[PATCH] virnetdevveth: Do report error if creating veth fails

[Martin Kletzander]

On Thu, Dec 02, 2021 at 01:10:20PM +0100, Michal Privoznik wrote:
>For some weird reason we are ignoring errors when creating veth
>pair that netlink reports. This affects the LXC driver which
>creates interfaces for container in
>virLXCProcessSetupInterfaces(). If creating a veth pair fails, no
>error is reported and the control jumps onto cleanup label where
>some cryptic error message is reported instead (something about
>inability to remove veth pair).
>
>Let's report error that netlink returned - it's probably the most
>accurate reason anyways.
>
>Resolves: https://gitlab.com/libvirt/libvirt/-/issues/225
>Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>---
> src/util/virnetdevveth.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
>diff --git a/src/util/virnetdevveth.c b/src/util/virnetdevveth.c
>index 7133af44a2..ddf304036a 100644
>--- a/src/util/virnetdevveth.c
>+++ b/src/util/virnetdevveth.c
>@@ -38,10 +38,17 @@ VIR_LOG_INIT("util.netdevveth");
> static int
> virNetDevVethCreateInternal(const char *veth1, const char *veth2)
> {
>-    int status;     /* Just ignore it */
>+    int error;
>     virNetlinkNewLinkData data = { .veth_peer = veth2 };
>
>-    return virNetlinkNewLink(veth1, "veth", &data, &status);
>+    if (virNetlinkNewLink(veth1, "veth", &data, &error) < 0) {
>+        virReportSystemError(-error,
>+                             _("unable to create %s <-> %s veth pair"),
>+                             veth1, veth2);

This might be overriding a previous error and @error might be just 0.

The function does not report an error in this one case only:

         if (err->error < 0) {
             if (error)
                 *error = err->error;
             else
                 virReportSystemError(-err->error, "%s", _("netlink error"));

which suggests you should either pass NULL to the function or report an
error only if @error != 0.

>+        return -1;
>+    }
>+
>+    return 0;
> }
>
> static int
>-- 
>2.32.0
>
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