[PATCH v6] dmabuf: Add the capability to expose DMA-BUF stats in sysfs
Hridya Valsaraju
hridya at google.com
Tue Jun 15 18:01:40 UTC 2021
On Tue, Jun 15, 2021 at 2:49 AM Daniel Vetter <daniel at ffwll.ch> wrote:
>
> On Thu, Jun 03, 2021 at 02:47:51PM -0700, Hridya Valsaraju wrote:
> > Overview
> > ========
> > The patch adds DMA-BUF statistics to /sys/kernel/dmabuf/buffers. It
> > allows statistics to be enabled for each DMA-BUF in sysfs by enabling
> > the config CONFIG_DMABUF_SYSFS_STATS.
> >
> > The following stats will be exposed by the interface:
> >
> > /sys/kernel/dmabuf/buffers/<inode_number>/exporter_name
> > /sys/kernel/dmabuf/buffers/<inode_number>/size
> > /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/device
> > /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/map_counter
> >
> > The inode_number is unique for each DMA-BUF and was added earlier [1]
> > in order to allow userspace to track DMA-BUF usage across different
> > processes.
> >
> > Use Cases
> > =========
> > The interface provides a way to gather DMA-BUF per-buffer statistics
> > from production devices. These statistics will be used to derive DMA-BUF
> > per-exporter stats and per-device usage stats for Android Bug reports.
> > The corresponding userspace changes can be found at [2].
> > Telemetry tools will also capture this information(along with other
> > memory metrics) periodically as well as on important events like a
> > foreground app kill (which might have been triggered by Low Memory
> > Killer). It will also contribute to provide a snapshot of the system
> > memory usage on other events such as OOM kills and Application Not
> > Responding events.
> >
> > Background
> > ==========
> > Currently, there are two existing interfaces that provide information
> > about DMA-BUFs.
> > 1) /sys/kernel/debug/dma_buf/bufinfo
> > debugfs is however unsuitable to be mounted in production systems and
> > cannot be considered as an alternative to the sysfs interface being
> > proposed.
> > 2) proc/<pid>/fdinfo/<fd>
> > The proc/<pid>/fdinfo/<fd> files expose information about DMA-BUF fds.
> > However, the existing procfs interfaces can only provide information
> > about the buffers for which processes hold fds or have the buffers
> > mmapped into their address space. Since the procfs interfaces alone
> > cannot provide a full picture of all DMA-BUFs in the system, there is
> > the need for an alternate interface to provide this information on
> > production systems.
> >
> > The patch contains the following major improvements over v1:
> > 1) Each attachment is represented by its own directory to allow creating
> > a symlink to the importing device and to also provide room for future
> > expansion.
> > 2) The number of distinct mappings of each attachment is exposed in a
> > separate file.
> > 3) The per-buffer statistics are now in /sys/kernel/dmabuf/buffers
> > inorder to make the interface expandable in future.
> >
> > All of the improvements above are based on suggestions/feedback from
> > Daniel Vetter and Christian König.
> >
> > A shell script that can be run on a classic Linux environment to read
> > out the DMA-BUF statistics can be found at [3](suggested by John
> > Stultz).
> >
> > [1]: https://lore.kernel.org/patchwork/patch/1088791/
> > [2]: https://android-review.googlesource.com/q/topic:%22dmabuf-sysfs%22+(status:open%20OR%20status:merged)
> > [3]: https://android-review.googlesource.com/c/platform/system/memory/libmeminfo/+/1549734
> >
> > Reviewed-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> > Signed-off-by: Hridya Valsaraju <hridya at google.com>
> > Reported-by: kernel test robot <lkp at intel.com>
> > ---
> >
> > Hello Daniel,
> >
> > I have added the documentation as a DOC: overview section in the
> > dma-buf-sysfs-stats.c file as per your suggestion. Please do take a look
> > when you get a chance. Thanks in advance!
> >
> > Regards,
> > Hridya
> >
> > Change in v6:
> > -Moved documentation content from Documentation/driver-api/dma-buf.rst
> > to drivers/dma-buf/dma-buf-sysfs-stats.c as a DOC section and linked to
> > it from Documentation/driver-api/dma-buf.rst. Based on feedback from
> > Daniel Vetter.
