[PATCH v4 02/10] user_events: Add minimal support for trace_event into ftrace

[Beau Belgrave]

Minimal support for interacting with dynamic events, trace_event and
ftrace. Core outline of flow between user process, ioctl and trace_event
APIs.

Signed-off-by: Beau Belgrave <beaub@xxxxxxxxxxxxxxxxxxx>
---
 kernel/trace/Kconfig             |   15 +
 kernel/trace/Makefile            |    1 +
 kernel/trace/trace_events_user.c | 1140 ++++++++++++++++++++++++++++++
 3 files changed, 1156 insertions(+)
 create mode 100644 kernel/trace/trace_events_user.c

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 3ee23f4d437f..deaaad421be4 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -725,6 +725,21 @@ config SYNTH_EVENTS
 
 	  If in doubt, say N.
 
+config USER_EVENTS
+	bool "User trace events"
+	select TRACING
+	select DYNAMIC_EVENTS
+	default n
+	help
+	  User trace events are user-defined trace events that
+	  can be used like an existing kernel trace event.  User trace
+	  events are generated by writing to a tracefs file.  User
+	  processes can determine if their tracing events should be
+	  generated by memory mapping a tracefs file and checking for
+	  an associated byte being non-zero.
+
+	  If in doubt, say N.
+
 config HIST_TRIGGERS
 	bool "Histogram triggers"
 	depends on ARCH_HAVE_NMI_SAFE_CMPXCHG
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index b1c47ccf4f73..a653b255e89c 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -80,6 +80,7 @@ obj-$(CONFIG_EVENT_TRACING) += trace_events_trigger.o
 obj-$(CONFIG_TRACE_EVENT_INJECT) += trace_events_inject.o
 obj-$(CONFIG_SYNTH_EVENTS) += trace_events_synth.o
 obj-$(CONFIG_HIST_TRIGGERS) += trace_events_hist.o
+obj-$(CONFIG_USER_EVENTS) += trace_events_user.o
 obj-$(CONFIG_BPF_EVENTS) += bpf_trace.o
 obj-$(CONFIG_KPROBE_EVENTS) += trace_kprobe.o
 obj-$(CONFIG_TRACEPOINTS) += error_report-traces.o
diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
new file mode 100644
index 000000000000..a68017ad7fdd
--- /dev/null
+++ b/kernel/trace/trace_events_user.c
@@ -0,0 +1,1140 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2021, Microsoft Corporation.
+ *
+ * Authors:
+ *   Beau Belgrave <beaub@xxxxxxxxxxxxxxxxxxx>
+ */
+
+#include <linux/bitmap.h>
+#include <linux/cdev.h>
+#include <linux/hashtable.h>
+#include <linux/list.h>
+#include <linux/io.h>
+#include <linux/uio.h>
+#include <linux/ioctl.h>
+#include <linux/jhash.h>
+#include <linux/trace_events.h>
+#include <linux/tracefs.h>
+#include <linux/types.h>
+#include <linux/uaccess.h>
+#include <uapi/linux/user_events.h>
+#include "trace.h"
+#include "trace_dynevent.h"
+
+#define USER_EVENTS_PREFIX_LEN (sizeof(USER_EVENTS_PREFIX)-1)
+
+#define FIELD_DEPTH_TYPE 0
+#define FIELD_DEPTH_NAME 1
+#define FIELD_DEPTH_SIZE 2
+
+/*
+ * Limits how many trace_event calls user processes can create:
+ * Must be multiple of PAGE_SIZE.
+ */
+#define MAX_PAGES 1
+#define MAX_EVENTS (MAX_PAGES * PAGE_SIZE)
+
+/* Limit how long of an event name plus args within the subsystem. */
+#define MAX_EVENT_DESC 512
+#define EVENT_NAME(user_event) ((user_event)->tracepoint.name)
+
+static char *register_page_data;
+
+static DEFINE_MUTEX(reg_mutex);
+static DEFINE_HASHTABLE(register_table, 4);
+static DECLARE_BITMAP(page_bitmap, MAX_EVENTS);
+
+struct user_event {
+	struct tracepoint tracepoint;
+	struct trace_event_call call;
+	struct trace_event_class class;
+	struct dyn_event devent;
+	struct hlist_node node;
+	struct list_head fields;
+	atomic_t refcnt;
+	int index;
+	int flags;
+};
+
+struct user_event_refs {
+	struct rcu_head rcu;
+	int count;
+	struct user_event *events[];
+};
+
+typedef void (*user_event_func_t) (struct user_event *user,
+				   void *data, u32 datalen,
+				   void *tpdata);
+
+static int user_event_parse(char *name, char *args, char *flags,
+			    struct user_event **newuser);
+
+static u32 user_event_key(char *name)
+{
+	return jhash(name, strlen(name), 0);
+}
+
+static struct list_head *user_event_get_fields(struct trace_event_call *call)
+{
+	struct user_event *user = (struct user_event *)call->data;
+
+	return &user->fields;
+}
+
+/*
+ * Parses a register command for user_events
+ * Format: event_name[:FLAG1[,FLAG2...]] [field1[;field2...]]
