Re: [PATCH] Use the same MAC address that is defined in domain XML for attached-mac field.

[Ansis Atteka <aatteka@xxxxxxxxxx>]

On Fri, Feb 17, 2012 at 10:55 AM, Laine Stump <laine@xxxxxxxxx> wrote:

On 02/16/2012 06:49 PM, Ansis Atteka wrote:
> Currently libvirt sets the attached-mac to altered MAC address that has
> first byte set to FE. This patch will change that behavior by using the
> original (unaltered) MAC address from the domain XML configuration file.

Maybe I didn't read thoroughly enough, but I don't see where it changes
the behavior - in the cases where previously the first byte was set to
0xFE, now you send discourage=true, and in the cases where it didn't,
now you send discourage=false.

"discourage" means whether bridge should be discouraged to use the newly added
TAP device's MAC address. Libvirt does that by setting the first MAC address byte
high enough.

And here is how this patch works:

1. Now in virNetDevTapCreateInBridgePort() function we always pass exactly the same MAC address that was defined in XML.
   
2. If "discourage" flag was set to true, then we create a copy of MAC address and set its first byte to 0xFE
   
3. virNetDevSetMAC() function would use the MAC address that was product of #2
4. while virNetDevOpenvswitchAddPort() function would use the original MAC address that was passed in #1 (this code did not need to be changed so most likely that was the reason why you did not notice behavior changes)
   

Is this a precursor to something else? Does openvswitch maybe not need
this extremely high MAC address?

