[PATCH v2 3/8] fwctl: FWCTL_INFO to return basic information about the device

[Jason Gunthorpe <jgg@nvidia.com>]

Userspace will need to know some details about the fwctl interface being
used to locate the correct userspace code to communicate with the
kernel. Provide a simple device_type enum indicating what the kernel
driver is.

Allow the device to provide a device specific info struct that contains
any additional information that the driver may need to provide to
userspace.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
 drivers/fwctl/main.c       | 53 ++++++++++++++++++++++++++++++++++++++
 include/linux/fwctl.h      |  8 ++++++
 include/uapi/fwctl/fwctl.h | 29 +++++++++++++++++++++
 3 files changed, 90 insertions(+)

diff --git a/drivers/fwctl/main.c b/drivers/fwctl/main.c
index 6872c01d5c62e8..f1dec0b590aee4 100644
--- a/drivers/fwctl/main.c
+++ b/drivers/fwctl/main.c
@@ -17,6 +17,8 @@ enum {
 static dev_t fwctl_dev;
 static DEFINE_IDA(fwctl_ida);
 
+DEFINE_FREE(kfree_errptr, void *, if (!IS_ERR_OR_NULL(_T)) kfree(_T));
+
 struct fwctl_ucmd {
 	struct fwctl_uctx *uctx;
 	void __user *ubuffer;
@@ -24,8 +26,58 @@ struct fwctl_ucmd {
 	u32 user_size;
 };
 
+static int ucmd_respond(struct fwctl_ucmd *ucmd, size_t cmd_len)
+{
+	if (copy_to_user(ucmd->ubuffer, ucmd->cmd,
+			 min_t(size_t, ucmd->user_size, cmd_len)))
+		return -EFAULT;
+	return 0;
+}
+
+static int copy_to_user_zero_pad(void __user *to, const void *from,
+				 size_t from_len, size_t user_len)
+{
+	size_t copy_len;
+
+	copy_len = min(from_len, user_len);
+	if (copy_to_user(to, from, copy_len))
+		return -EFAULT;
+	if (copy_len < user_len) {
+		if (clear_user(to + copy_len, user_len - copy_len))
+			return -EFAULT;
+	}
+	return 0;
+}
+
+static int fwctl_cmd_info(struct fwctl_ucmd *ucmd)
+{
+	struct fwctl_device *fwctl = ucmd->uctx->fwctl;
+	struct fwctl_info *cmd = ucmd->cmd;
+	size_t driver_info_len = 0;
+
+	if (cmd->flags)
+		return -EOPNOTSUPP;
+
+	if (cmd->device_data_len) {
+		void *driver_info __free(kfree_errptr) =
+			fwctl->ops->info(ucmd->uctx, &driver_info_len);
+		if (IS_ERR(driver_info))
+			return PTR_ERR(driver_info);
+
+		if (copy_to_user_zero_pad(u64_to_user_ptr(cmd->out_device_data),
+					  driver_info, driver_info_len,
+					  cmd->device_data_len))
+			return -EFAULT;
+	}
+
+	cmd->out_device_type = fwctl->ops->device_type;
+	cmd->device_data_len = driver_info_len;
+	return ucmd_respond(ucmd, sizeof(*cmd));
+}
+
 /* On stack memory for the ioctl structs */
 union ucmd_buffer {
+	struct fwctl_info info;
 };
 
 struct fwctl_ioctl_op {
@@ -45,6 +97,7 @@ struct fwctl_ioctl_op {
 		.execute = _fn,                                       \
 	}
 static const struct fwctl_ioctl_op fwctl_ioctl_ops[] = {
+	IOCTL_OP(FWCTL_INFO, fwctl_cmd_info, struct fwctl_info, out_device_data),
 };
 
 static long fwctl_fops_ioctl(struct file *filp, unsigned int cmd,
diff --git a/include/linux/fwctl.h b/include/linux/fwctl.h
index 1d9651de92fc19..9a906b861acf3a 100644
--- a/include/linux/fwctl.h
+++ b/include/linux/fwctl.h
@@ -7,12 +7,14 @@
 #include <linux/device.h>
 #include <linux/cdev.h>
 #include <linux/cleanup.h>
+#include <uapi/fwctl/fwctl.h>
 
 struct fwctl_device;
 struct fwctl_uctx;
 
 /**
  * struct fwctl_ops - Driver provided operations
+ * @device_type: The drivers assigned device_type number. This is uABI
  * @uctx_size: The size of the fwctl_uctx struct to allocate. The first
  *	bytes of this memory will be a fwctl_uctx. The driver can use the
  *	remaining bytes as its private memory.
@@ -20,11 +22,17 @@ struct fwctl_uctx;
  *	used.
  * @close_uctx: Called when the uctx is destroyed, usually when the FD is
  *	closed.
+ * @info: Implement FWCTL_INFO. Return a kmalloc() memory that is copied to
+ *	out_device_data. On input length indicates the size of the user buffer
+ *	on output it indicates the size of the memory. The driver can ignore
+ *	length on input, the core code will handle everything.
  */
 struct fwctl_ops {
+	enum fwctl_device_type device_type;
 	size_t uctx_size;
 	int (*open_uctx)(struct fwctl_uctx *uctx);
 	void (*close_uctx)(struct fwctl_uctx *uctx);
+	void *(*info)(struct fwctl_uctx *uctx, size_t *length);
 };
 
 /**
diff --git a/include/uapi/fwctl/fwctl.h b/include/uapi/fwctl/fwctl.h
index 0bdce95b6d69d9..39db9f09f8068e 100644
--- a/include/uapi/fwctl/fwctl.h
+++ b/include/uapi/fwctl/fwctl.h
@@ -36,6 +36,35 @@
  */
 enum {
 	FWCTL_CMD_BASE = 0,
+	FWCTL_CMD_INFO = 0,
+	FWCTL_CMD_RPC = 1,
 };
 
+enum fwctl_device_type {
+	FWCTL_DEVICE_TYPE_ERROR = 0,
+};
+
+/**
+ * struct fwctl_info - ioctl(FWCTL_INFO)
+ * @size: sizeof(struct fwctl_info)
+ * @flags: Must be 0
+ * @out_device_type: Returns the type of the device from enum fwctl_device_type
+ * @device_data_len: On input the length of the out_device_data memory. On
+ *	output the size of the kernel's device_data which may be larger or
+ *	smaller than the input. Maybe 0 on input.
+ * @out_device_data: Pointer to a memory of device_data_len bytes. Kernel will
+ *	fill the entire memory, zeroing as required.
+ *
+ * Returns basic information about this fwctl instance, particularly what driver
+ * is being used to define the device_data format.
+ */
+struct fwctl_info {
+	__u32 size;
+	__u32 flags;
+	__u32 out_device_type;
+	__u32 device_data_len;
+	__aligned_u64 out_device_data;
+};
+#define FWCTL_INFO _IO(FWCTL_TYPE, FWCTL_CMD_INFO)
+
 #endif
-- 
2.45.2