On 2016-08-08 at 21:04:20 +0200, Vadim Kochan <[email protected]> wrote:
> On Sat, Aug 06, 2016 at 01:36:26AM +0300, Vadim Kochan wrote:
> > On Wed, Aug 03, 2016 at 04:27:14PM +0200, Tobias Klauser wrote:
> > > On 2016-07-26 at 21:35:10 +0200, Vadim Kochan <[email protected]> wrote:
> > > > Extended 'struct packet_dyn' with proto fields which has
> > > > dynamically changing values at runtime.
> > > >
> > > > Implement incrementing of proto field at runtime with min & max
> > > > parameters, by default if the 'min' parameter is not specified
> > > > then original value is used. For fields which len is greater
> > > > than 4 - last 4 bytes are incremented as unsigned int value.
> > > >
> > > > Added 'field_changed' callback for proto header which
> > > > may be used for check if csum updating is needed. This callback
> > > > is called after field was changed at runtime.
> > > >
> > > > Added 'packet_update' callback to let proto header know
> > > > when to apply final proto header changes at runtime (csum update).
> > >
> > > The documentation of these callbacks would also make sense where they're
> > > defined.
> > >
> > > > Signed-off-by: Vadim Kochan <[email protected]>
> > > > ---
> > > > trafgen.c | 9 ++++++
> > > > trafgen_conf.h | 7 ++++
> > > > trafgen_proto.c | 99
> > > > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > > > trafgen_proto.h | 26 +++++++++++++++
> > > > 4 files changed, 141 insertions(+)
> > > >
> > > > diff --git a/trafgen.c b/trafgen.c
> > > > index b76b5d7..553dfa5 100644
> > > > --- a/trafgen.c
> > > > +++ b/trafgen.c
> > > > void proto_packet_finish(void)
> > > > {
> > > > struct proto_hdr **headers = ¤t_packet()->headers[0];
> > > > @@ -433,3 +446,89 @@ void proto_packet_finish(void)
> > > > p->packet_finish(p);
> > > > }
> > > > }
> > > > +
> > > > +static inline unsigned int field_inc(struct proto_field *field)
> > > > +{
> > > > + uint32_t val;
> > > > +
> > > > + val = field->func.val - field->func.min;
> > > > + val = (val + field->func.inc) % field->func.max;
> > >
> > > Shouldn't this be
> > >
> > > val = (val + field->func.inc) % (field->func.max - field->func.min + 1)
> > >
> > > to be consistent with apply_counter()?
>
> I simplified it and now it really works well:
>
> #define max_int32(a, b)
> \
> ({
> \
> int32_t _a = (int32_t) (a);
> \
> int32_t _b = (int32_t) (b);
> \
> _a - ((_a - _b) & ((_a - _b) >> (sizeof(int32_t) * 8 -
> 1))); \
The line above definitely needs an explanatory comment. How and why does
this work? Why is it implemented like this instead of the "obvious"
max() solution?
> })
>
> static inline unsigned int field_inc(struct proto_field *field)
> {
> uint32_t min = field->func.min;
> uint32_t max = field->func.max;
> uint32_t val = field->func.val;
> uint32_t inc = field->func.inc;
> uint32_t next;
>
> next = (val + inc) % (max + 1);
> field->func.val = max_int32(next, min);
>
> return val;
> }
>
> so max_int32(a,b) should be fast enough w/o branching.
Have you profiled this against other possible implementations,
especially the max_int32() implementation above? If your profiling doesn't
show significant improvements of this max_int32() variant I'd rather
stay with the "obvious" one, i.e. a > b ? a : b
> > Sure, I tried this approach while implementing 1st version but when I
> > used the following case:
> >
> > trafgen/trafgen -o lo -n 10 --cpu 1 '{ eth(type=0x800), fill(0xff, 10),
> > dinc(5, 20, 5) }'
> >
> > then interval between 5 & 20 changes very differently. But in my version
> > it repeats from 5 till 20 (yes here is a little difference that initial
> > value is incremented immideately). Also semantic of proto dinc is
> > dinc(step, min, max), and I will change it to looks like low-level one -
> > dinc(min, max, step).
> >
> > >
> > > Also, I think you should probably get rid of as many pointer
> > > dereferences as possible in these runtime functions, i.e. store max and
> > > min in temporary variables.
> >
> > OK, makes sense.
> >
> > >
> > > > + field->func.val = val + field->func.min;
> > > > +
> > > > + return field->func.val;
> > > > +}
> > > > +
> > > > +static void field_inc_func(struct proto_field *field)
> > > > +{
> > > > + if (field->len == 1) {
> > > > + uint8_t val;
> > > > +
> > > > + val = field_inc(field);
> > > > + proto_field_set_u8(field->hdr, field->id, val);
> > >
> > > Assignment on declaration please. Or even better:
> > >
> > > proto_field_set_u8(field->hdr, field->id, field_inc(field));
> >
> > OK
> >
> > >
> > > > + } else if (field->len == 2) {
> > > > + uint16_t val;
> > > > +
> > > > + val = field_inc(field);
> > > > + proto_field_set_be16(field->hdr, field->id, val);
> > >
> > > Same.
> > OK
> >
> > >
> > > > + } else if (field->len == 4) {
> > > > + uint32_t val;
> > > > +
> > > > + val = field_inc(field);
> > > > + proto_field_set_be32(field->hdr, field->id, val);
> > >
> > > Same.
> > OK
> >
> > >
> > > > + } else if (field->len > 4) {
> > > > + uint8_t *bytes = __proto_field_get_bytes(field);
> > > > + uint32_t val;
> > > > +
> > > > + bytes += field->len - 4;
> > > > + val = field_inc(field);
> > > > +
> > > > + *(uint32_t *)bytes = bswap_32(val);
> > >
> > > This part looks really odd. Did you actually verify it produces the
> > > correct result on both big/little endian and for various field lengths?
> > >
> > > To be honest I don't see much use for counters going beyond UINT32_T_MAX
> > > (or maybe UINT64_T_MAX, which should be handled as a separate case if
> > > then). Or do you know of a protocol with sequence numbers (or similar) >
> > > 64 bit for which this would really be useful?
>
> >
> > Hm, may be it looks & sounds odd but I use it for incrementing MAC & IPv6
> > addresses (the last 4 bytes, it might be improved to 8 bytes for x64
> > arch). In the future I think to extend syntax to allow specify interval
> > of incrementing like:
> >
> > ipv4(saddr[0:3]=dinc())
> >
> > or may be you have better idea, but I dont wanna extend dinc() for this.
>
> Also I think may be in case of MAC/IPv6 (field->len > 4) - use index of the
> current
> incremented byte and when it is reached 0xFF - pick the next one. But if
> you OK with current approach (but I am not sure you do) - I will change it in
> future patches.
Ok, I see. Incrementing MAC/IP adresses would indeed be useful.
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