Re: [PATCH net-next 0/5] rtnetlink: add IFA_IF_NETNSID for RTM_GETADDR

[Kirill Tkhai]

On 03.09.2018 16:50, Jiri Benc wrote:
> On Mon, 3 Sep 2018 16:41:45 +0300, Kirill Tkhai wrote:
>> But this is a synthetic test, while I asked about real workflow.
>> Is this real problem for lxd, and there is observed performance
>> decrease?
> 
> It's actually not as much a performance problem but rather the only way
> to get the data in some situations. Namely, when you have only netnsid.
> This happens e.g. when you want to query a veth peer in another netns.
> 
> setns() requires a file descriptor which you don't have. Nor there is
> a way to convert netnsid to a fd.
> 
> While developing the IFLA_IF_NETNSID patch, I was first thinking about
> implementing an API doing the conversion. The problem is there's no
> good place to put this into. It can't be done over netlink: netlink is
> unreliable and you can't have the kernel open a fd for you and lose it.
> There's no ioctl to use. So we'd be left with a procfs/sysfs or a
> syscall.
> 
> Using netnsid to refer to the target netns seems to be a nice solution -
> after all, netnsid is the identifier to use in netlink.

Ok, I have no objections, just mentioning that generic problem.

Thanks,
Kirill