> >
> > Change in v5:
> > -Added a section on DMA-BUF statistics to
> > Documentation/driver-api/dma-buf.rst. Organized the commit message to
> > clearly state the need for the new interface and provide the
> > background on why the existing means of DMA-BUF accounting will not
> > suffice. Based on feedback from Daniel Vetter.
> >
> > Changes in v4:
> > -Suppress uevents from kset creation to avoid waking up uevent listeners
> > on DMA-BUF export/release.
> >
> > Changes in v3:
> > -Fix a warning reported by the kernel test robot.
> >
> > Changes in v2:
> > -Move statistics to /sys/kernel/dmabuf/buffers in oder to allow addition
> > of other DMA-BUF-related sysfs stats in future. Based on feedback from
> > Daniel Vetter.
> > -Each attachment has its own directory to represent attached devices as
> > symlinks and to introduce map_count as a separate file. Based on
> > feedback from Daniel Vetter and Christian König. Thank you both!
> > -Commit messages updated to point to userspace code in AOSP that will
> > read the DMA-BUF sysfs stats.
>
> Pushed to drm-misc-next, thanks for your work. I think the timing just
> conspired that this might miss the next merge window though :-/
> -Daniel
>
No worries at all, thank you for all the help Daniel!
Regards,
Hridya
> >
> > .../ABI/testing/sysfs-kernel-dmabuf-buffers | 52 +++
> > Documentation/driver-api/dma-buf.rst | 5 +
> > drivers/dma-buf/Kconfig | 11 +
> > drivers/dma-buf/Makefile | 1 +
> > drivers/dma-buf/dma-buf-sysfs-stats.c | 337 ++++++++++++++++++
> > drivers/dma-buf/dma-buf-sysfs-stats.h | 62 ++++
> > drivers/dma-buf/dma-buf.c | 37 ++
> > include/linux/dma-buf.h | 20 ++
> > 8 files changed, 525 insertions(+)
> > create mode 100644 Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
> > create mode 100644 drivers/dma-buf/dma-buf-sysfs-stats.c
> > create mode 100644 drivers/dma-buf/dma-buf-sysfs-stats.h
> >
> > diff --git a/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers b/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
> > new file mode 100644
> > index 000000000000..a243984ed420
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
> > @@ -0,0 +1,52 @@
> > +What: /sys/kernel/dmabuf/buffers
> > +Date: May 2021
> > +KernelVersion: v5.13
> > +Contact: Hridya Valsaraju <hridya at google.com>
> > +Description: The /sys/kernel/dmabuf/buffers directory contains a
> > + snapshot of the internal state of every DMA-BUF.
> > + /sys/kernel/dmabuf/buffers/<inode_number> will contain the
> > + statistics for the DMA-BUF with the unique inode number
> > + <inode_number>
> > +Users: kernel memory tuning/debugging tools
> > +
> > +What: /sys/kernel/dmabuf/buffers/<inode_number>/exporter_name
> > +Date: May 2021
> > +KernelVersion: v5.13
> > +Contact: Hridya Valsaraju <hridya at google.com>
> > +Description: This file is read-only and contains the name of the exporter of
> > + the DMA-BUF.
> > +
> > +What: /sys/kernel/dmabuf/buffers/<inode_number>/size
> > +Date: May 2021
> > +KernelVersion: v5.13
> > +Contact: Hridya Valsaraju <hridya at google.com>
> > +Description: This file is read-only and specifies the size of the DMA-BUF in
> > + bytes.
> > +
> > +What: /sys/kernel/dmabuf/buffers/<inode_number>/attachments
> > +Date: May 2021
> > +KernelVersion: v5.13
> > +Contact: Hridya Valsaraju <hridya at google.com>
> > +Description: This directory will contain subdirectories representing every
> > + attachment of the DMA-BUF.
> > +
> > +What: /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>
> > +Date: May 2021
> > +KernelVersion: v5.13
> > +Contact: Hridya Valsaraju <hridya at google.com>
> > +Description: This directory will contain information on the attached device
> > + and the number of current distinct device mappings.
> > +
> > +What: /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>/device
> > +Date: May 2021
> > +KernelVersion: v5.13
> > +Contact: Hridya Valsaraju <hridya at google.com>
> > +Description: This file is read-only and is a symlink to the attached device's
> > + sysfs entry.
> > +
> > +What: /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>/map_counter
> > +Date: May 2021
> > +KernelVersion: v5.13
> > +Contact: Hridya Valsaraju <hridya at google.com>
> > +Description: This file is read-only and contains a map_counter indicating the
> > + number of distinct device mappings of the attachment.
> > diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst
> > index 7f37ec30d9fd..d47a429dc549 100644
> > --- a/Documentation/driver-api/dma-buf.rst
> > +++ b/Documentation/driver-api/dma-buf.rst
> > @@ -106,6 +106,11 @@ Implicit Fence Poll Support
> > .. kernel-doc:: drivers/dma-buf/dma-buf.c
> > :doc: implicit fence polling
> >
> > +DMA-BUF statistics
> > +~~~~~~~~~~~~~~~~~~
> > +.. kernel-doc:: drivers/dma-buf/dma-buf-sysfs-stats.c
> > + :doc: overview
> > +
> > Kernel Functions and Structures Reference
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
> > index 4e16c71c24b7..9561e3d2d428 100644
> > --- a/drivers/dma-buf/Kconfig
> > +++ b/drivers/dma-buf/Kconfig
> > @@ -72,6 +72,17 @@ menuconfig DMABUF_HEAPS
> > allows userspace to allocate dma-bufs that can be shared
> > between drivers.
> >
> > +menuconfig DMABUF_SYSFS_STATS
> > + bool "DMA-BUF sysfs statistics"
> > + select DMA_SHARED_BUFFER
> > + help
> > + Choose this option to enable DMA-BUF sysfs statistics
> > + in location /sys/kernel/dmabuf/buffers.
> > +
> > + /sys/kernel/dmabuf/buffers/<inode_number> will contain
> > + statistics for the DMA-BUF with the unique inode number
> > + <inode_number>.
> > +
> > source "drivers/dma-buf/heaps/Kconfig"
> >
> > endmenu
> > diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
> > index 995e05f609ff..40d81f23cacf 100644
> > --- a/drivers/dma-buf/Makefile
> > +++ b/drivers/dma-buf/Makefile
> > @@ -6,6 +6,7 @@ obj-$(CONFIG_DMABUF_HEAPS) += heaps/
> > obj-$(CONFIG_SYNC_FILE) += sync_file.o
> > obj-$(CONFIG_SW_SYNC) += sw_sync.o sync_debug.o
> > obj-$(CONFIG_UDMABUF) += udmabuf.o
> > +obj-$(CONFIG_DMABUF_SYSFS_STATS) += dma-buf-sysfs-stats.o
> >
> > dmabuf_selftests-y := \
> > selftest.o \
> > diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.c b/drivers/dma-buf/dma-buf-sysfs-stats.c
> > new file mode 100644
> > index 000000000000..a2638e84199c
> > --- /dev/null
> > +++ b/drivers/dma-buf/dma-buf-sysfs-stats.c
> > @@ -0,0 +1,337 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * DMA-BUF sysfs statistics.
> > + *
> > + * Copyright (C) 2021 Google LLC.
> > + */
> > +
> > +#include <linux/dma-buf.h>
> > +#include <linux/dma-resv.h>
> > +#include <linux/kobject.h>
> > +#include <linux/printk.h>
> > +#include <linux/slab.h>
> > +#include <linux/sysfs.h>
> > +
> > +#include "dma-buf-sysfs-stats.h"
> > +
> > +#define to_dma_buf_entry_from_kobj(x) container_of(x, struct dma_buf_sysfs_entry, kobj)
> > +
> > +/**
> > + * DOC: overview
> > + *
> > + * ``/sys/kernel/debug/dma_buf/bufinfo`` provides an overview of every DMA-BUF
> > + * in the system. However, since debugfs is not safe to be mounted in
> > + * production, procfs and sysfs can be used to gather DMA-BUF statistics on
> > + * production systems.
> > + *
> > + * The ``/proc/<pid>/fdinfo/<fd>`` files in procfs can be used to gather
> > + * information about DMA-BUF fds. Detailed documentation about the interface
> > + * is present in Documentation/filesystems/proc.rst.
> > + *
> > + * Unfortunately, the existing procfs interfaces can only provide information
> > + * about the DMA-BUFs for which processes hold fds or have the buffers mmapped
> > + * into their address space. This necessitated the creation of the DMA-BUF sysfs
> > + * statistics interface to provide per-buffer information on production systems.
