[PATCHv3,7/8] videobuf2: handle V4L2_MEMORY_FLAG_NON_COHERENT flag

  This patch lets user-space to request a non-coherent memory
allocation during CREATE_BUFS and REQBUFS ioctl calls.

= CREATE_BUFS

  struct v4l2_create_buffers has seven 4-byte reserved areas,
  so reserved[0] is renamed to ->flags. The struct, thus, now
  has six reserved 4-byte regions.

= CREATE_BUFS32

  struct v4l2_create_buffers32 has seven 4-byte reserved areas,
  so reserved[0] is renamed to ->flags. The struct, thus, now
  has six reserved 4-byte regions.

= REQBUFS

 We use one byte of a 4 byte ->reserved[1] member of struct
 v4l2_requestbuffers. The struct, thus, now has reserved 3 bytes.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 .../media/v4l/vidioc-create-bufs.rst          |  7 ++++-
 .../media/v4l/vidioc-reqbufs.rst              | 11 ++++---
 .../media/common/videobuf2/videobuf2-core.c   |  4 +--
 .../media/common/videobuf2/videobuf2-v4l2.c   | 31 +++++++++++++++++--
 drivers/media/v4l2-core/v4l2-compat-ioctl32.c |  9 +++++-
 drivers/media/v4l2-core/v4l2-ioctl.c          |  4 +--
 include/uapi/linux/videodev2.h                |  9 ++++--
 7 files changed, 60 insertions(+), 15 deletions(-)
  

On 09.07.21 11:20, Sergey Senozhatsky wrote:
> This patch lets user-space to request a non-coherent memory
> allocation during CREATE_BUFS and REQBUFS ioctl calls.
> 
> = CREATE_BUFS
> 
>    struct v4l2_create_buffers has seven 4-byte reserved areas,
>    so reserved[0] is renamed to ->flags. The struct, thus, now
>    has six reserved 4-byte regions.
> 
> = CREATE_BUFS32
> 
>    struct v4l2_create_buffers32 has seven 4-byte reserved areas,
>    so reserved[0] is renamed to ->flags. The struct, thus, now
>    has six reserved 4-byte regions.
> 
> = REQBUFS
> 
>   We use one byte of a 4 byte ->reserved[1] member of struct
>   v4l2_requestbuffers. The struct, thus, now has reserved 3 bytes.
> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> ---
>   .../media/v4l/vidioc-create-bufs.rst          |  7 ++++-
>   .../media/v4l/vidioc-reqbufs.rst              | 11 ++++---
>   .../media/common/videobuf2/videobuf2-core.c   |  4 +--
>   .../media/common/videobuf2/videobuf2-v4l2.c   | 31 +++++++++++++++++--
>   drivers/media/v4l2-core/v4l2-compat-ioctl32.c |  9 +++++-
>   drivers/media/v4l2-core/v4l2-ioctl.c          |  4 +--
>   include/uapi/linux/videodev2.h                |  9 ++++--
>   7 files changed, 60 insertions(+), 15 deletions(-)
> 
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> index f98f18c9e91c..a048a9f6b7b6 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> @@ -113,7 +113,12 @@ than the number requested.
>   	``V4L2_MEMORY_MMAP`` and ``format.type`` to the buffer type.
>   
>       * - __u32
> -      - ``reserved``\ [7]
> +      - ``flags``
> +      - Specifies additional buffer management attributes.
> +	See :ref:`memory-flags`.
> +
> +    * - __u32
> +      - ``reserved``\ [6]
>         - A place holder for future extensions. Drivers and applications
>   	must set the array to zero.
>   
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> index e59306aba2b0..099fa6695167 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> @@ -104,10 +104,13 @@ aborting or finishing any DMA in progress, an implicit
>   	``V4L2_MEMORY_MMAP`` and ``type`` set to the buffer type. This will
>   	free any previously allocated buffers, so this is typically something
>   	that will be done at the start of the application.
> -    * - __u32
> -      - ``reserved``\ [1]
> -      - A place holder for future extensions. Drivers and applications
> -	must set the array to zero.
> +    * - __u8
> +      - ``flags``
> +      - Specifies additional buffer management attributes.
> +	See :ref:`memory-flags`.
> +    * - __u8
> +      - ``reserved``\ [3]
> +      - Reserved for future extensions.
>   
>   .. _v4l2-buf-capabilities:
>   .. _V4L2-BUF-CAP-SUPPORTS-MMAP:
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index af4db310cf5e..38505783247e 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -762,7 +762,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
>   {
>   	unsigned int num_buffers, allocated_buffers, num_planes = 0;
>   	unsigned plane_sizes[VB2_MAX_PLANES] = { };
> -	bool coherent_mem = true;
> +	bool coherent_mem = !(flags & V4L2_MEMORY_FLAG_NON_COHERENT);
>   	unsigned int i;
>   	int ret;
>   
> @@ -906,7 +906,7 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
>   {
>   	unsigned int num_planes = 0, num_buffers, allocated_buffers;
>   	unsigned plane_sizes[VB2_MAX_PLANES] = { };
> -	bool coherent_mem = true;
> +	bool coherent_mem = !(flags & V4L2_MEMORY_FLAG_NON_COHERENT);
>   	int ret;
>   
>   	if (q->num_buffers == VB2_MAX_FRAME) {
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index b4f70ddb09b0..6edf4508c636 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -692,12 +692,32 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
>   #endif
>   }
>   
> +static void validate_memory_flags(struct vb2_queue *q,
> +				  int memory,
> +				  u32 *flags)
> +{
> +	if (!q->allow_cache_hints || memory != V4L2_MEMORY_MMAP) {
> +		/*
> +		 * This needs to clear V4L2_MEMORY_FLAG_NON_COHERENT only,
> +		 * but in order to avoid bugs we zero out all bits.
> +		 */
> +		*flags = 0;
> +	} else {
> +		/* Clear all unknown flags. */
> +		*flags &= V4L2_MEMORY_FLAG_NON_COHERENT;
> +	}
> +}
> +
>   int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
>   {
>   	int ret = vb2_verify_memory_type(q, req->memory, req->type);
> +	u32 flags = req->flags;
>   
>   	fill_buf_caps(q, &req->capabilities);
> -	return ret ? ret : vb2_core_reqbufs(q, req->memory, 0, &req->count);
> +	validate_memory_flags(q, req->memory, &flags);
> +	req->flags = flags;

