linux-kernel - Re: [PATCH 4.19 119/131] tracing: Fix event trigger to accept redundant spaces

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Message-ID: <20200703114000.GG2722994@sasha-vm>
Date:   Fri, 3 Jul 2020 07:40:00 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 4.19 119/131] tracing: Fix event trigger to accept
 redundant spaces

On Thu, Jul 02, 2020 at 11:17:28PM +0200, Pavel Machek wrote:
>Hi!
>
>> commit 6784beada631800f2c5afd567e5628c843362cee upstream.
>>
>> Fix the event trigger to accept redundant spaces in
>> the trigger input.
>>
>> For example, these return -EINVAL
>>
>> echo " traceon" > events/ftrace/print/trigger
>> echo "traceon  if common_pid == 0" > events/ftrace/print/trigger
>> echo "disable_event:kmem:kmalloc " > events/ftrace/print/trigger
>>
>> But these are hard to find what is wrong.
>>
>> To fix this issue, use skip_spaces() to remove spaces
>> in front of actual tokens, and set NULL if there is no
>> token.
>
>For the record, I'm not fan of this one. It is ABI change, not a
>bugfix.
>
>Yes, it makes kernel interface "easier to use". It also changes
>interface in the middle of stable series, and if people start relying
>on new interface and start putting extra spaces, they'll get nasty
>surprise when they move code to the older kernel.

We promise users that they can upgrade their kernels and we won't be
breaking any of their usecases no matter what. However, if they choose
to downgrade their kernels then all bets are off.

-- 
Thanks,
Sasha