linux-kernel - [PATCH 09/26] media: v4l2-dev: Add video_device_context_from

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Message-Id: <20250717-multicontext-mainline-2025-v1-9-81ac18979c03@ideasonboard.com>
Date: Thu, 17 Jul 2025 12:45:35 +0200
From: Jacopo Mondi <jacopo.mondi@...asonboard.com>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>, 
 Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, 
 Kieran Bingham <kieran.bingham@...asonboard.com>, 
 Nicolas Dufresne <nicolas.dufresne@...labora.com>, 
 Mauro Carvalho Chehab <mchehab@...nel.org>, 
 Tomasz Figa <tfiga@...omium.org>, 
 Marek Szyprowski <m.szyprowski@...sung.com>, 
 Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>, 
 Florian Fainelli <florian.fainelli@...adcom.com>, 
 Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, 
 Hans Verkuil <hverkuil@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-media@...r.kernel.org, 
 linux-rpi-kernel@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org, 
 Jacopo Mondi <jacopo.mondi@...asonboard.com>
Subject: [PATCH 09/26] media: v4l2-dev: Add
 video_device_context_from_file()

Introduce an helper function to get a video_device_context from file.
If no context has been bound to the file, return the video device
default context.

As a video device context lifetime is bound to the one of the file
handle it is associated with, and the intended user of this helper are
the v4l2_ioctl_ops handlers that operates on an open file handle, the
context returned by this function is guaranteed to be valid for the
whole function scope of the caller.

Signed-off-by: Jacopo Mondi <jacopo.mondi@...asonboard.com>
---
 drivers/media/v4l2-core/v4l2-dev.c | 15 +++++++++++++++
 include/media/v4l2-dev.h           | 30 ++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
index 2d78096931efd88215bc847b105e198a54035546..96696959314abfb1864ea5d96742e579b5a41f6f 100644
--- a/drivers/media/v4l2-core/v4l2-dev.c
+++ b/drivers/media/v4l2-core/v4l2-dev.c
@@ -1180,6 +1180,21 @@ struct dentry *v4l2_debugfs_root(void)
 EXPORT_SYMBOL_GPL(v4l2_debugfs_root);
 #endif
 
+struct video_device_context *
+video_device_context_from_file(struct file *filp, struct video_device *vfd)
+{
+	struct v4l2_fh *vfh =
+		test_bit(V4L2_FL_USES_V4L2_FH, &vfd->flags) ? filp->private_data
+							    : NULL;
+
+	/* If the file handle has been bound to a context return it. */
+	if (vfh && vfh->context)
+		return vfh->context;
+
+	return vfd->default_context;
+}
+EXPORT_SYMBOL_GPL(video_device_context_from_file);
+
 #if defined(CONFIG_MEDIA_CONTROLLER)
 
 __must_check int video_device_pipeline_start(struct video_device *vdev,
diff --git a/include/media/v4l2-dev.h b/include/media/v4l2-dev.h
index 9e1cf58623acc4ab5f503a9663fd999b38130226..a41afb81663bc9cb3bfc06dcf9b11ceeaf7c3415 100644
--- a/include/media/v4l2-dev.h
+++ b/include/media/v4l2-dev.h
@@ -789,6 +789,36 @@ int video_device_init_context(struct video_device *vdev,
  */
 void video_device_cleanup_context(struct video_device_context *ctx);
 
+/**
+ * video_device_context_from_file - Get the video device context associated with
+ *				    an open file handle
+ * @filp: The file handle
+ * @vdev: The video device
+ *
+ * If a video device context has been bound to an open file handle by a call
+ * to the VIDIOC_BIND_CONTEXT ioctl this function returns it, otherwise returns
+ * the default video device context.
+ *
+ * The intended callers of this helper are the driver-specific v4l2_ioctl_ops
+ * handlers, which receive as first argument a file pointer. By using this
+ * helper drivers can get the context associated with such file, if any.
+ * Otherwise, if the video device  has not been bound to any media device
+ * context, the default video device context is returned.
+ *
+ * As video device contexts are reference counted and their lifetime is
+ * guaranteed to be at least the one of the file handle they are associated
+ * with, callers of this function are guaranteed to always receive a valid
+ * context reference by this function. The reference will remain valid for the
+ * whole function scope of the caller that has received the open file handle as
+ * argument. Likewise, accessing the media context from the video device context
+ * returned by this function is always safe within the same function scope.
+ *
+ * This function does not increase the reference count of the returned video
+ * device context.
+ */
+struct video_device_context *
+video_device_context_from_file(struct file *filp, struct video_device *vdev);
+
 #endif /* CONFIG_MEDIA_CONTROLLER */
 
 #endif /* _V4L2_DEV_H */

-- 
2.49.0