Re: [PATCH v6 17/18] media: v4l2: Add DELETE_BUFS ioctl

[Benjamin Gaignard]

Le 05/09/2023 à 10:17, Hans Verkuil a écrit :
> On 01/09/2023 14:44, Benjamin Gaignard wrote:
> > VIDIOC_DELETE_BUFS ioctl allows to delete buffers from a queue.
> > The number of buffers to delete in given by count field of
> > struct v4l2_delete_buffers and the range start at the index
> > specified in the same structure.
> >
> > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxxxxx>
> > ---
> > v6:
> > - Add lock in vb2_core_delete_buf()
> > - Fix typo and comments
> > - Add flags in VIDIOC_DELETE_BUFS decalaration
> >
> >   .../userspace-api/media/v4l/user-func.rst     |  1 +
> >   .../media/v4l/vidioc-delete-bufs.rst          | 73 +++++++++++++++++++
> >   .../media/common/videobuf2/videobuf2-core.c   | 24 ++++++
> >   .../media/common/videobuf2/videobuf2-v4l2.c   | 38 +++++++++-
> >   drivers/media/v4l2-core/v4l2-dev.c            |  1 +
> >   drivers/media/v4l2-core/v4l2-ioctl.c          | 17 +++++
> >   include/media/v4l2-ioctl.h                    |  4 +
> >   include/media/videobuf2-core.h                |  9 +++
> >   include/media/videobuf2-v4l2.h                | 11 +++
> >   include/uapi/linux/videodev2.h                | 16 ++++
> >   10 files changed, 193 insertions(+), 1 deletion(-)
> >   create mode 100644 Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst
> >
> > diff --git a/Documentation/userspace-api/media/v4l/user-func.rst b/Documentation/userspace-api/media/v4l/user-func.rst
> > index 15ff0bf7bbe6..3fd567695477 100644
> > --- a/Documentation/userspace-api/media/v4l/user-func.rst
> > +++ b/Documentation/userspace-api/media/v4l/user-func.rst
> > @@ -17,6 +17,7 @@ Function Reference
> >       vidioc-dbg-g-chip-info
> >       vidioc-dbg-g-register
> >       vidioc-decoder-cmd
> > +    vidioc-delete-bufs
> >       vidioc-dqevent
> >       vidioc-dv-timings-cap
> >       vidioc-encoder-cmd
> > diff --git a/Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst b/Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst
> > new file mode 100644
> > index 000000000000..a55fe6331fc8
> > --- /dev/null
> > +++ b/Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst
> > @@ -0,0 +1,73 @@
> > +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
> > +.. c:namespace:: V4L
> > +
> > +.. _VIDIOC_DELETE_BUFS:
> > +
> > +************************
> > +ioctl VIDIOC_DELETE_BUFS
> > +************************
> > +
> > +Name
> > +====
> > +
> > +VIDIOC_DELETE_BUFS - Deletes buffers from a queue
> > +
> > +Synopsis
> > +========
> > +
> > +.. c:macro:: VIDIOC_DELETE_BUFs
> > +
> > +``int ioctl(int fd, VIDIOC_DELETE_BUFs, struct v4l2_delete_buffers *argp)``
> > +
> > +Arguments
> > +=========
> > +
> > +``fd``
> > +    File descriptor returned by :c:func:`open()`.
> > +
> > +``argp``
> > +    Pointer to struct :c:type:`v4l2_delete_buffers`.
> > +
> > +Description
> > +===========
> > +
> > +Applications can optionally call the :ref:`VIDIOC_DELETE_BUFS` ioctl to
> > +delete buffers from a queue.
> > +
> > +.. c:type:: v4l2_delete_buffers
> > +
> > +.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
> > +
> > +.. flat-table:: struct v4l2_delete_buffers
> > +    :header-rows:  0
> > +    :stub-columns: 0
> > +    :widths:       1 1 2
> > +
> > +    * - __u32
> > +      - ``index``
> > +      - The starting buffer index to delete.
> > +    * - __u32
> > +      - ``count``
> > +      - The number of buffers to be deleted.
> That's not quite correct. This function will delete the buffers with indices
> index until index+count-1. And indices in that range have to be valid buffers,
> i.e. you can't have already deleted buffers in that range.
>
> Or should we allow that? It is a fair question.
>
> All buffers also have to be in the DEQUEUED state.
>
> The text above suggests that given the following valid indices:
>
> 0, 1, 3, 4 (so the buffer with index 2 was already deleted)
>
> deleting 2 buffers from index 1 would delete buffers 1, 3. When in
> fact it will attempt to delete buffers 1 and 2.
>
> Also document explicitly that calling this with count=0 (and perhaps
> index=0 as well?) can be used to check if this ioctl is supported.

