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dma-buf: Remove DMA-BUF sysfs stats
Commitbdb8d06dfe("dmabuf: Add the capability to expose DMA-BUF stats in sysfs") added dmabuf statistics to sysfs in 2021 under CONFIG_DMABUF_SYSFS_STATS. After being used in production, performance problems were discovered leading to its deprecation in 2022 in commite0a9f1fe20("dma-buf: deprecate DMABUF_SYSFS_STATS"). Some of the problems with this interface were discussed in my LPC 2025 talk. [1][2] Android was probably the last user of the interface, which has since been migrated to use the dmabuf BPF iterator [3] to obtain the same information more cheaply. As promised in that series, now that the longterm stable 6.18 kernel has been released let's remove the sysfs dmabuf statistics from the kernel. [1] https://www.youtube.com/watch?v=D83qygudq9c [2] https://lpc.events/event/19/contributions/2118/ [3] https://lore.kernel.org/all/20250522230429.941193-1-tjmercier@google.com/ Signed-off-by: T.J. Mercier <tjmercier@google.com> Reviewed-by: Christian König <christian.koenig@amd.com> Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org> Link: https://patch.msgid.link/20260116190517.3268458-1-tjmercier@google.com
This commit is contained in:
T.J. Mercier
Sumit Semwal
parent
3c227be906
commit
ab4c3dcf9a
8 changed files with 0 additions and 312 deletions
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@ -1,24 +0,0 @@
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What: /sys/kernel/dmabuf/buffers
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Date: May 2021
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KernelVersion: v5.13
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Contact: Hridya Valsaraju <hridya@google.com>
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Description: The /sys/kernel/dmabuf/buffers directory contains a
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snapshot of the internal state of every DMA-BUF.
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/sys/kernel/dmabuf/buffers/<inode_number> will contain the
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statistics for the DMA-BUF with the unique inode number
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<inode_number>
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Users: kernel memory tuning/debugging tools
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What: /sys/kernel/dmabuf/buffers/<inode_number>/exporter_name
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Date: May 2021
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KernelVersion: v5.13
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Contact: Hridya Valsaraju <hridya@google.com>
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Description: This file is read-only and contains the name of the exporter of
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the DMA-BUF.
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What: /sys/kernel/dmabuf/buffers/<inode_number>/size
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Date: May 2021
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KernelVersion: v5.13
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Contact: Hridya Valsaraju <hridya@google.com>
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Description: This file is read-only and specifies the size of the DMA-BUF in
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bytes.
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@ -125,11 +125,6 @@ Implicit Fence Poll Support
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.. kernel-doc:: drivers/dma-buf/dma-buf.c
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:doc: implicit fence polling
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DMA-BUF statistics
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~~~~~~~~~~~~~~~~~~
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.. kernel-doc:: drivers/dma-buf/dma-buf-sysfs-stats.c
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:doc: overview
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DMA Buffer ioctls
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~~~~~~~~~~~~~~~~~
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@ -75,21 +75,6 @@ menuconfig DMABUF_HEAPS
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allows userspace to allocate dma-bufs that can be shared
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between drivers.
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menuconfig DMABUF_SYSFS_STATS
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bool "DMA-BUF sysfs statistics (DEPRECATED)"
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depends on DMA_SHARED_BUFFER
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help
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Choose this option to enable DMA-BUF sysfs statistics
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in location /sys/kernel/dmabuf/buffers.
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/sys/kernel/dmabuf/buffers/<inode_number> will contain
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statistics for the DMA-BUF with the unique inode number
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<inode_number>.
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This option is deprecated and should sooner or later be removed.
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Android is the only user of this and it turned out that this resulted
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in quite some performance problems.
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source "drivers/dma-buf/heaps/Kconfig"
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endmenu
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@ -6,7 +6,6 @@ obj-$(CONFIG_DMABUF_HEAPS) += heaps/
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obj-$(CONFIG_SYNC_FILE) += sync_file.o
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obj-$(CONFIG_SW_SYNC) += sw_sync.o sync_debug.o
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obj-$(CONFIG_UDMABUF) += udmabuf.o
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obj-$(CONFIG_DMABUF_SYSFS_STATS) += dma-buf-sysfs-stats.o
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dmabuf_selftests-y := \
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selftest.o \
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@ -1,202 +0,0 @@
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// SPDX-License-Identifier: GPL-2.0-only
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/*
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* DMA-BUF sysfs statistics.
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*
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* Copyright (C) 2021 Google LLC.
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*/
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#include <linux/dma-buf.h>
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#include <linux/dma-resv.h>
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#include <linux/kobject.h>
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#include <linux/printk.h>
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#include <linux/slab.h>
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#include <linux/sysfs.h>
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#include "dma-buf-sysfs-stats.h"
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#define to_dma_buf_entry_from_kobj(x) container_of(x, struct dma_buf_sysfs_entry, kobj)
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/**
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* DOC: overview
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*
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* ``/sys/kernel/debug/dma_buf/bufinfo`` provides an overview of every DMA-BUF
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* in the system. However, since debugfs is not safe to be mounted in
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* production, procfs and sysfs can be used to gather DMA-BUF statistics on
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* production systems.