you can do instead

validate_memory_flags(q, req->memory, &req->flags);

> +	return ret ? ret : vb2_core_reqbufs(q, req->memory,
> +					    req->flags, &req->count);
>   }
>   EXPORT_SYMBOL_GPL(vb2_reqbufs);
>   
> @@ -729,6 +749,7 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
>   	unsigned i;
>   
>   	fill_buf_caps(q, &create->capabilities);
> +	validate_memory_flags(q, create->memory, &create->flags);
>   	create->index = q->num_buffers;
>   	if (create->count == 0)
>   		return ret != -EBUSY ? ret : 0;
> @@ -772,7 +793,7 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
>   		if (requested_sizes[i] == 0)
>   			return -EINVAL;
>   	return ret ? ret : vb2_core_create_bufs(q, create->memory,
> -						0,
> +						create->flags,
>   						&create->count,
>   						requested_planes,
>   						requested_sizes);
> @@ -969,13 +990,16 @@ int vb2_ioctl_reqbufs(struct file *file, void *priv,
>   {
>   	struct video_device *vdev = video_devdata(file);
>   	int res = vb2_verify_memory_type(vdev->queue, p->memory, p->type);
> +	u32 flags = p->flags;
>   
>   	fill_buf_caps(vdev->queue, &p->capabilities);
> +	validate_memory_flags(vdev->queue, p->memory, &flags);
> +	p->flags = flags;

