Re: [PATCH v2 6/9] xen/gntdev: Add initial support for dma-buf UAPI
From: Oleksandr Andrushchenko
Date: Wed Jun 06 2018 - 05:06:12 EST
On 06/04/2018 11:49 PM, Boris Ostrovsky wrote:
On 06/01/2018 07:41 AM, Oleksandr Andrushchenko wrote:
From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
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.
I would also love to see their comments here ;)
Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
---
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?
One can use grant-table's DMA API without using dma-buf at all, e.g.
dma-buf is sort of functionality on top of DMA allocated memory.
We have a use-case for a driver domain (guest domain in fact)
backed with IOMMU and still requiring allocations created as
contiguous/DMA memory, so those buffers can be passed around to
drivers expecting DMA-only buffers.
So, IMO this is a valid use-case "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?
Just a copy-paste from gntdev, will change to usual /*..*/
+
+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.
Ok, will define what I have in the next patch, but won't
initialize anything until the next patch. Will this work for you?
+
+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.
The reason I have this code here is that it is heavily
tied to gntdev's internal functionality, e.g. map/unmap.
I do not want to extend gntdev's API, so gntdev-dmabuf can
access these. What is more dma-buf doesn't need to know about
maps done by gntdev as there is no use of that information
in gntdev-dmabuf. So, it seems more naturally to have
dma-buf's related map/unmap code where it is: in gntdev.
+/* ------------------------------------------------------------------ */
+/* 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.
Will remove the comment
-boris
+ *fd = -1;
+ return -EINVAL;
+}