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*
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* The ``/proc/<pid>/fdinfo/<fd>`` files in procfs can be used to gather
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* information about DMA-BUF fds. Detailed documentation about the interface
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* is present in Documentation/filesystems/proc.rst.
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*
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* Unfortunately, the existing procfs interfaces can only provide information
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* about the DMA-BUFs for which processes hold fds or have the buffers mmapped
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* into their address space. This necessitated the creation of the DMA-BUF sysfs
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* statistics interface to provide per-buffer information on production systems.
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*
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* The interface at ``/sys/kernel/dmabuf/buffers`` exposes information about
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* every DMA-BUF when ``CONFIG_DMABUF_SYSFS_STATS`` is enabled.
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*
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* The following stats are exposed by the interface:
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*
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* * ``/sys/kernel/dmabuf/buffers/<inode_number>/exporter_name``
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* * ``/sys/kernel/dmabuf/buffers/<inode_number>/size``
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*
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* The information in the interface can also be used to derive per-exporter
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* statistics. The data from the interface can be gathered on error conditions
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* or other important events to provide a snapshot of DMA-BUF usage.
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* It can also be collected periodically by telemetry to monitor various metrics.
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*
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* Detailed documentation about the interface is present in
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* Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers.
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*/
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struct dma_buf_stats_attribute {
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struct attribute attr;
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ssize_t (*show)(struct dma_buf *dmabuf,
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struct dma_buf_stats_attribute *attr, char *buf);
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};
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#define to_dma_buf_stats_attr(x) container_of(x, struct dma_buf_stats_attribute, attr)
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static ssize_t dma_buf_stats_attribute_show(struct kobject *kobj,
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struct attribute *attr,
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char *buf)
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{
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struct dma_buf_stats_attribute *attribute;
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struct dma_buf_sysfs_entry *sysfs_entry;
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struct dma_buf *dmabuf;
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attribute = to_dma_buf_stats_attr(attr);
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sysfs_entry = to_dma_buf_entry_from_kobj(kobj);
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dmabuf = sysfs_entry->dmabuf;
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if (!dmabuf || !attribute->show)
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return -EIO;
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return attribute->show(dmabuf, attribute, buf);
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}
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static const struct sysfs_ops dma_buf_stats_sysfs_ops = {
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.show = dma_buf_stats_attribute_show,
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};
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static ssize_t exporter_name_show(struct dma_buf *dmabuf,
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struct dma_buf_stats_attribute *attr,
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char *buf)
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{
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return sysfs_emit(buf, "%s\n", dmabuf->exp_name);
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}
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static ssize_t size_show(struct dma_buf *dmabuf,
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struct dma_buf_stats_attribute *attr,
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char *buf)
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{
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return sysfs_emit(buf, "%zu\n", dmabuf->size);
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}
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static struct dma_buf_stats_attribute exporter_name_attribute =
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__ATTR_RO(exporter_name);
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static struct dma_buf_stats_attribute size_attribute = __ATTR_RO(size);
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static struct attribute *dma_buf_stats_default_attrs[] = {
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&exporter_name_attribute.attr,
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&size_attribute.attr,
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NULL,
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};
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ATTRIBUTE_GROUPS(dma_buf_stats_default);
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static void dma_buf_sysfs_release(struct kobject *kobj)
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{
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struct dma_buf_sysfs_entry *sysfs_entry;
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sysfs_entry = to_dma_buf_entry_from_kobj(kobj);
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kfree(sysfs_entry);
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}
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static const struct kobj_type dma_buf_ktype = {
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.sysfs_ops = &dma_buf_stats_sysfs_ops,
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.release = dma_buf_sysfs_release,
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.default_groups = dma_buf_stats_default_groups,
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};
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void dma_buf_stats_teardown(struct dma_buf *dmabuf)
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{
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struct dma_buf_sysfs_entry *sysfs_entry;
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sysfs_entry = dmabuf->sysfs_entry;
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if (!sysfs_entry)
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return;
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kobject_del(&sysfs_entry->kobj);
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kobject_put(&sysfs_entry->kobj);
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}
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/* Statistics files do not need to send uevents. */
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static int dmabuf_sysfs_uevent_filter(const struct kobject *kobj)
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{
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return 0;
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}
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static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops = {
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.filter = dmabuf_sysfs_uevent_filter,
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};
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static struct kset *dma_buf_stats_kset;
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static struct kset *dma_buf_per_buffer_stats_kset;
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int dma_buf_init_sysfs_statistics(void)
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{
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dma_buf_stats_kset = kset_create_and_add("dmabuf",
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&dmabuf_sysfs_no_uevent_ops,
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kernel_kobj);
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if (!dma_buf_stats_kset)
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return -ENOMEM;
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dma_buf_per_buffer_stats_kset = kset_create_and_add("buffers",
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&dmabuf_sysfs_no_uevent_ops,
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&dma_buf_stats_kset->kobj);
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if (!dma_buf_per_buffer_stats_kset) {
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kset_unregister(dma_buf_stats_kset);
