rfkill: uapi: fix RFKILL_IOCTL_MAX_SIZE ioctl request definition

The definition of RFKILL_IOCTL_MAX_SIZE introduced by commit
54f586a91532 ("rfkill: make new event layout opt-in") is unusable
since it is based on RFKILL_IOC_EXT_SIZE which has not been defined.
Fix that by replacing the undefined constant with the constant which
is intended to be used in this definition.

Fixes: 54f586a91532 ("rfkill: make new event layout opt-in")
Cc: stable@vger.kernel.org # 5.11+
Signed-off-by: Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Link: https://lore.kernel.org/r/20220506172454.120319-1-glebfm@altlinux.org
[add commit message provided later by Dmitry]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

rfkill: make new event layout opt-in

Again new complaints surfaced that we had broken the ABI here,
although previously all the userspace tools had agreed that it
was their mistake and fixed it. Yet now there are cases (e.g.
RHEL) that want to run old userspace with newer kernels, and
thus are broken.

Since this is a bit of a whack-a-mole thing, change the whole
extensibility scheme of rfkill to no longer just rely on the
message lengths, but instead require userspace to opt in via a
new ioctl to a given maximum event size that it is willing to
understand.

By default, set that to RFKILL_EVENT_SIZE_V1 (8), so that the
behaviour for userspace not calling the ioctl will look as if
it's just running on an older kernel.

Fixes: 14486c82612a ("rfkill: add a reason to the HW rfkill state")
Cc: stable@vger.kernel.org # 5.11+
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220316212749.16491491b270.Ifcb1950998330a596f29a2a162e00b7546a1d6d0@changeid

rfkill: revert back to old userspace API by default

Recompiling with the new extended version of struct rfkill_event
broke systemd in *two* ways:
- It used "sizeof(struct rfkill_event)" to read the event, but
then complained if it actually got something != 8, this broke
it on new kernels (that include the updated API);
- It used sizeof(struct rfkill_event) to write a command, but
didn't implement the intended expansion protocol where the
kernel returns only how many bytes it accepted, and errored
out due to the unexpected smaller size on kernels that didn't
include the updated API.

Even though systemd has now been fixed, that fix may not be always
deployed, and other applications could potentially have similar
issues.

As such, in the interest of avoiding regressions, revert the
default API "struct rfkill_event" back to the original size.

Instead, add a new "struct rfkill_event_ext" that extends it by
the new field, and even more clearly document that applications
should be prepared for extensions in two ways:
* write might only accept fewer bytes on older kernels, and
will return how many to let userspace know which data may
have been ignored;
* read might return anything between 8 (the original size) and
whatever size the application sized its buffer at, indicating
how much event data was supported by the kernel.

Perhaps that will help avoid such issues in the future and we
won't have to come up with another version of the struct if we
ever need to extend it again.

Applications that want to take advantage of the new field will
have to be modified to use struct rfkill_event_ext instead now,
which comes with the danger of them having already been updated
to use it from 'struct rfkill_event', but I found no evidence
of that, and it's still relatively new.

Cc: stable@vger.kernel.org # 5.11
Reported-by: Takashi Iwai <tiwai@suse.de>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM/Clang v12.0.0-r4 (x86-64)
Link: https://lore.kernel.org/r/20210319232510.f1a139cfdd9c.Ic5c7c9d1d28972059e132ea653a21a427c326678@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

rfkill: add a reason to the HW rfkill state

The WLAN device may exist yet not be usable. This can happen
when the WLAN device is controllable by both the host and
some platform internal component.
We need some arbritration that is vendor specific, but when
the device is not available for the host, we need to reflect
this state towards the user space.

Add a reason field to the rfkill object (and event) so that
userspace can know why the device is in rfkill: because some
other platform component currently owns the device, or
because the actual hw rfkill signal is asserted.

Capable userspace can now determine the reason for the rfkill
and possibly do some negotiation on a side band channel using
a proprietary protocol to gain ownership on the device in case
the device is owned by some other component. When the host
gains ownership on the device, the kernel can remove the
RFKILL_HARD_BLOCK_NOT_OWNER reason and the hw rfkill state
will be off. Then, the userspace can bring the device up and
start normal operation.

The rfkill_event structure is enlarged to include the additional
byte, it is now 9 bytes long. Old user space will ask to read
only 8 bytes so that the kernel can know not to feed them with
more data. When the user space writes 8 bytes, new kernels will
just read what is present in the file descriptor. This new byte
is read only from the userspace standpoint anyway.

If a new user space uses an old kernel, it'll ask to read 9 bytes
but will get only 8, and it'll know that it didn't get the new
state. When it'll write 9 bytes, the kernel will again ignore
this new byte which is read only from the userspace standpoint.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Link: https://lore.kernel.org/r/20201104134641.28816-1-emmanuel.grumbach@intel.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

rfkill: Update userspace API documentation

Add a note to userspace on the effect of RFKILL_OP_CHANGE_ALL also
updating the default state for hotplugged devices.

Signed-off-by: João Paulo Rechi Vita <jprvita@endlessm.com>
[reword a bit]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

rfkill: Add NFC to the list of supported radios

And return the proper string for it.

Acked-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

UAPI: (Scripted) Disintegrate include/linux

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Michael Kerrisk <mtk.manpages@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Dave Jones <davej@redhat.com>