Re: [Xen-devel] use xs_watch from userspace and use epoll instead of select

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Mon, 2011-06-06 at 11:05 +0100, Vasiliy G Tolstov wrote:
> On Mon, 2011-06-06 at 10:48 +0100, Ian Campbell wrote:

> > What are you actually trying to build?

> I'm try to build daemon, that can recieve command via xenstore (xs_watch
> for specific path), via /dev/hvcN (serial char interface), now i'm try
> to use gntmem mechanism to do this too. If one method not available or
> not work or some errors accured - i'm try next. 
> /dev/hvcN Not good sometimes, becouse in some domU i have gentty on this
> port.
> xenstore - has limit in size of message...

Interesting.

> In kernel side xen thing more easy to understand. Use it under userspace
> need deep googling =).

I'm afraid so.

Remember that the underlying grant table hypercall's and mechanisms are
the same in both kernel and userspace and the APIs provided reflect that
-- userspace is not all that different.

In userspace you might need (actually I think it's probably required)
to use the gntalloc driver (added to pvops by Daniel de Graff around
2.6.39 I think) to get memory suitable for granting out.

> Ok if i use grant pages mechanism - do i have notify for new message
> after it arrives? If i use xs from domU i need libxc under it insted of
> libxenstore ?

Yes you need to notify, libxc provides an interface to event channels as
well as grant tables.

You will probably need both libxc and libxenstore. You use xenstore to
negotiated the event channel and shared page with your peer and libxc to
create, map, signal them etc.

Ian.



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