On Fri, 2018-08-10 at 16:02 +0900, Namhyung Kim wrote: > On Thu, Aug 09, 2018 at 09:34:14AM -0500, Tom Zanussi wrote: > > From: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx> > > > > Currently, tracing snapshots are context-free - they capture the > > ring > > buffer contents at the time the tracing_snapshot() function was > > invoked, and nothing else. Additionally, they're always taken > > unconditionally - the calling code can decide whether or not to > > take a > > snapshot, but the data used to make that decision is kept > > separately > > from the snapshot itself. > > > > This change adds the ability to associate with each trace instance > > some user data, along with an 'update' function that can use that > > data > > to determine whether or not to actually take a snapshot. The > > update > > function can then update that data along with any other state (as > > part > > of the data presumably), if warranted. > > > > Because snapshots are 'global' per-instance, only one user can > > enable > > and use a conditional snapshot for any given trace instance. To > > enable a conditional snapshot (see details in the function and data > > structure comments), the user calls tracing_snapshot_cond_enable(). > > Similarly, to disable a conditional snapshot and free it up for > > other > > users, tracing_snapshot_cond_disable() should be called. > > > > To actually initiate a conditional snapshot, > > tracing_snapshot_cond() > > should be called. tracing_snapshot_cond() will invoke the update() > > callback, allowing the user to decide whether or not to actually > > take > > the snapshot and update the user-defined data associated with the > > snapshot. If the callback returns 'true', tracing_snapshot_cond() > > will then actually take the snapshot and return. > > > > This scheme allows for flexibility in snapshot implementations - > > for > > example, by implementing slightly different update() callbacks, > > snapshots can be taken in situations where the user is only > > interested > > in taking a snapshot when a new maximum in hit versus when a value > > changes in any way at all. Future patches will demonstrate both > > cases. > > > > Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx> > > --- > > [SNIP] > > @@ -1741,9 +1788,16 @@ static inline bool > > event_command_needs_rec(struct event_command *cmd_ops) > > return cmd_ops->flags & EVENT_CMD_FL_NEEDS_REC; > > } > > > > +typedef bool (*cond_update)(struct trace_array *tr, void > > *cond_data); > > + > > I think it's better having "fn_t" suffix like 'cond_update_fn_t'. > Yeah, makes sense, will change. Thanks, Tom