ditto


thanks,
Dafna

>   	if (res)
>   		return res;
>   	if (vb2_queue_is_busy(vdev, file))
>   		return -EBUSY;
> -	res = vb2_core_reqbufs(vdev->queue, p->memory, 0, &p->count);
> +	res = vb2_core_reqbufs(vdev->queue, p->memory, p->flags, &p->count);
>   	/* If count == 0, then the owner has released all buffers and he
>   	   is no longer owner of the queue. Otherwise we have a new owner. */
>   	if (res == 0)
> @@ -993,6 +1017,7 @@ int vb2_ioctl_create_bufs(struct file *file, void *priv,
>   
>   	p->index = vdev->queue->num_buffers;
>   	fill_buf_caps(vdev->queue, &p->capabilities);
> +	validate_memory_flags(vdev->queue, p->memory, &p->flags);
>   	/*
>   	 * If count == 0, then just check if memory and type are valid.
>   	 * Any -EBUSY result from vb2_verify_memory_type can be mapped to 0.
> diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> index 47aff3b19742..8176769a89fa 100644
> --- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> +++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> @@ -126,6 +126,9 @@ struct v4l2_format32 {
>    * @memory:	buffer memory type
>    * @format:	frame format, for which buffers are requested
>    * @capabilities: capabilities of this buffer type.
> + * @flags:	additional buffer management attributes (ignored unless the
> + *		queue has V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS capability and
> + *		configured for MMAP streaming I/O).
>    * @reserved:	future extensions
>    */
>   struct v4l2_create_buffers32 {
> @@ -134,7 +137,8 @@ struct v4l2_create_buffers32 {
>   	__u32			memory;	/* enum v4l2_memory */
>   	struct v4l2_format32	format;
>   	__u32			capabilities;
> -	__u32			reserved[7];
> +	__u32			flags;
> +	__u32			reserved[6];
>   };
>   
>   static int get_v4l2_format32(struct v4l2_format *p64,
> @@ -182,6 +186,8 @@ static int get_v4l2_create32(struct v4l2_create_buffers *p64,
>   	if (copy_from_user(p64, p32,
>   			   offsetof(struct v4l2_create_buffers32, format)))
>   		return -EFAULT;
> +	if (copy_from_user(&p64->flags, &p32->flags, sizeof(p32->flags)))
> +		return -EFAULT;
>   	return get_v4l2_format32(&p64->format, &p32->format);
>   }
>   
> @@ -227,6 +233,7 @@ static int put_v4l2_create32(struct v4l2_create_buffers *p64,
>   	if (copy_to_user(p32, p64,
>   			 offsetof(struct v4l2_create_buffers32, format)) ||
>   	    put_user(p64->capabilities, &p32->capabilities) ||
> +	    put_user(p64->flags, &p32->flags) ||
>   	    copy_to_user(p32->reserved, p64->reserved, sizeof(p64->reserved)))
>   		return -EFAULT;
>   	return put_v4l2_format32(&p64->format, &p32->format);
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 05d5db3d85e5..6a941da33998 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -2004,7 +2004,7 @@ static int v4l_reqbufs(const struct v4l2_ioctl_ops *ops,
>   	if (ret)
>   		return ret;
>   
> -	CLEAR_AFTER_FIELD(p, capabilities);
> +	CLEAR_AFTER_FIELD(p, flags);
>   
>   	return ops->vidioc_reqbufs(file, fh, p);
>   }
> @@ -2045,7 +2045,7 @@ static int v4l_create_bufs(const struct v4l2_ioctl_ops *ops,
>   	if (ret)
>   		return ret;
>   
> -	CLEAR_AFTER_FIELD(create, capabilities);
> +	CLEAR_AFTER_FIELD(create, flags);
>   
>   	v4l_sanitize_format(&create->format);
>   
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 9d11e1d9c934..7973aa0465d2 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -953,7 +953,8 @@ struct v4l2_requestbuffers {
>   	__u32			type;		/* enum v4l2_buf_type */
>   	__u32			memory;		/* enum v4l2_memory */
>   	__u32			capabilities;
> -	__u32			reserved[1];
> +	__u8			flags;
> +	__u8			reserved[3];
>   };
>   
>   #define V4L2_MEMORY_FLAG_NON_COHERENT			(1 << 0)
> @@ -2501,6 +2502,9 @@ struct v4l2_dbg_chip_info {
>    * @memory:	enum v4l2_memory; buffer memory type
>    * @format:	frame format, for which buffers are requested
>    * @capabilities: capabilities of this buffer type.
> + * @flags:	additional buffer management attributes (ignored unless the
> + *		queue has V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS capability
> + *		and configured for MMAP streaming I/O).
>    * @reserved:	future extensions
>    */
>   struct v4l2_create_buffers {
> @@ -2509,7 +2513,8 @@ struct v4l2_create_buffers {
>   	__u32			memory;
>   	struct v4l2_format	format;
>   	__u32			capabilities;
> -	__u32			reserved[7];
> +	__u32			flags;
> +	__u32			reserved[6];
>   };
>   
>   /*
>
  

On (21/07/22 19:33), Dafna Hirschfeld wrote:
[..]
> >   int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
> >   {
> >   	int ret = vb2_verify_memory_type(q, req->memory, req->type);
> > +	u32 flags = req->flags;
> >   	fill_buf_caps(q, &req->capabilities);
> > -	return ret ? ret : vb2_core_reqbufs(q, req->memory, 0, &req->count);
> > +	validate_memory_flags(q, req->memory, &flags);
> > +	req->flags = flags;
> 
> you can do instead
> 
> validate_memory_flags(q, req->memory, &req->flags);

->flags are u32 for create-bufs and u8 for reqi-bufs. So `*flags = <value>`
can write to ->reserved[] for req-bufs (if the value is huge enough).
  

