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  3. [libvirt] [PATCH v2 0/2] Fix issues in qemuARPGetInterfaces and virArpTableGet
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[libvirt] [PATCH v2 1/2] qemu: Remove network type limitation for qemuARPGetInterfaces

Lin Ma posted 2 patches 7 years, 4 months ago
[libvirt] [PATCH v2 1/2] qemu: Remove network type limitation for qemuARPGetInterfaces
Posted by Lin Ma 7 years, 4 months ago 
When we call qemuARPGetInterfaces to get IP from the host's arp table, We
ignore VIR_DOMAIN_NET_TYPE_ETHERNET, VIR_DOMAIN_NET_TYPE_VHOSTUSER and
VIR_DOMAIN_NET_TYPE_DIRECT due to the host's arp table won't include the
ip <-> mac entries about these type of backends.

Signed-off-by: Lin Ma <lma@suse.com>
---
 src/qemu/qemu_driver.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 2f8d6915e1..f066e02f36 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -20940,7 +20940,9 @@ qemuARPGetInterfaces(virDomainObjPtr vm,
         goto cleanup;
 
     for (i = 0; i < vm->def->nnets; i++) {
-        if (vm->def->nets[i]->type != VIR_DOMAIN_NET_TYPE_NETWORK)
+        if (vm->def->nets[i]->type == VIR_DOMAIN_NET_TYPE_ETHERNET ||
+            vm->def->nets[i]->type == VIR_DOMAIN_NET_TYPE_VHOSTUSER ||
+            vm->def->nets[i]->type == VIR_DOMAIN_NET_TYPE_DIRECT)
             continue;
 
         virMacAddrFormat(&(vm->def->nets[i]->mac), macaddr);
-- 
2.15.1

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Re: [libvirt] [PATCH v2 1/2] qemu: Remove network type limitation for qemuARPGetInterfaces
Posted by John Ferlan 7 years, 4 months ago 

On 09/13/2018 03:54 AM, Lin Ma wrote:
> When we call qemuARPGetInterfaces to get IP from the host's arp table, We
> ignore VIR_DOMAIN_NET_TYPE_ETHERNET, VIR_DOMAIN_NET_TYPE_VHOSTUSER and

s/ignore/should ignore/

> VIR_DOMAIN_NET_TYPE_DIRECT due to the host's arp table won't include the
> ip <-> mac entries about these type of backends.
> 
> Signed-off-by: Lin Ma <lma@suse.com>
> ---
>  src/qemu/qemu_driver.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 

OK - so not my area of expertise - I'm CC'g laine to get his opinion
just in case he missed this...  I always get overly cautious since there
are many network types and this seems to be a rather far reaching change
of fetch...

You should reference commit e24d4c905 which added this code as it would
help focus on when the change was made.

Also since this really are disjoint problems, you should have created
separate patches especially since none of Sukrit's changes have anything
to do with this, but he's CC'd on the series because his change for
patch 2/2 did break something...

John

> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 2f8d6915e1..f066e02f36 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -20940,7 +20940,9 @@ qemuARPGetInterfaces(virDomainObjPtr vm,
>          goto cleanup;
>  
>      for (i = 0; i < vm->def->nnets; i++) {
> -        if (vm->def->nets[i]->type != VIR_DOMAIN_NET_TYPE_NETWORK)
> +        if (vm->def->nets[i]->type == VIR_DOMAIN_NET_TYPE_ETHERNET ||
> +            vm->def->nets[i]->type == VIR_DOMAIN_NET_TYPE_VHOSTUSER ||
> +            vm->def->nets[i]->type == VIR_DOMAIN_NET_TYPE_DIRECT)
>              continue;
>  
>          virMacAddrFormat(&(vm->def->nets[i]->mac), macaddr);
> 

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Re: [libvirt] [PATCH v2 1/2] qemu: Remove network type limitation for qemuARPGetInterfaces
Posted by Lin Ma 7 years, 4 months ago 

On 09/14/2018 11:27 PM, John Ferlan wrote:
>
> On 09/13/2018 03:54 AM, Lin Ma wrote:
>> When we call qemuARPGetInterfaces to get IP from the host's arp table, We
>> ignore VIR_DOMAIN_NET_TYPE_ETHERNET, VIR_DOMAIN_NET_TYPE_VHOSTUSER and
> s/ignore/should ignore/
>
>> VIR_DOMAIN_NET_TYPE_DIRECT due to the host's arp table won't include the
>> ip <-> mac entries about these type of backends.
>>
>> Signed-off-by: Lin Ma <lma@suse.com>
>> ---
>>   src/qemu/qemu_driver.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
> OK - so not my area of expertise - I'm CC'g laine to get his opinion
> just in case he missed this...  I always get overly cautious since there
> are many network types and this seems to be a rather far reaching change
> of fetch...
>
> You should reference commit e24d4c905 which added this code as it would
> help focus on when the change was made.
>
> Also since this really are disjoint problems, you should have created
> separate patches especially since none of Sukrit's changes have anything
> to do with this, but he's CC'd on the series because his change for
> patch 2/2 did break something...
>
> John

Thanks for your review!
Lin

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Re: [libvirt] [PATCH v2 1/2] qemu: Remove network type limitation for qemuARPGetInterfaces
Posted by Laine Stump 7 years, 4 months ago 
On 09/13/2018 03:54 AM, Lin Ma wrote:
> When we call qemuARPGetInterfaces to get IP from the host's arp table, We
> ignore VIR_DOMAIN_NET_TYPE_ETHERNET, VIR_DOMAIN_NET_TYPE_VHOSTUSER and
> VIR_DOMAIN_NET_TYPE_DIRECT due to the host's arp table won't include the
> ip <-> mac entries about these type of backends.