+ *
+ * Example event named test with a 20 char msg field with a unsigned int after:
+ * test char[20] msg;unsigned int id
+ *
+ * NOTE: Offsets are from the user data perspective, they are not from the
+ * trace_entry/buffer perspective. We automatically add the common properties
+ * sizes to the offset for the user.
+ */
+static int user_event_parse_cmd(char *raw_command, struct user_event **newuser)
+{
+	char *name = raw_command;
+	char *args = strpbrk(name, " ");
+	char *flags;
+
+	if (args)
+		*args++ = 0;
+
+	flags = strpbrk(name, ":");
+
+	if (flags)
+		*flags++ = 0;
+
+	return user_event_parse(name, args, flags, newuser);
+}
+
+static int user_field_array_size(const char *type)
+{
+	const char *start = strchr(type, '[');
+	int size = 0;
+
+	if (start == NULL)
+		return -EINVAL;
+
+	start++;
+
+	while (*start >= '0' && *start <= '9')
+		size = (size * 10) + (*start++ - '0');
+
+	if (*start != ']')
+		return -EINVAL;
+
+	return size;
+}
+
+static int user_field_size(const char *type)
+{
+	/* long is not allowed from a user, since it's ambigious in size */
+	if (strcmp(type, "s64") == 0)
+		return sizeof(s64);
+	if (strcmp(type, "u64") == 0)
+		return sizeof(u64);
+	if (strcmp(type, "s32") == 0)
+		return sizeof(s32);
+	if (strcmp(type, "u32") == 0)
+		return sizeof(u32);
+	if (strcmp(type, "int") == 0)
+		return sizeof(int);
+	if (strcmp(type, "unsigned int") == 0)
+		return sizeof(unsigned int);
+	if (strcmp(type, "s16") == 0)
+		return sizeof(s16);
+	if (strcmp(type, "u16") == 0)
+		return sizeof(u16);
+	if (strcmp(type, "short") == 0)
+		return sizeof(short);
+	if (strcmp(type, "unsigned short") == 0)
+		return sizeof(unsigned short);
+	if (strcmp(type, "s8") == 0)
+		return sizeof(s8);
+	if (strcmp(type, "u8") == 0)
+		return sizeof(u8);
+	if (strcmp(type, "char") == 0)
+		return sizeof(char);
+	if (strcmp(type, "unsigned char") == 0)
+		return sizeof(unsigned char);
+	if (strstr(type, "char[") == type)
+		return user_field_array_size(type);
+	if (strstr(type, "unsigned char[") == type)
+		return user_field_array_size(type);
+	if (strstr(type, "__data_loc ") == type)
+		return sizeof(u32);
+	if (strstr(type, "__rel_loc ") == type)
+		return sizeof(u32);
+
+	/* Uknown basic type, error */
+	return -EINVAL;
+}
+
+static void user_event_destroy_fields(struct user_event *user)
+{
+	struct ftrace_event_field *field, *next;
+	struct list_head *head = &user->fields;
+
+	list_for_each_entry_safe(field, next, head, link) {
+		list_del(&field->link);
+		kfree(field);
+	}
+}
+
+static int user_event_add_field(struct user_event *user, const char *type,
+				const char *name, int offset, int size,
+				int is_signed, int filter_type)
+{
+	struct ftrace_event_field *field;
+
+	field = kmalloc(sizeof(*field), GFP_KERNEL);
+
+	if (!field)
+		return -ENOMEM;
+
+	field->type = type;
+	field->name = name;
+	field->offset = offset;
+	field->size = size;
+	field->is_signed = is_signed;
+	field->filter_type = filter_type;
+
+	list_add(&field->link, &user->fields);
+
+	return 0;
+}
+
+/*
+ * Parses the values of a field within the description
+ * Format: type name [size]
+ */
+static int user_event_parse_field(char *field, struct user_event *user,
+				  u32 *offset)
+{
+	char *part, *type, *name;
+	u32 depth = 0, saved_offset = *offset;
+	int size = -EINVAL;
+	bool is_struct = false;
+
+	field = skip_spaces(field);
+
+	if (*field == 0)
+		return 0;
+
+	/* Handle types that have a space within */
+	if (strstr(field, "unsigned ") == field) {
+		type = field;
+		field = strpbrk(field + sizeof("unsigned"), " ");
