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'. Thanks, Namhyung > extern int trace_event_enable_disable(struct trace_event_file *file, > int enable, int soft_disable); > extern int tracing_alloc_snapshot(void); > +extern void tracing_snapshot_cond(struct trace_array *tr, void *cond_data); > +extern int tracing_snapshot_cond_enable(struct trace_array *tr, void *cond_data, cond_update update); > + > +extern int tracing_snapshot_cond_disable(struct trace_array *tr); > +extern void *tracing_cond_snapshot_data(struct trace_array *tr); > > extern const char *__start___trace_bprintk_fmt[]; > extern const char *__stop___trace_bprintk_fmt[];
