Re: [Xen-devel] /proc/xen/xenbus supports watch?

[Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>]

On Sun, Sep 25, 2005 at 12:33:33PM +0100, Keir Fraser wrote:
> 
> On 25 Sep 2005, at 12:02, Keir Fraser wrote:
> 
> >Yeah, I can live with this, although: What about multiple transactions 
> >within the kernel? Do you plan to continue serialising them (e.g., on 
> >a waitqueue)? An advantage of mux/demux would be that concurrent 
> >kernel transactions could easily use the same mechanism. Your scheme 
> >places restart mechanisms in user space, so they're out of reach for 
> >kernel transactions.
> 
> Also, page-per-connection won't entirely avoid sharing of 
> state/resource in xenstored. At some point we'll want to add per-domain 
> access policy, and space/bandwidth quotas (to prevent DoS). All of 
> those must be shared between the multiple connections of a domain -- so 
> the separate connections aren't as independent as you might like.

I believe that the only thing we really _need_ at the moment
is support for multiple concurrent transactions.  This avoids
having to hold the lock except for very short periods and it
allows the server to return EAGAIN on operations where it doesn't
have the state corresponding to the transaction anymore.  Since we
need to add some kind of transaction identifier to the interface
to support this, we should make this change now.

    christian


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