+		goto skip_next;
+	} else if (strstr(field, "struct ") == field) {
+		type = field;
+		field = strpbrk(field + sizeof("struct"), " ");
+		is_struct = true;
+		goto skip_next;
+	} else if (strstr(field, "__data_loc unsigned ") == field) {
+		type = field;
+		field = strpbrk(field + sizeof("__data_loc unsigned"), " ");
+		goto skip_next;
+	} else if (strstr(field, "__data_loc ") == field) {
+		type = field;
+		field = strpbrk(field + sizeof("__data_loc"), " ");
+		goto skip_next;
+	} else if (strstr(field, "__rel_loc unsigned ") == field) {
+		type = field;
+		field = strpbrk(field + sizeof("__rel_loc unsigned"), " ");
+		goto skip_next;
+	} else if (strstr(field, "__rel_loc ") == field) {
+		type = field;
+		field = strpbrk(field + sizeof("__rel_loc"), " ");
+		goto skip_next;
+	}
+	goto parse;
+skip_next:
+	if (field == NULL)
+		return -EINVAL;
+
+	*field++ = 0;
+	depth++;
+parse:
+	while ((part = strsep(&field, " ")) != NULL) {
+		switch (depth++) {
+		case FIELD_DEPTH_TYPE:
+			type = part;
+			break;
+		case FIELD_DEPTH_NAME:
+			name = part;
+			break;
+		case FIELD_DEPTH_SIZE:
+			if (!is_struct)
+				return -EINVAL;
+
+			if (kstrtou32(part, 10, &size))
+				return -EINVAL;
+			break;
+		default:
+			return -EINVAL;
+		}
+	}
+
+	if (depth < FIELD_DEPTH_SIZE)
+		return -EINVAL;
+
+	if (depth == FIELD_DEPTH_SIZE)
+		size = user_field_size(type);
+
+	if (size == 0)
+		return -EINVAL;
+
+	if (size < 0)
+		return size;
+
+	*offset = saved_offset + size;
+
+	return user_event_add_field(user, type, name, saved_offset, size,
+				    type[0] != 'u', FILTER_OTHER);
+}
+
+static void user_event_parse_flags(struct user_event *user, char *flags)
+{
+	char *flag;
+
+	if (flags == NULL)
+		return;
+
+	while ((flag = strsep(&flags, ",")) != NULL) {
+		if (strcmp(flag, "BPF_ITER") == 0)
+			user->flags |= FLAG_BPF_ITER;
+	}
+}
+
+static int user_event_parse_fields(struct user_event *user, char *args)
+{
+	char *field;
+	u32 offset = sizeof(struct trace_entry);
+	int ret = -EINVAL;
+
+	if (args == NULL)
+		return 0;
+
+	while ((field = strsep(&args, ";")) != NULL) {
+		ret = user_event_parse_field(field, user, &offset);
+
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
+
+static struct trace_event_fields user_event_fields_array[] = {
+	{}
+};
+
+static enum print_line_t user_event_print_trace(struct trace_iterator *iter,
+						int flags,
+						struct trace_event *event)
+{
+	/* Unsafe to try to decode user provided print_fmt, use hex */
+	trace_print_hex_dump_seq(&iter->seq, "", DUMP_PREFIX_OFFSET, 16,
+				 1, iter->ent, iter->ent_size, true);
+
+	return trace_handle_return(&iter->seq);
+}
+
+static struct trace_event_functions user_event_funcs = {
+	.trace = user_event_print_trace,
+};
+
+static int destroy_user_event(struct user_event *user)
+{
+	int ret = 0;
+
+	/* Must destroy fields before call removal */
+	user_event_destroy_fields(user);
+
+	ret = trace_remove_event_call(&user->call);
+
+	if (ret)
+		return ret;
+
+	dyn_event_remove(&user->devent);
+
+	register_page_data[user->index] = 0;
+	clear_bit(user->index, page_bitmap);
+	hash_del(&user->node);
+
+	kfree(EVENT_NAME(user));
+	kfree(user);
+
+	return ret;
+}
+
+static struct user_event *find_user_event(char *name, u32 *outkey)
+{
+	struct user_event *user;
+	u32 key = user_event_key(name);
+
+	*outkey = key;
+
+	hash_for_each_possible(register_table, user, node, key)
+		if (!strcmp(EVENT_NAME(user), name))
+			return user;
+
+	return NULL;
+}
+
+/*
+ * Writes the user supplied payload out to a trace file.
