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Re: [libvirt] [PATCH v2]: set and restore MAC address of a NIC when using PASSTHROUGH mode



On Thu, Jun 16, 2011 at 02:23:07PM +0200, Gerhard Stenzel wrote:
> 
> This is a rework of the patch Dirk sent out last week.
> 
> The attached patch addresses the problem that when a PASSTHROUGH 
> mode DIRECT NIC connection is made the MAC address of the NIC is 
> not automatically set and reset to the configured VM MAC and 
> back again.
> 
> The patch fixes this problem by setting and resetting the MAC
> while remembering the previous setting while the VM is running.
> This also works if libvirtd is restarted while the VM is running.

> Index: libvirt/src/qemu/qemu_command.c
> ===================================================================
> --- libvirt.orig/src/qemu/qemu_command.c
> +++ libvirt/src/qemu/qemu_command.c
> @@ -125,6 +125,77 @@ qemuPhysIfaceConnect(virDomainDefPtr def
>          net->model && STREQ(net->model, "virtio"))
>          vnet_hdr = 1;
>  
> +    /** Note: When using PASSTHROUGH mode with MACVTAP devices the link
> +     * device's MAC address must be set to the VMs MAC address. In
> +     * order to not confuse the first switch or bridge in line this MAC
> +     * address must be reset when the VM is shut down.
> +     * This is especially important when using SRIOV capable cards that
> +     * emulate their switch in firmware.
> +     */
> +    if (net->data.direct.mode == VIR_DOMAIN_NETDEV_MACVTAP_MODE_PASSTHRU) {
> +        unsigned char oldmac[6];
> +        rc = getMacaddr(&oldmac,  net->data.direct.linkdev);
> +        if (rc) {
> +            virReportSystemError(rc,
> +                                 _("Getting MAC address from '%s' "
> +                                 "to '%02x:%02x:%02x:%02x:%02x:%02x' failed."),
> +                                 net->data.direct.linkdev,
> +                                 oldmac[0], oldmac[1], oldmac[2],
> +                                 oldmac[3], oldmac[4], oldmac[5]);
> +        } else {
> +            char *oldmacpath = NULL;
> +            char *oldmacname = NULL;
> +            char *newmacname = NULL;
> +            char *basedir = "/var/run/libvirt/network";

This doesn't honour the prefix passed into configure, or take
account of libvirtd running non-root. Finally, the 'network'
subdirectory is for use by the virtual netowrk driver, not the
QEMU driver. Transient state files stored by the QEMU driver
should go into the path specified in the field 'driver->stateDir'
(from struct qemud_driver)

> +
> +            if (virAsprintf(&oldmacname,"%02x:%02x:%02x:%02x:%02x:%02x",
> +                            oldmac[0], oldmac[1], oldmac[2],
> +                            oldmac[3], oldmac[4], oldmac[5]) < 0) {
> +                virReportOOMError();
> +            }
> +            if (virAsprintf(&oldmacpath,"%s/%s", basedir, oldmacname) < 0) {
> +                virReportOOMError();
> +            }
> +
> +            if (virAsprintf(&newmacname, "%s/%s %02x:%02x:%02x:%02x:%02x:%02x",
> +                            basedir,
> +                            net->data.direct.linkdev,
> +                            net->mac[0],net->mac[1],net->mac[2],
> +                            net->mac[3],net->mac[4],net->mac[5]) < 0) {
> +                virReportOOMError();
> +            }
> +
> +            rc = symlink (oldmacname, newmacname);
> +            if (rc) {
> +                virReportSystemError(errno,
> +                                     _("MAC link file creation failed for %s."),
> +                                     net->data.direct.linkdev);
> +            }
> +            rc = creat(oldmacpath, S_IWUSR);
> +            if (rc) {
> +                virReportSystemError(errno,
> +                                     _("MAC link file creation failed for %s."),
> +                                     oldmacpath);
> +            }
> +            rc = VIR_CLOSE(rc);
> +            if (rc) {
> +                virReportSystemError(errno,
> +                                     _("MAC link file closing failed for %s."),
> +                                     oldmacpath);
> +            }

So, IIUC, this is creating a symlink

     eth0 00:11:22:33:44:55  -> 00:aa:bb:cc:ee:dd

And creating a zero length file '00:aa:bb:cc:ee:dd'. This all seems
rather convuluted & overly clever to me. Why can't there just be a
plain file 'eth0' containing the original mac address '00:aa:bb:cc:ee:dd'.

             char macstr[VIR_MAC_STRING_BUFLEN];
             if (virAsprintf(&path, "%s/%s",
                             basedir,
                             net->data.direct.linkdev) < 0) {
                virReportOOMError();
                goto error;
             }
             virFormatMacAddr(net->mac, macstr);
             if (virFileWriteStr(path, macstr, O_CREAT|O_TRUNC|O_WRONLY, 0700) < 0) {
                virReportSystemError(errno, _("Unable to preserve mac for %s"),
                                     net->data.direct.linkdev);
                goto error;
             }


