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Date:   Mon, 6 Nov 2023 11:30:05 +0100
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Subject: Re: [PATCH] rfkill: return ENOTTY on invalid ioctl
To:     =?UTF-8?Q?Thomas_Wei=c3=9fschuh?= <linux@weissschuh.net>
CC:     Johannes Berg <johannes@sipsolutions.net>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        <linux-wireless@vger.kernel.org>, <netdev@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
References: <20231101-rfkill-ioctl-enosys-v1-1-5bf374fabffe@weissschuh.net>
 <a069393c-86b3-ef79-82dd-0b60caf2a907@intel.com>
 <613039a4-41af-48ff-8113-3b0ee8077bcf@t-8ch.de>
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From:   Przemek Kitszel <przemyslaw.kitszel@intel.com>
In-Reply-To: <613039a4-41af-48ff-8113-3b0ee8077bcf@t-8ch.de>
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On 11/2/23 20:14, Thomas Weißschuh wrote:
> Hi!
> 
> On 2023-11-02 09:57:45+0100, Przemek Kitszel wrote:
>> On 11/1/23 20:41, Thomas Weißschuh wrote:
>>> For unknown ioctls the correct error is
>>> ENOTTY "Inappropriate ioctl for device".
>>
>> For sure!
>>
>> I would like to learn more of why this is not an UAPI breaking change?
> 
> "break" would mean that some user application worked correctly before
> but does not do so anymore with this change.
> 
> This seems highly unlikely and I was not able to find such an
> application via Debian code search.
> 
> In general I did *not* mark this change for stable so if some
> application would indeed break it gets detected before the patch hits
> a release.
> 
>>>
>>> ENOSYS as returned before should only be used to indicate that a syscall
>>> is not available at all.
>>>
>>> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
>>> ---
>>>    net/rfkill/core.c | 4 ++--
>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/net/rfkill/core.c b/net/rfkill/core.c
>>> index 14cc8fe8584b..c3feb4f49d09 100644
>>> --- a/net/rfkill/core.c
>>> +++ b/net/rfkill/core.c
>>> @@ -1351,11 +1351,11 @@ static long rfkill_fop_ioctl(struct file *file, unsigned int cmd,
>>>    			     unsigned long arg)
>>>    {
>>>    	struct rfkill_data *data = file->private_data;
>>> -	int ret = -ENOSYS;
>>> +	int ret = -ENOTTY;
>>>    	u32 size;
>>>    	if (_IOC_TYPE(cmd) != RFKILL_IOC_MAGIC)
>>> -		return -ENOSYS;
>>> +		return -ENOTTY;
>>>    	mutex_lock(&data->mtx);
>>>    	switch (_IOC_NR(cmd)) {
>>>
>>> ---
>>> base-commit: 7d461b291e65938f15f56fe58da2303b07578a76
>>> change-id: 20231101-rfkill-ioctl-enosys-00a2bb0a4ab1
>>>
>>> Best regards,
>>

Thanks!

Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>