On (21/07/26 10:40), Sergey Senozhatsky wrote:
> On (21/07/22 19:33), Dafna Hirschfeld wrote:
> [..]
> > >   int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
> > >   {
> > >   	int ret = vb2_verify_memory_type(q, req->memory, req->type);
> > > +	u32 flags = req->flags;
> > >   	fill_buf_caps(q, &req->capabilities);
> > > -	return ret ? ret : vb2_core_reqbufs(q, req->memory, 0, &req->count);
> > > +	validate_memory_flags(q, req->memory, &flags);
> > > +	req->flags = flags;
> > 
> > you can do instead
> > 
> > validate_memory_flags(q, req->memory, &req->flags);
> 
> ->flags are u32 for create-bufs and u8 for reqi-bufs. So `*flags = <value>`
> can write to ->reserved[] for req-bufs (if the value is huge enough).

I guess ->flags can become u8 for both create-bufs and req-bufs.
We had ->flags in both structs as u32, but then decided to leave
some reserved[] space in req-bufs and switched to u8 there.
  

On (21/07/26 13:05), Sergey Senozhatsky wrote:
> On (21/07/26 10:40), Sergey Senozhatsky wrote:
> > On (21/07/22 19:33), Dafna Hirschfeld wrote:
> > [..]
> > > >   int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
> > > >   {
> > > >   	int ret = vb2_verify_memory_type(q, req->memory, req->type);
> > > > +	u32 flags = req->flags;
> > > >   	fill_buf_caps(q, &req->capabilities);
> > > > -	return ret ? ret : vb2_core_reqbufs(q, req->memory, 0, &req->count);
> > > > +	validate_memory_flags(q, req->memory, &flags);
> > > > +	req->flags = flags;
> > > 
> > > you can do instead
> > > 
> > > validate_memory_flags(q, req->memory, &req->flags);
> > 
> > ->flags are u32 for create-bufs and u8 for reqi-bufs. So `*flags = <value>`
> > can write to ->reserved[] for req-bufs (if the value is huge enough).
> 
> I guess ->flags can become u8 for both create-bufs and req-bufs.
> We had ->flags in both structs as u32, but then decided to leave
> some reserved[] space in req-bufs and switched to u8 there.

Something like this

---

diff --git a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
index a048a9f6b7b6..cf633b5a4919 100644
--- a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
+++ b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
@@ -112,13 +112,13 @@ than the number requested.
 	other changes, then set ``count`` to 0, ``memory`` to
 	``V4L2_MEMORY_MMAP`` and ``format.type`` to the buffer type.
 
-    * - __u32
+    * - __u8
       - ``flags``
       - Specifies additional buffer management attributes.
 	See :ref:`memory-flags`.
 
-    * - __u32
-      - ``reserved``\ [6]
+    * - __u8
+      - ``reserved``\ [27]
       - A place holder for future extensions. Drivers and applications
 	must set the array to zero.
 
diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
index 6edf4508c636..2ae949ec0afa 100644
--- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
+++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
@@ -694,7 +694,7 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
 
 static void validate_memory_flags(struct vb2_queue *q,
 				  int memory,
-				  u32 *flags)
+				  u8 *flags)
 {
 	if (!q->allow_cache_hints || memory != V4L2_MEMORY_MMAP) {
 		/*
@@ -711,11 +711,9 @@ static void validate_memory_flags(struct vb2_queue *q,
 int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
 {
 	int ret = vb2_verify_memory_type(q, req->memory, req->type);
-	u32 flags = req->flags;
 
