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

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Message-ID: <4051ac2a919c34e44113669e84ca7e8b.squirrel@localhost>
Date:	Tue, 24 Dec 2013 05:04:54 -0000
From:	shawn@...rchofgit.com
To:	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Cc:	"Shawn Landden" <shawn@...rchofgit.com>,
	"Jiri Slaby" <jslaby@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: only print sysrq help for handlers that are
 enabled

> 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
>
> thanks,
>
> greg k-h
>


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