On Mon, May 30, 2022 at 09:09:30AM +0200, Christian König wrote:
Am 27.05.22 um 09:34 schrieb Simon Ser:
To discover support for new DMA-BUF IOCTLs, user-space has no choice but to try to perform the IOCTL on an existing DMA-BUF. However, user-space may want to figure out whether or not the IOCTL is available before it has a DMA-BUF at hand, e.g. at initialization time in a Wayland compositor.
Add a /sys/kernel/dmabuf/caps directory which allows the DMA-BUF subsystem to advertise supported features. Add a sync_file_import_export entry which indicates that importing and exporting sync_files from/to DMA-BUFs is supported.
I find a separate directory rather unusual, but can't come up with any better idea either.
IIRC the security module had a mask file with names for the supported capabilities.
v2: Add missing files lost in a rebase
v3:
- Create separate file in Documentation/ABI/testing/, add it to MAINTAINERS
- Fix kernel version (Daniel)
- Remove unnecessary brackets (Jason)
- Fix SPDX comment style
Signed-off-by: Simon Ser contact@emersion.fr Reviewed-by: Jason Ekstrand jason.ekstrand@collabora.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Bas Nieuwenhuizen bas@basnieuwenhuizen.nl Cc: Christian König christian.koenig@amd.com Cc: Greg KH greg@kroah.com
.../ABI/testing/sysfs-kernel-dmabuf-caps | 13 +++++ MAINTAINERS | 1 + drivers/dma-buf/Makefile | 2 +- drivers/dma-buf/dma-buf-sysfs-caps.c | 51 +++++++++++++++++++ drivers/dma-buf/dma-buf-sysfs-caps.h | 16 ++++++ drivers/dma-buf/dma-buf-sysfs-stats.c | 16 ++---- drivers/dma-buf/dma-buf-sysfs-stats.h | 6 ++- drivers/dma-buf/dma-buf.c | 43 ++++++++++++++-- include/uapi/linux/dma-buf.h | 6 +++ 9 files changed, 134 insertions(+), 20 deletions(-) create mode 100644 Documentation/ABI/testing/sysfs-kernel-dmabuf-caps create mode 100644 drivers/dma-buf/dma-buf-sysfs-caps.c create mode 100644 drivers/dma-buf/dma-buf-sysfs-caps.h
diff --git a/Documentation/ABI/testing/sysfs-kernel-dmabuf-caps b/Documentation/ABI/testing/sysfs-kernel-dmabuf-caps new file mode 100644 index 000000000000..f83af422fd18 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-kernel-dmabuf-caps @@ -0,0 +1,13 @@ +What: /sys/kernel/dmabuf/caps +Date: May 2022 +KernelVersion: v5.20 +Contact: Simon Ser contact@emersion.fr +Description: This directory advertises DMA-BUF capabilities supported by the
kernel.+What: /sys/kernel/dmabuf/caps/sync_file_import_export +Date: May 2022 +KernelVersion: v5.20 +Contact: Simon Ser contact@emersion.fr +Description: This file is read-only and advertises support for importing and
exporting sync_files from/to DMA-BUFs.diff --git a/MAINTAINERS b/MAINTAINERS index 11da16bfa123..8966686f7231 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -5871,6 +5871,7 @@ L: dri-devel@lists.freedesktop.org L: linaro-mm-sig@lists.linaro.org (moderated for non-subscribers) S: Maintained T: git git://anongit.freedesktop.org/drm/drm-misc +F: Documentation/ABI/testing/sysfs-kernel-dmabuf-caps F: Documentation/driver-api/dma-buf.rst F: drivers/dma-buf/ F: include/linux/*fence.h diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile index 4c9eb53ba3f8..afc874272710 100644 --- a/drivers/dma-buf/Makefile +++ b/drivers/dma-buf/Makefile @@ -1,6 +1,6 @@ # SPDX-License-Identifier: GPL-2.0-only obj-y := dma-buf.o dma-fence.o dma-fence-array.o dma-fence-chain.o \
dma-resv.o
dma-resv.o dma-buf-sysfs-caps.odiff --git a/drivers/dma-buf/dma-buf-sysfs-caps.c b/drivers/dma-buf/dma-buf-sysfs-caps.c new file mode 100644 index 000000000000..82b91eb874a9 --- /dev/null +++ b/drivers/dma-buf/dma-buf-sysfs-caps.c @@ -0,0 +1,51 @@ +// SPDX-License-Identifier: GPL-2.0-only +/*
- DMA-BUF sysfs capabilities.
- Copyright (C) 2022 Simon Ser
- */
+#include <linux/kobject.h> +#include <linux/sysfs.h>
+#include "dma-buf-sysfs-caps.h"
+static ssize_t sync_file_import_export_show(struct kobject *kobj,
struct kobj_attribute *attr,char *buf)+{
- return sysfs_emit(buf, "1\n");
+}
+static struct kobj_attribute dma_buf_sync_file_import_export_attr =
- __ATTR_RO(sync_file_import_export);
+static struct attribute *dma_buf_caps_attrs[] = {
- &dma_buf_sync_file_import_export_attr.attr,
- NULL,
+};
+static const struct attribute_group dma_buf_caps_attr_group = {
- .attrs = dma_buf_caps_attrs,
+};
Didn't we had macros for those? I think I have seen something for that.
Yes, please use ATTRIBUTE_GROUPS()
+static struct kobject *dma_buf_caps_kobj;
+int dma_buf_init_sysfs_capabilities(struct kset *kset) +{
- int ret;
- dma_buf_caps_kobj = kobject_create_and_add("caps", &kset->kobj);
- if (!dma_buf_caps_kobj)
return -ENOMEM;- ret = sysfs_create_group(dma_buf_caps_kobj, &dma_buf_caps_attr_group);
Why do we have "raw" kobjects here?
A group can have a name, which puts it in the subdirectory of the object it is attached to. Please do that and do not create a new kobject.
thanks,
greg k-h