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.
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
v4: improve sysfs code (Greg)
Signed-off-by: Simon Ser <contact@xxxxxxxxxxx>
Reviewed-by: Jason Ekstrand <jason.ekstrand@xxxxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Bas Nieuwenhuizen <bas@xxxxxxxxxxxxxxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Greg KH <greg@xxxxxxxxx>
---
.../ABI/testing/sysfs-kernel-dmabuf-caps | 13 ++++++
MAINTAINERS | 1 +
drivers/dma-buf/Makefile | 2 +-
drivers/dma-buf/dma-buf-sysfs-caps.c | 31 +++++++++++++
drivers/dma-buf/dma-buf-sysfs-caps.h | 15 +++++++
drivers/dma-buf/dma-buf-sysfs-stats.c | 16 ++-----
drivers/dma-buf/dma-buf-sysfs-stats.h | 6 ++-
drivers/dma-buf/dma-buf.c | 45 +++++++++++++++++--
include/uapi/linux/dma-buf.h | 6 +++
9 files changed, 115 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@xxxxxxxxxxx>
+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@xxxxxxxxxxx>
+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@xxxxxxxxxxxxxxxxxxxxx
L: linaro-mm-sig@xxxxxxxxxxxxxxxx (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.o
obj-$(CONFIG_DMABUF_HEAPS) += dma-heap.o
obj-$(CONFIG_DMABUF_HEAPS) += heaps/
obj-$(CONFIG_SYNC_FILE) += sync_file.o
diff --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..6eb27b81469f
--- /dev/null
+++ b/drivers/dma-buf/dma-buf-sysfs-caps.c
@@ -0,0 +1,31 @@
+// 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,
+};
+
+const struct attribute_group dma_buf_caps_group = {
+ .name = "caps",
+ .attrs = dma_buf_caps_attrs,
+};
diff --git a/drivers/dma-buf/dma-buf-sysfs-caps.h b/drivers/dma-buf/dma-buf-sysfs-caps.h
new file mode 100644
index 000000000000..e40a93513f06
--- /dev/null
+++ b/drivers/dma-buf/dma-buf-sysfs-caps.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * DMA-BUF sysfs capabilities.
+ *
+ * Copyright (C) 2022 Simon Ser
+ */
+
+#ifndef _DMA_BUF_SYSFS_CAPS_H
+#define _DMA_BUF_SYSFS_CAPS_H
+
+struct attribute_group;
+
+extern const struct attribute_group dma_buf_caps_group;
+
+#endif // _DMA_BUF_SYSFS_CAPS_H
diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.c b/drivers/dma-buf/dma-buf-sysfs-stats.c
index 2bba0babcb62..e2e62f83ce18 100644
--- a/drivers/dma-buf/dma-buf-sysfs-stats.c
+++ b/drivers/dma-buf/dma-buf-sysfs-stats.c
@@ -141,23 +141,14 @@ static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops = {
.filter = dmabuf_sysfs_uevent_filter,
};
-static struct kset *dma_buf_stats_kset;
static struct kset *dma_buf_per_buffer_stats_kset;
-int dma_buf_init_sysfs_statistics(void)
+int dma_buf_init_sysfs_statistics(struct kset *kset)
{
- dma_buf_stats_kset = kset_create_and_add("dmabuf",
- &dmabuf_sysfs_no_uevent_ops,
- kernel_kobj);
- if (!dma_buf_stats_kset)
- return -ENOMEM;
-
dma_buf_per_buffer_stats_kset = kset_create_and_add("buffers",
&dmabuf_sysfs_no_uevent_ops,
- &dma_buf_stats_kset->kobj);
- if (!dma_buf_per_buffer_stats_kset) {
- kset_unregister(dma_buf_stats_kset);
+ &kset->kobj);
+ if (!dma_buf_per_buffer_stats_kset)
return -ENOMEM;
- }
return 0;
}
@@ -165,7 +156,6 @@ int dma_buf_init_sysfs_statistics(void)
void dma_buf_uninit_sysfs_statistics(void)
{
kset_unregister(dma_buf_per_buffer_stats_kset);
- kset_unregister(dma_buf_stats_kset);
}
int dma_buf_stats_setup(struct dma_buf *dmabuf)
diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.h b/drivers/dma-buf/dma-buf-sysfs-stats.h
index a49c6e2650cc..798c54fb8ee3 100644
--- a/drivers/dma-buf/dma-buf-sysfs-stats.h