I will do that.

> > +    * - __u32
> > +      - ``type``
> > +      - Type of the stream or buffers, this is the same as the struct
> > +	:c:type:`v4l2_format` ``type`` field. See
> > +	:c:type:`v4l2_buf_type` for valid values.
> > +    * - __u32
> > +      - ``reserved``\ [13]
> > +      - A place holder for future extensions. Drivers and applications
> > +	must set the array to zero.
> What should happen if you delete ALL buffers with this call? I.e., the
> equivalent to REQBUFS with count=0.
>
> Thinking about this the main difference is that DELETE_BUFS can only delete
> dequeued buffers and it does not stop streaming if all buffers are deleted.
>
> So REQBUFS with count=0 (or a STREAMOFF) is still needed to officially stop
> streaming and cancel the queue.
>
> Basically REQBUFS with count=0 is almost the equivalent of calling STREAMOFF followed
> by DELETE_BUFS for all buffers. Almost, but not quite: REQBUFS(0) also reports
> if the queue is unbalanced, and it sets q->num_buffers to 0. And in vb2_ioctl_reqbufs
> it will set vdev->queue->owner to NULL.
>
> I am inclined to do the same if DELETE_BUFS deletes all buffers.

Unlike REQBUFS DELETE_BUFS can delete buffers while streaming so for me the ownership
should not change even if there is no more dequeued buffers.
For REQBUFS with count=0 means that the going stream is stopped so we can delete all the buffers
while DELETE_BUFS usage is to delete buffers while keeping the stream alive.

> > +
> > +Return Value
> > +============
> > +
> > +On success 0 is returned, on error -1 and the ``errno`` variable is set
> > +appropriately. The generic error codes are described at the
> > +:ref:`Generic Error Codes <gen-errors>` chapter.
> > +
> > +EBUSY
> > +    File I/O is in progress.
> > +
> > +EINVAL
> > +    The buffer ``index`` doesn't exist in the queue.
> > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> > index dc7f6b59d237..9edb2a1e95fc 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-core.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> > @@ -1633,6 +1633,30 @@ int vb2_core_prepare_buf(struct vb2_queue *q, struct vb2_buffer *vb, void *pb)
> >   }
> >   EXPORT_SYMBOL_GPL(vb2_core_prepare_buf);
> >   
> > +int vb2_core_delete_buf(struct vb2_queue *q, struct vb2_buffer *vb)
> > +{
> > +	mutex_lock(&q->mmap_lock);
> > +	if (vb->planes[0].mem_priv)
> > +		call_void_vb_qop(vb, buf_cleanup, vb);
> > +
> > +	/* Free MMAP buffers or release USERPTR buffers */
> > +	if (q->memory == VB2_MEMORY_MMAP)
> > +		__vb2_buf_mem_free(vb);
> > +	else if (q->memory == VB2_MEMORY_DMABUF)
> > +		__vb2_buf_dmabuf_put(vb);
> > +	else
> > +		__vb2_buf_userptr_put(vb);
> > +
> > +	vb2_queue_remove_buffer(q, vb);
> > +	mutex_unlock(&q->mmap_lock);
> > +
> > +	dprintk(q, 2, "buffer %d deleted\n", vb->index);
> > +	kfree(vb);
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(vb2_core_delete_buf);
> This is duplicating what already happens in __vb2_free_mem and __vb2_queue_free.
>
> That code needs to be refactored.
>
> What you want is a __vb2_delete_buffers(struct vb2_queue *q, unsigned int index, unsigned int buffers)
> function that is called with mmap_lock held and that deletes buffers in the range 'index'
> to 'index + count - 1'. Buffers may already be deleted.
>
> __vb2_free_mem does almost do all of that already.
>
> Then this new function can be called from __vb2_queue_free() and you can make
> a vb2_core_delete_bufs() function that takes the lock and calls __vb2_delete_buffers.
>
> Another note: currently __vb2_queue_free checks if any of the buffers had unbalanced
> operations. That check needs to be moved to __vb2_delete_buffers as well otherwise
> that would never be reported when using DELETE_BUFS.