 	fill_buf_caps(q, &req->capabilities);
-	validate_memory_flags(q, req->memory, &flags);
-	req->flags = flags;
+	validate_memory_flags(q, req->memory, &req->flags);
 	return ret ? ret : vb2_core_reqbufs(q, req->memory,
 					    req->flags, &req->count);
 }
@@ -990,11 +988,9 @@ int vb2_ioctl_reqbufs(struct file *file, void *priv,
 {
 	struct video_device *vdev = video_devdata(file);
 	int res = vb2_verify_memory_type(vdev->queue, p->memory, p->type);
-	u32 flags = p->flags;
 
 	fill_buf_caps(vdev->queue, &p->capabilities);
-	validate_memory_flags(vdev->queue, p->memory, &flags);
-	p->flags = flags;
+	validate_memory_flags(vdev->queue, p->memory, &p->flags);
 	if (res)
 		return res;
 	if (vb2_queue_is_busy(vdev, file))
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index 7973aa0465d2..ad4f7cee53f2 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -2513,8 +2513,8 @@ struct v4l2_create_buffers {
 	__u32			memory;
 	struct v4l2_format	format;
 	__u32			capabilities;
-	__u32			flags;
-	__u32			reserved[6];
+	__u8			flags;
+	__u8			reserved[27];
 };
 
 /*
  

On Mon, Jul 26, 2021 at 1:20 PM Sergey Senozhatsky
<senozhatsky@chromium.org> wrote:
>
> On (21/07/26 13:05), Sergey Senozhatsky wrote:
> > On (21/07/26 10:40), Sergey Senozhatsky wrote:
> > > On (21/07/22 19:33), Dafna Hirschfeld wrote:
> > > [..]
> > > > >   int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
> > > > >   {
> > > > >         int ret = vb2_verify_memory_type(q, req->memory, req->type);
> > > > > +       u32 flags = req->flags;
> > > > >         fill_buf_caps(q, &req->capabilities);
> > > > > -       return ret ? ret : vb2_core_reqbufs(q, req->memory, 0, &req->count);
> > > > > +       validate_memory_flags(q, req->memory, &flags);
> > > > > +       req->flags = flags;
> > > >
> > > > you can do instead
> > > >
> > > > validate_memory_flags(q, req->memory, &req->flags);
> > >
> > > ->flags are u32 for create-bufs and u8 for reqi-bufs. So `*flags = <value>`
> > > can write to ->reserved[] for req-bufs (if the value is huge enough).
> >
> > I guess ->flags can become u8 for both create-bufs and req-bufs.
> > We had ->flags in both structs as u32, but then decided to leave
> > some reserved[] space in req-bufs and switched to u8 there.
>
> Something like this
>
> ---
>
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> index a048a9f6b7b6..cf633b5a4919 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> @@ -112,13 +112,13 @@ than the number requested.
>         other changes, then set ``count`` to 0, ``memory`` to
>         ``V4L2_MEMORY_MMAP`` and ``format.type`` to the buffer type.
>
> -    * - __u32
> +    * - __u8
>        - ``flags``
>        - Specifies additional buffer management attributes.
>         See :ref:`memory-flags`.
>
> -    * - __u32
> -      - ``reserved``\ [6]
> +    * - __u8
> +      - ``reserved``\ [27]
>        - A place holder for future extensions. Drivers and applications
>         must set the array to zero.
>
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index 6edf4508c636..2ae949ec0afa 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -694,7 +694,7 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
>
>  static void validate_memory_flags(struct vb2_queue *q,
>                                   int memory,
> -                                 u32 *flags)
> +                                 u8 *flags)
>  {
>         if (!q->allow_cache_hints || memory != V4L2_MEMORY_MMAP) {
>                 /*
> @@ -711,11 +711,9 @@ static void validate_memory_flags(struct vb2_queue *q,
>  int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
>  {
>         int ret = vb2_verify_memory_type(q, req->memory, req->type);
> -       u32 flags = req->flags;
>
>         fill_buf_caps(q, &req->capabilities);
> -       validate_memory_flags(q, req->memory, &flags);
> -       req->flags = flags;
> +       validate_memory_flags(q, req->memory, &req->flags);
>         return ret ? ret : vb2_core_reqbufs(q, req->memory,
>                                             req->flags, &req->count);
>  }
> @@ -990,11 +988,9 @@ int vb2_ioctl_reqbufs(struct file *file, void *priv,
>  {
>         struct video_device *vdev = video_devdata(file);
>         int res = vb2_verify_memory_type(vdev->queue, p->memory, p->type);
> -       u32 flags = p->flags;
>
>         fill_buf_caps(vdev->queue, &p->capabilities);
> -       validate_memory_flags(vdev->queue, p->memory, &flags);
> -       p->flags = flags;
> +       validate_memory_flags(vdev->queue, p->memory, &p->flags);
>         if (res)
>                 return res;
>         if (vb2_queue_is_busy(vdev, file))
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 7973aa0465d2..ad4f7cee53f2 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -2513,8 +2513,8 @@ struct v4l2_create_buffers {
>         __u32                   memory;
>         struct v4l2_format      format;
>         __u32                   capabilities;
> -       __u32                   flags;
> -       __u32                   reserved[6];
> +       __u8                    flags;
> +       __u8                    reserved[27];
>  };
>
>  /*

