Re: [MirageOS-devel] adding `replace_listener` function to Mirage_net.S

[Thomas Leonard <talex5@xxxxxxxxx>]

On Wed, 19 Jun 2019 at 14:27, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
> > On 18 Jun 2019, at 19:08, Hannes Mehnert <hannes@xxxxxxxxxxx> wrote:
> >
> > Hello,
> >
> > On 18/06/2019 17:33, Mindy Preston wrote:
> >> In mirage_net.mli, the documentation for `val listen` says:
> >> "this function can be stopped by calling disconnect in the device layer".
> >>
> >> This is the only method mentioned to stop the call to `listen`. There
> >> isn't any API call for replacing the callback established in `listen`.
> >> In mirage-vnetif, `disconnect` just stops the listener, and we can
> >> continue to use the device after. This does not work for mirage-net-xen
> >> (and maybe solo5), because disconnect cleans up the interface and we can
> >> not continue using it.
> >
> > As far as I can read both mirage-net-unix and mirage-net-solo5 are fine
> > with sequences of connect followed by disconnect calls; maybe we should
> > revise the documentation in mirage-net (that connect ; disconnect ;
> > connect should work fine) and adapt mirage-net-xen to follow that behaviour?
>
> Agreed; fixing mirage-net-xen sounds better here. It might become a
> new interface (with a different vif number), but that shouldn't matter
> to the unikernel I think.

You pass the vif ID to `connect`, so that shouldn't change. I think
disconnect on Xen devices should put them back the way they were
before the connect, so connecting multiple times should be allowed
(i.e. the current code is wrong). Calling `disconnect` should stop the
listener somehow, but it doesn't look like the current code does that.

But I vaguely recall that there are some problems closing event
channels on Xen (e.g. a local listener doesn't get woken up when that
happens).

-- 
talex5 (GitHub/Twitter)        http://roscidus.com/blog/
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