> > + *
> > + * The interface at ``/sys/kernel/dma-buf/buffers`` exposes information about
> > + * every DMA-BUF when ``CONFIG_DMABUF_SYSFS_STATS`` is enabled.
> > + *
> > + * The following stats are exposed by the interface:
> > + *
> > + * * ``/sys/kernel/dmabuf/buffers/<inode_number>/exporter_name``
> > + * * ``/sys/kernel/dmabuf/buffers/<inode_number>/size``
> > + * * ``/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/device``
> > + * * ``/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/map_counter``
> > + *
> > + * The information in the interface can also be used to derive per-exporter and
> > + * per-device usage statistics. The data from the interface can be gathered
> > + * on error conditions or other important events to provide a snapshot of
> > + * DMA-BUF usage. It can also be collected periodically by telemetry to monitor
> > + * various metrics.
> > + *
> > + * Detailed documentation about the interface is present in
> > + * Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers.
> > + */
> > +
> > +struct dma_buf_stats_attribute {
> > + struct attribute attr;
> > + ssize_t (*show)(struct dma_buf *dmabuf,
> > + struct dma_buf_stats_attribute *attr, char *buf);
> > +};
> > +#define to_dma_buf_stats_attr(x) container_of(x, struct dma_buf_stats_attribute, attr)
> > +
> > +static ssize_t dma_buf_stats_attribute_show(struct kobject *kobj,
> > + struct attribute *attr,
> > + char *buf)
> > +{
> > + struct dma_buf_stats_attribute *attribute;
> > + struct dma_buf_sysfs_entry *sysfs_entry;
> > + struct dma_buf *dmabuf;
> > +
> > + attribute = to_dma_buf_stats_attr(attr);
> > + sysfs_entry = to_dma_buf_entry_from_kobj(kobj);
> > + dmabuf = sysfs_entry->dmabuf;
> > +
> > + if (!dmabuf || !attribute->show)
> > + return -EIO;
> > +
> > + return attribute->show(dmabuf, attribute, buf);
> > +}
> > +
> > +static const struct sysfs_ops dma_buf_stats_sysfs_ops = {
> > + .show = dma_buf_stats_attribute_show,
> > +};
> > +
> > +static ssize_t exporter_name_show(struct dma_buf *dmabuf,
> > + struct dma_buf_stats_attribute *attr,
> > + char *buf)
> > +{
> > + return sysfs_emit(buf, "%s\n", dmabuf->exp_name);
> > +}
> > +
> > +static ssize_t size_show(struct dma_buf *dmabuf,
> > + struct dma_buf_stats_attribute *attr,
> > + char *buf)
> > +{
> > + return sysfs_emit(buf, "%zu\n", dmabuf->size);
> > +}
> > +
> > +static struct dma_buf_stats_attribute exporter_name_attribute =
> > + __ATTR_RO(exporter_name);
> > +static struct dma_buf_stats_attribute size_attribute = __ATTR_RO(size);
> > +
> > +static struct attribute *dma_buf_stats_default_attrs[] = {
> > + &exporter_name_attribute.attr,
> > + &size_attribute.attr,
> > + NULL,
> > +};
> > +ATTRIBUTE_GROUPS(dma_buf_stats_default);
> > +
> > +static void dma_buf_sysfs_release(struct kobject *kobj)
> > +{
> > + struct dma_buf_sysfs_entry *sysfs_entry;
> > +
> > + sysfs_entry = to_dma_buf_entry_from_kobj(kobj);
> > + kfree(sysfs_entry);
> > +}
> > +
> > +static struct kobj_type dma_buf_ktype = {
> > + .sysfs_ops = &dma_buf_stats_sysfs_ops,
> > + .release = dma_buf_sysfs_release,
> > + .default_groups = dma_buf_stats_default_groups,
> > +};
> > +
> > +#define to_dma_buf_attach_entry_from_kobj(x) container_of(x, struct dma_buf_attach_sysfs_entry, kobj)
> > +
> > +struct dma_buf_attach_stats_attribute {