> ---
>  src/network/bridge_driver.c |    2 +-
>  src/qemu/qemu_command.c     |    5 +----
>  src/uml/uml_conf.c          |    5 +----
>  src/util/virnetdevtap.c     |   11 ++++++++++-
>  src/util/virnetdevtap.h     |    1 +
>  5 files changed, 14 insertions(+), 10 deletions(-)
>
> diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
> index 8575d3e..3e1e031 100644
> --- a/src/network/bridge_driver.c
> +++ b/src/network/bridge_driver.c
> @@ -1766,7 +1766,7 @@ networkStartNetworkVirtual(struct network_driver *driver,
>          }
>          if (virNetDevTapCreateInBridgePort(network->def->bridge,
>                                             &macTapIfName, network->def->mac,
> -                                           0, false, NULL, NULL) < 0) {
> +                                           false, 0, false, NULL, NULL) < 0) {
>              VIR_FREE(macTapIfName);
>              goto err0;
>          }
> diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
> index 5a34504..671054c 100644
> --- a/src/qemu/qemu_command.c
> +++ b/src/qemu/qemu_command.c
> @@ -180,7 +180,6 @@ qemuNetworkIfaceConnect(virDomainDefPtr def,
>      int tapfd = -1;
>      int vnet_hdr = 0;
>      bool template_ifname = false;
> -    unsigned char tapmac[VIR_MAC_BUFLEN];
>      int actualType = virDomainNetGetActualType(net);
>
>      if (actualType == VIR_DOMAIN_NET_TYPE_NETWORK) {
> @@ -244,9 +243,7 @@ qemuNetworkIfaceConnect(virDomainDefPtr def,
>          net->model && STREQ(net->model, "virtio"))
>          vnet_hdr = 1;
>
> -    memcpy(tapmac, net->mac, VIR_MAC_BUFLEN);
> -    tapmac[0] = 0xFE; /* Discourage bridge from using TAP dev MAC */
> -    err = virNetDevTapCreateInBridgePort(brname, &net->ifname, tapmac,
> +    err = virNetDevTapCreateInBridgePort(brname, &net->ifname, net->mac, true,
>                                           vnet_hdr, true, &tapfd,
>                                           virDomainNetGetActualVirtPortProfile(net));
>      virDomainAuditNetDevice(def, net, "/dev/net/tun", tapfd >= 0);
> diff --git a/src/uml/uml_conf.c b/src/uml/uml_conf.c
> index dbbbfda..c7b29a0 100644
> --- a/src/uml/uml_conf.c
> +++ b/src/uml/uml_conf.c
> @@ -127,7 +127,6 @@ umlConnectTapDevice(virConnectPtr conn,
>                      const char *bridge)
>  {
>      bool template_ifname = false;
> -    unsigned char tapmac[VIR_MAC_BUFLEN];
>
>      if (!net->ifname ||
>          STRPREFIX(net->ifname, VIR_NET_GENERATED_PREFIX) ||
> @@ -139,9 +138,7 @@ umlConnectTapDevice(virConnectPtr conn,
>          template_ifname = true;
>      }
>
> -    memcpy(tapmac, net->mac, VIR_MAC_BUFLEN);
> -    tapmac[0] = 0xFE; /* Discourage bridge from using TAP dev MAC */
> -    if (virNetDevTapCreateInBridgePort(bridge, &net->ifname, tapmac,
> +    if (virNetDevTapCreateInBridgePort(bridge, &net->ifname, net->mac, true,
>                                         0, true, NULL,
>                                         virDomainNetGetActualVirtPortProfile(net)) < 0) {
>          if (template_ifname)
> diff --git a/src/util/virnetdevtap.c b/src/util/virnetdevtap.c
> index 0fce08d..868ba57 100644
> --- a/src/util/virnetdevtap.c
> +++ b/src/util/virnetdevtap.c
> @@ -22,6 +22,7 @@
>
>  #include <config.h>
>
> +#include "virmacaddr.h"
>  #include "virnetdevtap.h"
>  #include "virnetdev.h"
>  #include "virnetdevbridge.h"
> @@ -248,6 +249,7 @@ int virNetDevTapDelete(const char *ifname ATTRIBUTE_UNUSED)
>   * @brname: the bridge name
>   * @ifname: the interface name (or name template)
>   * @macaddr: desired MAC address (VIR_MAC_BUFLEN long)
> + * @discourage: whether bridge should be discouraged from using macaddr
>   * @vnet_hdr: whether to try enabling IFF_VNET_HDR
>   * @tapfd: file descriptor return value for the new tap device
>   * @virtPortProfile: bridge/port specific configuration
> @@ -265,11 +267,14 @@ int virNetDevTapDelete(const char *ifname ATTRIBUTE_UNUSED)
>  int virNetDevTapCreateInBridgePort(const char *brname,
>                                     char **ifname,
>                                     const unsigned char *macaddr,
> +                                   bool discourage,
>                                     int vnet_hdr,
>                                     bool up,
>                                     int *tapfd,
>                                     virNetDevVPortProfilePtr virtPortProfile)
>  {
> +    unsigned char tapmac[VIR_MAC_BUFLEN];
> +
>      if (virNetDevTapCreate(ifname, vnet_hdr, tapfd) < 0)
>          return -1;
>
> @@ -279,7 +284,11 @@ int virNetDevTapCreateInBridgePort(const char *brname,
>       * seeing the kernel allocate random MAC for the TAP
>       * device before we set our static MAC.
>       */
> -    if (virNetDevSetMAC(*ifname, macaddr) < 0)
> +    memcpy(tapmac, macaddr, VIR_MAC_BUFLEN);
> +    if (discourage)
> +        tapmac[0] = 0xFE; /* Discourage bridge from using TAP dev MAC */
> +
> +    if (virNetDevSetMAC(*ifname, tapmac) < 0)
>          goto error;
>
>      /* We need to set the interface MTU before adding it
> diff --git a/src/util/virnetdevtap.h b/src/util/virnetdevtap.h
> index 918f3dc..fc50e22 100644
> --- a/src/util/virnetdevtap.h
> +++ b/src/util/virnetdevtap.h
> @@ -37,6 +37,7 @@ int virNetDevTapDelete(const char *ifname)
>  int virNetDevTapCreateInBridgePort(const char *brname,
>                                     char **ifname,
>                                     const unsigned char *macaddr,
> +                                   bool discourage,
>                                     int vnet_hdr,
>                                     bool up,
>                                     int *tapfd,

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