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Subject: Re: [PATCH v2 6/9] xen/gntdev: Add initial support for dma-buf UAPI
To:     Oleksandr Andrushchenko <andr2000@gmail.com>,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org,
        jgross@suse.com, konrad.wilk@oracle.com
Cc:     daniel.vetter@intel.com, dongwon.kim@intel.com,
        matthew.d.roper@intel.com,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
References: <20180601114132.22596-1-andr2000@gmail.com>
 <20180601114132.22596-7-andr2000@gmail.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Date:   Mon, 4 Jun 2018 16:49:58 -0400
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On 06/01/2018 07:41 AM, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>
> Add UAPI and IOCTLs for dma-buf grant device driver extension:
> the extension allows userspace processes and kernel modules to
> use Xen backed dma-buf implementation. With this extension grant
> references to the pages of an imported dma-buf can be exported
> for other domain use and grant references coming from a foreign
> domain can be converted into a local dma-buf for local export.
> Implement basic initialization and stubs for Xen DMA buffers'
> support.


It would be very helpful if people advocating for this interface
reviewed it as well.


>
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> ---
>  drivers/xen/Kconfig         |  10 +++
>  drivers/xen/Makefile        |   1 +
>  drivers/xen/gntdev-dmabuf.c |  75 +++++++++++++++++++
>  drivers/xen/gntdev-dmabuf.h |  41 +++++++++++
>  drivers/xen/gntdev.c        | 142 ++++++++++++++++++++++++++++++++++++
>  include/uapi/xen/gntdev.h   |  91 +++++++++++++++++++++++
>  6 files changed, 360 insertions(+)
>  create mode 100644 drivers/xen/gntdev-dmabuf.c
>  create mode 100644 drivers/xen/gntdev-dmabuf.h
>
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index 39536ddfbce4..52d64e4b6b81 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -152,6 +152,16 @@ config XEN_GNTDEV
>  	help
>  	  Allows userspace processes to use grants.
>  
> +config XEN_GNTDEV_DMABUF
> +	bool "Add support for dma-buf grant access device driver extension"
> +	depends on XEN_GNTDEV && XEN_GRANT_DMA_ALLOC && DMA_SHARED_BUFFER


Is there a reason to have XEN_GRANT_DMA_ALLOC without XEN_GNTDEV_DMABUF?


> +	help
> +	  Allows userspace processes and kernel modules to use Xen backed
> +	  dma-buf implementation. With this extension grant references to
> +	  the pages of an imported dma-buf can be exported for other domain
> +	  use and grant references coming from a foreign domain can be
> +	  converted into a local dma-buf for local export.
> +
>  config XEN_GRANT_DEV_ALLOC
>  	tristate "User-space grant reference allocator driver"
>  	depends on XEN
> diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
> index 3c87b0c3aca6..33afb7b2b227 100644
> --- a/drivers/xen/Makefile
> +++ b/drivers/xen/Makefile
> @@ -41,5 +41,6 @@ obj-$(CONFIG_XEN_PVCALLS_BACKEND)	+= pvcalls-back.o
>  obj-$(CONFIG_XEN_PVCALLS_FRONTEND)	+= pvcalls-front.o
>  xen-evtchn-y				:= evtchn.o
>  xen-gntdev-y				:= gntdev.o
> +xen-gntdev-$(CONFIG_XEN_GNTDEV_DMABUF)	+= gntdev-dmabuf.o
>  xen-gntalloc-y				:= gntalloc.o
>  xen-privcmd-y				:= privcmd.o
> diff --git a/drivers/xen/gntdev-dmabuf.c b/drivers/xen/gntdev-dmabuf.c
> new file mode 100644
> index 000000000000..6bedd1387bd9
> --- /dev/null
> +++ b/drivers/xen/gntdev-dmabuf.c
> @@ -0,0 +1,75 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Xen dma-buf functionality for gntdev.
> + *
> + * Copyright (c) 2018 Oleksandr Andrushchenko, EPAM Systems Inc.
> + */
> +
> +#include <linux/slab.h>
> +
> +#include "gntdev-dmabuf.h"
> +
> +struct gntdev_dmabuf_priv {
> +	int dummy;
> +};
> +
> +/* ------------------------------------------------------------------ */
> +/* DMA buffer export support.                                         */
> +/* ------------------------------------------------------------------ */
> +
> +/* ------------------------------------------------------------------ */
> +/* Implementation of wait for exported DMA buffer to be released.     */
> +/* ------------------------------------------------------------------ */

Why this comment style?

