[PATCH] network: explicitly set the MTU of the bridge device.

Ján Tomko jtomko at redhat.com
Fri Jan 15 07:51:43 UTC 2021

There is no need fo the period at the end of the commit summary.

On a Thursday in 2021, Laine Stump wrote:
>In the past, the MTU of libvirt virtual network bridge devices was
>implicitly set by setting the MTU of the "dummy tap device" (which was
>being added in order to force a particular MAC address from the
>bridge). But the dummy tap device was removed in commit ee6c936fbb
>(libvirt-6.8.0), and so the mtu setting in the network is ignored.
>The solution is, of course, to explicitly set the bridge device MTU
>when it is created.
>Note that any guest interface with a larger MTU that is attached will
>cause the bridge to (temporarily) assume the larger MTU, but it will
>revert to the bridge's own MTU when that device is deleted (this is
>not due to anything libvirt does; it's just how Linux host bridges
>Resolves: https://bugzilla.redhat.com/1913561
>Signed-off-by: Laine Stump <laine at redhat.com>
>    ee6c936fbbo-set-mtu

This looks like a name of a branch. If you want to preserve the commit
this improves upon, I have been using the following format:

Fixes: ee6c936fbbfb217175326f0201d59cc6727a0678

>Signed-off-by: Laine Stump <laine at redhat.com>
> src/network/bridge_driver.c | 3 +++
> 1 file changed, 3 insertions(+)
>diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
>index b7c604eaea..519a473995 100644
>--- a/src/network/bridge_driver.c
>+++ b/src/network/bridge_driver.c
>@@ -2336,6 +2336,9 @@ networkStartNetworkVirtual(virNetworkDriverStatePtr driver,
>     /* Set bridge options */
>+    if (def->mtu && virNetDevSetMTU(def->bridge, def->mtu) < 0)
>+        goto error;
>     /* delay is configured in seconds, but virNetDevBridgeSetSTPDelay
>      * expects milliseconds
>      */

Reviewed-by: Ján Tomko <jtomko at redhat.com>

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