Implement RPMSG_CREATE_EPT_FD_IOCTL, new uAPI for rpmsg ctrl, which
shares most of operations of RPMSG_CREATE_EPT_IOCTL except that it
returns fd representing eptdev to userspace directly.

Possible calling procedures for userspace are:
- fd = open("/dev/rpmsg_ctrlX")
- ioctl(fd, RPMSG_CREATE_EPT_FD_IOCTL, &info);
- fd_ep = info.fd
- operations on fd_ep(write, read, poll ioctl)
- ioctl(fd_ep, RPMSG_DESTROY_EPT_IOCTL)
- close(fd_ep)
- close(fd)

Signed-off-by: Dawei Li <dawei.li@linux.dev>
---
 drivers/rpmsg/rpmsg_ctrl.c | 37 +++++++++++++++++++++++++++++--------
 include/uapi/linux/rpmsg.h | 19 +++++++++++++++++++
 2 files changed, 48 insertions(+), 8 deletions(-)

diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c
index 28f57945ccd9..c2cfdf46ccc6 100644
--- a/drivers/rpmsg/rpmsg_ctrl.c
+++ b/drivers/rpmsg/rpmsg_ctrl.c
@@ -75,19 +75,32 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd,
 				unsigned long arg)
 {
 	struct rpmsg_ctrldev *ctrldev = fp->private_data;
+	struct rpmsg_endpoint_fd_info ept_fd_info;
 	void __user *argp = (void __user *)arg;
 	struct rpmsg_endpoint_info eptinfo;
 	struct rpmsg_channel_info chinfo;
 	struct rpmsg_device *rpdev;
 	int ret = 0;
-
-	if (copy_from_user(&eptinfo, argp, sizeof(eptinfo)))
-		return -EFAULT;
-
-	memcpy(chinfo.name, eptinfo.name, RPMSG_NAME_SIZE);
-	chinfo.name[RPMSG_NAME_SIZE - 1] = '\0';
-	chinfo.src = eptinfo.src;
-	chinfo.dst = eptinfo.dst;
+	int fd = -1;
+
+	if (cmd == RPMSG_CREATE_EPT_IOCTL || cmd == RPMSG_CREATE_DEV_IOCTL ||
+	    cmd == RPMSG_RELEASE_DEV_IOCTL) {
+		if (copy_from_user(&eptinfo, argp, sizeof(eptinfo)))
+			return -EFAULT;
+
+		memcpy(chinfo.name, eptinfo.name, RPMSG_NAME_SIZE);
+		chinfo.name[RPMSG_NAME_SIZE - 1] = '\0';
+		chinfo.src = eptinfo.src;
+		chinfo.dst = eptinfo.dst;
+	} else if (cmd == RPMSG_CREATE_EPT_FD_IOCTL) {
+		if (copy_from_user(&ept_fd_info, argp, sizeof(ept_fd_info)))
+			return -EFAULT;
+
+		memcpy(chinfo.name, ept_fd_info.name, RPMSG_NAME_SIZE);
+		chinfo.name[RPMSG_NAME_SIZE - 1] = '\0';
+		chinfo.src = ept_fd_info.src;
+		chinfo.dst = ept_fd_info.dst;
+	}
 
 	mutex_lock(&ctrldev->ctrl_lock);
 	switch (cmd) {
@@ -110,6 +123,14 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd,
 				chinfo.name, ret);
 		break;
 
+	case RPMSG_CREATE_EPT_FD_IOCTL:
+		ret = rpmsg_eptdev_create(ctrldev->rpdev, &ctrldev->dev, chinfo, &fd);
+		if (!ret) {
+			ept_fd_info.fd = fd;
+			ret = copy_to_user(argp, &ept_fd_info, sizeof(ept_fd_info));
+		}
+		break;
+
 	default:
 		ret = -EINVAL;
 	}
diff --git a/include/uapi/linux/rpmsg.h b/include/uapi/linux/rpmsg.h
index f0c8da2b185b..934c0e76bfe3 100644
--- a/include/uapi/linux/rpmsg.h
+++ b/include/uapi/linux/rpmsg.h
@@ -53,4 +53,23 @@ struct rpmsg_endpoint_info {
  */
 #define RPMSG_SET_INCOMING_FLOWCONTROL _IOR(0xb5, 0x6, int)
 
+/**
+ * struct rpmsg_endpoint_fd_info - endpoint & fd info representation
+ * @name: name of service
+ * @src: local address. To set to RPMSG_ADDR_ANY if not used.
+ * @dst: destination address. To set to RPMSG_ADDR_ANY if not used.
+ * @fd: fd returned from driver
+ */
+struct rpmsg_endpoint_fd_info {
+	char name[32];
+	__u32 src;
+	__u32 dst;
+	__s32 fd;
+};
+
+/**
+ * Instantiate a new rmpsg endpoint which is represented by fd
+ */
+#define RPMSG_CREATE_EPT_FD_IOCTL _IOWR(0xb5, 0x7, struct rpmsg_endpoint_fd_info)
+
 #endif
-- 
2.25.1

Hi Dawei,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 92a09c47464d040866cf2b4cd052bc60555185fb]

url:    https://github.com/intel-lab-lkp/linux/commits/Dawei-Li/rpmsg-char-Reuse-eptdev-logic-for-anon-device/20250507-223209
base:   92a09c47464d040866cf2b4cd052bc60555185fb
patch link:    https://lore.kernel.org/r/20250507141712.4276-4-dawei.li%40linux.dev
patch subject: [PATCH 3/3] rpmsg: ctrl: Introduce RPMSG_CREATE_EPT_FD_IOCTL uAPI
config: i386-randconfig-011-20250508 (https://download.01.org/0day-ci/archive/20250509/202505090716.iB4qQAf2-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250509/202505090716.iB4qQAf2-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202505090716.iB4qQAf2-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from drivers/rpmsg/rpmsg_ctrl.c:28:
   drivers/rpmsg/rpmsg_char.h:54:1: error: expected identifier or '(' before '{' token
      54 | {
         | ^
>> drivers/rpmsg/rpmsg_char.h:52:19: warning: 'rpmsg_eptdev_create' used but never defined
      52 | static inline int rpmsg_eptdev_create(struct rpmsg_device *rpdev, struct device *parent,
         |                   ^~~~~~~~~~~~~~~~~~~


vim +/rpmsg_eptdev_create +52 drivers/rpmsg/rpmsg_char.h

69265bc12b6567 Arnaud Pouliquen 2022-01-24  51  
73c9f094eaac8b Dawei Li         2025-05-07 @52  static inline int rpmsg_eptdev_create(struct rpmsg_device *rpdev, struct device *parent,
73c9f094eaac8b Dawei Li         2025-05-07  53  				      struct rpmsg_channel_info chinfo, int *pfd);
73c9f094eaac8b Dawei Li         2025-05-07 @54  {
73c9f094eaac8b Dawei Li         2025-05-07  55  	return -ENXIO;
73c9f094eaac8b Dawei Li         2025-05-07  56  }
73c9f094eaac8b Dawei Li         2025-05-07  57  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki