sids2xids in winbind

[Volker Lendecke]

Hi!

Simo told me that when he changed the idmap subsystem I
oppsed to the idea of a sids2gids operation. I was wrong,
sorry for that. It is needed in particular in the cluster
case where a user being member of hundreds of groups logs in
for the first time with none of the groups in idmap yet.
Transactions in the cluster case are pretty slow, so
allocating all gids individually can make that login even
time out.

http://git.samba.org/?p=vl/samba.git/.git;a=shortlog;h=refs/heads/sids-to-xids

contains the code that optimizes this operation by
coalescing all the allocations into one tdb-level
transaction. It's quite a bit more complicated than it first
sounds, because sid2gid needs a lookupsid first. So the
patchset implements a proper, optimized, wb_lookupsids
operation in winbind also available via the winbind pipe.

To be optimized (as little roundtrips and transactions as
sanely possible), this patchset has to fiddle with arrays a
lot. That's why I'm asking for review here. Watch out, this
is pretty tricky code.

Thanks,

Volker

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