+ */
+static void user_event_ftrace(struct user_event *user, void *data, u32 datalen,
+			      void *tpdata)
+{
+	struct trace_event_file *file;
+	struct trace_entry *entry;
+	struct trace_event_buffer event_buffer;
+
+	file = (struct trace_event_file *)tpdata;
+
+	if (!file ||
+	    !(file->flags & EVENT_FILE_FL_ENABLED) ||
+	    trace_trigger_soft_disabled(file))
+		return;
+
+	entry = trace_event_buffer_reserve(&event_buffer, file,
+					   sizeof(*entry) + datalen);
+
+	if (unlikely(!entry))
+		return;
+
+	memcpy(entry + 1, data, datalen);
+
+	trace_event_buffer_commit(&event_buffer);
+}
+
+/*
+ * Update the register page that is shared between user processes.
+ */
+static void update_reg_page_for(struct user_event *user)
+{
+	struct tracepoint *tp = &user->tracepoint;
+	char status = 0;
+
+	if (atomic_read(&tp->key.enabled) > 0) {
+		struct tracepoint_func *probe_func_ptr;
+		user_event_func_t probe_func;
+
+		rcu_read_lock_sched();
+
+		probe_func_ptr = rcu_dereference_sched(tp->funcs);
+
+		if (probe_func_ptr) {
+			do {
+				probe_func = probe_func_ptr->func;
+
+				if (probe_func == user_event_ftrace)
+					status |= EVENT_STATUS_FTRACE;
+				else
+					status |= EVENT_STATUS_OTHER;
+			} while ((++probe_func_ptr)->func);
+		}
+
+		rcu_read_unlock_sched();
+	}
+
+	register_page_data[user->index] = status;
+}
+
+/*
+ * Register callback for our events from tracing sub-systems.
+ */
+static int user_event_reg(struct trace_event_call *call,
+			  enum trace_reg type,
+			  void *data)
+{
+	struct user_event *user = (struct user_event *)call->data;
+	int ret = 0;
+
+	if (!user)
+		return -ENOENT;
+
+	switch (type) {
+	case TRACE_REG_REGISTER:
+		ret = tracepoint_probe_register(call->tp,
+						call->class->probe,
+						data);
+		if (!ret)
+			goto inc;
+		break;
+
+	case TRACE_REG_UNREGISTER:
+		tracepoint_probe_unregister(call->tp,
+					    call->class->probe,
+					    data);
+		goto dec;
+
+#ifdef CONFIG_PERF_EVENTS
+	case TRACE_REG_PERF_REGISTER:
+	case TRACE_REG_PERF_UNREGISTER:
+	case TRACE_REG_PERF_OPEN:
+	case TRACE_REG_PERF_CLOSE:
+	case TRACE_REG_PERF_ADD:
+	case TRACE_REG_PERF_DEL:
+		break;
+#endif
+	}
+
+	return ret;
+inc:
+	atomic_inc(&user->refcnt);
+	update_reg_page_for(user);
+	return 0;
+dec:
+	update_reg_page_for(user);
+	atomic_dec(&user->refcnt);
+	return 0;
+}
+
+static int user_event_create(const char *raw_command)
+{
+	struct user_event *user;
+	char *name;
+	int ret;
+
+	if (strstr(raw_command, USER_EVENTS_PREFIX) != raw_command)
+		return -ECANCELED;
+
+	raw_command += USER_EVENTS_PREFIX_LEN;
+	raw_command = skip_spaces(raw_command);
+
+	name = kstrdup(raw_command, GFP_KERNEL);
+
+	if (!name)
+		return -ENOMEM;
+
+	mutex_lock(&reg_mutex);
+	ret = user_event_parse_cmd(name, &user);
+	mutex_unlock(&reg_mutex);
+
+	return ret;
+}
+
+static int user_event_show(struct seq_file *m, struct dyn_event *ev)
+{
+	struct user_event *user = container_of(ev, struct user_event, devent);
+	struct ftrace_event_field *field, *next;
+	struct list_head *head;
+	int depth = 0;
+
+	seq_printf(m, "%s%s", USER_EVENTS_PREFIX, EVENT_NAME(user));
+
+	head = trace_get_fields(&user->call);
+
+	list_for_each_entry_safe_reverse(field, next, head, link) {
