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Re: [Xen-devel] [PATCH] netback: allow arbitrary mtu size until frontend

>>> On 07.02.11 at 10:11, Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx> wrote:
> On Mon, 2011-02-07 at 09:03 +0000, Jan Beulich wrote:
>> >>> On 06.02.11 at 14:42, Olaf Hering <olaf@xxxxxxxxx> wrote:
>> > Allow arbitrary mtu size until the frontend is connected.  Once the
>> > connection is established, adjust mtu by checking if the backend
>> > supports the 'feature-sg'.  If the backend does support it, keep the
>> > current mtu. Otherwise set it to the default value, which is 1500.
>> > 
>> > This helps the vif-bridge hotplug script to set the mtu size to 9000
>> > while bringing up the guest.
>> Isn't this functionally the same as
> http://xenbits.xen.org/XCP/linux-2.6.32.pq.hg?file/043b76e4943c/xen-netback-A 
> llow-setting-of-large-MTU-before-rings.patch
>> or its pv-ops parent 
> https://git.kernel.org/?p=linux/kernel/git/jeremy/xen.git;a=commitdiff;h=bee2 
> eec2355c4bf4e149a426d5e30527162de566
>> (in which case it would seem preferable to pull in that change)?
>> Ian, looking at that patch of yours again, the adjustment to
>> netbk_set_sg() seems a little odd: Why is it necessary to
>> reduce dev->mtu unconditionally (i.e. independent of the
>> value of "data") here?
> Hmm. I don't recall. Seems like a bug looking at it now...
> Luckily for me it appears to have been correct by Paul in
> d532fa93d4eeabbfc0176a6a9a93b0d6ade3f6c4

Indeed, to some part: How would dev->mtu grow again if sg
got re-enabled after having been disabled?


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