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// 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``
*
* The information in the interface can also be used to derive per-exporter
* 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,
};
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;
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;
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;
return 0;
err_sysfs_dmabuf:
kobject_put(&sysfs_entry->kobj);
dmabuf->sysfs_entry = NULL;
return ret;
}
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