linux-kernel - [PATCH] WIP: drivers/base: Add virtual_device

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Message-ID: <20250130212843.659437-1-lyude@redhat.com>
Date: Thu, 30 Jan 2025 16:28:26 -0500
From: Lyude Paul <lyude@...hat.com>
To: rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Danilo Krummrich <dakr@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Maíra Canal <mairacanal@...eup.net>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Zijun Hu <quic_zijuhu@...cinc.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Robin Murphy <robin.murphy@....com>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	Lukas Wunner <lukas@...ner.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: [PATCH] WIP: drivers/base: Add virtual_device_create()

As Greg KH pointed out, we have a nice /sys/devices/virtual directory free
for the taking - but the vast majority of device drivers concerned with
virtual devices do not use this and instead misuse the platform device API.

To fix this, let's start by adding a simple function that can be used for
creating virtual devices - virtual_device_create().

Signed-off-by: Lyude Paul <lyude@...hat.com>

---

So, WIP obviously because I wrote this up in a few minutes - but this goes
off the idea that Danilo suggested to me off-list of coming up with a
simple API for handling virtual devices that's a little more obvious to
use. I wanted to get people's feedback and if we're happy with this idea,
I'm willing to go through and add some pointers to this function in various
platform API docs - along with porting over the C version of VKMS over to
this API.
---
 drivers/base/core.c    | 28 ++++++++++++++++++++++++++++
 include/linux/device.h |  2 ++
 2 files changed, 30 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 5a1f051981149..050e644ba11d5 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -4390,6 +4390,34 @@ struct device *device_create(const struct class *class, struct device *parent,
 }
 EXPORT_SYMBOL_GPL(device_create);
 
+/**
+ * virtual_device_create - creates a virtual device and registers it with sysfs
+ * @class: optional pointer to a struct class this device should be registered to
+ * @drvdata: the data to be added to the device for the callbacks
+ * @fmt: string for the device's name
+ *
+ * This function can be used to create standalone virtual devices, optionally
+ * registered to a specific class. Drivers which create virtual devices can use
+ * this. The device will live in /sys/devices/virtual.
+ *
+ * A pointer to the struct device will be returned from the call. Any further
+ * sysfs files that might be required can be created using this pointer.
+ *
+ * Returns &struct device pointer on success or ERR_PTR() on error.
+ */
+struct device *virtual_device_create(void *drvdata, const char *fmt, ...)
+{
+	va_list vargs;
+	struct device *dev;
+
+	va_start(vargs, fmt);
+	dev = device_create_groups_vargs(NULL, NULL, 0, drvdata, NULL,
+					 fmt, vargs);
+	va_end(vargs);
+	return dev;
+}
+EXPORT_SYMBOL_GPL(virtual_device_create);
+
 /**
  * device_create_with_groups - creates a device and registers it with sysfs
  * @class: pointer to the struct class that this device should be registered to
diff --git a/include/linux/device.h b/include/linux/device.h
index 80a5b32689866..74e07ec942f4e 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -1244,6 +1244,8 @@ bool device_is_bound(struct device *dev);
 __printf(5, 6) struct device *
 device_create(const struct class *cls, struct device *parent, dev_t devt,
 	      void *drvdata, const char *fmt, ...);
+__printf(2, 3) struct device *
+virtual_device_create(void *drvdata, const char *fmt, ...);
 __printf(6, 7) struct device *
 device_create_with_groups(const struct class *cls, struct device *parent, dev_t devt,
 			  void *drvdata, const struct attribute_group **groups,

base-commit: b323d8e7bc03d27dec646bfdccb7d1a92411f189
-- 
2.47.1