linux-kernel - Re: [PATCH] tty: only print sysrq help for handlers that are enabled

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Message-ID: <52B9818A.2060402@hurleysoftware.com>
Date:	Tue, 24 Dec 2013 07:43:54 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	shawn@...rchofgit.com,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: only print sysrq help for handlers that are enabled

On 12/24/2013 12:04 AM, shawn@...rchofgit.com wrote:
>> On Tue, Dec 03, 2013 at 07:55:25AM -0800, Shawn Landden wrote:
>>> Also print out a notice when sysrq is in selective mode.
>>>
>>> Signed-off-by: Shawn Landden <shawn@...rchofgit.com>
>>> ---
>>>   drivers/tty/sysrq.c | 7 ++++++-
>>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
>>> index ce396ec..4eee0e4 100644
>>> --- a/drivers/tty/sysrq.c
>>> +++ b/drivers/tty/sysrq.c
>>> @@ -548,9 +548,14 @@ void __handle_sysrq(int key, bool check_mask)
>>>   					;
>>>   				if (j != i)
>>>   					continue;
>>> -				printk("%s ", sysrq_key_table[i]->help_msg);
>>> +				/* only print if handler is enabled */
>>> +				if (sysrq_enabled & 1 ||
>>> +				    sysrq_enabled & sysrq_key_table[i]->enable_mask)
>>> +					printk("%s ", sysrq_key_table[i]->help_msg);
>>>   			}
>>>   		}
>>> +		if (!(sysrq_enabled & 1))
>>> +			printk("(some options are disabled)");
>>>   		printk("\n");
>>>   		console_loglevel = orig_log_level;
>>>   	}
>>
>> What exactly is this fixing?  What is broken here that this change
>> resolves?  Where is it applicable?  I need a lot more context here
>> please.
>
> Without this patch you get something like
> re[b]oot [r]aw [s]ync [h]elp ....
> even if none of these sysrq triggers are available because of the setting
> mask of
> kernel.sysrq
> With this patch then if (e.g.)
> kernel.sysrq = 16
> then you will only see
> [s]ync
> i.e. those commands you have privilege to issue via sysrq keypresses.
> Contact me if you need more,
> Shawn

But all operations are enabled when triggered via /proc/sysrq-trigger.
How about indicating key-disabled operations with a symbol instead?

Regards,
Peter Hurley

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