Re: [Xen-users] more than 3 vifs in domU

[Andrew Ross <aross@xxxxxxxxxxxxxx>]

Ernie Fontes wrote:
> I have been trying to create a DomU with 5 virtual ethernet cards.  While
> booting, eth0, eth1, and eth2 work fine.  However, for eth3, and eth4, the
> following error messages pop up.
> 
> netfront: Initialising virtual ethernet driver.
> #### netfront can't alloc rx grant refs
> vif vif-3: 12 creating netdev
> vif vif-3: 12 xenbus_dev_probe on device/vif/3
> #### netfront can't alloc rx grant refs
> vif vif-4: 12 creating netdev
> vif vif-4: 12 xenbus_dev_probe on device/vif/4
> 
> Has anyone run into this before or know how to work around this limitation?
> I would really like to work with more than 3 ethernet cards on my VMs.

Next time you ask a question on a mailing list, please remember to check
the associated FAQ (http://wiki.xensource.com/xenwiki/XenFaq) and
mailing list archives
(http://lists.xensource.com/archives/html/xen-users/) first - there's a
good chance your question has already been asked (and answered).

It also helps if you choose a meaningful subject line, as more people
are likely to read your email. Not everyone has the time to read every
post on this list, and they decide what to read (and what NOT to read)
based on the subject line.

Now, to answer your question... :-)

This is a copy and paste from two emails I sent to the list just a few
days ago, in response to an identical question:

> The maximum number of virtual network interfaces you can create for each
> domU is 3 - this is clearly stated at
> http://wiki.xensource.com/xenwiki/XenFaq

> The workaround for most people appears to be adding additional network
> cards to the physical machine and making them available directly to the
> domUs in question (using pcihide, as recently discussed on this mailling
> list).

> Just found this at
> http://lists.xensource.com/archives/html/xen-devel/2006-07/msg00424.html
> 
> "We need to add a hypercall to xen to allow a guest to extend the size
>  of it's grant table. This should be straightforward, but in its
>  current absence is the restriction which leads to the current ``max 3
>  VIF's per guest'' limit. Actually, this restriction could also be
>  solved by making the allocation of grant table entries to a VIF
>  dynamic, as already happens with the blkfront driver. We should
>  implement both strategies forthwith."
> 
> It isn't the original source of my information, but does confirm it.

Cheers

Andrew

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