+		if (depth == 0)
+			seq_puts(m, " ");
+		else
+			seq_puts(m, "; ");
+		seq_printf(m, "%s %s", field->type, field->name);
+		depth++;
+	}
+
+	seq_puts(m, "\n");
+
+	return 0;
+}
+
+static bool user_event_is_busy(struct dyn_event *ev)
+{
+	struct user_event *user = container_of(ev, struct user_event, devent);
+
+	return atomic_read(&user->refcnt) != 0;
+}
+
+static int user_event_free(struct dyn_event *ev)
+{
+	struct user_event *user = container_of(ev, struct user_event, devent);
+
+	return destroy_user_event(user);
+}
+
+static bool user_event_match(const char *system, const char *event,
+			     int argc, const char **argv, struct dyn_event *ev)
+{
+	struct user_event *user = container_of(ev, struct user_event, devent);
+
+	return strcmp(EVENT_NAME(user), event) == 0 &&
+		(!system || strcmp(system, USER_EVENTS_SYSTEM) == 0);
+}
+
+static struct dyn_event_operations user_event_dops = {
+	.create = user_event_create,
+	.show = user_event_show,
+	.is_busy = user_event_is_busy,
+	.free = user_event_free,
+	.match = user_event_match,
+};
+
+static int user_event_trace_register(struct user_event *user)
+{
+	int ret;
+
+	ret = register_trace_event(&user->call.event);
+
+	if (!ret)
+		return -ENODEV;
+
+	ret = trace_add_event_call(&user->call);
+
+	if (ret)
+		unregister_trace_event(&user->call.event);
+
+	return ret;
+}
+
+/*
+ * Parses the event name, arguments and flags then registers if successful.
+ */
+static int user_event_parse(char *name, char *args, char *flags,
+			    struct user_event **newuser)
+{
+	int ret;
+	int index;
+	u32 key;
+	struct user_event *user = find_user_event(name, &key);
+
+	if (user) {
+		*newuser = user;
+		ret = 0;
+		goto put_name;
+	}
+
+	index = find_first_zero_bit(page_bitmap, MAX_EVENTS);
+
+	if (index == MAX_EVENTS) {
+		ret = -EMFILE;
+		goto put_name;
+	}
+
+	user = kzalloc(sizeof(*user), GFP_KERNEL);
+
+	if (!user) {
+		ret = -ENOMEM;
+		goto put_name;
+	}
+
+	INIT_LIST_HEAD(&user->class.fields);
+	INIT_LIST_HEAD(&user->fields);
+
+	user->tracepoint.name = name;
+
+	user_event_parse_flags(user, flags);
+
+	ret = user_event_parse_fields(user, args);
+
+	if (ret)
+		goto put_user;
+
+	/* Minimal print format */
+	user->call.print_fmt = "\"\"";
+
+	user->call.data = user;
+	user->call.class = &user->class;
+	user->call.name = name;
+	user->call.flags = TRACE_EVENT_FL_TRACEPOINT;
+	user->call.tp = &user->tracepoint;
+	user->call.event.funcs = &user_event_funcs;
+
+	user->class.system = USER_EVENTS_SYSTEM;
+	user->class.fields_array = user_event_fields_array;
+	user->class.get_fields = user_event_get_fields;
+	user->class.reg = user_event_reg;
+	user->class.probe = user_event_ftrace;
+
+	mutex_lock(&event_mutex);
+	ret = user_event_trace_register(user);
+	mutex_unlock(&event_mutex);
+
+	if (ret)
+		goto put_user;
+
+	user->index = index;
+	dyn_event_init(&user->devent, &user_event_dops);
+	dyn_event_add(&user->devent);
+	set_bit(user->index, page_bitmap);
+	hash_add(register_table, &user->node, key);
+
+	*newuser = user;
+	return 0;
+put_user:
+	user_event_destroy_fields(user);
+	kfree(user);
+put_name:
+	kfree(name);
+	return ret;
+}
+
+/*
+ * Deletes a previously created event if it is no longer being used.