> > + struct attribute attr;
> > + ssize_t (*show)(struct dma_buf_attach_sysfs_entry *sysfs_entry,
> > + struct dma_buf_attach_stats_attribute *attr, char *buf);
> > +};
> > +#define to_dma_buf_attach_stats_attr(x) container_of(x, struct dma_buf_attach_stats_attribute, attr)
> > +
> > +static ssize_t dma_buf_attach_stats_attribute_show(struct kobject *kobj,
> > + struct attribute *attr,
> > + char *buf)
> > +{
> > + struct dma_buf_attach_stats_attribute *attribute;
> > + struct dma_buf_attach_sysfs_entry *sysfs_entry;
> > +
> > + attribute = to_dma_buf_attach_stats_attr(attr);
> > + sysfs_entry = to_dma_buf_attach_entry_from_kobj(kobj);
> > +
> > + if (!attribute->show)
> > + return -EIO;
> > +
> > + return attribute->show(sysfs_entry, attribute, buf);
> > +}
> > +
> > +static const struct sysfs_ops dma_buf_attach_stats_sysfs_ops = {
> > + .show = dma_buf_attach_stats_attribute_show,
> > +};
> > +
> > +static ssize_t map_counter_show(struct dma_buf_attach_sysfs_entry *sysfs_entry,
> > + struct dma_buf_attach_stats_attribute *attr,
> > + char *buf)
> > +{
> > + return sysfs_emit(buf, "%u\n", sysfs_entry->map_counter);
> > +}
> > +
> > +static struct dma_buf_attach_stats_attribute map_counter_attribute =
> > + __ATTR_RO(map_counter);
> > +
> > +static struct attribute *dma_buf_attach_stats_default_attrs[] = {
> > + &map_counter_attribute.attr,
> > + NULL,
> > +};
> > +ATTRIBUTE_GROUPS(dma_buf_attach_stats_default);
> > +
> > +static void dma_buf_attach_sysfs_release(struct kobject *kobj)
> > +{
> > + struct dma_buf_attach_sysfs_entry *sysfs_entry;
> > +
> > + sysfs_entry = to_dma_buf_attach_entry_from_kobj(kobj);
> > + kfree(sysfs_entry);
> > +}
> > +
> > +static struct kobj_type dma_buf_attach_ktype = {
> > + .sysfs_ops = &dma_buf_attach_stats_sysfs_ops,
> > + .release = dma_buf_attach_sysfs_release,
> > + .default_groups = dma_buf_attach_stats_default_groups,
> > +};
> > +
> > +void dma_buf_attach_stats_teardown(struct dma_buf_attachment *attach)
> > +{
> > + struct dma_buf_attach_sysfs_entry *sysfs_entry;
> > +
> > + sysfs_entry = attach->sysfs_entry;
> > + if (!sysfs_entry)
> > + return;
> > +
> > + sysfs_delete_link(&sysfs_entry->kobj, &attach->dev->kobj, "device");
> > +
> > + kobject_del(&sysfs_entry->kobj);
> > + kobject_put(&sysfs_entry->kobj);
> > +}
> > +
> > +int dma_buf_attach_stats_setup(struct dma_buf_attachment *attach,
> > + unsigned int uid)
> > +{
> > + struct dma_buf_attach_sysfs_entry *sysfs_entry;
> > + int ret;
> > + struct dma_buf *dmabuf;
> > +
> > + if (!attach)
> > + return -EINVAL;
> > +
> > + dmabuf = attach->dmabuf;
> > +
> > + sysfs_entry = kzalloc(sizeof(struct dma_buf_attach_sysfs_entry),
> > + GFP_KERNEL);
> > + if (!sysfs_entry)
> > + return -ENOMEM;
> > +
> > + sysfs_entry->kobj.kset = dmabuf->sysfs_entry->attach_stats_kset;
> > +
> > + attach->sysfs_entry = sysfs_entry;
> > +
> > + ret = kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_attach_ktype,
> > + NULL, "%u", uid);
> > + if (ret)
> > + goto kobj_err;
> > +
> > + ret = sysfs_create_link(&sysfs_entry->kobj, &attach->dev->kobj,
> > + "device");
> > + if (ret)
> > + goto link_err;
> > +
> > + return 0;
> > +
> > +link_err:
> > + kobject_del(&sysfs_entry->kobj);
> > +kobj_err:
> > + kobject_put(&sysfs_entry->kobj);