> +        }
> +
> +        rc = setMacaddr(net->mac, net->data.direct.linkdev);
> +        if (rc) {
> +            virReportSystemError(errno,
> +                                 _("Setting MAC address on  '%s' to "
> +                                 "'%02x:%02x:%02x:%02x:%02x:%02x' failed."),
> +                                 net->data.direct.linkdev,
> +                                 net->mac[0], net->mac[1], net->mac[2],
> +                                 net->mac[3], net->mac[4], net->mac[5]);
> +        }
> +    }
> +
>      rc = openMacvtapTap(net->ifname, net->mac, net->data.direct.linkdev,
>                          net->data.direct.mode, vnet_hdr, def->uuid,
>                          &net->data.direct.virtPortProfile, &res_ifname,

We're already passing 'net->mac' into the openMacvtapTap() method
here, so I think it would be better if that function was responsible
for setting the MAC on the device. It isn't nice to have this huge
block of MAC setting code in every caller of openMacvtapTap().


> Index: libvirt/src/qemu/qemu_process.c
> ===================================================================
> --- libvirt.orig/src/qemu/qemu_process.c
> +++ libvirt/src/qemu/qemu_process.c
> @@ -2708,6 +2708,48 @@ void qemuProcessStop(struct qemud_driver
>          if (net->type == VIR_DOMAIN_NET_TYPE_DIRECT) {
>              delMacvtap(net->ifname, net->mac, net->data.direct.linkdev,
>                         &net->data.direct.virtPortProfile);
> +
> +            if (net->data.direct.mode == VIR_DOMAIN_NETDEV_MACVTAP_MODE_PASSTHRU) {

And, likewise here, I'd expect  delMacvtap() to restore the original
MAC address of the device, rather than making the caller do it.

> +                char *newmacname = NULL;
> +                char *oldmacname = NULL;
> +                char *oldmacpath = NULL;
> +                char *basedir = "/var/run/libvirt/network";
> +
> +                if (virAsprintf(&newmacname, "%s/%s %02x:%02x:%02x:%02x:%02x:%02x",
> +                                basedir,
> +                                net->data.direct.linkdev,
> +                                net->mac[0],net->mac[1],net->mac[2],
> +                                net->mac[3],net->mac[4],net->mac[5]) < 0) {
> +                    virReportOOMError();
> +                }
> +
> +                ret = virFileResolveLink(newmacname, &oldmacpath);
> +                if (ret < 0) {
> +                    virReportSystemError(errno,
> +                                         _("Reading MAC address from '%s' failed !"),
> +                                         newmacname);
> +                } else {
> +                    unsigned char oldmac[6];
> +
> +                    oldmacname = basename(oldmacpath);
> +
> +                    if (virParseMacAddr(oldmacname, &oldmac[0]) != 0) {
> +                        virReportSystemError(VIR_ERR_INTERNAL_ERROR,
> +                                              _("Cannot parse MAC address from '%s'"),
> +                                              oldmacname);
> +                    }
> +
> +                    VIR_WARN(("Resetting MAC address on '%s' "
> +                              "to '%02x:%02x:%02x:%02x:%02x:%02x'."),
> +                             net->data.direct.linkdev,
> +                             oldmac[0],oldmac[1],oldmac[2],
> +                             oldmac[3],oldmac[4],oldmac[5]);
> +                    /*reset mac and remove link file-ignore results*/
> +                    ret = setMacaddr(oldmac, net->data.direct.linkdev);
> +                    ret = unlink(oldmacpath);
> +                    ret = unlink(newmacname);
> +                }
> +            }

This could be far simpler too

             char macstr = NULL;
             if (virAsprintf(&path, "%s/%s",
                             basedir,
                             net->data.direct.linkdev) < 0) {
                virReportOOMError();
                goto error;
             }
             if (virFileReadAll(path, VIR_MAC_STRING_BUFLEN, &macstr) < 0) {
                virReportSystemError(errno, _("Unable to preserve mac for %s"),
                                     net->data.direct.linkdev);
                goto error;
             }
              ...
             VIR_FREE(macstr);