Loops in __vb2_queue_free() and __vb2_free_mem() try to delete buffers at the end of the
queue, I could just modify these functions prototype and loops to start from a given index.
That should do the job but have impact on create_bufs (see below)

> > +
> >   /*
> >    * vb2_start_streaming() - Attempt to start streaming.
> >    * @q:		videobuf2 queue
> > diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > index 8ba658ad9891..d0098f58a65c 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > @@ -385,7 +385,7 @@ static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct media_device *md
> >   
> >   	vb = vb2_get_buffer(q, b->index);
> >   	if (!vb) {
> > -		dprintk(q, 1, "%s: buffer is NULL\n", opname);
> > +		dprintk(q, 1, "%s: buffer %u was deleted\n", opname, b->index);
> >   		return -EINVAL;
> >   	}
> >   
> > @@ -757,6 +757,42 @@ int vb2_prepare_buf(struct vb2_queue *q, struct media_device *mdev,
> >   }
> >   EXPORT_SYMBOL_GPL(vb2_prepare_buf);
> >   
> > +int vb2_delete_bufs(struct vb2_queue *q, struct v4l2_delete_buffers *d)
> > +{
> > +	struct vb2_buffer *vb;
> > +	unsigned int index;
> > +	int ret = 0;
> > +
> Add:
>
> 	if (!d->count)
> 		return 0;
>
> (possibly also check if !d->index)
>
> > +	if (d->index > q->num_buffers ||
> > should be >= here.
> > +	    d->count > q->num_buffers ||
> > +	    (d->index + d->count) > q->num_buffers) {
> > +		return -EINVAL;
> > +	}
> Once we can delete buffers, how does that change the meaning of num_buffers?
> Isn't this really max_buffer_index or something similar? But we probably also
> still need to keep track of the actual number of buffers.
>
> And create_bufs still allocated buffers from the last index onwards, it does
> not attempt to reuse indices of previously deleted buffers.

Reuse previous indices require to be sure that a range of index is free because
create_bufs returns, in index parameter, the starting buffer index.
I will add a function to find the first available range and use it in vb2_create_bufs()
to change how create->index is set.
Hans, sound good for you ?

