Re: [PATCH v6] dmabuf: Add the capability to expose DMA-BUF stats in sysfs
From: Daniel Vetter
Date: Tue Jun 15 2021 - 05:49:51 EST
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@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Hridya Valsaraju <hridya@xxxxxxxxxx>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> ---
>
> 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
>
> .../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@xxxxxxxxxx>
> +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@xxxxxxxxxx>
> +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@xxxxxxxxxx>
> +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@xxxxxxxxxx>
> +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@xxxxxxxxxx>
> +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@xxxxxxxxxx>
> +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@xxxxxxxxxx>
> +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