Re: [Xen-devel] [PATCH 3/7] ioreq: allow dispatching ioreqs to internal servers

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Aug 21, 2019 at 06:29:04PM +0200, Paul Durrant wrote:
> > -----Original Message-----
> > From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> > Sent: 21 August 2019 15:59
> > To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> > Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>; Paul Durrant 
> > <Paul.Durrant@xxxxxxxxxx>; Jan Beulich
> > <jbeulich@xxxxxxxx>; Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Wei Liu 
> > <wl@xxxxxxx>
> > Subject: [PATCH 3/7] ioreq: allow dispatching ioreqs to internal servers
> > 
> > Internal ioreq servers are always processed first, and ioreqs are
> > dispatched by calling the handler function. If no internal servers have
> > registered for an ioreq it's then forwarded to external callers.
> 
> Distinct id ranges would help here... Internal ids could be walked first, 
> then external. If there's no possibility of interleaving then you don't need 
> the retry.

So if internal vs external is keyed on the ID then we would end up
with two different arrays in hvm_domain, one for internal and one for
external ioreq servers.

Maybe instead of my previous suggestion it would be better to just
define consecutive ranges for external and internal servers, like:

#define MAX_NR_EXTERNAL_IOREQ_SERVERS 8
#define MAX_NR_INTERNAL_IOREQ_SERVERS 1
#define MAX_NR_IOREQ_SERVERS \
    (MAX_NR_EXTERNAL_IOREQ_SERVERS + MAX_NR_INTERNAL_IOREQ_SERVERS)

#define FOR_EACH_IOREQ_SERVER(d, id, s) \
    for ( (id) = MAX_NR_IOREQ_SERVERS * 2; (id) != 0; ) \
        if ( !(s = GET_IOREQ_SERVER(d, --(id))) ) \
            continue; \
        else

#define FOR_EACH_INTERNAL_IOREQ_SERVER(d, id, s) \
    for ( (id) = MAX_NR_IOREQ_SERVERS; (id) > MAX_NR_INTERNAL_IOREQ_SERVERS && 
(id) != 0; ) \
        if ( !(s = GET_IOREQ_SERVER(d, --(id))) ) \
            continue; \
        else

#define FOR_EACH_EXTERNAL_IOREQ_SERVER(d, id, s) \
    for ( (id) = MAX_NR_INTERNAL_IOREQ_SERVERS; (id) != 0; ) \
        if ( !(s = GET_IOREQ_SERVER(d, --(id))) ) \
            continue; \
        else

That would also force FOR_EACH_IOREQ_SERVER to always process internal
ioreq servers first.

We could even have something like:

union {
    struct {
        struct hvm_ioreq_server *external_server[MAX_NR_EXTERNAL_IOREQ_SERVERS];
        struct hvm_ioreq_server *internal_server[MAX_NR_INTERNAL_IOREQ_SERVERS];
    }
    struct hvm_ioreq_server *server[MAX_NR_IOREQ_SERVERS];
}

In order to split the arrays if required.

Thanks, Roger.

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