+ */
+static int delete_user_event(char *name)
+{
+	u32 key;
+	int ret;
+	struct user_event *user = find_user_event(name, &key);
+
+	if (!user)
+		return -ENOENT;
+
+	if (atomic_read(&user->refcnt) != 0)
+		return -EBUSY;
+
+	mutex_lock(&event_mutex);
+	ret = destroy_user_event(user);
+	mutex_unlock(&event_mutex);
+
+	return ret;
+}
+
+/*
+ * Validates the user payload and writes via iterator.
+ */
+static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
+{
+	struct user_event_refs *refs;
+	struct user_event *user = NULL;
+	struct tracepoint *tp;
+	ssize_t ret = i->count;
+	int idx;
+
+	if (unlikely(copy_from_iter(&idx, sizeof(idx), i) != sizeof(idx)))
+		return -EFAULT;
+
+	rcu_read_lock_sched();
+
+	refs = rcu_dereference_sched(file->private_data);
+
+	if (likely(refs && idx < refs->count))
+		user = refs->events[idx];
+
+	rcu_read_unlock_sched();
+
+	if (unlikely(user == NULL))
+		return -ENOENT;
+
+	tp = &user->tracepoint;
+
+	if (likely(atomic_read(&tp->key.enabled) > 0)) {
+		struct tracepoint_func *probe_func_ptr;
+		user_event_func_t probe_func;
+		void *tpdata;
+		void *kdata;
+		u32 datalen;
+
+		kdata = kmalloc(i->count, GFP_KERNEL);
+
+		if (unlikely(!kdata))
+			return -ENOMEM;
+
+		datalen = copy_from_iter(kdata, i->count, i);
+
+		rcu_read_lock_sched();
+
+		probe_func_ptr = rcu_dereference_sched(tp->funcs);
+
+		if (probe_func_ptr) {
+			do {
+				probe_func = probe_func_ptr->func;
+				tpdata = probe_func_ptr->data;
+				probe_func(user, kdata, datalen, tpdata);
+			} while ((++probe_func_ptr)->func);
+		}
+
+		rcu_read_unlock_sched();
+
+		kfree(kdata);
+	}
+
+	return ret;
+}
+
+static ssize_t user_events_write(struct file *file, const char __user *ubuf,
+				 size_t count, loff_t *ppos)
+{
+	struct iovec iov;
+	struct iov_iter i;
+
+	if (unlikely(*ppos != 0))
+		return -EFAULT;
+
+	if (unlikely(import_single_range(READ, (char *)ubuf, count, &iov, &i)))
+		return -EFAULT;
+
+	return user_events_write_core(file, &i);
+}
+
+static ssize_t user_events_write_iter(struct kiocb *kp, struct iov_iter *i)
+{
+	return user_events_write_core(kp->ki_filp, i);
+}
+
+static int user_events_ref_add(struct file *file, struct user_event *user)
+{
+	struct user_event_refs *refs, *new_refs;
+	int i, size, count = 0;
+
+	rcu_read_lock_sched();
+	refs = rcu_dereference_sched(file->private_data);
+	rcu_read_unlock_sched();
+
+	if (refs) {
+		count = refs->count;
+
+		for (i = 0; i < count; ++i)
+			if (refs->events[i] == user)
+				return i;
+	}
+
+	size = sizeof(*refs) + (sizeof(struct user_event *) * (count + 1));
+
+	new_refs = kzalloc(size, GFP_KERNEL);
+
+	if (!new_refs)
+		return -ENOMEM;
+
+	new_refs->count = count + 1;
+
+	for (i = 0; i < count; ++i)
+		new_refs->events[i] = refs->events[i];
+
+	new_refs->events[i] = user;
+
+	atomic_inc(&user->refcnt);
+
+	rcu_assign_pointer(file->private_data, new_refs);
+
+	if (refs)
+		kfree_rcu(refs, rcu);
+
+	return i;
+}
+
+static long user_reg_get(struct user_reg __user *ureg, struct user_reg *kreg)
+{
+	u32 size;
+	long ret;
+
+	ret = get_user(size, &ureg->size);
+
+	if (ret)
+		return ret;
+
+	if (size > PAGE_SIZE)
+		return -E2BIG;
+
+	return copy_struct_from_user(kreg, sizeof(*kreg), ureg, size);
+}
+
+/*
+ * Registers a user_event on behalf of a user process.
