On Oct 24, 2024, at 00:40, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > > On Wed, Oct 23, 2024 at 02:58:07PM +0800, Alan Huang wrote: >> On Oct 22, 2024, at 22:26, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: >>> >>> On Tue, Oct 22, 2024 at 12:13:12AM -0700, Christoph Hellwig wrote: >>>> On Tue, Oct 22, 2024 at 09:10:18AM +0200, Peter Zijlstra wrote: >>>>> Ah, well, the thing that got us here is that we (Andrii and me) wanted >>>>> to use -1 as an 'invalid' value to indicate SRCU is not currently in >>>>> use. >>>>> >>>>> So it all being int is really rather convenient :-) >>>> >>>> Then please document that use. Maybe even with a symolic name for >>>> -1 that clearly describes these uses. >>> >>> Would this work? >>> >>> #define SRCU_INVALID_INDEX -1 >> >> Is there any similar guarantee of the return value of get_state_synchronize_rcu >> or start_poll_synchronize_rcu, like invalid value? > > Yes, there is a get_completed_synchronize_rcu() function that returns a > value that causes poll_state_synchronize_rcu() to always return true. > There is also a get_completed_synchronize_rcu_full() function that > returns a value that causes poll_state_synchronize_rcu_full() to always > return true. This is exactly the API I was searching for, didn’t read the doc thoroughly : ) Thanks! > > There has been some discussion of another set of values that cause > poll_state_synchronize_rcu() and poll_state_synchronize_rcu_full() to > always return false, but there is not yet a use case for this. Easy to > provide if required, but why further explode the RCU API unless it really > is required? > > Thanx, Paul > >>> Whatever the name, maybe Peter and Andrii define this under #ifndef >>> right now, and we get it into include/linux/srcu.h over time. >>> >>> Or is there a better way? Or name, for that matter. >>> >>> Thanx, Paul >>> >>
