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Document some potential plans for sequence number magic to disambiguate spurious retries again

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git-svn-id: https://svn.code.sf.net/p/xcat/code/xcat-core/trunk@14128 8638fb3e-16cb-4fca-ae20-7b5d299a9bcd
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jbjohnso
2012-10-25 19:53:58 +00:00
parent ba08481381
commit d4fa1ed91a
1 changed files with 11 additions and 0 deletions
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xCAT-server/lib/perl/xCAT/IPMI.pm
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@@ -689,6 +689,17 @@ sub init {
#448 instead of 64 transactions are now required before ambiguity is possible
#A stale reply has to come in after the conversation has advanced at least 448 transactions, meaning longer delay on extraneous reply before this is a problem
#even if a stale reply comes in at *about* the right time, it has to match an exact multiple of 448 instead of 64, which is significantly less likely.
#I abandoned this strategy, but leaving it documented for posterity. The issue is that some operations don't like the client changing software id
#midstream (notably SDR reservations).
#ipmi spec does contain some guidance in the BT section of the spec 'Using the Seq Field'. There is guidance elsewhere about sequence numbers higher than 8 beyond current
#but I'm not sure if thet means 'session sequence number' or 'seq', which are very very different.
#one tangible recommendation is for the combination of command+seq+netfn to be unique, which can certainly help, so we should track netfn and command to make sure response
#matches at least the expected command and netfn.
#additionally, it looks like we could implement a sort of 'taboo' sequence number scheme. When we ascertain that we are retrying, we flag the current sequence number to be
#'taboo' in the future. When the time comes to increment sequence number, we mark the current combination of command+netfn+seq as 'taboo'
#should circumstances suggest that we are about to transmit a packet with a taboo combination, we bump sequence number until no longer taboo, no more than 8 bumps.
#if we should incur 7 bumps, clear the taboo list and continue on, hoping for best (pessimistically assuming the spec means seq number or that someone could at least interpret it that way)
#I'll implement this later...
$self->{'logged'}=0;
}
sub relog {