That's not necessarily true. A tap device created by <interface
type='ethernet'> can be given a host-side IP address/prefix (right in
the XML as a matter of fact:
https://libvirt.org/formatdomain.html#ipconfig ) thus making traffic on
that interface available to the host's IP stack, and this adds a direct
route on the host to the subnet for that address/prefix. If the guest
has an IP on that same subnet, then the arp table on the host will
contain an entry for the guest (if the guest has sent any traffic from
that IP address).

Likewise, if an interface is of type='direct' (macvtap) and the switch
connected to the physdev of that macvtap device is "hairpinning" traffic
(to enable guest<->host communication), or alternately if there is a
different physdev on the host connected to the same switch, then there
will be an entry in the arp table on the host (again, if the guest has
sent or broadcast packets from the IP address of that interface).

Likewise, I have no personal experience with vhostuser but it's entirely
possible that the vhostuser interface of the guest ends up being in the
same broadcast domain as one of the devices (physical or virtual) on the
host that has an IP address, and in that case there will be an entry in
the host's arp table for the vhostuser device's MAC.

I guess the conclusion I would draw from this is that we shouldn't
immediately discount *any* type of interface (e.g., a hostdev interface
could also show up in the arp table, but of course the change that
you've made here actually *adds* the ability to look for those). I would
say we should check for the MAC regardless of the type.

(BTW, if you were going to do something based on the type of interface,
it would be more correct to use
virDomainNetGetActualType(vm->dev->nets[i]) rather than
vm->dev->nets[i]->type, although I'm saying that you simply shouldn't
check the type at all in this case.)

> Signed-off-by: Lin Ma <lma@suse.com>
> ---
>  src/qemu/qemu_driver.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 2f8d6915e1..f066e02f36 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -20940,7 +20940,9 @@ qemuARPGetInterfaces(virDomainObjPtr vm,
>          goto cleanup;
>  
>      for (i = 0; i < vm->def->nnets; i++) {
> -        if (vm->def->nets[i]->type != VIR_DOMAIN_NET_TYPE_NETWORK)
> +        if (vm->def->nets[i]->type == VIR_DOMAIN_NET_TYPE_ETHERNET ||
> +            vm->def->nets[i]->type == VIR_DOMAIN_NET_TYPE_VHOSTUSER ||
> +            vm->def->nets[i]->type == VIR_DOMAIN_NET_TYPE_DIRECT)
>              continue;
>  
>          virMacAddrFormat(&(vm->def->nets[i]->mac), macaddr);


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Re: [libvirt] [PATCH v2 1/2] qemu: Remove network type limitation for qemuARPGetInterfaces
Posted by Lin Ma 7 years, 4 months ago 

On 09/15/2018 07:14 AM, Laine Stump wrote:
> On 09/13/2018 03:54 AM, Lin Ma wrote:
>> When we call qemuARPGetInterfaces to get IP from the host's arp table, We
>> ignore VIR_DOMAIN_NET_TYPE_ETHERNET, VIR_DOMAIN_NET_TYPE_VHOSTUSER and
>> VIR_DOMAIN_NET_TYPE_DIRECT due to the host's arp table won't include the
>> ip <-> mac entries about these type of backends.
> That's not necessarily true. A tap device created by <interface
> type='ethernet'> can be given a host-side IP address/prefix (right in
> the XML as a matter of fact:
> https://libvirt.org/formatdomain.html#ipconfig ) thus making traffic on
> that interface available to the host's IP stack, and this adds a direct
> route on the host to the subnet for that address/prefix. If the guest
> has an IP on that same subnet, then the arp table on the host will
> contain an entry for the guest (if the guest has sent any traffic from
> that IP address).
>
> Likewise, if an interface is of type='direct' (macvtap) and the switch
> connected to the physdev of that macvtap device is "hairpinning" traffic
> (to enable guest<->host communication), or alternately if there is a
> different physdev on the host connected to the same switch, then there
> will be an entry in the arp table on the host (again, if the guest has
> sent or broadcast packets from the IP address of that interface).
>
> Likewise, I have no personal experience with vhostuser but it's entirely
> possible that the vhostuser interface of the guest ends up being in the
> same broadcast domain as one of the devices (physical or virtual) on the
> host that has an IP address, and in that case there will be an entry in
> the host's arp table for the vhostuser device's MAC.
>
> I guess the conclusion I would draw from this is that we shouldn't
> immediately discount *any* type of interface (e.g., a hostdev interface
> could also show up in the arp table, but of course the change that
> you've made here actually *adds* the ability to look for those). I would
> say we should check for the MAC regardless of the type.
>
> (BTW, if you were going to do something based on the type of interface,
> it would be more correct to use
> virDomainNetGetActualType(vm->dev->nets[i]) rather than
> vm->dev->nets[i]->type, although I'm saying that you simply shouldn't
> check the type at all in this case.)

Thanks for your detailed explanation!

So It seems that we don't need to check any of type of interface in this 
case,
Actually, No type check at all is the design of patch V1, Please refer to
https://www.redhat.com/archives/libvir-list/2018-September/msg00243.html

If I use the patch v1's code plus commit message modification, What do 
you think?

Thanks,
Lin

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