+++ b/drivers/dma-buf/dma-buf-sysfs-stats.h
@@ -8,9 +8,11 @@
#ifndef _DMA_BUF_SYSFS_STATS_H
#define _DMA_BUF_SYSFS_STATS_H
+struct kset;
+
#ifdef CONFIG_DMABUF_SYSFS_STATS
-int dma_buf_init_sysfs_statistics(void);
+int dma_buf_init_sysfs_statistics(struct kset *kset);
void dma_buf_uninit_sysfs_statistics(void);
int dma_buf_stats_setup(struct dma_buf *dmabuf);
@@ -18,7 +20,7 @@ int dma_buf_stats_setup(struct dma_buf *dmabuf);
void dma_buf_stats_teardown(struct dma_buf *dmabuf);
#else
-static inline int dma_buf_init_sysfs_statistics(void)
+static inline int dma_buf_init_sysfs_statistics(struct kset *kset)
{
return 0;
}
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 5e1b0534b3ce..61c5be57558e 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -30,6 +30,7 @@
#include <uapi/linux/dma-buf.h>
#include <uapi/linux/magic.h>
+#include "dma-buf-sysfs-caps.h"
#include "dma-buf-sysfs-stats.h"
static inline int is_dma_buf_file(struct file *);
@@ -1546,22 +1547,57 @@ static inline void dma_buf_uninit_debugfs(void)
}
#endif
+/* Capabilities and statistics files do not need to send uevents. */
+static int dmabuf_sysfs_uevent_filter(struct kobject *kobj)
+{
+ return 0;
+}
+
+static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops = {
+ .filter = dmabuf_sysfs_uevent_filter,
+};
+
+static const struct attribute_group *dma_buf_sysfs_groups[] = {
+ &dma_buf_caps_group,
+ NULL,
+};
+
+static struct kset *dma_buf_kset;
+
static int __init dma_buf_init(void)
{
int ret;
- ret = dma_buf_init_sysfs_statistics();
+ dma_buf_kset = kset_create_and_add("dmabuf",
+ &dmabuf_sysfs_no_uevent_ops,
+ kernel_kobj);
+ if (!dma_buf_kset)
+ return -ENOMEM;
+
+ ret = sysfs_create_groups(&dma_buf_kset->kobj, dma_buf_sysfs_groups);
if (ret)
- return ret;
+ goto err_kset;
+
+ ret = dma_buf_init_sysfs_statistics(dma_buf_kset);
+ if (ret)
+ goto err_kset;
dma_buf_mnt = kern_mount(&dma_buf_fs_type);
- if (IS_ERR(dma_buf_mnt))
- return PTR_ERR(dma_buf_mnt);
+ if (IS_ERR(dma_buf_mnt)) {
+ ret = PTR_ERR(dma_buf_mnt);
+ goto err_sysfs_stats;
+ }
mutex_init(&db_list.lock);
INIT_LIST_HEAD(&db_list.head);
dma_buf_init_debugfs();
return 0;
+
+err_sysfs_stats:
+ dma_buf_uninit_sysfs_statistics();
+err_kset:
+ kset_unregister(dma_buf_kset);
+ return ret;
}
subsys_initcall(dma_buf_init);
@@ -1570,5 +1606,6 @@ static void __exit dma_buf_deinit(void)
dma_buf_uninit_debugfs();
kern_unmount(dma_buf_mnt);
dma_buf_uninit_sysfs_statistics();
+ kset_unregister(dma_buf_kset);
}
__exitcall(dma_buf_deinit);
diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h
index 70e213a0d7d9..ab3afd5da75a 100644
--- a/include/uapi/linux/dma-buf.h
+++ b/include/uapi/linux/dma-buf.h
@@ -114,6 +114,9 @@ struct dma_buf_sync {
* ordering via these fences, it is the respnosibility of userspace to use
* locks or other mechanisms to ensure that no other context adds fences or
* submits work between steps 1 and 3 above.
+ *
+ * Userspace can check the availability of this API via
+ * /sys/kernel/dmabuf/caps/sync_file_import_export.
*/
struct dma_buf_export_sync_file {
/**
@@ -146,6 +149,9 @@ struct dma_buf_export_sync_file {
* synchronized APIs such as Vulkan to inter-op with dma-buf consumers
* which expect implicit synchronization such as OpenGL or most media
* drivers/video.
+ *
+ * Userspace can check the availability of this API via
+ * /sys/kernel/dmabuf/caps/sync_file_import_export.
*/
struct dma_buf_import_sync_file {
/**
--
2.36.1
