Re: [PATCH] dracut-module-setup.sh: skip installing driver for loopback device

[Martin Pitt]

Hello Coiby,

thanks for the fix!

Coiby Xu [2022-12-14 14:48 +0800]:
> diff --git a/dracut-module-setup.sh b/dracut-module-setup.sh
> index 13e99015..f82349cb 100755
> --- a/dracut-module-setup.sh
> +++ b/dracut-module-setup.sh
> @@ -387,6 +387,7 @@ kdump_install_nic_driver() {
>      _drivers=()
>  for _netif in $1; do
>    ! ip addr show "$_netif" | grep "link/loopback" || continue

I confirm that this works, in the sense of "kdump to ssh localhost succeeds
again".

But it is a bit heavy (calling `ip` and `grep`) and brittle (relying on precise
output format of `ip show`, which isn't very machine-readable).  I'm also
worried that this might apply to other virtual devices as well, such as veth or
wireguard. My laptop has a wireguard device which might also cause trouble:

$ ip link show wgpitti
    4: wgpitti: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1420 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
        link/none

$  ls -l /sys/class/net/wgpitti/device
    ls: cannot access '/sys/class/net/wgpitti/device': No such file or directory

Hence I would recommend this instead:

[ -e "/sys/class/net/$_netif/device/driver" ] || continue

and rename the commit to "skip installing driver for virtual devices" or so.

I tested this with ssh/localhost as well. It has the added benefit of not
relying on "ip show" format, is more robust, more generic, and not even a new
concept: that script already looks at /sys/class/net anyway.
>      _driver=$(_get_nic_driver "$_netif")
>      if [[ -z $_driver ]]; then
>          derror "Failed to get the driver of $_netif"
>
> @@ -404,6 +405,7 @@ kdump_install_nic_driver() {
>          _drivers+=("$_driver")
>      done
> [[ -n ${_drivers[*]} ]] || return

This is fine of course.
>  instmods "${_drivers[@]}"
>
> }

Thanks,

Martin