On Sun, Aug 12, 2007 at 10:48:05AM -0700, Casey Schaufler wrote:
You don't necessarily need more list management if you don't
plan to remove entries, but just replace them.
e.g. what could work to atomically replace is:
- Make the buffer a pointer to an allocated buffer that also
contains a struct rcu_head.
- Reader: Does rcu_read_lock() around list walk (that just disables
preemption on preemptible kernels and is otherwise a nop).
Also uses rcu_reference for reading the pointer.
- Writer: Continues using the mutex to protect against other writers.
When changing an entry allocate a new buffer + rcu_head. Initialize
buffer. Replace pointer. Free old buffer using call_rcu()
The RCU would just make sure the buffer is not freed while other
CPUs are still accessing it. It also means they can use stale
rules for a time, but it is a strictly bounded time
(bounded to max time walking the list plus max time any interrupt
handlers inbetween run [admittedly that can be very long in theory,
but it's all logically only a single rule check])
-Andi
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