[PATCH] WIP: drivers/base: Add virtual_device_create()

Lyude Paul
2025-01-30T21:28:59Z

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@redhat.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