On Tue, Jul 10, 2018 at 07:25:53PM -0700, Cong Wang wrote:
> On Mon, Jul 9, 2018 at 2:40 PM Marcelo Ricardo Leitner
> <[email protected]> wrote:
> >
> > On Mon, Jul 09, 2018 at 05:03:31PM -0400, Michel Machado wrote:
> > > Changing TC_PRIO_MAX from 15 to 63 risks breaking backward
> > > compatibility
> > > with applications.
> >
> > If done, it needs to be done carefully, indeed. I don't know if it's
> > doable, neither I know how hard is your requirement for 64 different
> > priorities.
>
> struct tc_prio_qopt {
> int bands; /* Number of bands */
> __u8 priomap[TC_PRIO_MAX+1]; /* Map: logical priority -> PRIO band
> */
> };
>
> How would you do it carefully?
quick shot, multiplex v1 and v2 formats based on bands and sizeof():
#define TCQ_PRIO_BANDS_V1 16
#define TCQ_PRIO_BANDS_V2 64
#define TC_PRIO_MAX_V2 64
struct tc_prio_qopt_v2 {
int bands; /* Number of bands */
__u8 priomap[TC_PRIO_MAX_V2+1]; /* Map: logical priority -> PRIO
band */
};
static int prio_tune(struct Qdisc *sch, struct nlattr *opt,
struct netlink_ext_ack *extack)
{
struct prio_sched_data *q = qdisc_priv(sch);
struct Qdisc *queues[TCQ_PRIO_BANDS_V2];
int oldbands = q->bands, i;
struct tc_prio_qopt_v2 *qopt;
if (nla_len(opt) < sizeof(int))
return -EINVAL;
qopt = nla_data(opt);
if (qopt->bands <= TCQ_PRIO_BANDS_V1 &&
nla_len(opt) < sizeof(struct tc_prio_qopt))
return -EINVAL;
if (qopt->bands <= TCQ_PRIO_BANDS_V2 &&
nla_len(opt) < sizeof(*qopt))
return -EINVAL;
/* By here, if it has up to 3 bands, we can assume it is using the _v1
* layout, while if it has up to TCQ_PRIO_BANDS_V2 it is using the _v2
* format.
*/
if (qopt->bands > TCQ_PRIO_BANDS_V2 || qopt->bands < 2)
return -EINVAL;
...
With something like this I think it can keep compatibility with old
software while also allowing the new usage.
> Also, it is not only used by prio but also pfifo_fast.
Yes. More is needed, indeed. prio2band would also need to be expanded,
etc. Yet, I still don't see any blocker.
