Re: [Xen-devel] Setting devid for emulated NICs (Xen 4.3.1 / libvirt 1.2.0) using libxl driver

[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

On 17.12.2013 17:58, Ian Campbell wrote:
> On Tue, 2013-12-17 at 17:34 +0100, Stefan Bader wrote:
>> Using virt-manager "hypervisor default" type:
>>
>>     <interface type='bridge'>
>>       <mac address='00:16:3e:5e:09:9d'/>
>>       <source bridge='br0'/>
>>       <script path='vif-bridge'/>
>>     </interface>
>>
>> This causes the qemu call to have "-net none" which removes PXE boot
>> abilities. A linux kernel has network through the xen pv-driver.
>>
>> Changing in virt-manager to "e1000" type:
>>
>>     <interface type='bridge'>
>>       <mac address='00:16:3e:5e:09:9d'/>
>>       <source bridge='br0'/>
>>       <script path='vif-bridge'/>
>>       <model type='e1000'/>
>>     </interface>
>>
>> This currently (Xen 4.3.1 + libvirt 1.2.0) fails and the qemu arguments
>> in the log look suspicious:
>>   -device e1000,id=nic-1,netdev=net-1,mac=00:16:3e:5e:09:9d
>>   -netdev type=tap,id=net-1,ifname=vif1.-1-emu,script=no,downscript=no
>>
>> Looking through git I found ba64b97134a6129a48684f22f31be92c3b6eef96
>>   libxl: Allow libxl to set NIC devid
> 
> Is that a libvirt commit? Not seeing it in xen.git.

Oh, sorry, yes it is.
> 
> Might this libxl fix be relevant:
>         commit 5420f26507fc5c9853eb1076401a8658d72669da
>         Author: Jim Fehlig <jfehlig@xxxxxxxx>
>         Date:   Fri Jan 11 12:22:26 2013 +0000
>         
>             libxl: Set vfb and vkb devid if not done so by the caller
>             
>             Other devices set a sensible devid if the caller has not done so.
>             Do the same for vfb and vkb.  While at it, factor out the common 
> code
>             used to determine a sensible devid, so it can be used by other
>             libxl__device_*_add functions.
>             
>             Signed-off-by: Jim Fehlig <jfehlig@xxxxxxxx>
>             Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
>             Committed-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
>         
> and a follow up in dfeccbeaa. Although the comment implies that nic's
> were already correctly assigning a devid if the caller specified -1, so
> I don't know why it doesn't work for you :-(

Ok, yes, the commit above indeed changes libxl__device_nic_add to call
libxl__device_nextid for the devid... Just how is this actually called.
Maybe not sufficient but "git grep libxl__device_nic_add" in the xen code only
shows the definition and a declaration in libxl_internal.h to me...


> 
>>
>> which removes a line that sets the devid of new NICs. I assume the comment
>> says (sorry I always seem to get confused reading it) that devid should
>> be auto-set by the libxl library provided by Xen.
> 
> Correct.
> 
>> But I could not find where that would be done.
> 
> I expect the above commits have pointed you to the right line, but the
> code should be quite near the top of libxl__device_nic_add in libxl.c
> 
>>  Even the xl command implementation sets it
>> explicitly.
> 
> The caller is also allowed to do this if it cares what number is used.
> 
>>  libxl_device_nic_init sets it to -1 which would explain the
>> wrong qemu arguments above.
> 
> Right, libxl_device_nic_init sets everything to "the defaults please"
> and __device_nic_add will instantiate any defaults which the application
> didn't supply.
> 
>> For testing I re-added the following after the libxlMakeNic call:
>>
>> --- libvirt-1.2.0.orig/src/libxl/libxl_conf.c   2013-12-11 
>> 17:04:17.000000000 +0
>> +++ libvirt-1.2.0/src/libxl/libxl_conf.c        2013-12-16 
>> 19:08:46.830016646 +0
>> @@ -907,6 +907,8 @@ libxlMakeNicList(virDomainDefPtr def,  l
>>      for (i = 0; i < nnics; i++) {
>>          if (libxlMakeNic(l_nics[i], &x_nics[i]))
>>              goto error;
>> +       if (x_nics[i].devid < 0)
>> +               x_nics[i].devid = i;
>>      }
>>
>>      d_config->nics = x_nics;
>>
>> And with that I get a working PXE boot when I set the device type
>> in the config. (Side note that I think not using a type defaults to
>> rtl8139 in the old xend driver. Maybe this should be the same for the
>> xl driver).
>> I am not sure how the right fix for it should look like as I am unsure
>> which part was supposed to set the devid. Just right now it does not
>> seem to be done.
>>
>> -Stefan
>>
> 
> 
> 
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