> There are a lot of drivers that use num_buffers, they will have to be audited.
>
> This needs a lot more thought.
>
> > +
> > +	for (index = d->index; index < d->index + d->count; index++) {
> > +		vb = vb2_get_buffer(q, index);
> > +		if (!vb) {
> > +			dprintk(q, 1, "can't find the requested buffer\n");
> > +			ret = -EINVAL;
> > +			goto error;
> > +		}
> > +		if (vb->state != VB2_BUF_STATE_DEQUEUED) {
> > +			dprintk(q, 1, "can't delete non dequeued buffer index %d\n", vb->index);
> > +			ret = -EINVAL;
> > +			goto error;
> > +		}
> These checks have to take place first, then, if all is OK, you call vb2_core_delete_bufs.
>
> Actually, thinking this over, I would move all these checks to vb2_core_delete_bufs.
>
> It can all be put under the mmap_lock mutex to ensure nobody is messing around
> with the queue while this takes place.
>
> Note that when vb2_core_reqbufs() is called with count=0, then if it sees that
> a buffer is still in use (mmaped), it will log a debug message that the buffers
> are orphaned. We should keep that, I believe.
>
> > +
> > +		ret = vb2_core_delete_buf(q, vb);
> > +		if (ret)
> > +			break;
> > +	}
> > +
> > +error:
> > +	d->index = index;
> I wouldn't do this. I don't think this is useful.
>
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(vb2_delete_bufs);
> > +
> >   int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
> >   {
> >   	unsigned requested_planes = 1;
> > diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
> > index f81279492682..215654fd6581 100644
> > --- a/drivers/media/v4l2-core/v4l2-dev.c
> > +++ b/drivers/media/v4l2-core/v4l2-dev.c
> > @@ -720,6 +720,7 @@ static void determine_valid_ioctls(struct video_device *vdev)
> >   		SET_VALID_IOCTL(ops, VIDIOC_PREPARE_BUF, vidioc_prepare_buf);
> >   		SET_VALID_IOCTL(ops, VIDIOC_STREAMON, vidioc_streamon);
> >   		SET_VALID_IOCTL(ops, VIDIOC_STREAMOFF, vidioc_streamoff);
> > +		SET_VALID_IOCTL(ops, VIDIOC_DELETE_BUFS, vidioc_delete_bufs);
> >   	}
> >   
> >   	if (is_vid || is_vbi || is_meta) {
> > diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> > index f4d9d6279094..aac3a0ea0126 100644
> > --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> > +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> > @@ -489,6 +489,13 @@ static void v4l_print_create_buffers(const void *arg, bool write_only)
> >   	v4l_print_format(&p->format, write_only);
> >   }
> >   
> > +static void v4l_print_delete_buffers(const void *arg, bool write_only)
> > +{
> > +	const struct v4l2_delete_buffers *p = arg;
> > +
> > +	pr_cont("index=%d, count=%d\n", p->index, p->count);
> Use %u since both args are unsigned.
>
> > +}
> > +
> >   static void v4l_print_streamparm(const void *arg, bool write_only)
> >   {
> >   	const struct v4l2_streamparm *p = arg;
> > @@ -2160,6 +2167,15 @@ static int v4l_prepare_buf(const struct v4l2_ioctl_ops *ops,
> >   	return ret ? ret : ops->vidioc_prepare_buf(file, fh, b);
> >   }
> >   
> > +static int v4l_delete_bufs(const struct v4l2_ioctl_ops *ops,
> > +			   struct file *file, void *fh, void *arg)
> > +{
> > +	struct v4l2_delete_buffers *delete = arg;
> > +	int ret = check_fmt(file, delete->type);
> > +
> > +	return ret ? ret : ops->vidioc_delete_bufs(file, fh, delete);
> > +}
> > +
> >   static int v4l_g_parm(const struct v4l2_ioctl_ops *ops,
> >   				struct file *file, void *fh, void *arg)
> >   {
> > @@ -2909,6 +2925,7 @@ static const struct v4l2_ioctl_info v4l2_ioctls[] = {
> >   	IOCTL_INFO(VIDIOC_ENUM_FREQ_BANDS, v4l_enum_freq_bands, v4l_print_freq_band, 0),
> >   	IOCTL_INFO(VIDIOC_DBG_G_CHIP_INFO, v4l_dbg_g_chip_info, v4l_print_dbg_chip_info, INFO_FL_CLEAR(v4l2_dbg_chip_info, match)),
> >   	IOCTL_INFO(VIDIOC_QUERY_EXT_CTRL, v4l_query_ext_ctrl, v4l_print_query_ext_ctrl, INFO_FL_CTRL | INFO_FL_CLEAR(v4l2_query_ext_ctrl, id)),
> > +	IOCTL_INFO(VIDIOC_DELETE_BUFS, v4l_delete_bufs, v4l_print_delete_buffers, INFO_FL_PRIO | INFO_FL_QUEUE | INFO_FL_CLEAR(v4l2_delete_buffers, type)),
> >   };
> >   #define V4L2_IOCTLS ARRAY_SIZE(v4l2_ioctls)
> >   
> > diff --git a/include/media/v4l2-ioctl.h b/include/media/v4l2-ioctl.h
> > index edb733f21604..55afbde54211 100644
> > --- a/include/media/v4l2-ioctl.h
