linux-kernel - Re: [PATCH-next 3/3] serial/sysrq: Add MAGIC_SYSRQ_SERIAL

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Message-ID: <41435a7b-48a2-438c-998a-14481fbc3a1a@arista.com>
Date:   Tue, 14 Jan 2020 19:10:47 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Jiri Slaby <jslaby@...e.com>,
        Vasiliy Khoruzhick <vasilykh@...sta.com>,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH-next 3/3] serial/sysrq: Add MAGIC_SYSRQ_SERIAL_SEQUENCE

On 1/10/20 10:32 PM, Dmitry Safonov wrote:
> On 1/10/20 4:46 PM, Greg Kroah-Hartman wrote:
> [..]
>>> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
>>> index 6ac9dfed3423..f70eba032d0b 100644
>>> --- a/drivers/tty/serial/serial_core.c
>>> +++ b/drivers/tty/serial/serial_core.c
>>> @@ -3081,6 +3081,38 @@ void uart_insert_char(struct uart_port *port, unsigned int status,
>>>  }
>>>  EXPORT_SYMBOL_GPL(uart_insert_char);
>>>  
>>> +const char sysrq_toggle_seq[] = CONFIG_MAGIC_SYSRQ_SERIAL_SEQUENCE;
>>> +
>>> +static void uart_sysrq_on(struct work_struct *w)
>>> +{
>>> +	sysrq_toggle_support(1);
>>> +	pr_info("SysRq is enabled by magic sequience on serial\n");
>>
>> Do we want to say what serial port it is enabled on?
> 
> Makes sense, will add.

Ah, I've managed to forget to mention that I didn't add the port name
into the message in v2. I experimented a bit - it's getting a bit
complicated how-to protect (char *name) for just this message.
Like, SysRq can be theoretically enabled on two serials at the same
moment - so some locking is needed to make the printed name sane.

As sysrq_toggle_support() is a global-enable knob for sysrq (also can be
switched in /proc/sys/kernel/sysrq) I'm not sure if it's worth to
complicate code to print through which serial console SysRq has been
enabled.

I can still do it in v3 if you insist.

And sorry about forgetting to mention this - thought I'll write reply
after I send v2 and somehow it slipped my mind.

Thanks,
           Dmitry