> > + attach->sysfs_entry = NULL;
> > +
> > + return ret;
> > +}
> > +void dma_buf_stats_teardown(struct dma_buf *dmabuf)
> > +{
> > + struct dma_buf_sysfs_entry *sysfs_entry;
> > +
> > + sysfs_entry = dmabuf->sysfs_entry;
> > + if (!sysfs_entry)
> > + return;
> > +
> > + kset_unregister(sysfs_entry->attach_stats_kset);
> > + kobject_del(&sysfs_entry->kobj);
> > + kobject_put(&sysfs_entry->kobj);
> > +}
> > +
> > +
> > +/* Statistics files do not need to send uevents. */
> > +static int dmabuf_sysfs_uevent_filter(struct kset *kset, struct kobject *kobj)
> > +{
> > + return 0;
> > +}
> > +
> > +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)
> > +{
> > + 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);
> > + return -ENOMEM;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +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)
> > +{
> > + struct dma_buf_sysfs_entry *sysfs_entry;
> > + int ret;
> > + struct kset *attach_stats_kset;
> > +
> > + if (!dmabuf || !dmabuf->file)
> > + return -EINVAL;
> > +
> > + if (!dmabuf->exp_name) {
> > + pr_err("exporter name must not be empty if stats needed\n");
> > + return -EINVAL;
> > + }
> > +
> > + sysfs_entry = kzalloc(sizeof(struct dma_buf_sysfs_entry), GFP_KERNEL);
> > + if (!sysfs_entry)
> > + return -ENOMEM;
> > +
> > + sysfs_entry->kobj.kset = dma_buf_per_buffer_stats_kset;
> > + sysfs_entry->dmabuf = dmabuf;
> > +
> > + dmabuf->sysfs_entry = sysfs_entry;
> > +
> > + /* create the directory for buffer stats */
> > + ret = kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_ktype, NULL,
> > + "%lu", file_inode(dmabuf->file)->i_ino);
> > + if (ret)
> > + goto err_sysfs_dmabuf;
> > +
> > + /* create the directory for attachment stats */
> > + attach_stats_kset = kset_create_and_add("attachments",
> > + &dmabuf_sysfs_no_uevent_ops,
> > + &sysfs_entry->kobj);
> > + if (!attach_stats_kset) {
> > + ret = -ENOMEM;
> > + goto err_sysfs_attach;
> > + }
> > +
> > + sysfs_entry->attach_stats_kset = attach_stats_kset;
> > +
> > + return 0;
> > +
> > +err_sysfs_attach:
> > + kobject_del(&sysfs_entry->kobj);
> > +err_sysfs_dmabuf:
> > + kobject_put(&sysfs_entry->kobj);
> > + dmabuf->sysfs_entry = NULL;
> > + return ret;
> > +}
> > diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.h b/drivers/dma-buf/dma-buf-sysfs-stats.h
> > new file mode 100644
> > index 000000000000..5f4703249117
> > --- /dev/null
> > +++ b/drivers/dma-buf/dma-buf-sysfs-stats.h
> > @@ -0,0 +1,62 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * DMA-BUF sysfs statistics.
> > + *
> > + * Copyright (C) 2021 Google LLC.
> > + */
> > +
> > +#ifndef _DMA_BUF_SYSFS_STATS_H
> > +#define _DMA_BUF_SYSFS_STATS_H
> > +
> > +#ifdef CONFIG_DMABUF_SYSFS_STATS
> > +
> > +int dma_buf_init_sysfs_statistics(void);
> > +void dma_buf_uninit_sysfs_statistics(void);
> > +
> > +int dma_buf_stats_setup(struct dma_buf *dmabuf);
> > +int dma_buf_attach_stats_setup(struct dma_buf_attachment *attach,
> > + unsigned int uid);
> > +static inline void dma_buf_update_attachment_map_count(struct dma_buf_attachment *attach,
> > + int delta)
> > +{
> > + struct dma_buf_attach_sysfs_entry *entry = attach->sysfs_entry;
> > +
> > + entry->map_counter += delta;
> > +}
> > +void dma_buf_stats_teardown(struct dma_buf *dmabuf);