> > +++ b/include/media/v4l2-ioctl.h
> > @@ -163,6 +163,8 @@ struct v4l2_fh;
> >    *	:ref:`VIDIOC_CREATE_BUFS <vidioc_create_bufs>` ioctl
> >    * @vidioc_prepare_buf: pointer to the function that implements
> >    *	:ref:`VIDIOC_PREPARE_BUF <vidioc_prepare_buf>` ioctl
> > + * @vidioc_delete_bufs: pointer to the function that implements
> > + *	:ref:`VIDIOC_DELETE_BUFS <vidioc_delete_bufs>` ioctl
> >    * @vidioc_overlay: pointer to the function that implements
> >    *	:ref:`VIDIOC_OVERLAY <vidioc_overlay>` ioctl
> >    * @vidioc_g_fbuf: pointer to the function that implements
> > @@ -422,6 +424,8 @@ struct v4l2_ioctl_ops {
> >   				  struct v4l2_create_buffers *b);
> >   	int (*vidioc_prepare_buf)(struct file *file, void *fh,
> >   				  struct v4l2_buffer *b);
> > +	int (*vidioc_delete_bufs)(struct file *file, void *fh,
> > +				  struct v4l2_delete_buffers *d);
> >   
> >   	int (*vidioc_overlay)(struct file *file, void *fh, unsigned int i);
> >   	int (*vidioc_g_fbuf)(struct file *file, void *fh,
> > diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> > index 97153c69583f..e2c5ff31efd0 100644
> > --- a/include/media/videobuf2-core.h
> > +++ b/include/media/videobuf2-core.h
> > @@ -843,6 +843,15 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
> >    */
> >   int vb2_core_prepare_buf(struct vb2_queue *q, struct vb2_buffer *vb, void *pb);
> >   
> > +/**
> > + * vb2_core_delete_buf() -
> > + * @q: pointer to &struct vb2_queue with videobuf2 queue.
> > + * @vb:		pointer to struct &vb2_buffer.
> > + *
> > + *  Return: returns zero on success; an error code otherwise.
> > + */
> > +int vb2_core_delete_buf(struct vb2_queue *q, struct vb2_buffer *vb);
> > +
> >   /**
> >    * vb2_core_qbuf() - Queue a buffer from userspace
> >    *
> > diff --git a/include/media/videobuf2-v4l2.h b/include/media/videobuf2-v4l2.h
> > index 5a845887850b..2ef68fdf388f 100644
> > --- a/include/media/videobuf2-v4l2.h
> > +++ b/include/media/videobuf2-v4l2.h
> > @@ -118,6 +118,17 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create);
> >    */
> >   int vb2_prepare_buf(struct vb2_queue *q, struct media_device *mdev,
> >   		    struct v4l2_buffer *b);
> > +/**
> > + * vb2_delete_bufs() - Delete buffers from the queue
> > + *
> > + * @q:		pointer to &struct vb2_queue with videobuf2 queue.
> > + * @d:		delete parameter, passed from userspace to
> > + *		&v4l2_ioctl_ops->vidioc_delete_bufs handler in driver
> > + *
> > + * The return values from this function are intended to be directly returned
> > + * from &v4l2_ioctl_ops->vidioc_delete_bufs handler in driver.
> > + */
> > +int vb2_delete_bufs(struct vb2_queue *q, struct v4l2_delete_buffers *d);
> I'm missing the vb2_ioctl_delete_bufs function with a call to vb2_queue_is_busy().
>
> >   
> >   /**
> >    * vb2_qbuf() - Queue a buffer from userspace
> > diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> > index 78260e5d9985..9cc7f570d995 100644
> > --- a/include/uapi/linux/videodev2.h
> > +++ b/include/uapi/linux/videodev2.h
> > @@ -2616,6 +2616,20 @@ struct v4l2_create_buffers {
> >   	__u32			reserved[6];
> >   };
> >   
> > +/**
> > + * struct v4l2_delete_buffers - VIDIOC_DELETE_BUFS argument
> > + * @index:	the first buffer to be deleted
> > + * @count:	number of buffers to delete
> > + * @type:	enum v4l2_buf_type
> > + * @reserved:	future extensions
> > + */
> > +struct v4l2_delete_buffers {
> > +	__u32			index;
> > +	__u32			count;
> > +	__u32			type;
> > +	__u32			reserved[13];
> > +};
> > +
> >   /*
> >    *	I O C T L   C O D E S   F O R   V I D E O   D E V I C E S
> >    *
> > @@ -2715,6 +2729,8 @@ struct v4l2_create_buffers {
> >   #define VIDIOC_DBG_G_CHIP_INFO  _IOWR('V', 102, struct v4l2_dbg_chip_info)
> >   
> >   #define VIDIOC_QUERY_EXT_CTRL	_IOWR('V', 103, struct v4l2_query_ext_ctrl)
> > +#define VIDIOC_DELETE_BUFS	_IOWR('V', 104, struct v4l2_delete_buffers)
> > +
> >   
> >   /* Reminder: when adding new ioctls please add support for them to
> >      drivers/media/v4l2-core/v4l2-compat-ioctl32.c as well! */
> You need much more extensive compliance checks for this, esp. mixing
> create_bufs and delete_bufs. And test it with the test-media test script.
>
> Regards,
>
> 	Hans