linux-kernel - Re: [PATCH] tty: Remove dead termiox code

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Message-ID: <c1c9fc04-02eb-2260-195b-44c357f057c0@kernel.org>
Date:   Tue, 8 Dec 2020 12:23:05 +0100
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jann Horn <jannh@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: Remove dead termiox code

On 08. 12. 20, 12:13, Christoph Hellwig wrote:
> On Fri, Dec 04, 2020 at 09:20:39AM +0100, Jiri Slaby wrote:
>>>>> 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?
> 
> Um, we do guarantee a stable ABI.  We have never guaranteed that all old
> crappy code will continue to compile, although we avoid gratious
> breakage.  And assuming there ever was code using termiox (which I'm not
> sure about to start with) it will surely have some form of feature
> check, and I think we are better off with that feature check not
> detecting the presence as that would be completely pointless.
> 
> Or in short: by keeping the uapi definition we do userspace software a
> disfavor.

OK, even better. I will remove it once I get to it (if noone beats me to 
it, of course).

thanks,
-- 
js
suse labs