sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/include/net/bluetooth/iso.h b/include/net/bluetooth/iso.h
new file mode 100644
index 000000000..3f4fe8b78
--- /dev/null
+++ b/include/net/bluetooth/iso.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * BlueZ - Bluetooth protocol stack for Linux
+ *
+ * Copyright (C) 2022 Intel Corporation
+ */
+
+#ifndef __ISO_H
+#define __ISO_H
+
+/* ISO defaults */
+#define ISO_DEFAULT_MTU		251
+#define ISO_MAX_NUM_BIS		0x1f
+
+/* ISO socket broadcast address */
+struct sockaddr_iso_bc {
+	bdaddr_t	bc_bdaddr;
+	__u8		bc_bdaddr_type;
+	__u8		bc_sid;
+	__u8		bc_num_bis;
+	__u8		bc_bis[ISO_MAX_NUM_BIS];
+};
+
+/* ISO socket address */
+struct sockaddr_iso {
+	sa_family_t	iso_family;
+	bdaddr_t	iso_bdaddr;
+	__u8		iso_bdaddr_type;
+	struct sockaddr_iso_bc iso_bc[];
+};
+
+#endif /* __ISO_H */