> > +void dma_buf_attach_stats_teardown(struct dma_buf_attachment *attach);
> > +static inline unsigned int dma_buf_update_attach_uid(struct dma_buf *dmabuf)
> > +{
> > + struct dma_buf_sysfs_entry *entry = dmabuf->sysfs_entry;
> > +
> > + return entry->attachment_uid++;
> > +}
> > +#else
> > +
> > +static inline int dma_buf_init_sysfs_statistics(void)
> > +{
> > + return 0;
> > +}
> > +
> > +static inline void dma_buf_uninit_sysfs_statistics(void) {}
> > +
> > +static inline int dma_buf_stats_setup(struct dma_buf *dmabuf)
> > +{
> > + return 0;
> > +}
> > +static inline int dma_buf_attach_stats_setup(struct dma_buf_attachment *attach,
> > + unsigned int uid)
> > +{
> > + return 0;
> > +}
> > +
> > +static inline void dma_buf_stats_teardown(struct dma_buf *dmabuf) {}
> > +static inline void dma_buf_attach_stats_teardown(struct dma_buf_attachment *attach) {}
> > +static inline void dma_buf_update_attachment_map_count(struct dma_buf_attachment *attach,
> > + int delta) {}
> > +static inline unsigned int dma_buf_update_attach_uid(struct dma_buf *dmabuf)
> > +{
> > + return 0;
> > +}
> > +#endif
> > +#endif // _DMA_BUF_SYSFS_STATS_H
> > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > index f264b70c383e..184dd7acb1ed 100644
> > --- a/drivers/dma-buf/dma-buf.c
> > +++ b/drivers/dma-buf/dma-buf.c
> > @@ -29,6 +29,8 @@
> > #include <uapi/linux/dma-buf.h>
> > #include <uapi/linux/magic.h>
> >
> > +#include "dma-buf-sysfs-stats.h"
> > +
> > static inline int is_dma_buf_file(struct file *);
> >
> > struct dma_buf_list {
> > @@ -79,6 +81,7 @@ static void dma_buf_release(struct dentry *dentry)
> > if (dmabuf->resv == (struct dma_resv *)&dmabuf[1])
> > dma_resv_fini(dmabuf->resv);
> >
> > + dma_buf_stats_teardown(dmabuf);
> > module_put(dmabuf->owner);
> > kfree(dmabuf->name);
> > kfree(dmabuf);
> > @@ -580,6 +583,10 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
> > file->f_mode |= FMODE_LSEEK;
> > dmabuf->file = file;
> >
> > + ret = dma_buf_stats_setup(dmabuf);
> > + if (ret)
> > + goto err_sysfs;
> > +
> > mutex_init(&dmabuf->lock);
> > INIT_LIST_HEAD(&dmabuf->attachments);
> >
> > @@ -589,6 +596,14 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
> >
> > return dmabuf;
> >
> > +err_sysfs:
> > + /*
> > + * Set file->f_path.dentry->d_fsdata to NULL so that when
> > + * dma_buf_release() gets invoked by dentry_ops, it exits
> > + * early before calling the release() dma_buf op.
> > + */
> > + file->f_path.dentry->d_fsdata = NULL;
> > + fput(file);
> > err_dmabuf:
> > kfree(dmabuf);
> > err_module:
> > @@ -723,6 +738,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> > {
> > struct dma_buf_attachment *attach;
> > int ret;
> > + unsigned int attach_uid;
> >
> > if (WARN_ON(!dmabuf || !dev))
> > return ERR_PTR(-EINVAL);
> > @@ -748,8 +764,13 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> > }
> > dma_resv_lock(dmabuf->resv, NULL);
> > list_add(&attach->node, &dmabuf->attachments);
> > + attach_uid = dma_buf_update_attach_uid(dmabuf);
> > dma_resv_unlock(dmabuf->resv);
> >
> > + ret = dma_buf_attach_stats_setup(attach, attach_uid);
> > + if (ret)
> > + goto err_sysfs;
> > +
> > /* When either the importer or the exporter can't handle dynamic
> > * mappings we cache the mapping here to avoid issues with the
> > * reservation object lock.
