linux-kernel - [PATCH v3 2/3] rpmsg: char: Implement eptdev based on anonymous inode

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Message-Id: <20250519150823.62350-3-dawei.li@linux.dev>
Date: Mon, 19 May 2025 23:08:22 +0800
From: Dawei Li <dawei.li@...ux.dev>
To: andersson@...nel.org,
	mathieu.poirier@...aro.org
Cc: linux-remoteproc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	dawei.li@...ux.dev,
	set_pte_at@...look.com
Subject: [PATCH v3 2/3] rpmsg: char: Implement eptdev based on anonymous inode

Introduce new eptdev abstraction based on anonymous inode. The new API
is exactly same with legacy one except:

- It's anonymous and devnode/path free.
- Its fops->open() is empty.

Signed-off-by: Dawei Li <dawei.li@...ux.dev>
---
 drivers/rpmsg/rpmsg_char.c | 49 ++++++++++++++++++++++++++++++++++++++
 drivers/rpmsg/rpmsg_char.h | 23 ++++++++++++++++++
 2 files changed, 72 insertions(+)

diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
index 6c19f2146698..babc63cc4238 100644
--- a/drivers/rpmsg/rpmsg_char.c
+++ b/drivers/rpmsg/rpmsg_char.c
@@ -13,6 +13,7 @@
 
 #define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt
 
+#include <linux/anon_inodes.h>
 #include <linux/cdev.h>
 #include <linux/device.h>
 #include <linux/fs.h>
@@ -517,6 +518,54 @@ int rpmsg_chrdev_eptdev_create(struct rpmsg_device *rpdev, struct device *parent
 }
 EXPORT_SYMBOL(rpmsg_chrdev_eptdev_create);
 
+static const struct file_operations rpmsg_anonymous_eptdev_fops = {
+	.owner = THIS_MODULE,
+	.release = rpmsg_eptdev_release,
+	.read_iter = rpmsg_eptdev_read_iter,
+	.write_iter = rpmsg_eptdev_write_iter,
+	.poll = rpmsg_eptdev_poll,
+	.unlocked_ioctl = rpmsg_eptdev_ioctl,
+	.compat_ioctl = compat_ptr_ioctl,
+};
+
+int rpmsg_anonymous_eptdev_create(struct rpmsg_device *rpdev, struct device *parent,
+				  struct rpmsg_channel_info chinfo, unsigned int flags,
+				  int *pfd)
+{
+	struct rpmsg_eptdev *eptdev;
+	int ret, fd;
+
+	/* Anonymous inode only supports these file flags */
+	if (flags & ~(O_ACCMODE | O_NONBLOCK | O_CLOEXEC))
+		return -EINVAL;
+
+	eptdev = rpmsg_eptdev_alloc(rpdev, parent, false);
+	if (IS_ERR(eptdev))
+		return PTR_ERR(eptdev);
+
+	ret =  rpmsg_eptdev_add(eptdev, chinfo, false);
+	if (ret) {
+		dev_err(&eptdev->dev, "failed to add %s\n", eptdev->chinfo.name);
+		return ret;
+	}
+
+	fd = anon_inode_getfd("rpmsg-eptdev", &rpmsg_anonymous_eptdev_fops, eptdev, flags);
+	if (fd < 0) {
+		put_device(&eptdev->dev);
+		return fd;
+	}
+
+	mutex_lock(&eptdev->ept_lock);
+	ret = __rpmsg_eptdev_open(eptdev);
+	mutex_unlock(&eptdev->ept_lock);
+
+	if (!ret)
+		*pfd = fd;
+
+	return ret;
+}
+EXPORT_SYMBOL(rpmsg_anonymous_eptdev_create);
+
 static int rpmsg_chrdev_probe(struct rpmsg_device *rpdev)
 {
 	struct rpmsg_channel_info chinfo;
diff --git a/drivers/rpmsg/rpmsg_char.h b/drivers/rpmsg/rpmsg_char.h
index 117d9cbc52f0..70ce2c511f13 100644
--- a/drivers/rpmsg/rpmsg_char.h
+++ b/drivers/rpmsg/rpmsg_char.h
@@ -19,6 +19,22 @@
 int rpmsg_chrdev_eptdev_create(struct rpmsg_device *rpdev, struct device *parent,
 			       struct rpmsg_channel_info chinfo);
 
+/**
+ * rpmsg_anonymous_eptdev_create() - register anonymous device and its associated
+ *                                   fd based on an endpoint
+ * @rpdev:  prepared rpdev to be used for creating endpoints
+ * @parent: parent device
+ * @chinfo: associated endpoint channel information.
+ * @flag: file flag
+ * @pfd: fd in represent of endpoint device
+ *
+ * This function create a new rpmsg endpoint device and its associated fd to instantiate a new
+ * endpoint based on chinfo information.
+ */
+int rpmsg_anonymous_eptdev_create(struct rpmsg_device *rpdev, struct device *parent,
+				  struct rpmsg_channel_info chinfo, unsigned int flags,
+				  int *pfd);
+
 /**
  * rpmsg_chrdev_eptdev_destroy() - destroy created char device endpoint.
  * @data: private data associated to the endpoint device
@@ -36,6 +52,13 @@ static inline int rpmsg_chrdev_eptdev_create(struct rpmsg_device *rpdev, struct
 	return -ENXIO;
 }
 
+static inline int rpmsg_anonymous_eptdev_create(struct rpmsg_device *rpdev, struct device *parent,
+						struct rpmsg_channel_info chinfo,
+						unsigned int flags, int *pfd)
+{
+	return -ENXIO;
+}
+
 static inline int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
 {
 	return -ENXIO;
-- 
2.25.1