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Subject: Re: [RFC 4/6] dma-buf: Add DMA-BUF exporter op to charge a DMA-BUF to
 a cgroup.
To:     Hridya Valsaraju <hridya@google.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
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Cc:     Kenny.Ho@amd.com, daniels@collabora.com, kaleshsingh@google.com,
        tjmercier@google.com
References: <20220115010622.3185921-1-hridya@google.com>
 <20220115010622.3185921-5-hridya@google.com>
From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
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Date:   Mon, 17 Jan 2022 08:46:16 +0100
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Am 15.01.22 um 02:06 schrieb Hridya Valsaraju:
> The optional exporter op provides a way for processes to transfer
> charge of a buffer to a different process. This is essential for the
> cases where a central allocator process does allocations for various
> subsystems, hands over the fd to the client who
> requested the memory and drops all references to the allocated memory.
>
> Signed-off-by: Hridya Valsaraju <hridya@google.com>
> ---
>   include/linux/dma-buf.h | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)
>
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index 7ab50076e7a6..d5e52f81cc6f 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -13,6 +13,7 @@
>   #ifndef __DMA_BUF_H__
>   #define __DMA_BUF_H__
>   
> +#include <linux/cgroup_gpu.h>
>   #include <linux/dma-buf-map.h>
>   #include <linux/file.h>
>   #include <linux/err.h>
> @@ -285,6 +286,23 @@ struct dma_buf_ops {
>   
>   	int (*vmap)(struct dma_buf *dmabuf, struct dma_buf_map *map);
>   	void (*vunmap)(struct dma_buf *dmabuf, struct dma_buf_map *map);
> +
> +	/**
> +	 * @charge_to_cgroup:
> +	 *
> +	 * This is called by an exporter to charge a buffer to the specified
> +	 * cgroup.

Well that sentence makes absolutely no sense at all.

The dma_buf_ops are supposed to be called by the DMA-buf subsystem on 
behalves of the importer and never by the exporter itself.

I hope that this is just a documentation mixup.

Regards,
Christian.

>   The caller must hold a reference to @gpucg obtained via
> +	 * gpucg_get(). The DMA-BUF will be uncharged from the cgroup it is
> +	 * currently charged to before being charged to @gpucg. The caller must
> +	 * belong to the cgroup the buffer is currently charged to.
> +	 *
> +	 * This callback is optional.
> +	 *
> +	 * Returns:
> +	 *
> +	 * 0 on success or negative error code on failure.
> +	 */
> +	int (*charge_to_cgroup)(struct dma_buf *dmabuf, struct gpucg *gpucg);
>   };
>   
>   /**