[PATCH 1/3] thunderbolt: stream: Add tbstream_dev_from_file()

[Alan Borzeszkowski <alan.borzeszkowski@linux.intel.com>]

Add tbstream_dev_from_file() which returns USB4STREAM device behind a
file. Expose it to in-kernel users via separate header.

Required by the 9P Thunderbolt transport driver to validate mount
source.

Signed-off-by: Alan Borzeszkowski <alan.borzeszkowski@linux.intel.com>
---
 MAINTAINERS                        |  1 +
 drivers/thunderbolt/stream.c       | 16 ++++++++++++++++
 include/linux/thunderbolt_stream.h | 14 ++++++++++++++
 3 files changed, 31 insertions(+)
 create mode 100644 include/linux/thunderbolt_stream.h

diff --git a/MAINTAINERS b/MAINTAINERS
index cc3cae2e378b..a626e81d1724 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -27211,6 +27211,7 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/westeri/thunderbolt.git
 F:	Documentation/admin-guide/thunderbolt.rst
 F:	drivers/thunderbolt/
 F:	include/linux/thunderbolt.h
+F:	include/linux/thunderbolt_stream.h
 
 THUNDERBOLT NETWORK DRIVER
 M:	Mika Westerberg <westeri@kernel.org>
diff --git a/drivers/thunderbolt/stream.c b/drivers/thunderbolt/stream.c
index 25c259dd0760..d6d0aafd5984 100644
--- a/drivers/thunderbolt/stream.c
+++ b/drivers/thunderbolt/stream.c
@@ -21,6 +21,7 @@
 #include <linux/poll.h>
 #include <linux/sizes.h>
 #include <linux/thunderbolt.h>
+#include <linux/thunderbolt_stream.h>
 #include <linux/uaccess.h>
 #include <linux/uio.h>
 #include <linux/uuid.h>
@@ -1024,6 +1025,21 @@ tbstream_dev_from_group(struct config_group *group)
 	return container_of(group, struct tbstream_dev, group);
 }
 
+/**
+ * tbstream_dev_from_file() - Return USB4STREAM device behind a file
+ * @file: File to check
+ *
+ * Return: Pointer to &struct tbstream_dev, %NULL if file is not
+ * USB4STREAM device.
+ */
+struct tbstream_dev *tbstream_dev_from_file(struct file *file)
+{
+	if (file->f_op != &tbstream_dev_fops)
+		return NULL;
+	return to_tbstream_dev(file->private_data);
+}
+EXPORT_SYMBOL_GPL(tbstream_dev_from_file);
+
 static ssize_t tbstream_dev_busy_poll_show(struct config_item *item, char *buf)
 {
 	struct config_group *group = to_config_group(item);
diff --git a/include/linux/thunderbolt_stream.h b/include/linux/thunderbolt_stream.h
new file mode 100644
index 000000000000..ed4fdba7c7e9
--- /dev/null
+++ b/include/linux/thunderbolt_stream.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Thunderbolt Stream API
+ *
+ * Copyright (C) 2026, Intel Corporation
+ * Author: Alan Borzeszkowski <alan.borzeszkowski@linux.intel.com>
+ */
+
+#ifndef THUNDERBOLT_STREAM_H_
+#define THUNDERBOLT_STREAM_H_
+
+struct tbstream_dev *tbstream_dev_from_file(struct file *file);
+
+#endif /* THUNDERBOLT_STREAM_H_ */
-- 
2.53.0