Re: [PATCH v2] kprobes: use DEFINE_DEBUGFS_ATTRIBUTE for the enabled knob

[Bradley Morgan]

On 19 August 2026 00:08:13 BST, Masami Hiramatsu <mhiramat@xxxxxxxxxx>
wrote:
>On Tue, 18 Aug 2026 01:53:18 +0000
>Bradley Morgan <include@xxxxxxxxx> wrote:
>
>> This enabled knob is a disgusting terrible hack. It has rolled its
>> own read/write pair since 2007, writing '1' or '0' into a three byte
>> buffer by hand just to print a single character, with an XXX comment
>> begging debugfs for write callbacks on bool files.
>> DEFINE_DEBUGFS_ATTRIBUTE showed up in 2016 and does exactly that, so
>> the disgusting terrible hack has outlived its excuse for nine years.
>> Kill it, and the stale comment with it.
>
>In other words, does this mean something like the following?
>
>This "enable" knob implemented custom read/write logic, manually writing
>"1" or "0" to a 3-byte buffer solely to output a single character. As
>suggested by comments calling for `debugfs` to support write callbacks
>for boolean files, using `DEFINE_DEBUGFS_ATTRIBUTE` eliminates the need
>for these callbacks.
>

ehhhhh, well, my description very well tells someone about why this is
bad, and a hack, and everything. 

Your description is good though... But I love to have my personality in my
descriptions :(


>Thanks,
>
>> 
>> The behavior does not change, except the write only accepts 0/1 now
>> instead of y/n/on/off, and nothing uses anything else.
>> 
>> Signed-off-by: Bradley Morgan <include@xxxxxxxxx>
>> ---
>> Changes since v1:
>>  - Added the missing Signed-off-by, sorry.
>> 
>>  kernel/kprobes.c | 43 +++++++++----------------------------------
>>  1 file changed, 9 insertions(+), 34 deletions(-)
>> 
>> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
>> index bfc89083daa9..044c6b5fd2aa 100644
>> --- a/kernel/kprobes.c
>> +++ b/kernel/kprobes.c
>> @@ -3013,47 +3013,22 @@ static int disarm_all_kprobes(void)
>>  	return ret;
>>  }
>>  
>> -/*
>> - * XXX: The debugfs bool file interface doesn't allow for callbacks
>> - * when the bool state is switched. We can reuse that facility when
>> - * available
>> - */
>> -static ssize_t read_enabled_file_bool(struct file *file,
>> -	       char __user *user_buf, size_t count, loff_t *ppos)
>> +static int kprobes_enabled_set(void *data, u64 val)
>>  {
>> -	char buf[3];
>> +	if (val)
>> +		return arm_all_kprobes();
>>  
>> -	if (!kprobes_all_disarmed)
>> -		buf[0] = '1';
>> -	else
>> -		buf[0] = '0';
>> -	buf[1] = '\n';
>> -	buf[2] = 0x00;
>> -	return simple_read_from_buffer(user_buf, count, ppos, buf, 2);
>> +	return disarm_all_kprobes();
>>  }
>>  
>> -static ssize_t write_enabled_file_bool(struct file *file,
>> -	       const char __user *user_buf, size_t count, loff_t *ppos)
>> +static int kprobes_enabled_get(void *data, u64 *val)
>>  {
>> -	bool enable;
>> -	int ret;
>> -
>> -	ret = kstrtobool_from_user(user_buf, count, &enable);
>> -	if (ret)
>> -		return ret;
>> -
>> -	ret = enable ? arm_all_kprobes() : disarm_all_kprobes();
>> -	if (ret)
>> -		return ret;
>> -
>> -	return count;
>> +	*val = !kprobes_all_disarmed;
>> +	return 0;
>>  }
>>  
>> -static const struct file_operations fops_kp = {
>> -	.read =         read_enabled_file_bool,
>> -	.write =        write_enabled_file_bool,
>> -	.llseek =	default_llseek,
>> -};
>> +DEFINE_DEBUGFS_ATTRIBUTE(fops_kp, kprobes_enabled_get,
>> +			 kprobes_enabled_set, "%llu\n");
>>  
>>  static int __init debugfs_kprobe_init(void)
>>  {
>> -- 
>> 2.47.3
>> 
>
>
>

Thanks!