dmabuf: Add the capability to expose DMA-BUF stats in sysfs

This patch allows statistics to be enabled for each DMA-BUF in
sysfs by enabling the config CONFIG_DMABUF_SYSFS_STATS.

The following stats will be exposed by the interface:

/sys/kernel/dmabuf/buffers/<inode_number>/exporter_name
/sys/kernel/dmabuf/buffers/<inode_number>/size
/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/device
/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/map_counter

The inode_number is unique for each DMA-BUF and was added earlier [1]
in order to allow userspace to track DMA-BUF usage across different
processes.

Currently, this information is exposed in
/sys/kernel/debug/dma_buf/bufinfo.
However, since debugfs is considered unsafe to be mounted in production,
it is being duplicated in sysfs.

This information will be used to derive DMA-BUF
per-exporter stats and per-device usage stats for Android Bug reports.
The corresponding userspace changes can be found at [2].
Telemetry tools will also capture this information(along with other
memory metrics) periodically as well as on important events like a
foreground app kill (which might have been triggered by Low Memory
Killer). It will also contribute to provide a snapshot of the system
memory usage on other events such as OOM kills and Application Not
Responding events.

A shell script that can be run on a classic Linux environment to read
out the DMA-BUF statistics can be found at [3](suggested by John
Stultz).

The patch contains the following improvements over the previous version:
1) Each attachment is represented by its own directory to allow creating
a symlink to the importing device and to also provide room for future
expansion.
2) The number of distinct mappings of each attachment is exposed in a
separate file.
3) The per-buffer statistics are now in /sys/kernel/dmabuf/buffers
inorder to make the interface expandable in future.

All of the improvements above are based on suggestions/feedback from
Daniel Vetter and Christian König.

[1]: https://lore.kernel.org/patchwork/patch/1088791/
[2]: https://android-review.googlesource.com/q/topic:%22dmabuf-sysfs%22+(status:open%20OR%20status:merged)
[3]: https://android-review.googlesource.com/c/platform/system/memory/libmeminfo/+/1549734

Signed-off-by: Hridya Valsaraju <hridya@google.com>

Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers

@@ -0,0 +1,52 @@
+What:		/sys/kernel/dmabuf/buffers
+Date:		January 2021
+KernelVersion:	v5.12
+Contact:	Hridya Valsaraju <hridya@google.com>
+Description:	The /sys/kernel/dmabuf/buffers directory contains a
+		snapshot of the internal state of every DMA-BUF.
+		/sys/kernel/dmabuf/buffers/<inode_number> will contain the
+		statistics for the DMA-BUF with the unique inode number
+		<inode_number>
+Users:		kernel memory tuning/debugging tools
+
+What:		/sys/kernel/dmabuf/buffers/<inode_number>/exporter_name
+Date:		January 2021
+KernelVersion:	v5.12
+Contact:	Hridya Valsaraju <hridya@google.com>
+Description:	This file is read-only and contains the name of the exporter of
+		the DMA-BUF.
+
+What:		/sys/kernel/dmabuf/buffers/<inode_number>/size
+Date:		January 2021
+KernelVersion:	v5.12
+Contact:	Hridya Valsaraju <hridya@google.com>
+Description:	This file is read-only and specifies the size of the DMA-BUF in
+		bytes.
+
+What:		/sys/kernel/dmabuf/buffers/<inode_number>/attachments
+Date:		January 2021
+KernelVersion:	v5.12
+Contact:	Hridya Valsaraju <hridya@google.com>
+Description:	This directory will contain subdirectories representing every
+		attachment of the DMA-BUF.
+
+What:		/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>
+Date:		January 2021
+KernelVersion:	v5.12
+Contact:	Hridya Valsaraju <hridya@google.com>
+Description:	This directory will contain information on the attaching device
+		and the number of current distinct device mappings.
+
+What:		/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>/device
+Date:		January 2021
+KernelVersion:	v5.12
+Contact:	Hridya Valsaraju <hridya@google.com>
+Description:	This file is read-only and is a symlink to the attaching devices's
+		sysfs entry.
+
+What:		/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>/map_counter
+Date:		January 2021
+KernelVersion:	v5.12
+Contact:	Hridya Valsaraju <hridya@google.com>
+Description:	This file is read-only and contains a map_counter indicating the
+		number of distinct device mappings of the attachment.

drivers/dma-buf/Kconfig

@@ -64,6 +64,17 @@ menuconfig DMABUF_HEAPS
 	  allows userspace to allocate dma-bufs that can be shared
 	  between drivers.
 
+menuconfig DMABUF_SYSFS_STATS
+	bool "DMA-BUF sysfs statistics"
+	select DMA_SHARED_BUFFER
+	help
+	   Choose this option to enable DMA-BUF sysfs statistics
+	   in location /sys/kernel/dmabuf/buffers.
+
+	   /sys/kernel/dmabuf/buffers/<inode_number> will contain
+	   statistics for the DMA-BUF with the unique inode number
+	   <inode_number>.
+
 source "drivers/dma-buf/heaps/Kconfig"
 
 endmenu

drivers/dma-buf/Makefile

@@ -6,6 +6,7 @@ obj-$(CONFIG_DMABUF_HEAPS)	+= heaps/
 obj-$(CONFIG_SYNC_FILE)		+= sync_file.o
 obj-$(CONFIG_SW_SYNC)		+= sw_sync.o sync_debug.o
 obj-$(CONFIG_UDMABUF)		+= udmabuf.o
+obj-$(CONFIG_DMABUF_SYSFS_STATS) += dma-buf-sysfs-stats.o
 
