[PATCH v4 15/25] nvdimm/ocxl: Register a character device for userspace to interact with

["Alastair D'Silva" <alastair@d-silva.org>]

This patch introduces a character device (/dev/ocxlpmemX) which further
patches will use to interact with userspace, such as error logs,
controller stats and card debug functionality.

Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
---
 drivers/nvdimm/ocxl/main.c     | 117 ++++++++++++++++++++++++++++++++-
 drivers/nvdimm/ocxl/ocxlpmem.h |   2 +
 2 files changed, 117 insertions(+), 2 deletions(-)

diff --git a/drivers/nvdimm/ocxl/main.c b/drivers/nvdimm/ocxl/main.c
index 8db573036423..9b85fcd3f1c9 100644
--- a/drivers/nvdimm/ocxl/main.c
+++ b/drivers/nvdimm/ocxl/main.c
@@ -10,6 +10,7 @@
 #include <misc/ocxl.h>
 #include <linux/delay.h>
 #include <linux/ndctl.h>
+#include <linux/fs.h>
 #include <linux/mm_types.h>
 #include <linux/memory_hotplug.h>
 #include "ocxlpmem.h"
@@ -356,6 +357,67 @@ static int ocxlpmem_register(struct ocxlpmem *ocxlpmem)
 	return device_register(&ocxlpmem->dev);
 }
 
+static void ocxlpmem_put(struct ocxlpmem *ocxlpmem)
+{
+	put_device(&ocxlpmem->dev);
+}
+
+static struct ocxlpmem *ocxlpmem_get(struct ocxlpmem *ocxlpmem)
+{
+	return (!get_device(&ocxlpmem->dev)) ? NULL : ocxlpmem;
+}
+
+static struct ocxlpmem *find_and_get_ocxlpmem(dev_t devno)
+{
+	struct ocxlpmem *ocxlpmem;
+	int minor = MINOR(devno);
+
+	mutex_lock(&minors_idr_lock);
+	ocxlpmem = idr_find(&minors_idr, minor);
+	if (ocxlpmem)
+		ocxlpmem_get(ocxlpmem);
+	mutex_unlock(&minors_idr_lock);
+
+	return ocxlpmem;
+}
+
+static int file_open(struct inode *inode, struct file *file)
+{
+	struct ocxlpmem *ocxlpmem;
+
+	ocxlpmem = find_and_get_ocxlpmem(inode->i_rdev);
+	if (!ocxlpmem)
+		return -ENODEV;
+
+	file->private_data = ocxlpmem;
+	return 0;
+}
+
+static int file_release(struct inode *inode, struct file *file)
+{
+	struct ocxlpmem *ocxlpmem = file->private_data;
+
+	ocxlpmem_put(ocxlpmem);
+	return 0;
+}
+
+static const struct file_operations fops = {
+	.owner		= THIS_MODULE,
+	.open		= file_open,
+	.release	= file_release,
+};
+
+/**
+ * create_cdev() - Create the chardev in /dev for the device
+ * @ocxlpmem: the SCM metadata
+ * Return: 0 on success, negative on failure
+ */
+static int create_cdev(struct ocxlpmem *ocxlpmem)
+{
+	cdev_init(&ocxlpmem->cdev, &fops);
+	return cdev_add(&ocxlpmem->cdev, ocxlpmem->dev.devt, 1);
+}
+
 /**
  * ocxlpmem_remove() - Free an OpenCAPI persistent memory device
  * @pdev: the PCI device information struct
@@ -376,6 +438,13 @@ static void remove(struct pci_dev *pdev)
 		if (ocxlpmem->nvdimm_bus)
 			nvdimm_bus_unregister(ocxlpmem->nvdimm_bus);
 
+		/*
+		 * Remove the cdev early to prevent a race against userspace
+		 * via the char dev
+		 */
+		if (ocxlpmem->cdev.owner)
+			cdev_del(&ocxlpmem->cdev);
+
 		device_unregister(&ocxlpmem->dev);
 	}
 }
@@ -527,11 +596,18 @@ static int probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 		goto err;
 	}
 
-	if (setup_command_metadata(ocxlpmem)) {
+	rc = setup_command_metadata(ocxlpmem);
+	if (rc) {
 		dev_err(&pdev->dev, "Could not read command metadata\n");
 		goto err;
 	}
 
+	rc = create_cdev(ocxlpmem);
+	if (rc) {
+		dev_err(&pdev->dev, "Could not create character device\n");
+		goto err;
+	}
+
 	elapsed = 0;
 	timeout = ocxlpmem->readiness_timeout +
 		  ocxlpmem->memory_available_timeout;
@@ -599,6 +675,36 @@ static struct pci_driver pci_driver = {
 	.shutdown = remove,
 };
 
+static int file_init(void)
+{
+	int rc;
+
+	rc = alloc_chrdev_region(&ocxlpmem_dev, 0, NUM_MINORS, "ocxlpmem");
+	if (rc) {
+		idr_destroy(&minors_idr);
+		pr_err("Unable to allocate OpenCAPI persistent memory major number: %d\n",
+		       rc);
+		return rc;
+	}
+
+	ocxlpmem_class = class_create(THIS_MODULE, "ocxlpmem");
+	if (IS_ERR(ocxlpmem_class)) {
+		idr_destroy(&minors_idr);
+		pr_err("Unable to create ocxlpmem class\n");
+		unregister_chrdev_region(ocxlpmem_dev, NUM_MINORS);
+		return PTR_ERR(ocxlpmem_class);
+	}
+
+	return 0;
+}
+
+static void file_exit(void)
+{
+	class_destroy(ocxlpmem_class);
+	unregister_chrdev_region(ocxlpmem_dev, NUM_MINORS);
+	idr_destroy(&minors_idr);
+}
+
 static int __init ocxlpmem_init(void)
 {
 	int rc;
@@ -606,16 +712,23 @@ static int __init ocxlpmem_init(void)
 	mutex_init(&minors_idr_lock);
 	idr_init(&minors_idr);
 
-	rc = pci_register_driver(&pci_driver);
+	rc = file_init();
 	if (rc)
 		return rc;
 
+	rc = pci_register_driver(&pci_driver);
+	if (rc) {
+		file_exit();
+		return rc;
+	}
+
 	return 0;
 }
 
 static void ocxlpmem_exit(void)
 {
 	pci_unregister_driver(&pci_driver);
+	file_exit();
 }
 
 module_init(ocxlpmem_init);
diff --git a/drivers/nvdimm/ocxl/ocxlpmem.h b/drivers/nvdimm/ocxl/ocxlpmem.h
index b72b3f909fc3..ee3bd651f254 100644
--- a/drivers/nvdimm/ocxl/ocxlpmem.h
+++ b/drivers/nvdimm/ocxl/ocxlpmem.h
@@ -2,6 +2,7 @@
 // Copyright 2020 IBM Corp.
 
 #include <linux/pci.h>
+#include <linux/cdev.h>
 #include <misc/ocxl.h>
 #include <linux/libnvdimm.h>
 #include <linux/mm.h>
@@ -103,6 +104,7 @@ struct command_metadata {
 struct ocxlpmem {
 	struct device dev;
 	struct pci_dev *pdev;
+	struct cdev cdev;
 	struct ocxl_fn *ocxl_fn;
 	struct nd_interleave_set nd_set;
 	struct nvdimm_bus_descriptor bus_desc;
-- 
2.24.1