Re: [PATCHv13 04/28] media-request: add media_request_get_by_fd

[Mauro Carvalho Chehab <mchehab+samsung@kernel.org>]

Em Thu,  3 May 2018 16:52:54 +0200
Hans Verkuil <hverkuil@xs4all.nl> escreveu:

> From: Hans Verkuil <hans.verkuil@cisco.com>
> 
> Add media_request_get_by_fd() to find a request based on the file
> descriptor.
> 
> The caller has to call media_request_put() for the returned
> request since this function increments the refcount.
> 
> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
> ---
>  drivers/media/media-request.c | 32 ++++++++++++++++++++++++++++++++
>  include/media/media-request.h | 24 ++++++++++++++++++++++++
>  2 files changed, 56 insertions(+)
> 
> diff --git a/drivers/media/media-request.c b/drivers/media/media-request.c
> index c216c4ab628b..edc1c3af1959 100644
> --- a/drivers/media/media-request.c
> +++ b/drivers/media/media-request.c
> @@ -218,6 +218,38 @@ static const struct file_operations request_fops = {
>  	.release = media_request_close,
>  };
>  
> +struct media_request *
> +media_request_get_by_fd(struct media_device *mdev, int request_fd)
> +{
> +	struct file *filp;
> +	struct media_request *req;
> +
> +	if (!mdev || !mdev->ops ||
> +	    !mdev->ops->req_validate || !mdev->ops->req_queue)
> +		return ERR_PTR(-EPERM);
> +
> +	filp = fget(request_fd);
> +	if (!filp)
> +		return ERR_PTR(-ENOENT);
> +
> +	if (filp->f_op != &request_fops)
> +		goto err_fput;
> +	req = filp->private_data;
> +	if (req->mdev != mdev)
> +		goto err_fput;
> +
> +	media_request_get(req);

Hmm... this function changes the req struct (by calling kref_get) without
holding neither the mutex or the spin lock...

> +	fput(filp);
> +
> +	return req;
> +
> +err_fput:
> +	fput(filp);
> +
> +	return ERR_PTR(-ENOENT);
> +}
> +EXPORT_SYMBOL_GPL(media_request_get_by_fd);
> +
>  int media_request_alloc(struct media_device *mdev,
>  			struct media_request_alloc *alloc)
>  {
> diff --git a/include/media/media-request.h b/include/media/media-request.h
> index e39122dfd717..997e096d7128 100644
> --- a/include/media/media-request.h
> +++ b/include/media/media-request.h
> @@ -86,6 +86,24 @@ static inline void media_request_get(struct media_request *req)
>   */
>  void media_request_put(struct media_request *req);
>  
> +/**
> + * media_request_get_by_fd - Get a media request by fd
> + *
> + * @mdev: Media device this request belongs to
> + * @request_fd: The file descriptor of the request
> + *
> + * Get the request represented by @request_fd that is owned
> + * by the media device.
> + *
> + * Return a -EPERM error pointer if requests are not supported
> + * by this driver. Return -ENOENT if the request was not found.
> + * Return the pointer to the request if found: the caller will
> + * have to call @media_request_put when it finished using the
> + * request.

... so, it should be said here how this should be serialized, in order
to avoid it to be destroyed by a task while some other task might be
trying to instantiate it.

> + */
> +struct media_request *
> +media_request_get_by_fd(struct media_device *mdev, int request_fd);
> +
>  /**
>   * media_request_alloc - Allocate the media request
>   *
> @@ -107,6 +125,12 @@ static inline void media_request_put(struct media_request *req)
>  {
>  }
>  
> +static inline struct media_request *
> +media_request_get_by_fd(struct media_device *mdev, int request_fd)
> +{
> +	return ERR_PTR(-EPERM);
> +}
> +
>  #endif
>  
>  /**



Thanks,
Mauro