I don't think we want this UABI churn anymore for a trivial
simplification in the implementation.

Best regards,
Tomasz
  

On (21/07/26 13:22), Tomasz Figa wrote:
> > > I guess ->flags can become u8 for both create-bufs and req-bufs.
> > > We had ->flags in both structs as u32, but then decided to leave
> > > some reserved[] space in req-bufs and switched to u8 there.
> >
> > diff --git a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> > index a048a9f6b7b6..cf633b5a4919 100644
> > --- a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> > +++ b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> > @@ -112,13 +112,13 @@ than the number requested.
> >         other changes, then set ``count`` to 0, ``memory`` to
> >         ``V4L2_MEMORY_MMAP`` and ``format.type`` to the buffer type.
> >
> > -    * - __u32
> > +    * - __u8
> >        - ``flags``
> >        - Specifies additional buffer management attributes.
> >         See :ref:`memory-flags`.
> >
> > -    * - __u32
> > -      - ``reserved``\ [6]
> > +    * - __u8
> > +      - ``reserved``\ [27]
> >        - A place holder for future extensions. Drivers and applications
> >         must set the array to zero.
> >
> > diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > index 6edf4508c636..2ae949ec0afa 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > @@ -694,7 +694,7 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
> >
> >  static void validate_memory_flags(struct vb2_queue *q,
> >                                   int memory,
> > -                                 u32 *flags)
> > +                                 u8 *flags)
> >  {
> >         if (!q->allow_cache_hints || memory != V4L2_MEMORY_MMAP) {
> >                 /*
> > @@ -711,11 +711,9 @@ static void validate_memory_flags(struct vb2_queue *q,
> >  int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
> >  {
> >         int ret = vb2_verify_memory_type(q, req->memory, req->type);
> > -       u32 flags = req->flags;
> >
> >         fill_buf_caps(q, &req->capabilities);
> > -       validate_memory_flags(q, req->memory, &flags);
> > -       req->flags = flags;
> > +       validate_memory_flags(q, req->memory, &req->flags);
> >         return ret ? ret : vb2_core_reqbufs(q, req->memory,
> >                                             req->flags, &req->count);
> >  }
> > @@ -990,11 +988,9 @@ int vb2_ioctl_reqbufs(struct file *file, void *priv,
> >  {
> >         struct video_device *vdev = video_devdata(file);
> >         int res = vb2_verify_memory_type(vdev->queue, p->memory, p->type);
> > -       u32 flags = p->flags;
> >
> >         fill_buf_caps(vdev->queue, &p->capabilities);
> > -       validate_memory_flags(vdev->queue, p->memory, &flags);
> > -       p->flags = flags;
> > +       validate_memory_flags(vdev->queue, p->memory, &p->flags);
> >         if (res)
> >                 return res;
> >         if (vb2_queue_is_busy(vdev, file))
> > diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> > index 7973aa0465d2..ad4f7cee53f2 100644
> > --- a/include/uapi/linux/videodev2.h
> > +++ b/include/uapi/linux/videodev2.h
> > @@ -2513,8 +2513,8 @@ struct v4l2_create_buffers {
> >         __u32                   memory;
> >         struct v4l2_format      format;
> >         __u32                   capabilities;
> > -       __u32                   flags;
> > -       __u32                   reserved[6];
> > +       __u8                    flags;
> > +       __u8                    reserved[27];
> >  };
> >
> >  /*
> 
> I don't think we want this UABI churn anymore for a trivial
> simplification in the implementation.

OK, I can scratch it. I thought that for API symmetry we can have
::memory-flags of the same type/size in create-bufs and req-bufs,
but don't have any strong opinion on this.