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/dma-buf/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 
53 struct 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 
60 static 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 
78 static const struct sysfs_ops dma_buf_stats_sysfs_ops = {
79 	.show = dma_buf_stats_attribute_show,
80 };
81 
82 static 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 
89 static 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 
96 static struct dma_buf_stats_attribute exporter_name_attribute =
97 	__ATTR_RO(exporter_name);
98 static struct dma_buf_stats_attribute size_attribute = __ATTR_RO(size);
99 
100 static struct attribute *dma_buf_stats_default_attrs[] = {
101 	&exporter_name_attribute.attr,
102 	&size_attribute.attr,
103 	NULL,
104 };
105 ATTRIBUTE_GROUPS(dma_buf_stats_default);
106 
107 static 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 
115 static 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 
121 void 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. */
135 static int dmabuf_sysfs_uevent_filter(struct kset *kset, struct kobject *kobj)
136 {
137 	return 0;
138 }
139 
140 static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops = {
141 	.filter = dmabuf_sysfs_uevent_filter,
142 };
143 
144 static struct kset *dma_buf_stats_kset;
145 static struct kset *dma_buf_per_buffer_stats_kset;
146 int 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 
165 void 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 
171 int dma_buf_stats_setup(struct dma_buf *dmabuf)
172 {
173 	struct dma_buf_sysfs_entry *sysfs_entry;
174 	int ret;
175 
176 	if (!dmabuf || !dmabuf->file)
177 		return -EINVAL;
178 
179 	if (!dmabuf->exp_name) {
180 		pr_err("exporter name must not be empty if stats needed\n");
181 		return -EINVAL;
182 	}
183 
184 	sysfs_entry = kzalloc(sizeof(struct dma_buf_sysfs_entry), GFP_KERNEL);
185 	if (!sysfs_entry)
186 		return -ENOMEM;
187 
188 	sysfs_entry->kobj.kset = dma_buf_per_buffer_stats_kset;
189 	sysfs_entry->dmabuf = dmabuf;
190 
191 	dmabuf->sysfs_entry = sysfs_entry;
192 
193 	/* create the directory for buffer stats */
194 	ret = kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_ktype, NULL,
195 				   "%lu", file_inode(dmabuf->file)->i_ino);
196 	if (ret)
197 		goto err_sysfs_dmabuf;
198 
199 	return 0;
200 
201 err_sysfs_dmabuf:
202 	kobject_put(&sysfs_entry->kobj);
203 	dmabuf->sysfs_entry = NULL;
204 	return ret;
205 }
206