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

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Fri, 21 Aug 2026 09:23:16 +0100
Bradley Morgan <include@grrlz.net> wrote:

> On 21 August 2026 02:56:48 BST, Masami Hiramatsu <mhiramat@kernel.org>
> wrote:
> >On Thu, 20 Aug 2026 16:14:42 +0100
> >Bradley Morgan <include@grrlz.net> wrote:
> >
> >> On 19 August 2026 00:12:40 BST, Bradley Morgan <include@grrlz.net>
> >wrote:
> >> >On 19 August 2026 00:08:13 BST, Masami Hiramatsu <mhiramat@kernel.org>
> >> >wrote:
> >> >>On Tue, 18 Aug 2026 01:53:18 +0000
> >> >>Bradley Morgan <include@grrlz.net> 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)

OK, I picked this to probes/core. (sorry for late notice)

Thanks,

> 
> >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@grrlz.net>
> >> >>> ---
> >> >>> 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!


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>