[CRIU] restoring sockets with data pending

[Tycho Andersen]

On Fri, Oct 10, 2014 at 02:12:39PM +0400, Pavel Emelyanov wrote:
> On 10/10/2014 12:23 AM, Tycho Andersen wrote:
> > Hi Pavel, Andrew,
> > 
> > On Mon, Sep 15, 2014 at 02:21:18PM +0400, Pavel Emelyanov wrote:
> >> On 09/13/2014 04:55 AM, Tycho Andersen wrote:
> >>> Hi all,
> >>>
> >>> One of the errors that I sometimes get when dumping things is:
> >>>
> >>> Error (sk-netlink.c:73): The socket has data to read
> >>
> >> Yup :) These are netlink sockets with some data from the krenel.
> >>
> >>> What is necessary to fix this problem? I guess there is some work to
> >>> be done on the kernel side to provide an API for getting these
> >>> buffers? Is there some other trick we can use?
> >>
> >> Strictly speaking, we should patch the kernel to be able to peek
> >> this data from socket and to put it back. But maybe in some cases
> >> we could invent some workaround (I'm not quite sure netdev@ people
> >> would be happy with such hacks :) ).
> >>
> >> Can we investigate what kind of socket is it and what data is in
> >> there?
> > 
> > Finally getting around to looking at this; lsof says:
> > 
> > systemd-u 179 root    4u  netlink                         0t0  13252 KOBJECT_UEVENT
> > 
> > There are 88 bytes of data pending on the socket, and when I read them
> > off, NLMSG_OK seems to think they're not a valid netlink message:
> > 
> > Error (sk-netlink.c:114): nlmsg_len: 1080321121, nlmsg_type: 27951,
> > nlmsg_seq 795176053, nlmsg_pid 2020175477
> 
> And what does the 1st pr_err from your patch show?

The full output from my prints is,

(00.166053) Error (sk-netlink.c:73): The socket has data to read
(00.166066) Error (sk-netlink.c:102): failed dumping lfd: 66, id 42
(00.166075) Error (sk-netlink.c:113): received message of length 88, 0
(00.166081) Error (sk-netlink.c:114): nlmsg_len: 1080321121, nlmsg_type: 27951, nlmsg_seq 795176053, nlmsg_pid 2020175477

Tycho

> > Here's the code I used, I guess I'm misunderstanding something?
> > 
> > https://github.com/tych0/criu/commit/ae9a5405232976ca2f5234477b3c3bce0f87a22f
> > 
> > Thanks,
> > 
> > Tycho
> > 
>