> +
> +int gntdev_dmabuf_exp_wait_released(struct gntdev_dmabuf_priv *priv, int fd,
> +				    int wait_to_ms)
> +{
> +	return -EINVAL;
> +}
> +
> +/* ------------------------------------------------------------------ */
> +/* DMA buffer export support.                                         */
> +/* ------------------------------------------------------------------ */
> +
> +int gntdev_dmabuf_exp_from_pages(struct gntdev_dmabuf_export_args *args)
> +{
> +	return -EINVAL;
> +}
> +
> +/* ------------------------------------------------------------------ */
> +/* DMA buffer import support.                                         */
> +/* ------------------------------------------------------------------ */
> +
> +struct gntdev_dmabuf *
> +gntdev_dmabuf_imp_to_refs(struct gntdev_dmabuf_priv *priv, struct device *dev,
> +			  int fd, int count, int domid)
> +{
> +	return ERR_PTR(-ENOMEM);
> +}
> +
> +u32 *gntdev_dmabuf_imp_get_refs(struct gntdev_dmabuf *gntdev_dmabuf)
> +{
> +	return NULL;
> +}
> +
> +int gntdev_dmabuf_imp_release(struct gntdev_dmabuf_priv *priv, u32 fd)
> +{
> +	return -EINVAL;
> +}
> +
> +struct gntdev_dmabuf_priv *gntdev_dmabuf_init(void)
> +{
> +	struct gntdev_dmabuf_priv *priv;
> +
> +	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return ERR_PTR(-ENOMEM);
> +
> +	return priv;
> +}
> +
> +void gntdev_dmabuf_fini(struct gntdev_dmabuf_priv *priv)
> +{
> +	kfree(priv);
> +}
> diff --git a/drivers/xen/gntdev-dmabuf.h b/drivers/xen/gntdev-dmabuf.h
> new file mode 100644
> index 000000000000..040b2de904ac
> --- /dev/null
> +++ b/drivers/xen/gntdev-dmabuf.h
> @@ -0,0 +1,41 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * Xen dma-buf functionality for gntdev.
> + *
> + * Copyright (c) 2018 Oleksandr Andrushchenko, EPAM Systems Inc.
> + */
> +
> +#ifndef _GNTDEV_DMABUF_H
> +#define _GNTDEV_DMABUF_H
> +
> +#include <linux/kernel.h>
> +#include <linux/errno.h>
> +#include <linux/types.h>
> +
> +struct gntdev_dmabuf_priv;
> +struct gntdev_dmabuf;
> +struct device;
> +
> +struct gntdev_dmabuf_export_args {
> +	int dummy;
> +};


Please define the full structure (at least what you have in the next
patch) here.


> +
> +struct gntdev_dmabuf_priv *gntdev_dmabuf_init(void);
> +
> +void gntdev_dmabuf_fini(struct gntdev_dmabuf_priv *priv);
> +
> +int gntdev_dmabuf_exp_from_pages(struct gntdev_dmabuf_export_args *args);
> +
> +int gntdev_dmabuf_exp_wait_released(struct gntdev_dmabuf_priv *priv, int fd,
> +				    int wait_to_ms);
> +
> +struct gntdev_dmabuf *
> +gntdev_dmabuf_imp_to_refs(struct gntdev_dmabuf_priv *priv, struct device *dev,
> +			  int fd, int count, int domid);
> +
> +u32 *gntdev_dmabuf_imp_get_refs(struct gntdev_dmabuf *gntdev_dmabuf);
> +
> +int gntdev_dmabuf_imp_release(struct gntdev_dmabuf_priv *priv, u32 fd);
> +
> +#endif
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index 9813fc440c70..7d58dfb3e5e8 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c

...

>  
> +#ifdef CONFIG_XEN_GNTDEV_DMABUF

This code belongs in gntdev-dmabuf.c.

> +/* ------------------------------------------------------------------ */
> +/* DMA buffer export support.                                         */
> +/* ------------------------------------------------------------------ */
> +
> +int gntdev_dmabuf_exp_from_refs(struct gntdev_priv *priv, int flags,
> +				int count, u32 domid, u32 *refs, u32 *fd)
> +{
> +	/* XXX: this will need to work with gntdev's map, so leave it here. */

This doesn't help understanding what's going on (at least to me) and is
removed in the next patch. So no need for this comment.

-boris

> +	*fd = -1;
> +	return -EINVAL;
> +}