Hello,
We are having some issues for handling the address pool of a DHCP server
implemented with eBPF.
We tried to implement it using a map containing all the available
addresses, this map is filled at the beginning and then addresses are
taken (and also released), however we cannot find a way to get an
arbitrary element from a map in eBPF. (something like a pop() function)
By suggestion of Brenden Blanco, we had a look at the LRU [1] map, we
expected to find some function like "get_oldest_element()" but we cannot
find anything similar.
We decided to implement it in a different way, the pool is handled by a
map of type array where all the addresses are saved, each of them has a
flag that indicates whether it is available or not. Then, in order to
get an available address it is necessary to perform a loop through the
map (values are saved using integer keys) until an available entry is
found.
With this approach a lot of instructions are wasted just to perform the
lookup of an available address, this limits the size of the pool. Hence,
we think having a kind of "pop()" function is necessary to handle "maps"
of free elements.
1. Would it make sense to have a map of kind "set" that only implements
the push() and pop() methods?
2. Does it make sense to have a get_oldest_element() in the LRU map?
Thanks in advance,
Mauricio V.
[1]
https://git.kernel.org/cgit/linux/kernel/git/davem/net-next.git/commit/?id=29ba732acbeece1e34c68483d1ec1f3720fa1bb3
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