1 files changed, 202 insertions, 0 deletions
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 0000000000..b5b62e40cc
--- /dev/null
+++ b/drivers/dma-buf/dma-buf-sysfs-stats.c
@@ -0,0 +1,202 @@
+// 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/dmabuf/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 const 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(const 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 file *file)
+{
+	struct dma_buf_sysfs_entry *sysfs_entry;
+	int ret;
+
+	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(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;
+}