[PATCH v2] RFC: ksmbd: Create module_kobject if builtin

[Linus Walleij <linus.walleij@linaro.org>]

Adding a call to lookup_or_create_module_kobject() to ksmbd
makes /sys/modules/ksmbd appear even when ksmbd is compiled
into the kernel.

This is nice when you boot a custom kernel on OpenWrt because
the startup script does things such as:

[ ! -e /sys/module/ksmbd ] && modprobe ksmbd 2> /dev/null
if [ ! -e /sys/module/ksmbd ]; then
    logger -p daemon.error -t 'ksmbd' "modprobe of ksmbd "
    "module failed, can\'t start ksmbd!"
     exit 1
fi

which makes the script not work with a compiled-in ksmbd.

Since I actually turn off modules and compile all my modules
into the kernel, I can't change the script to just check
cat /lib/modules/$(uname -r)/modules.builtin | grep ksmbd
either: no /lib/modules directory.

An option would be to change the script to proceed and
just assume the module is compiled in but it feels wrong.

If this approach is acceptable I am happy to generalize this
to something that any module that wants a /sys/modules/foo
file can use to get just that.

I can think of other ways to just create a dummy dir in
/sys/modules but it is probably unwise if someone would later
actually add a parameter or version string to the module and
get unpredictable bugs. It's probably better like this if
we do this thing.

Cc: Rosen Penev <rosenp@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
Changes in v2:
- Adding MODULE_VERSION() just to get /sys/module/ksmbd was wrong.
- Try this other approach to call lookup_or_create_module_kobject()
  if and only if ksmbd is compiled in.
- Link to v1: https://lore.kernel.org/r/20250531-ksmbd-sysfs-module-v1-1-248cf10fa87d@linaro.org
---
 fs/smb/server/server.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/fs/smb/server/server.c b/fs/smb/server/server.c
index 40420544cc25a2f7767695641e85d126022a30f9..f12ec149899664efdc9587db749dc8a1d6ccfdae 100644
--- a/fs/smb/server/server.c
+++ b/fs/smb/server/server.c
@@ -588,8 +588,24 @@ static int __init ksmbd_server_init(void)
 	if (ret)
 		goto err_crypto_destroy;
 
+	if (IS_BUILTIN(CONFIG_SMB_SERVER)) {
+		static struct module_kobject *mk;
+
+		/*
+		 * All this does is assure that /sys/module/ksmbd comes
+		 * into existence if ksmbd is compiled in so that userspace
+		 * can rely on its existence to identify that ksmbd is
+		 * available.
+		 */
+		mk = lookup_or_create_module_kobject(KBUILD_MODNAME);
+		if (!mk)
+			goto err_workqueue_destroy;
+	}
+
 	return 0;
 
+err_workqueue_destroy:
+	ksmbd_workqueue_destroy();
 err_crypto_destroy:
 	ksmbd_crypto_destroy();
 err_release_inode_hash:

---
base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
change-id: 20250531-ksmbd-sysfs-module-efaf2d1a86ca

Best regards,
-- 
Linus Walleij <linus.walleij@linaro.org>