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

On Fri, 21 Aug 2026 09:23:16 +0100
Bradley Morgan [off-list ref] wrote:

On 21 August 2026 02:56:48 BST, Masami Hiramatsu [off-list ref]
wrote:

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On Thu, 20 Aug 2026 16:14:42 +0100
Bradley Morgan [off-list ref] wrote:

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On 19 August 2026 00:12:40 BST, Bradley Morgan [off-list ref]

wrote:

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On 19 August 2026 00:08:13 BST, Masami Hiramatsu [off-list ref]
wrote:

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On Tue, 18 Aug 2026 01:53:18 +0000
Bradley Morgan [off-list ref] wrote:

quoted

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

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"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

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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

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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,

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Thanks.

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Thanks,

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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 <redacted>
---
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) [off-list ref]