[libvirt] [PATCH v2 08/11] util: if setting admin MAC to 00:00:00:00:00:00 fails, try 02:00:00:00:00:00

[Laine Stump]

Some PF drivers allow setting the admin MAC (that is the MAC address
that the VF will be initialized to the next time the VF's driver is
loaded) to 00:00:00:00:00:00, and some don't. Multiple drivers
initialize the admin MACs to all 0, but don't allow setting it to that
very same value. It has been an uphill battle convincing the driver
people that it's reasonable to expect The argument that's used is
that an all 0 device MAC address on a device is invalid; however, from
an outsider's point of view, when the admin MAC is set to 0 at the
time the VF driver is loaded, the VF's MAC is *not* set to 0, but to a
random non-0 value. But that's beside the point - even if I could
convince one or two SRIOV driver maintainers to permit setting the
admin MAC to 0, there are still several other drivers.

So rather than fighting that losing battle, this patch checks for a
failure to set the admin MAC due to an all 0 value, and retries it
with 02:00:00:00:00:00. That won't result in a random value being set
in the VF MAC at next VF driver init, but that's okay, because we
always want to set a specific value anyway. Rather, the "almost 0"
setting makes it easy to visually detect from the output of "ip link
show" which VFs are currently in use and which are free.
---
 src/util/virnetdev.c | 42 ++++++++++++++++++++++++++++++++++++++----
 1 file changed, 38 insertions(+), 4 deletions(-)

diff --git a/src/util/virnetdev.c b/src/util/virnetdev.c
index 6dafc87..eb2c679 100644
--- a/src/util/virnetdev.c
+++ b/src/util/virnetdev.c
@@ -1460,6 +1460,14 @@ virNetDevSysfsFile(char **pf_sysfs_device_link ATTRIBUTE_UNUSED,
 #if defined(__linux__) && defined(HAVE_LIBNL) && defined(IFLA_VF_MAX)
 
 
+static virMacAddr zeroMAC = { .addr = { 0, 0, 0, 0, 0, 0 } };
+
+/* if a net driver doesn't allow setting MAC to all 0, try setting
+ * to this (the only bit that is set is the "locally administered" bit")
+ */
+static virMacAddr altZeroMAC = { .addr = { 2, 0, 0, 0, 0, 0 } };
+
+
 static struct nla_policy ifla_vf_policy[IFLA_VF_MAX+1] = {
     [IFLA_VF_MAC]       = { .type = NLA_UNSPEC,
                             .maxlen = sizeof(struct ifla_vf_mac) },
@@ -1470,7 +1478,8 @@ static struct nla_policy ifla_vf_policy[IFLA_VF_MAX+1] = {
 
 static int
 virNetDevSetVfConfig(const char *ifname, int vf,
-                     const virMacAddr *macaddr, int vlanid)
+                     const virMacAddr *macaddr, int vlanid,
+                     bool *allowRetry)
 {
     int rc = -1;
     struct nlmsghdr *resp = NULL;
@@ -1547,7 +1556,15 @@ virNetDevSetVfConfig(const char *ifname, int vf,
         if (resp->nlmsg_len < NLMSG_LENGTH(sizeof(*err)))
             goto malformed_resp;
 
-        if (err->error) {
+        /* if allowRetry is true and the error was EINVAL, then
+         * silently return a failure so the caller can retry with a
+         * different MAC address
+         */
+        if (err->error == -EINVAL && *allowRetry &&
+            macaddr && !virMacAddrCmp(macaddr, &zeroMAC)) {
+            goto cleanup;
+        } else if (err->error) {
+            /* other errors are permanent */
             char macstr[VIR_MAC_STRING_BUFLEN];
 
             virReportSystemError(-err->error,
@@ -1559,6 +1576,7 @@ virNetDevSetVfConfig(const char *ifname, int vf,
                                  vlanid,
                                  ifname ? ifname : "(unspecified)",
                                  vf);
+            *allowRetry = false; /* no use retrying */
             goto cleanup;
         }
         break;
@@ -2195,8 +2213,24 @@ virNetDevSetNetConfig(const char *linkdev, int vf,
          * guest or host). if there is a vlanTag to set, it will take
          * effect immediately though.
          */
-        if (virNetDevSetVfConfig(pfDevName, vf, adminMAC, vlanTag) < 0)
-            goto cleanup;
+        bool allowRetry = true;
+
+        if (virNetDevSetVfConfig(pfDevName, vf,
+                                 adminMAC, vlanTag, &allowRetry) < 0) {
+            /* allowRetry will still be true if the failure was due to
+             * trying to set the MAC address to all 0. In that case,
+             * we can retry with "altZeroMAC", which is just an all-0 MAC
+             * with the "locally administered" bit set.
+             */
+            if (!allowRetry)
+                goto cleanup;
+
+            allowRetry = false;
+            if (virNetDevSetVfConfig(pfDevName, vf,
+                                     &altZeroMAC, vlanTag, &allowRetry) < 0) {
+                goto cleanup;
+            }
+        }
     }
 
     ret = 0;
-- 
2.9.3