> > @@ -776,6 +797,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> > dma_resv_unlock(attach->dmabuf->resv);
> > attach->sgt = sgt;
> > attach->dir = DMA_BIDIRECTIONAL;
> > + dma_buf_update_attachment_map_count(attach, 1 /* delta */);
> > }
> >
> > return attach;
> > @@ -792,6 +814,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> > if (dma_buf_is_dynamic(attach->dmabuf))
> > dma_resv_unlock(attach->dmabuf->resv);
> >
> > +err_sysfs:
> > dma_buf_detach(dmabuf, attach);
> > return ERR_PTR(ret);
> > }
> > @@ -841,6 +864,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
> > dma_resv_lock(attach->dmabuf->resv, NULL);
> >
> > __unmap_dma_buf(attach, attach->sgt, attach->dir);
> > + dma_buf_update_attachment_map_count(attach, -1 /* delta */);
> >
> > if (dma_buf_is_dynamic(attach->dmabuf)) {
> > dma_buf_unpin(attach);
> > @@ -854,6 +878,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
> > if (dmabuf->ops->detach)
> > dmabuf->ops->detach(dmabuf, attach);
> >
> > + dma_buf_attach_stats_teardown(attach);
> > kfree(attach);
> > }
> > EXPORT_SYMBOL_GPL(dma_buf_detach);
> > @@ -993,6 +1018,9 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
> > }
> > #endif /* CONFIG_DMA_API_DEBUG */
> >
> > + if (!IS_ERR(sg_table))
> > + dma_buf_update_attachment_map_count(attach, 1 /* delta */);
> > +
> > return sg_table;
> > }
> > EXPORT_SYMBOL_GPL(dma_buf_map_attachment);
> > @@ -1030,6 +1058,8 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
> > if (dma_buf_is_dynamic(attach->dmabuf) &&
> > !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))
> > dma_buf_unpin(attach);
> > +
> > + dma_buf_update_attachment_map_count(attach, -1 /* delta */);
> > }
> > EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
> >
> > @@ -1480,6 +1510,12 @@ static inline void dma_buf_uninit_debugfs(void)
> >
> > static int __init dma_buf_init(void)
> > {
> > + int ret;
> > +
> > + ret = dma_buf_init_sysfs_statistics();
> > + if (ret)
> > + return ret;
> > +
> > dma_buf_mnt = kern_mount(&dma_buf_fs_type);
> > if (IS_ERR(dma_buf_mnt))
> > return PTR_ERR(dma_buf_mnt);
> > @@ -1495,5 +1531,6 @@ static void __exit dma_buf_deinit(void)
> > {
> > dma_buf_uninit_debugfs();
> > kern_unmount(dma_buf_mnt);
> > + dma_buf_uninit_sysfs_statistics();
> > }
> > __exitcall(dma_buf_deinit);
> > diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> > index efdc56b9d95f..342585bd6dff 100644
> > --- a/include/linux/dma-buf.h
> > +++ b/include/linux/dma-buf.h
> > @@ -295,6 +295,9 @@ struct dma_buf_ops {
> > * @poll: for userspace poll support
> > * @cb_excl: for userspace poll support
> > * @cb_shared: for userspace poll support
> > + * @sysfs_entry: for exposing information about this buffer in sysfs.
> > + * The attachment_uid member of @sysfs_entry is protected by dma_resv lock
> > + * and is incremented on each attach.
> > *
> > * This represents a shared buffer, created by calling dma_buf_export(). The
> > * userspace representation is a normal file descriptor, which can be created by
> > @@ -330,6 +333,15 @@ struct dma_buf {
> >
> > __poll_t active;
> > } cb_excl, cb_shared;
> > +#ifdef CONFIG_DMABUF_SYSFS_STATS
> > + /* for sysfs stats */
> > + struct dma_buf_sysfs_entry {
> > + struct kobject kobj;
> > + struct dma_buf *dmabuf;
> > + unsigned int attachment_uid;
> > + struct kset *attach_stats_kset;
> > + } *sysfs_entry;
> > +#endif
> > };
> >
> > /**
> > @@ -379,6 +391,7 @@ struct dma_buf_attach_ops {
> > * @importer_ops: importer operations for this attachment, if provided
> > * dma_buf_map/unmap_attachment() must be called with the dma_resv lock held.
> > * @importer_priv: importer specific attachment data.
> > + * @sysfs_entry: For exposing information about this attachment in sysfs.
> > *
> > * This structure holds the attachment information between the dma_buf buffer
> > * and its user device(s). The list contains one attachment struct per device
> > @@ -399,6 +412,13 @@ struct dma_buf_attachment {
> > const struct dma_buf_attach_ops *importer_ops;
> > void *importer_priv;
> > void *priv;
> > +#ifdef CONFIG_DMABUF_SYSFS_STATS
> > + /* for sysfs stats */
> > + struct dma_buf_attach_sysfs_entry {
> > + struct kobject kobj;
> > + unsigned int map_counter;
> > + } *sysfs_entry;
> > +#endif
> > };
> >
> > /**
> > --
> > 2.32.0.rc1.229.g3e70b5a671-goog
> >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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