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, 90 insertions, 0 deletions

diff --git a/drivers/input/tablet/Kconfig b/drivers/input/tablet/Kconfig
new file mode 100644
index 000000000..ec27eff6a
--- /dev/null
+++ b/drivers/input/tablet/Kconfig
@@ -0,0 +1,90 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Tablet driver configuration
+#
+menuconfig INPUT_TABLET
+	bool "Tablets"
+	help
+	  Say Y here, and a list of supported tablets will be displayed.
+	  This option doesn't affect the kernel.
+
+	  If unsure, say Y.
+
+if INPUT_TABLET
+
+config TABLET_USB_ACECAD
+	tristate "Acecad Flair tablet support (USB)"
+	depends on USB_ARCH_HAS_HCD
+	select USB
+	help
+	  Say Y here if you want to use the USB version of the Acecad Flair
+	  tablet.  Make sure to say Y to "Mouse support"
+	  (CONFIG_INPUT_MOUSEDEV) and/or "Event interface support"
+	  (CONFIG_INPUT_EVDEV) as well.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called acecad.
+
+config TABLET_USB_AIPTEK
+	tristate "Aiptek 6000U/8000U and Genius G_PEN tablet support (USB)"
+	depends on USB_ARCH_HAS_HCD
+	select USB
+	help
+	  Say Y here if you want to use the USB version of the Aiptek 6000U,
+	  Aiptek 8000U or Genius G-PEN 560 tablet.  Make sure to say Y to
+	  "Mouse support" (CONFIG_INPUT_MOUSEDEV) and/or "Event interface
+	  support" (CONFIG_INPUT_EVDEV) as well.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called aiptek.
+
+config TABLET_USB_HANWANG
+	tristate "Hanwang Art Master III tablet support (USB)"
+	depends on USB_ARCH_HAS_HCD
+	select USB
+	help
+	  Say Y here if you want to use the USB version of the Hanwang Art
+	  Master III tablet.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called hanwang.
+
+config TABLET_USB_KBTAB
+	tristate "KB Gear JamStudio tablet support (USB)"
+	depends on USB_ARCH_HAS_HCD
+	select USB
+	help
+	  Say Y here if you want to use the USB version of the KB Gear
+	  JamStudio tablet.  Make sure to say Y to "Mouse support"
+	  (CONFIG_INPUT_MOUSEDEV) and/or "Event interface support"
+	  (CONFIG_INPUT_EVDEV) as well.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called kbtab.
+
+config TABLET_USB_PEGASUS
+	tristate "Pegasus Mobile Notetaker Pen input tablet support"
+	depends on USB_ARCH_HAS_HCD
+	select USB
+	help
+	  Say Y here if you want to use the Pegasus Mobile Notetaker,
+	  also known as:
+	  Genie e-note The Notetaker,
+	  Staedtler Digital ballpoint pen 990 01,
+	  IRISnotes Express or
+	  NEWLink Digital Note Taker.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called pegasus_notetaker.
+
+config TABLET_SERIAL_WACOM4
+	tristate "Wacom protocol 4 serial tablet support"
+	select SERIO
+	help
+	  Say Y here if you want to use Wacom protocol 4 serial tablets.
+	  E.g. serial versions of the Cintiq, Graphire or Penpartner.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called wacom_serial4.
+
+endif