linux-kernel - Re: [PATCH 4.19 19/57] Bluetooth: hidp: Let hidp_send

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Message-ID: <c7aa8abe-86c1-e401-67b4-a9fbb85bf475@gmail.com>
Date:   Tue, 10 Sep 2019 08:27:10 +0200
From:   Fabian Henneke <fabian.henneke@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Pavel Machek <pavel@...x.de>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Marcel Holtmann <marcel@...tmann.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 19/57] Bluetooth: hidp: Let hidp_send_message return
 number of queued bytes



On 10.09.19 00:59, Greg Kroah-Hartman wrote:
> On Mon, Sep 09, 2019 at 03:00:46PM +0200, Fabian Henneke wrote:
>> Hi,
>>
>> On Mon, Sep 9, 2019 at 2:15 PM Pavel Machek <pavel@...x.de> wrote:
>>
>>> Hi!
>>>
>>>> [ Upstream commit 48d9cc9d85dde37c87abb7ac9bbec6598ba44b56 ]
>>>>
>>>> Let hidp_send_message return the number of successfully queued bytes
>>>> instead of an unconditional 0.
>>>>
>>>> With the return value fixed to 0, other drivers relying on hidp, such as
>>>> hidraw, can not return meaningful values from their respective
>>>> implementations of write(). In particular, with the current behavior, a
>>>> hidraw device's write() will have different return values depending on
>>>> whether the device is connected via USB or Bluetooth, which makes it
>>>> harder to abstract away the transport layer.
>>>
>>> So, does this change any actual behaviour?
>>>
>>> Is it fixing a bug, or is it just preparation for a patch that is not
>>> going to make it to stable?
>>>
>>
>> I created this patch specifically in order to ensure that user space
>> applications can use HID devices with hidraw without needing to care about
>> whether the transport is USB or Bluetooth. Without the patch, every
>> hidraw-backed Bluetooth device needs to be treated specially as its write()
>> violates the usual return value contract, which could be viewed as a bug.
>>
>> Please note that a later patch (
>> https://www.spinics.net/lists/linux-input/msg63291.html) fixes some
>> important error checks that were relying on the old behavior (and were
>> unfortunately missed by me).
> 
> As that patch doesn't seem to be in Linus's tree yet, we should postpone
> taking this one in the stable tree right now, correct?
> 
> thanks,
> 
> greg k-h
> 

Yes, please wait for the other patch if it's not in his tree yet and apply the two together.

Thank you,
Fabian