1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * DMA-BUF sysfs statistics.
4 *
5 * Copyright (C) 2021 Google LLC.
6 */
7
8#include <linux/dma-buf.h>
9#include <linux/dma-resv.h>
10#include <linux/kobject.h>
11#include <linux/printk.h>
12#include <linux/slab.h>
13#include <linux/sysfs.h>
14
15#include "dma-buf-sysfs-stats.h"
16
17#define to_dma_buf_entry_from_kobj(x) container_of(x, struct dma_buf_sysfs_entry, kobj)
18
19/**
20 * DOC: overview
21 *
22 * ``/sys/kernel/debug/dma_buf/bufinfo`` provides an overview of every DMA-BUF
23 * in the system. However, since debugfs is not safe to be mounted in
24 * production, procfs and sysfs can be used to gather DMA-BUF statistics on
25 * production systems.
26 *
27 * The ``/proc/<pid>/fdinfo/<fd>`` files in procfs can be used to gather
28 * information about DMA-BUF fds. Detailed documentation about the interface
29 * is present in Documentation/filesystems/proc.rst.
30 *
31 * Unfortunately, the existing procfs interfaces can only provide information
32 * about the DMA-BUFs for which processes hold fds or have the buffers mmapped
33 * into their address space. This necessitated the creation of the DMA-BUF sysfs
34 * statistics interface to provide per-buffer information on production systems.
35 *
36 * The interface at ``/sys/kernel/dmabuf/buffers`` exposes information about
37 * every DMA-BUF when ``CONFIG_DMABUF_SYSFS_STATS`` is enabled.
38 *
39 * The following stats are exposed by the interface:
40 *
41 * * ``/sys/kernel/dmabuf/buffers/<inode_number>/exporter_name``
42 * * ``/sys/kernel/dmabuf/buffers/<inode_number>/size``
43 *
44 * The information in the interface can also be used to derive per-exporter
45 * statistics. The data from the interface can be gathered on error conditions
46 * or other important events to provide a snapshot of DMA-BUF usage.
47 * It can also be collected periodically by telemetry to monitor various metrics.
48 *
49 * Detailed documentation about the interface is present in
50 * Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers.
51 */
52
53struct dma_buf_stats_attribute {
54	struct attribute attr;
55	ssize_t (*show)(struct dma_buf *dmabuf,
56			struct dma_buf_stats_attribute *attr, char *buf);
57};
58#define to_dma_buf_stats_attr(x) container_of(x, struct dma_buf_stats_attribute, attr)
59
60static ssize_t dma_buf_stats_attribute_show(struct kobject *kobj,
61					    struct attribute *attr,
62					    char *buf)
63{
64	struct dma_buf_stats_attribute *attribute;
65	struct dma_buf_sysfs_entry *sysfs_entry;
66	struct dma_buf *dmabuf;
67
68	attribute = to_dma_buf_stats_attr(attr);
69	sysfs_entry = to_dma_buf_entry_from_kobj(kobj);
70	dmabuf = sysfs_entry->dmabuf;
71
72	if (!dmabuf || !attribute->show)
73		return -EIO;
74
75	return attribute->show(dmabuf, attribute, buf);
76}
77
78static const struct sysfs_ops dma_buf_stats_sysfs_ops = {
79	.show = dma_buf_stats_attribute_show,
80};
81
82static ssize_t exporter_name_show(struct dma_buf *dmabuf,
83				  struct dma_buf_stats_attribute *attr,
84				  char *buf)
85{
86	return sysfs_emit(buf, "%s\n", dmabuf->exp_name);
87}
88
89static ssize_t size_show(struct dma_buf *dmabuf,
90			 struct dma_buf_stats_attribute *attr,
91			 char *buf)
92{
93	return sysfs_emit(buf, "%zu\n", dmabuf->size);
94}
95
96static struct dma_buf_stats_attribute exporter_name_attribute =
97	__ATTR_RO(exporter_name);
98static struct dma_buf_stats_attribute size_attribute = __ATTR_RO(size);
99
100static struct attribute *dma_buf_stats_default_attrs[] = {
101	&exporter_name_attribute.attr,
102	&size_attribute.attr,
103	NULL,
104};
105ATTRIBUTE_GROUPS(dma_buf_stats_default);
106
107static void dma_buf_sysfs_release(struct kobject *kobj)
108{
109	struct dma_buf_sysfs_entry *sysfs_entry;
110
111	sysfs_entry = to_dma_buf_entry_from_kobj(kobj);
112	kfree(sysfs_entry);
113}
114
115static const struct kobj_type dma_buf_ktype = {
116	.sysfs_ops = &dma_buf_stats_sysfs_ops,
117	.release = dma_buf_sysfs_release,
118	.default_groups = dma_buf_stats_default_groups,
119};
120
121void dma_buf_stats_teardown(struct dma_buf *dmabuf)
122{
123	struct dma_buf_sysfs_entry *sysfs_entry;
124
125	sysfs_entry = dmabuf->sysfs_entry;
126	if (!sysfs_entry)
127		return;
128
129	kobject_del(&sysfs_entry->kobj);
130	kobject_put(&sysfs_entry->kobj);
131}
132
133
134/* Statistics files do not need to send uevents. */
135static int dmabuf_sysfs_uevent_filter(const struct kobject *kobj)
136{
137	return 0;
138}
139
140static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops = {
141	.filter = dmabuf_sysfs_uevent_filter,
142};
143
144static struct kset *dma_buf_stats_kset;
145static struct kset *dma_buf_per_buffer_stats_kset;
146int dma_buf_init_sysfs_statistics(void)
147{
148	dma_buf_stats_kset = kset_create_and_add("dmabuf",
149						 &dmabuf_sysfs_no_uevent_ops,
150						 kernel_kobj);
151	if (!dma_buf_stats_kset)
152		return -ENOMEM;
153
154	dma_buf_per_buffer_stats_kset = kset_create_and_add("buffers",
155							    &dmabuf_sysfs_no_uevent_ops,
156							    &dma_buf_stats_kset->kobj);
157	if (!dma_buf_per_buffer_stats_kset) {
158		kset_unregister(dma_buf_stats_kset);
159		return -ENOMEM;
160	}
161
162	return 0;
163}
164
165void dma_buf_uninit_sysfs_statistics(void)
166{
167	kset_unregister(dma_buf_per_buffer_stats_kset);
168	kset_unregister(dma_buf_stats_kset);
169}
170
171int dma_buf_stats_setup(struct dma_buf *dmabuf, struct file *file)
172{
173	struct dma_buf_sysfs_entry *sysfs_entry;
174	int ret;
175
176	if (!dmabuf->exp_name) {
177		pr_err("exporter name must not be empty if stats needed\n");
178		return -EINVAL;
179	}
180
181	sysfs_entry = kzalloc(sizeof(struct dma_buf_sysfs_entry), GFP_KERNEL);
182	if (!sysfs_entry)
183		return -ENOMEM;
184
185	sysfs_entry->kobj.kset = dma_buf_per_buffer_stats_kset;
186	sysfs_entry->dmabuf = dmabuf;
187
188	dmabuf->sysfs_entry = sysfs_entry;
189
190	/* create the directory for buffer stats */
191	ret = kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_ktype, NULL,
192				   "%lu", file_inode(file)->i_ino);
193	if (ret)
194		goto err_sysfs_dmabuf;
195
196	return 0;
197
198err_sysfs_dmabuf:
199	kobject_put(&sysfs_entry->kobj);
200	dmabuf->sysfs_entry = NULL;
201	return ret;
202}
203