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

[Bradley Morgan]

On 21 August 2026 02:56:48 BST, Masami Hiramatsu <mhiramat@xxxxxxxxxx>
wrote:
>On Thu, 20 Aug 2026 16:14:42 +0100
>Bradley Morgan <include@xxxxxxxxx> wrote:
>
>> On 19 August 2026 00:12:40 BST, Bradley Morgan <include@xxxxxxxxx>
>wrote:
>> >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 :(
>> >
>> 
>> Masami, could you give a round down of your nits for V3?
>
>Ah, OK. The phrasing aside, what you said wasn't wrong, so if you're happy
>with it, I'll pick it. (Let me pick it to probes/core)
>

I'm happy with this patch as is, how accurate?

Do the roar! (Pick it, Shrek reference)

>Thanks.
>
>
>
>> 
>> 
>> >
>> >>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!
>> 
>> Thanks!
>
>
>

Thanks!