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Subject: Re: [PATCH] tty: Remove dead termiox code
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Jann Horn <jannh@google.com>, linux-kernel@vger.kernel.org
References: <20201203020331.2394754-1-jannh@google.com>
 <5cca5126-60ba-d123-0f7d-47fdbac4c4db@kernel.org>
 <X8nwnXQKOYWBWBZ+@kroah.com>
From:   Jiri Slaby <jirislaby@kernel.org>
Message-ID: <93834a92-b342-aaee-c400-2883d5df0cdc@kernel.org>
Date:   Fri, 4 Dec 2020 09:20:39 +0100
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On 04. 12. 20, 9:17, Greg Kroah-Hartman wrote:
> On Fri, Dec 04, 2020 at 08:22:41AM +0100, Jiri Slaby wrote:
>> On 03. 12. 20, 3:03, Jann Horn wrote:
>>> set_termiox() and the TCGETX handler bail out with -EINVAL immediately
>>> if ->termiox is NULL, but there are no code paths that can set
>>> ->termiox to a non-NULL pointer; and no such code paths seem to have
>>> existed since the termiox mechanism was introduced back in
>>> commit 1d65b4a088de ("tty: Add termiox") in v2.6.28.
>>> Similarly, no driver actually implements .set_termiox; and it looks like
>>> no driver ever has.
>>
>> Nice!
>>
>>> Delete this dead code; but leave the definition of struct termiox in the
>>> UAPI headers intact.
>>
>> I am thinking -- can/should we mark the structure as deprecated so that
>> userspace stops using it eventually?
> 
> If it doesn't do anything, how can userspace even use it today?  :)

Well, right. I am in favor to remove it, BUT: what if someone tries that 
ioctl and bails out if EINVAL is returned. I mean: if they define a 
local var of that struct type and pass it to the ioctl, we would break 
the build by removing the struct completely. Even if the code didn't do 
anything useful, it still could be built. So is this very potential 
breakage OK?

thanks,
-- 
js