bound to (we do want
>> to know this in checkpoint-restore project) I propose to make this option
>> getsockopt-able and report the respective device index.
>>
>> Another solution to the problem might be to teach the sock-diag reporting
>> info on unhashed sockets. Should I go this way instead?
>>
>> Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
> 
> Applied.  I can't believe we didn't support this when the feature
> was added.
> 
> I guess we figured that if the application made this setting, then
> it knows and doesn't need to query it.
> .

AFAIS such decision (application that configures something knows what it is) was
made for many things. The same is true at least for the SO_ATTACH_FILTER option
and for the shutdown syscall. Both add something to a socket that cannot be queried
back. And I'm now thinking which way for getting one would be better.

Thanks,
Pavel