+ */
+static long user_events_ioctl_reg(struct file *file, unsigned long uarg)
+{
+	struct user_reg __user *ureg = (struct user_reg __user *)uarg;
+	struct user_reg reg;
+	struct user_event *user;
+	char *name;
+	long ret;
+
+	ret = user_reg_get(ureg, &reg);
+
+	if (ret)
+		return ret;
+
+	name = strndup_user((const char __user *)(uintptr_t)reg.name_args,
+			    MAX_EVENT_DESC);
+
+	if (IS_ERR(name)) {
+		ret = PTR_ERR(name);
+		return ret;
+	}
+
+	ret = user_event_parse_cmd(name, &user);
+
+	if (ret < 0)
+		return ret;
+
+	ret = user_events_ref_add(file, user);
+
+	if (ret < 0)
+		return ret;
+
+	put_user((u32)ret, &ureg->write_index);
+	put_user(user->index, &ureg->status_index);
+
+	return 0;
+}
+
+/*
+ * Deletes a user_event on behalf of a user process.
+ */
+static long user_events_ioctl_del(struct file *file, unsigned long uarg)
+{
+	void __user *ubuf = (void __user *)uarg;
+	char *name;
+	long ret;
+
+	name = strndup_user(ubuf, MAX_EVENT_DESC);
+
+	if (IS_ERR(name))
+		return PTR_ERR(name);
+
+	ret = delete_user_event(name);
+
+	kfree(name);
+
+	return ret;
+}
+
+/*
+ * Handles the ioctl from user mode to register or alter operations.
+ */
+static long user_events_ioctl(struct file *file, unsigned int cmd,
+			      unsigned long uarg)
+{
+	long ret = -ENOTTY;
+
+	switch (cmd) {
+	case DIAG_IOCSREG:
+		mutex_lock(&reg_mutex);
+		ret = user_events_ioctl_reg(file, uarg);
+		mutex_unlock(&reg_mutex);
+		break;
+
+	case DIAG_IOCSDEL:
+		mutex_lock(&reg_mutex);
+		ret = user_events_ioctl_del(file, uarg);
+		mutex_unlock(&reg_mutex);
+		break;
+	}
+
+	return ret;
+}
+
+/*
+ * Handles the final close of the file from user mode.
+ */
+static int user_events_release(struct inode *node, struct file *file)
+{
+	struct user_event_refs *refs;
+	struct user_event *user;
+	int i;
+
+	rcu_read_lock_sched();
+	refs = rcu_dereference_sched(file->private_data);
+	rcu_read_unlock_sched();
+
+	if (!refs)
+		goto out;
+
+	for (i = 0; i < refs->count; ++i) {
+		user = refs->events[i];
+
+		if (user)
+			atomic_dec(&user->refcnt);
+	}
+
+	kfree_rcu(refs, rcu);
+out:
+	return 0;
+}
+
+static const struct file_operations user_data_fops = {
+	.write = user_events_write,
+	.write_iter = user_events_write_iter,
+	.unlocked_ioctl	= user_events_ioctl,
+	.release = user_events_release,
+};
+
+/*
+ * Maps the shared page into the user process for checking if event is enabled.