> Index: libvirt/src/util/macvtap.c
> ===================================================================
> --- libvirt.orig/src/util/macvtap.c
> +++ libvirt/src/util/macvtap.c
> @@ -87,6 +87,7 @@
>  
>  # define LLDPAD_PID_FILE  "/var/run/lldpad.pid"
>  
> +#define MACADDRSIZE 6
>  
>  enum virVirtualPortOp {
>      ASSOCIATE = 0x1,
> @@ -191,6 +192,149 @@ err_exit:
>  
>  # if WITH_MACVTAP
>  
> +/**
> + * getMacaddr:
> + * Get the MAC address of a network device
> + *
> + * @macaddress: Pointer where the MAC address will be stored
> + * @srcdev: The interface name of the NIC to get the MAC from
> + *
> + * Returns zero in case of success,
> + * negative value otherwise with error reported.
> + *
> + */
> +int
> +getMacaddr(const unsigned char *macaddress, const char *srcdev )
> +{
> +    int sockfd;
> +    int io;
> +    struct ifreq ifr;
> +
> +    strcpy(ifr.ifr_name, srcdev);
> +
> +    sockfd = socket(AF_INET, SOCK_STREAM, 0);
> +    if(sockfd < 0){
> +        return -1;
> +    }
> +
> +    io = ioctl(sockfd, SIOCGIFHWADDR, (char *)&ifr);
> +    if(io < 0){
> +        return -1;
> +    }
> +
> +    memcpy(macaddress, ifr.ifr_ifru.ifru_hwaddr.sa_data, MACADDRSIZE);
> +
> +    return 0;
> +}
> +
> +/**
> + * setMacaddr:
> + * Set the MAC address of a network device
> + *
> + * @macaddress: MAC address to assign to the NIC
> + * @srcdev: The interface name of the NIC
> + *
> + * Returns zero in case of success,
> + * negative value otherwise with error reported.
> + *
> + */
> +int
> +setMacaddr(const unsigned char *macaddress, const char *srcdev )
> +{
> +    int rc = 0;
> +    struct nlmsghdr *resp;
> +    struct nlmsgerr *err;
> +    struct ifinfomsg ifinfo = { .ifi_family = AF_UNSPEC };
> +    int ifindex;
> +    unsigned char *recvbuf = NULL;
> +    unsigned int recvbuflen;
> +    struct nl_msg *nl_msg;
> +
> +    if (ifaceGetIndex(true, srcdev, &ifindex) != 0)
> +        return -1;
> +
> +    nl_msg = nlmsg_alloc_simple(RTM_SETLINK, NLM_F_REQUEST);
> +
> +    if (!nl_msg) {
> +        virReportOOMError();
> +        return -1;
> +    }
> +
> +    if (nlmsg_append(nl_msg,  &ifinfo, sizeof(ifinfo), NLMSG_ALIGNTO) < 0)
> +        goto buffer_too_small;
> +
> +    if (nla_put_u32(nl_msg, IFLA_LINK, ifindex) < 0)
> +        goto buffer_too_small;
> +
> +    if (nla_put(nl_msg, IFLA_ADDRESS, MACADDRSIZE, macaddress) < 0)
> +        goto buffer_too_small;
> +
> +    if (srcdev &&
> +        nla_put(nl_msg, IFLA_IFNAME, strlen(srcdev)+1, srcdev) < 0)
> +        goto buffer_too_small;
> +
> +    if (nlComm(nl_msg, &recvbuf, &recvbuflen, 0) < 0) {
> +        rc = -1;
> +        goto err_exit;
> +    }
> +
> +    if (recvbuflen < NLMSG_LENGTH(0) || recvbuf == NULL)
> +        goto malformed_resp;
> +
> +    resp = (struct nlmsghdr *)recvbuf;
> +
> +    switch (resp->nlmsg_type) {
> +    case NLMSG_ERROR:
> +        err = (struct nlmsgerr *)NLMSG_DATA(resp);
> +        if (resp->nlmsg_len < NLMSG_LENGTH(sizeof(*err)))
> +            goto malformed_resp;
> +
> +        switch (err->error) {
> +
> +        case 0:
> +            break;
> +
> +        case -EEXIST:
> +            rc = -1;
> +            break;
> +
> +        default:
> +            macvtapError(VIR_ERR_INTERNAL_ERROR, "%s",
> +                         _("error setting device mac address"));
> +            rc = -1;
> +        }
> +        break;
> +
> +    case NLMSG_DONE:
> +        break;
> +
> +    default:
> +        goto malformed_resp;
> +    }
> +
> +err_exit:
> +    nlmsg_free(nl_msg);
> +
> +    VIR_FREE(recvbuf);
> +
> +    return rc;
> +
> +malformed_resp:
> +    nlmsg_free(nl_msg);
> +
> +    macvtapError(VIR_ERR_INTERNAL_ERROR, "%s",
> +                 _("malformed netlink response message"));
> +    VIR_FREE(recvbuf);
> +    return -1;
> +
> +buffer_too_small:
> +    nlmsg_free(nl_msg);
> +
> +    macvtapError(VIR_ERR_INTERNAL_ERROR, "%s",
> +                 _("allocated netlink buffer is too small"));
> +    return -1;
> +}

There are already (static) functions in src/util/bridge.c, which are
able to get and set the MAC address on network devices. So I think we
should just make them non-static and call them instead of duplicating
it here.

Regards,
Daniel
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