[CRIU] restoring sockets with data pending

[Andrew Vagin]

On Thu, Oct 09, 2014 at 03:23:20PM -0500, 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

http://www.makelinux.net/books/lkd2/ch17lev1sec9

How often do you see data in this socket?
If "systemd-u" is systemd-udev, you can try to use "udevadm monitor" to
find out which events are here.

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