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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>
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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>
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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>
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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>
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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>
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Johannes Berg
Emmanuel Grumbach
João Paulo Rechi Vita
Samuel Ortiz
David Howells