+/*
+ * Contraints to check before allowing this new breakpoint counter:
+ *
+ * == Non-pinned counter == (Considered as pinned for now)
+ *
+ * - If attached to a single cpu, check:
+ *
+ * (per_cpu(nr_bp_flexible, cpu) || (per_cpu(nr_cpu_bp_pinned, cpu)
+ * + max(per_cpu(nr_task_bp_pinned, cpu)))) < HBP_NUM
+ *
+ * -> If there are already non-pinned counters in this cpu, it means
+ * there is already a free slot for them.
+ * Otherwise, we check that the maximum number of per task
+ * breakpoints (for this cpu) plus the number of per cpu breakpoint
+ * (for this cpu) doesn't cover every registers.
+ *
+ * - If attached to every cpus, check:
+ *
+ * (per_cpu(nr_bp_flexible, *) || (max(per_cpu(nr_cpu_bp_pinned, *))
+ * + max(per_cpu(nr_task_bp_pinned, *)))) < HBP_NUM
+ *
+ * -> This is roughly the same, except we check the number of per cpu
+ * bp for every cpu and we keep the max one. Same for the per tasks
+ * breakpoints.
+ *
+ *
+ * == Pinned counter ==
+ *
+ * - If attached to a single cpu, check:
+ *
+ * ((per_cpu(nr_bp_flexible, cpu) > 1) + per_cpu(nr_cpu_bp_pinned, cpu)
+ * + max(per_cpu(nr_task_bp_pinned, cpu))) < HBP_NUM
+ *
+ * -> Same checks as before. But now the nr_bp_flexible, if any, must keep
+ * one register at least (or they will never be fed).
+ *
+ * - If attached to every cpus, check:
+ *
+ * ((per_cpu(nr_bp_flexible, *) > 1) + max(per_cpu(nr_cpu_bp_pinned, *))
+ * + max(per_cpu(nr_task_bp_pinned, *))) < HBP_NUM
+ */
+static int __reserve_bp_slot(struct perf_event *bp)