Frédéric BERNON
HYMATOM SA
Chef de projet informatique
Microsoft Certified Professional
Tél. : +33 (0)4-67-87-61-10
Fax. : +33 (0)4-67-70-85-44
Email : address@hiddenr
Web Site : http://www.hymatom.fr
====================================
-----Message d'origine-----
De : address@hidden [mailto:address@hidden De la part de Frédéric BERNON
Envoyé : lundi 10 mars 2008 15:49
À : address@hidden; lwip-devel
Objet : RE : [lwip-devel] IGMP - Adding Random DelayI would have a preference to move the "random" call inside igmp_start_timer, and so, to do the call like this : " igmp_start_timer(group, maxresp);" About the RFC compliance, I will take a look and give you my point of view...====================================
Frédéric BERNON
HYMATOM SA
Chef de projet informatique
Microsoft Certified Professional
Tél. : +33 (0)4-67-87-61-10
Fax. : +33 (0)4-67-70-85-44
Email : address@hiddenr
Web Site : http://www.hymatom.fr
====================================P Avant d'imprimer, penser à l'environnement-----Message d'origine-----
De : address@hidden [mailto:address@hidden De la part de Edward Kerekes
Envoyé : lundi 10 mars 2008 02:00
À : address@hidden
Objet : [lwip-devel] IGMP - Adding Random DelayHi again,
I thought this discussion would be more appropriate in a separate thread.
The following discussion pertains to the current HEAD (also V1.3.0RC1) version
of igmp.c.
Id like to add a macro hook into the igmp.c module to allow
the user to specify a random number function for setting the delay timer.
Im using a macro in the same spirit as the existing lwIP implementation of
MEMCPY() which could have a simple default and could be overridden by the user
in his lwipopts.h file.
As I read RFC 2236 the delaying member should use a random number between 0 and
the Max Response Time. The existing igmp_delaying_member() function
simply starts the timer with (maxresp)/2, rather than a random value. (This works fine but
doesnt match the RFC. Im planning on using a large number of members and would
prefer the random delay.)
1. The enhancement:
Im basically replacing the (maxresp)/2 with a macro that will default
to the existing (maxresp)/2 that can be overridden by the user to provide a random delay.
Im also adding an if statement to start the timer with 1 if the macro returns 0.
This trick avoids having to send the message directly by calling igmp_send() That would
be fine also, however Im not sure of the consequence of calling igmp_send() directly in a
preemptive environment. This trick might also result in a few less bytes of code.
The big question is: Should any other calls use a random delay? I dont see that
indicated in the RFC, but Im certainly not an expert on IGMP
2. Bug Fix:
On line 669, the term
&& (maxresp > group->timer)
seems wrong based on my interpretation of RFC 2236. I believe it should be replaced
with:
&& ((group->timer == 0) || (maxresp < group->timer))
For reference, Im basing this on RFC 2236 Section 3 Protocol Description.
The 4th paragraph contains this sentence:
If a timer for the group is already running,it is reset to the random value only if therequested Max Response Time is less than theremaining value of the running timer.
I believe the intent of the RFC is to let any existing running timers
CONTINUE TO RUN if they are less than the maxresp and only start
stopped timers or timers with values that exceed the maxresp time.
Im hoping to get this or some similar implementation incorporated into the lwIP source.
So if anyone has any comments or suggestions or has a preference in how this is
implemented, please let me know,
See the attached patch file for reference.
For convenience, I have also provided the original and modified routines below.
Thanks again to all contributors!
Ed
Original function for reference:
void
igmp_delaying_member( struct igmp_group *group, u8_t maxresp)
{
if ( (group->group_state == IGMP_GROUP_IDLE_MEMBER)
|| ((group->group_state == IGMP_GROUP_DELAYING_MEMBER)
&& (maxresp > group->timer)) <<<< wrong ????
) {
igmp_start_timer(group, (maxresp)/2);
group->group_state = IGMP_GROUP_DELAYING_MEMBER;
}
}
New proposed macro:
#ifndef LWIP_IGMP_RANDOM
/* The end user can override this macro to provide his own random number routine
For example, to use the standard c rand() function, include the following
in your lwipopts.h file:
#define IGMP_RANDOM(max) ((u8_t) ((long) max * rand()/RAND_MAX))
The user routine should return a random u8_t ranging from 0 to max.
Default to the original source, which simply used max/2:
*/
#define IGMP_RANDOM(max) ((u8_t) ((max)/2))
#endif
New proposed function:
void
igmp_delaying_member( struct igmp_group *group, u8_t maxresp)
{
u8_t time;
if ( (group->group_state == IGMP_GROUP_IDLE_MEMBER)
|| ((group->group_state == IGMP_GROUP_DELAYING_MEMBER) && ((group->timer==0) || (maxresp > group->timer)))
) {
time = LWIP_IGMP_RANDOM(maxresp); /* Generate a random u8_t integer 0 to maxresp */
if (time==0) { /* For now change 0 to 1 to force a send the next timer tick. */
time = 1; /* In the future, a developer can change this to send message */
} /* right now if time == 0 without macro breakage. */
igmp_start_timer(group, time);
group->group_state = IGMP_GROUP_DELAYING_MEMBER;
}
}