+ */
+static int user_status_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	unsigned long size = vma->vm_end - vma->vm_start;
+
+	if (size != MAX_EVENTS)
+		return -EINVAL;
+
+	return remap_pfn_range(vma, vma->vm_start,
+			       virt_to_phys(register_page_data) >> PAGE_SHIFT,
+			       size, vm_get_page_prot(VM_READ));
+}
+
+static int user_status_show(struct seq_file *m, void *p)
+{
+	struct user_event *user;
+	char status;
+	int i, active = 0, busy = 0, flags;
+
+	mutex_lock(&reg_mutex);
+
+	hash_for_each(register_table, i, user, node) {
+		status = register_page_data[user->index];
+		flags = user->flags;
+
+		seq_printf(m, "%d:%s", user->index, EVENT_NAME(user));
+
+		if (flags != 0 || status != 0)
+			seq_puts(m, " #");
+
+		if (status != 0) {
+			seq_puts(m, " Used by");
+			if (status & EVENT_STATUS_FTRACE)
+				seq_puts(m, " ftrace");
+			if (status & EVENT_STATUS_PERF)
+				seq_puts(m, " perf");
+			if (status & EVENT_STATUS_OTHER)
+				seq_puts(m, " other");
+			busy++;
+		}
+
+		if (flags & FLAG_BPF_ITER)
+			seq_puts(m, " FLAG:BPF_ITER");
+
+		seq_puts(m, "\n");
+		active++;
+	}
+
+	mutex_unlock(&reg_mutex);
+
+	seq_puts(m, "\n");
+	seq_printf(m, "Active: %d\n", active);
+	seq_printf(m, "Busy: %d\n", busy);
+	seq_printf(m, "Max: %ld\n", MAX_EVENTS);
+
+	return 0;
+}
+
+static ssize_t user_status_read(struct file *file, char __user *ubuf,
+				size_t count, loff_t *ppos)
+{
+	/*
+	 * Delay allocation of seq data until requested, most callers
+	 * will never read the status file. They will only mmap.
+	 */
+	if (file->private_data == NULL) {
+		int ret;
+
+		if (*ppos != 0)
+			return -EINVAL;
+
+		ret = single_open(file, user_status_show, NULL);
+
+		if (ret)
+			return ret;
+	}
+
+	return seq_read(file, ubuf, count, ppos);
+}
+
+static loff_t user_status_seek(struct file *file, loff_t offset, int whence)
+{
+	if (file->private_data == NULL)
+		return 0;
+
+	return seq_lseek(file, offset, whence);
+}
+
+static int user_status_release(struct inode *node, struct file *file)
+{
+	if (file->private_data == NULL)
+		return 0;
+
+	return single_release(node, file);
+}
+
+static const struct file_operations user_status_fops = {
+	.mmap = user_status_mmap,
+	.read = user_status_read,
+	.llseek  = user_status_seek,
+	.release = user_status_release,
+};
+
+/*
+ * Creates a set of tracefs files to allow user mode interactions.
+ */
+static int create_user_tracefs(void)
+{
+	struct dentry *edata, *emmap;
+
+	edata = tracefs_create_file("user_events_data", 0644, NULL,
+				    NULL, &user_data_fops);
+
+	if (!edata) {
+		pr_warn("Could not create tracefs 'user_events_data' entry\n");
+		goto err;
+	}
+
+	/* mmap with MAP_SHARED requires writable fd */
+	emmap = tracefs_create_file("user_events_status", 0644, NULL,
+				    NULL, &user_status_fops);
+
+	if (!emmap) {
+		tracefs_remove(edata);
+		pr_warn("Could not create tracefs 'user_events_mmap' entry\n");
+		goto err;
+	}
+
+	return 0;
+err:
+	return -ENODEV;
+}
+
+static void set_page_reservations(bool set)
+{
+	int page;
+
+	for (page = 0; page < MAX_PAGES; ++page) {
+		void *addr = register_page_data + (PAGE_SIZE * page);
+
+		if (set)
+			SetPageReserved(virt_to_page(addr));
+		else
+			ClearPageReserved(virt_to_page(addr));
+	}
+}
+
+static int __init trace_events_user_init(void)
+{
+	int ret;
+
+	/* Zero all bits beside 0 (which is reserved for failures) */
+	bitmap_zero(page_bitmap, MAX_EVENTS);
+	set_bit(0, page_bitmap);
+
+	register_page_data = kzalloc(MAX_EVENTS, GFP_KERNEL);
+
+	if (!register_page_data)
+		return -ENOMEM;
+
+	set_page_reservations(true);
+
+	ret = create_user_tracefs();
+
+	if (ret) {
+		pr_warn("user_events could not register with tracefs\n");
+		set_page_reservations(false);
+		kfree(register_page_data);
+		return ret;
+	}
+
+	if (dyn_event_register(&user_event_dops))
+		pr_warn("user_events could not register with dyn_events\n");
+
+	return 0;
+}
+
+fs_initcall(trace_events_user_init);
-- 
2.17.1