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return -ENOMEM;
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}
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return 0;
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}
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void dma_buf_uninit_sysfs_statistics(void)
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{
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kset_unregister(dma_buf_per_buffer_stats_kset);
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kset_unregister(dma_buf_stats_kset);
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}
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int dma_buf_stats_setup(struct dma_buf *dmabuf, struct file *file)
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{
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struct dma_buf_sysfs_entry *sysfs_entry;
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int ret;
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if (!dmabuf->exp_name) {
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pr_err("exporter name must not be empty if stats needed\n");
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return -EINVAL;
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}
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sysfs_entry = kzalloc(sizeof(struct dma_buf_sysfs_entry), GFP_KERNEL);
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if (!sysfs_entry)
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return -ENOMEM;
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sysfs_entry->kobj.kset = dma_buf_per_buffer_stats_kset;
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sysfs_entry->dmabuf = dmabuf;
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dmabuf->sysfs_entry = sysfs_entry;
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/* create the directory for buffer stats */
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ret = kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_ktype, NULL,
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"%lu", file_inode(file)->i_ino);
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if (ret)
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goto err_sysfs_dmabuf;
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return 0;
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err_sysfs_dmabuf:
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kobject_put(&sysfs_entry->kobj);
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dmabuf->sysfs_entry = NULL;
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return ret;
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}
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@ -1,35 +0,0 @@
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/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* DMA-BUF sysfs statistics.
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*
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* Copyright (C) 2021 Google LLC.
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*/
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#ifndef _DMA_BUF_SYSFS_STATS_H
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#define _DMA_BUF_SYSFS_STATS_H
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#ifdef CONFIG_DMABUF_SYSFS_STATS
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int dma_buf_init_sysfs_statistics(void);
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void dma_buf_uninit_sysfs_statistics(void);
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int dma_buf_stats_setup(struct dma_buf *dmabuf, struct file *file);
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void dma_buf_stats_teardown(struct dma_buf *dmabuf);
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#else
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static inline int dma_buf_init_sysfs_statistics(void)
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{
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return 0;
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}
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static inline void dma_buf_uninit_sysfs_statistics(void) {}
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static inline int dma_buf_stats_setup(struct dma_buf *dmabuf, struct file *file)
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{
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return 0;
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}
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static inline void dma_buf_stats_teardown(struct dma_buf *dmabuf) {}
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#endif
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#endif // _DMA_BUF_SYSFS_STATS_H
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@ -33,8 +33,6 @@
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#include <uapi/linux/dma-buf.h>
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#include <uapi/linux/magic.h>
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#include "dma-buf-sysfs-stats.h"
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#define CREATE_TRACE_POINTS
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#include <trace/events/dma_buf.h>
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@ -184,7 +182,6 @@ static void dma_buf_release(struct dentry *dentry)
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*/
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BUG_ON(dmabuf->cb_in.active || dmabuf->cb_out.active);
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dma_buf_stats_teardown(dmabuf);
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dmabuf->ops->release(dmabuf);
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if (dmabuf->resv == (struct dma_resv *)&dmabuf[1])
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@ -765,10 +762,6 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
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dmabuf->resv = resv;
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}
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ret = dma_buf_stats_setup(dmabuf, file);
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if (ret)
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goto err_dmabuf;
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file->private_data = dmabuf;
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file->f_path.dentry->d_fsdata = dmabuf;
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dmabuf->file = file;
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@ -779,10 +772,6 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
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return dmabuf;
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err_dmabuf:
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if (!resv)
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dma_resv_fini(dmabuf->resv);
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kfree(dmabuf);
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err_file:
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fput(file);
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err_module:
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@ -1802,12 +1791,6 @@ static inline void dma_buf_uninit_debugfs(void)
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static int __init dma_buf_init(void)
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{
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int ret;
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ret = dma_buf_init_sysfs_statistics();
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if (ret)
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return ret;
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dma_buf_mnt = kern_mount(&dma_buf_fs_type);
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if (IS_ERR(dma_buf_mnt))
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return PTR_ERR(dma_buf_mnt);
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@ -1821,6 +1804,5 @@ static void __exit dma_buf_deinit(void)
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{
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dma_buf_uninit_debugfs();
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kern_unmount(dma_buf_mnt);
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dma_buf_uninit_sysfs_statistics();
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}
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__exitcall(dma_buf_deinit);
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@ -429,18 +429,6 @@ struct dma_buf {
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__poll_t active;
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} cb_in, cb_out;
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#ifdef CONFIG_DMABUF_SYSFS_STATS
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/**
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* @sysfs_entry:
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*
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* For exposing information about this buffer in sysfs. See also
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* `DMA-BUF statistics`_ for the uapi this enables.
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*/
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struct dma_buf_sysfs_entry {
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struct kobject kobj;
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struct dma_buf *dmabuf;
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} *sysfs_entry;
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#endif
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};
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/**
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