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

[Michal Privoznik]

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.

Michal