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

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

[Bradley Morgan]

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.

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

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

[Masami Hiramatsu]

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.

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
> 


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

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@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 :(


>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!