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From:   Hridya Valsaraju <hridya@google.com>
Date:   Thu, 3 Jun 2021 10:42:10 -0700
Message-ID: <CA+wgaPPOH0Zdf7V_7de6MdTBgiU9OtCT+=VsPbUeR5dTjewd9A@mail.gmail.com>
Subject: Re: [PATCH v5] dmabuf: Add the capability to expose DMA-BUF stats in sysfs
To:     Hridya Valsaraju <hridya@google.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@lists.linaro.org>, linux-doc@vger.kernel.org,
        Android Kernel Team <kernel-team@android.com>,
        John Stultz <john.stultz@linaro.org>,
        Suren Baghdasaryan <surenb@google.com>,
        kernel test robot <lkp@intel.com>
Cc:     Daniel Vetter <daniel@ffwll.ch>
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On Thu, Jun 3, 2021 at 1:51 AM Daniel Vetter <daniel@ffwll.ch> wrote:
>
> On Wed, Jun 02, 2021 at 03:29:30PM -0700, Hridya Valsaraju wrote:
> > Overview
> > =3D=3D=3D=3D=3D=3D=3D=3D
> > 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>/devi=
ce
> > /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
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D
> > The interface provides a way to gather DMA-BUF per-buffer statistics
> > from production devices. These statistics will be used to derive DMA-BU=
F
> > 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
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > 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 creatin=
g
> > 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 K=C3=B6nig.
> >
> > 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/l=
ibmeminfo/+/1549734
> >
> > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Signed-off-by: Hridya Valsaraju <hridya@google.com>
> > Reported-by: kernel test robot <lkp@intel.com>
> > ---
> >
> > Hi Daniel,
> >
> > I rewrote the commit message and added a new section to
> > Documentation/driver-api/dma-buf.rst as per your suggestions. Please
> > do take another look when you get a chance. Thanks again for the
> > guidance.
> >
> > Regards,
> > Hridya
> >
> > 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 listener=
s
> > 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 additio=
n
> > 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 K=C3=B6nig. Thank you both!
> > -Commit messages updated to point to userspace code in AOSP that will
> > read the DMA-BUF sysfs stats.
> >
> >  .../ABI/testing/sysfs-kernel-dmabuf-buffers   |  52 +++
> >  Documentation/driver-api/dma-buf.rst          |  34 ++
> >  drivers/dma-buf/Kconfig                       |  11 +
> >  drivers/dma-buf/Makefile                      |   1 +
> >  drivers/dma-buf/dma-buf-sysfs-stats.c         | 300 ++++++++++++++++++
> >  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, 517 insertions(+)
> >  create mode 100644 Documentation/ABI/testing/sysfs-kernel-dmabuf-buffe=
rs
> >  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/Do=
cumentation/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@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 th=
e
> > +             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>/exporte=
r_name
> > +Date:                May 2021
> > +KernelVersion:       v5.13
> > +Contact:     Hridya Valsaraju <hridya@google.com>
> > +Description: This file is read-only and contains the name of the expor=
ter of
> > +             the DMA-BUF.
> > +
> > +What:                /sys/kernel/dmabuf/buffers/<inode_number>/size
> > +Date:                May 2021
> > +KernelVersion:       v5.13
> > +Contact:     Hridya Valsaraju <hridya@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>/attachm=
ents
> > +Date:                May 2021
> > +KernelVersion:       v5.13
> > +Contact:     Hridya Valsaraju <hridya@google.com>
> > +Description: This directory will contain subdirectories representing e=
very
> > +             attachment of the DMA-BUF.
> > +
> > +What:                /sys/kernel/dmabuf/buffers/<inode_number>/attachm=
ents/<attachment_uid>
> > +Date:                May 2021
> > +KernelVersion:       v5.13
> > +Contact:     Hridya Valsaraju <hridya@google.com>
> > +Description: This directory will contain information on the attached d=
evice
> > +             and the number of current distinct device mappings.
> > +
> > +What:                /sys/kernel/dmabuf/buffers/<inode_number>/attachm=
ents/<attachment_uid>/device
> > +Date:                May 2021
> > +KernelVersion:       v5.13
> > +Contact:     Hridya Valsaraju <hridya@google.com>
> > +Description: This file is read-only and is a symlink to the attached d=
evice's
> > +             sysfs entry.
> > +
> > +What:                /sys/kernel/dmabuf/buffers/<inode_number>/attachm=
ents/<attachment_uid>/map_counter
> > +Date:                May 2021
> > +KernelVersion:       v5.13
> > +Contact:     Hridya Valsaraju <hridya@google.com>
> > +Description: This file is read-only and contains a map_counter indicat=
ing the
> > +             number of distinct device mappings of the attachment.
> > diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/drive=
r-api/dma-buf.rst
> > index 7f37ec30d9fd..4027762a824a 100644
> > --- a/Documentation/driver-api/dma-buf.rst
> > +++ b/Documentation/driver-api/dma-buf.rst
> > @@ -106,6 +106,40 @@ Implicit Fence Poll Support
> >  .. kernel-doc:: drivers/dma-buf/dma-buf.c
> >     :doc: implicit fence polling
> >
> > +DMA-BUF statistics
> > +~~~~~~~~~~~~~~~~~~
> > +
> > +``/sys/kernel/debug/dma_buf/bufinfo`` provides an overview of every DM=
A-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 productio=
n 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 prese=
nt in
> > +Documentation/filesystems/proc.rst.
> > +Unfortunately, the existing procfs interfaces can only provide informa=
tion 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 sta=
tistics
> > +interface to provide per-buffer information on production systems.
> > +
> > +The interface at ``/sys/kernel/dma-buf/buffers`` exposes information a=
bout
> > +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-export=
er and
> > +per-device usage statistics. The data from the interface can be gather=
ed
> > +on error conditions or other important events to provide a snapshot of
> > +DMA-BUF usage. It can also be collected periodically by telemetry to m=
onitor
> > +various metrics.
> > +
> > +Detailed documentation about the interface is present in
> > +Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
>
> Ok this looks neat, but I prefer if this is done as a DOC: overview
> section in the source code, and pulled into the documentation with an
> include directive. That way the docs are closer to the code, and so highe=
r
> chances they get updated if something changes.
>
> And since add an entire new file for this I think this makes more sense.
>
> Can you pls respin once more with that? I think then we're really good fo=
r
> sure.

Of course! Thank you Daniel, yes let me do that and send out another versio=
n.

Regards,
Hridya

> -Daniel
>
> > +
> >  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-$(CONFIG_DMABUF_HEAPS)    +=3D heaps/
> >  obj-$(CONFIG_SYNC_FILE)              +=3D sync_file.o
> >  obj-$(CONFIG_SW_SYNC)                +=3D sw_sync.o sync_debug.o
> >  obj-$(CONFIG_UDMABUF)                +=3D udmabuf.o
> > +obj-$(CONFIG_DMABUF_SYSFS_STATS) +=3D dma-buf-sysfs-stats.o
> >
> >  dmabuf_selftests-y :=3D \
> >       selftest.o \
> > diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.c b/drivers/dma-buf/dm=
a-buf-sysfs-stats.c
> > new file mode 100644
> > index 000000000000..45717c8108c8
> > --- /dev/null
> > +++ b/drivers/dma-buf/dma-buf-sysfs-stats.c
> > @@ -0,0 +1,300 @@
> > +// 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_s=
ysfs_entry, kobj)
> > +
> > +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 =3D to_dma_buf_stats_attr(attr);
> > +     sysfs_entry =3D to_dma_buf_entry_from_kobj(kobj);
> > +     dmabuf =3D 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 =3D {
> > +     .show =3D 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 =3D
> > +     __ATTR_RO(exporter_name);
> > +static struct dma_buf_stats_attribute size_attribute =3D __ATTR_RO(siz=
e);
> > +
> > +static struct attribute *dma_buf_stats_default_attrs[] =3D {
> > +     &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 =3D to_dma_buf_entry_from_kobj(kobj);
> > +     kfree(sysfs_entry);
> > +}
> > +
> > +static struct kobj_type dma_buf_ktype =3D {
> > +     .sysfs_ops =3D &dma_buf_stats_sysfs_ops,
> > +     .release =3D dma_buf_sysfs_release,
> > +     .default_groups =3D dma_buf_stats_default_groups,
> > +};
> > +
> > +#define to_dma_buf_attach_entry_from_kobj(x) container_of(x, struct dm=
a_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 *kob=
j,
> > +                                                struct attribute *attr=
,
> > +                                                char *buf)
> > +{
> > +     struct dma_buf_attach_stats_attribute *attribute;
> > +     struct dma_buf_attach_sysfs_entry *sysfs_entry;
> > +
> > +     attribute =3D to_dma_buf_attach_stats_attr(attr);
> > +     sysfs_entry =3D 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 =3D {
> > +     .show =3D dma_buf_attach_stats_attribute_show,
> > +};
> > +
> > +static ssize_t map_counter_show(struct dma_buf_attach_sysfs_entry *sys=
fs_entry,
> > +                             struct dma_buf_attach_stats_attribute *at=
tr,
> > +                             char *buf)
> > +{
> > +     return sysfs_emit(buf, "%u\n", sysfs_entry->map_counter);
> > +}
> > +
> > +static struct dma_buf_attach_stats_attribute map_counter_attribute =3D
> > +     __ATTR_RO(map_counter);
> > +
> > +static struct attribute *dma_buf_attach_stats_default_attrs[] =3D {
> > +     &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 =3D to_dma_buf_attach_entry_from_kobj(kobj);
> > +     kfree(sysfs_entry);
> > +}
> > +
> > +static struct kobj_type dma_buf_attach_ktype =3D {
