[libvirt] [PATCH v2] nodedev: Increase the netlink socket buffer size to the one used by udev

[Erik Skultety]

On Mon, May 29, 2017 at 02:16:17PM +0200, Michal Privoznik wrote:
> On 05/19/2017 03:16 PM, Erik Skultety wrote:
> > From: "ning.bo" <ning.bo9 at zte.com.cn>
> >
> > When a number of SRIOV VFs (up to 128 on Intel XL710) is created:
> > for i in `seq 0 1`; do
> >   echo 63 > /sys/class/net/<interface>/device/sriov_numvfs
> > done
> >
> > libvirtd will then report "udev_monitor_receive_device returned NULL"
> > error because the netlink socket buffer is not big enough (using GDB on
> > libudev confirmed this with ENOBUFFS) and thus some udev events were
> > dropped. This results in some devices being missing in the nodedev-list
> > output. This patch overrides the system's rmem_max limit but for that,
> > we need to make sure we've got root privileges.
> >
> > https://bugzilla.redhat.com/show_bug.cgi?id=1450960
> >
> > Signed-off-by: ning.bo <ning.bo9 at zte.com.cn>
> > Signed-off-by: Erik Skultety <eskultet at redhat.com>
> > ---
> > Additionally, we might want to check for the errno, providing a specific
> > message if such issue occurs again in a further non-specified point in time and
> > return the generic, yet cryptic one for all other cases.
> >
> >  src/node_device/node_device_udev.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/src/node_device/node_device_udev.c b/src/node_device/node_device_udev.c
> > index 4ecb0b18f..0b3717397 100644
> > --- a/src/node_device/node_device_udev.c
> > +++ b/src/node_device/node_device_udev.c
> > @@ -1728,6 +1728,13 @@ static int nodeStateInitialize(bool privileged,
> >
> >      udev_monitor_enable_receiving(priv->udev_monitor);
> >
> > +    /* mimic udevd's behaviour and override the systems rmem_max limit in case
> > +     * there's a significant number of device 'add' events
> > +     */
> > +    if (geteuid() == 0)
> > +        udev_monitor_set_receive_buffer_size(priv->udev_monitor,
> > +                                             128 * 1024 * 1024);
> > +
> >      /* We register the monitor with the event callback so we are
> >       * notified by udev of device changes before we enumerate existing
> >       * devices because libvirt will simply recreate the device if we
>
> ACK and safe for freeze. Although on my system it works even without the
> check for euid.

Are you sure? Because the session daemon should not have the CAP_NET_ADMIN
capability. Though it's true that since we don't care about the return value
the check is unnecessary I give you that. Still, the check is harmless and we
know that it will fail for non-privileged user, so I'm going to keep it here.

Thanks for review,
Erik

>
> Michal
>
> --
> libvir-list mailing list
> libvir-list at redhat.com
> https://www.redhat.com/mailman/listinfo/libvir-list