 dmabuf_selftests-y := \
 	selftest.o \

drivers/dma-buf/dma-buf-sysfs-stats.c

@@ -0,0 +1,283 @@
+// 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>
+
+#define to_dma_buf_entry_from_kobj(x) container_of(x, struct dma_buf_sysfs_entry, kobj)
+
+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,
+};
+
+#define to_dma_buf_attach_entry_from_kobj(x) container_of(x, struct dma_buf_attach_sysfs_entry, kobj)
+
+struct dma_buf_attach_stats_attribute {
+	struct attribute attr;
+	ssize_t (*show)(struct dma_buf_attach_sysfs_entry *sysfs_entry,
+			struct dma_buf_attach_stats_attribute *attr, char *buf);
+};
+#define to_dma_buf_attach_stats_attr(x) container_of(x, struct dma_buf_attach_stats_attribute, attr)
+
+static ssize_t dma_buf_attach_stats_attribute_show(struct kobject *kobj,
+						   struct attribute *attr,
+						   char *buf)
+{
+	struct dma_buf_attach_stats_attribute *attribute;
+	struct dma_buf_attach_sysfs_entry *sysfs_entry;
+
+	attribute = to_dma_buf_attach_stats_attr(attr);
+	sysfs_entry = to_dma_buf_attach_entry_from_kobj(kobj);
+
+	if (!attribute->show)
+		return -EIO;
+
+	return attribute->show(sysfs_entry, attribute, buf);
+}
+
+static const struct sysfs_ops dma_buf_attach_stats_sysfs_ops = {
+	.show = dma_buf_attach_stats_attribute_show,
+};
+
+static ssize_t map_counter_show(struct dma_buf_attach_sysfs_entry *sysfs_entry,
+				struct dma_buf_attach_stats_attribute *attr,
+				char *buf)
+{
+	return sysfs_emit(buf, "%u\n", sysfs_entry->map_counter);
+}
+
+static struct dma_buf_attach_stats_attribute map_counter_attribute =
+	__ATTR_RO(map_counter);
+
+static struct attribute *dma_buf_attach_stats_default_attrs[] = {
+	&map_counter_attribute.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(dma_buf_attach_stats_default);
+
+static void dma_buf_attach_sysfs_release(struct kobject *kobj)
+{
+	struct dma_buf_attach_sysfs_entry *sysfs_entry;
+
+	sysfs_entry = to_dma_buf_attach_entry_from_kobj(kobj);
+	kfree(sysfs_entry);
+}
+
+static struct kobj_type dma_buf_attach_ktype = {
+	.sysfs_ops = &dma_buf_attach_stats_sysfs_ops,
+	.release = dma_buf_attach_sysfs_release,
+	.default_groups = dma_buf_attach_stats_default_groups,
+};
+
+void dma_buf_attach_stats_teardown(struct dma_buf_attachment *attach)
+{
+	struct dma_buf_attach_sysfs_entry *sysfs_entry;
+
+	sysfs_entry = attach->sysfs_entry;
+	if (!sysfs_entry)
+		return;
+
+	sysfs_delete_link(&sysfs_entry->kobj, &attach->dev->kobj, "device");
+
+	kobject_del(&sysfs_entry->kobj);
+	kobject_put(&sysfs_entry->kobj);
+}
+
+int dma_buf_attach_stats_setup(struct dma_buf_attachment *attach,
+			       unsigned int uid)
+{
+	struct dma_buf_attach_sysfs_entry *sysfs_entry;
+	int ret;
+	struct dma_buf *dmabuf;
+
+	if (!attach)
+		return -EINVAL;
+
+	dmabuf = attach->dmabuf;
+
+	sysfs_entry = kzalloc(sizeof(struct dma_buf_attach_sysfs_entry),
+			      GFP_KERNEL);
+	if (!sysfs_entry)
+		return -ENOMEM;
+
+	sysfs_entry->kobj.kset = dmabuf->sysfs_entry->attach_stats_kset;
+
+	attach->sysfs_entry = sysfs_entry;
+
+	ret = kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_attach_ktype,
+				   NULL, "%u", uid);
+	if (ret)
+		goto kobj_err;
+
+	ret = sysfs_create_link(&sysfs_entry->kobj, &attach->dev->kobj,
+				"device");
+	if (ret)
+		goto link_err;
+
+	return 0;
+
+link_err:
+	kobject_del(&sysfs_entry->kobj);
+kobj_err:
+	kobject_put(&sysfs_entry->kobj);
+	attach->sysfs_entry = NULL;
+
+	return ret;
+}
+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;
+
+	kset_unregister(sysfs_entry->attach_stats_kset);
+	kobject_del(&sysfs_entry->kobj);
+	kobject_put(&sysfs_entry->kobj);
+}
+
+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", NULL, kernel_kobj);
+	if (!dma_buf_stats_kset)
+		return -ENOMEM;
+
+	dma_buf_per_buffer_stats_kset = kset_create_and_add("buffers", NULL,
+							    &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;
+	struct kset *attach_stats_kset;
+
+	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;
+
+	/* create the directory for attachment stats */
+	attach_stats_kset = kset_create_and_add("attachments", NULL,
+						&sysfs_entry->kobj);
+	if (!attach_stats_kset) {
+		ret = -ENOMEM;
+		goto err_sysfs_attach;
+	}
+
+	sysfs_entry->attach_stats_kset = attach_stats_kset;
+
+	return 0;
+
+err_sysfs_attach:
+	kobject_del(&sysfs_entry->kobj);
+err_sysfs_dmabuf:
+	kobject_put(&sysfs_entry->kobj);
+	dmabuf->sysfs_entry = NULL;
+	return ret;
+}