> > +     .sysfs_ops =3D &dma_buf_attach_stats_sysfs_ops,
> > +     .release =3D dma_buf_attach_sysfs_release,
> > +     .default_groups =3D 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 =3D 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 =3D attach->dmabuf;
> > +
> > +     sysfs_entry =3D kzalloc(sizeof(struct dma_buf_attach_sysfs_entry)=
,
> > +                           GFP_KERNEL);
> > +     if (!sysfs_entry)
> > +             return -ENOMEM;
> > +
> > +     sysfs_entry->kobj.kset =3D dmabuf->sysfs_entry->attach_stats_kset=
;
> > +
> > +     attach->sysfs_entry =3D sysfs_entry;
> > +
> > +     ret =3D kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_attach_=
ktype,
> > +                                NULL, "%u", uid);
> > +     if (ret)
> > +             goto kobj_err;
> > +
> > +     ret =3D 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 =3D NULL;
> > +
> > +     return ret;
> > +}
> > +void dma_buf_stats_teardown(struct dma_buf *dmabuf)
> > +{
> > +     struct dma_buf_sysfs_entry *sysfs_entry;
> > +
> > +     sysfs_entry =3D 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 kobjec=
t *kobj)
> > +{
> > +     return 0;
> > +}
> > +
> > +static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops =3D {
> > +     .filter =3D 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 =3D 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 =3D kset_create_and_add("buffers",
> > +                                                         &dmabuf_sysfs=
_no_uevent_ops,
> > +                                                         &dma_buf_stat=
s_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 =3D kzalloc(sizeof(struct dma_buf_sysfs_entry), GFP_K=
ERNEL);
> > +     if (!sysfs_entry)
> > +             return -ENOMEM;
> > +
> > +     sysfs_entry->kobj.kset =3D dma_buf_per_buffer_stats_kset;
> > +     sysfs_entry->dmabuf =3D dmabuf;
> > +
> > +     dmabuf->sysfs_entry =3D sysfs_entry;
> > +
> > +     /* create the directory for buffer stats */
> > +     ret =3D 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 =3D kset_create_and_add("attachments",
> > +                                             &dmabuf_sysfs_no_uevent_o=
ps,
> > +                                             &sysfs_entry->kobj);
> > +     if (!attach_stats_kset) {
> > +             ret =3D -ENOMEM;
> > +             goto err_sysfs_attach;
> > +     }
> > +
> > +     sysfs_entry->attach_stats_kset =3D attach_stats_kset;
> > +
> > +     return 0;
> > +
> > +err_sysfs_attach:
> > +     kobject_del(&sysfs_entry->kobj);
> > +err_sysfs_dmabuf:
> > +     kobject_put(&sysfs_entry->kobj);
> > +     dmabuf->sysfs_entry =3D NULL;
> > +     return ret;
> > +}
> > diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.h b/drivers/dma-buf/dm=
a-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 =3D attach->sysfs_entry;
> > +
> > +     entry->map_counter +=3D 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 *d=
mabuf)
> > +{
> > +     struct dma_buf_sysfs_entry *entry =3D 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_attach=
ment *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 *d=
mabuf)
> > +{
> > +     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 =3D=3D (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_bu=
f_export_info *exp_info)
> >       file->f_mode |=3D FMODE_LSEEK;
> >       dmabuf->file =3D file;
> >
> > +     ret =3D 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_bu=
f_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 =3D NULL;
> > +     fput(file);
> >  err_dmabuf:
> >       kfree(dmabuf);
> >  err_module:
> > @@ -723,6 +738,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, stru=
ct 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, str=
uct device *dev,
> >       }
> >       dma_resv_lock(dmabuf->resv, NULL);
> >       list_add(&attach->node, &dmabuf->attachments);
> > +     attach_uid =3D dma_buf_update_attach_uid(dmabuf);
> >       dma_resv_unlock(dmabuf->resv);
> >
> > +     ret =3D 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, stru=
ct device *dev,
> >                       dma_resv_unlock(attach->dmabuf->resv);
> >               attach->sgt =3D sgt;
> >               attach->dir =3D 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, stru=
ct 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_atta=
chment *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 =3D dma_buf_init_sysfs_statistics();
> > +     if (ret)
> > +             return ret;
> > +
> >       dma_buf_mnt =3D 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 loc=
k held.
> >   * @importer_priv: importer specific attachment data.
> > + * @sysfs_entry: For exposing information about this attachment in sys=
fs.
> >   *
> >   * 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.rc0.204.g9fa02ecfa5-goog
> >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch