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Date:   Tue,  5 Oct 2021 15:44:28 -0700
From:   Beau Belgrave <beaub@...ux.microsoft.com>
To:     rostedt@...dmis.org, mhiramat@...nel.org
Cc:     linux-trace-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        beaub@...ux.microsoft.com
Subject: [PATCH] user_events: Enable user processes to create and write to trace events

User mode processes that wish to use trace events to get data into
ftrace, perf, eBPF, etc are limited to uprobes today. The user events
features enables an ABI for user mode processes to create and write to
trace events that are isolated from kernel level trace events. This
enables a faster path for tracing from user mode data as well as opens
managed code to participate in trace events, where stub locations are
dynamic.

User processes often want to trace only when it's useful. To enable this
a set of pages are mapped into the user process space that indicate the
current state of the user events that have been registered. User
processes can check if their event is hooked to a trace/probe, and if it
is, emit the event data out via the write() syscall.

Two files are added to tracefs to accomplish this:
user_events_mmap - This file is mmap'd into participating user mode
processes to indicate event status.

user_events_data - This file is opened and register/delete ioctl's are
issued to create/open/delete trace events that can be used for tracing.

The typical scenario is on process start to mmap user_events_mmap. Processes
then register the events they plan to use via the REG ioctl. The return value
of the ioctl indicates the byte in the mmap to use for status. The file that
was used for the ioctl is now accepting data via write() to emit out into the
trace event.

Psuedo code example of typical usage:
page_fd = open("user_events_mmap", O_RDWR);
page_data = mmap(NULL, PAGE_SIZE, PROT_READ, MAP_SHARED, page_fd, 0);

data_fd = open("user_events_data", O_RDWR);
data_id = ioctl(data_fd, DIAG_IOCSREG, "test");

if (page_data[data_id]) write(data_fd, &payload, sizeof(payload));

User events are also exposed via the dynamic_events tracefs file for
both create, delete and current status.

Simple example to register a user event via dynamic_events and get status:
        echo ue:test >> dynamic_events
        cat dynamic_events
        ue:test

If an event is hooked to a probe, the probe hooked shows up:
        echo 1 > events/user_events/test/enable
        cat dynamic_events
        ue:test (Used by ftrace)

Users can describe the trace event format via the following format:
        name[;field1;field2]

Each field has the following format:
        type\tname\tsize\toffset

Example for char array with a size of 20 named msg:
        echo -e 'ue:detailed;char[]\tmsg\t20\t0' >> dynamic_events
        cat dynamic_events
        ue:detailed;char[] msg

Data offsets are based on the data written out via write() and will be
updated to reflect the correct offset in the trace_event fields. __data_loc
types must be aware of the size of trace_entry/common properties to ensure
proper decoding. An ioctl is provided that enables user mode processes that
only have access to user_events_data that returns the correct offset to use
within the data payload (nothing needs to be done on registration).

The above format is valid for both the ioctl and the dynamic_events file.

Signed-off-by: Beau Belgrave <beaub@...ux.microsoft.com>
---
 kernel/trace/Kconfig             |  15 +
 kernel/trace/Makefile            |   1 +
 kernel/trace/trace_events_user.c | 845 +++++++++++++++++++++++++++++++
 3 files changed, 861 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..9afa72b55fa8
--- /dev/null
+++ b/kernel/trace/trace_events_user.c
@@ -0,0 +1,845 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2021, Microsoft Corporation.
+ *
+ * Authors:
+ *   Beau Belgrave <beaub@...ux.microsoft.com>
+ */
+
+#include <linux/bitmap.h>
+#include <linux/cdev.h>
+#include <linux/hashtable.h>
+#include <linux/io.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 "trace.h"
+#include "trace_dynevent.h"
+
+#define USER_EVENTS_SYSTEM "user_events"
+#define USER_EVENTS_PREFIX "ue:"
+#define USER_EVENTS_PREFIX_LEN (sizeof(USER_EVENTS_PREFIX)-1)
+
+/* Bits 0-6 are for known probe types, Bit 7 is for unknown probes */
+#define EVENT_BIT_FTRACE 0
+#define EVENT_BIT_PERF 1
+#define EVENT_BIT_OTHER 7
+
+#define EVENT_STATUS_FTRACE (1 << EVENT_BIT_FTRACE)
+#define EVENT_STATUS_PERF (1 << EVENT_BIT_PERF)
+#define EVENT_STATUS_OTHER (1 << EVENT_BIT_OTHER)
+
+#define FIELD_DEPTH_TYPE 0
+#define FIELD_DEPTH_NAME 1
+#define FIELD_DEPTH_SIZE 2
+#define FIELD_DEPTH_OFFSET 3
+
+/*
+ * 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)
+
+#define DIAG_IOC_MAGIC '*'
+#define DIAG_IOCSREG _IOW(DIAG_IOC_MAGIC, 0, char*)
+#define DIAG_IOCSDEL _IOW(DIAG_IOC_MAGIC, 1, char*)
+#define DIAG_IOCQLOCOFFSET _IO(DIAG_IOC_MAGIC, 2)
+
+static char *register_page_data;
+
+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;
+	atomic_t refs;
+	int index;
+	char *args;
+};
+
+#ifdef CONFIG_PERF_EVENTS
+struct user_bpf_context {
+	int udatalen;
+	const char __user *udata;
+};
+#endif
+
+typedef void (*user_event_func_t) (struct user_event *user,
+				   const char __user *udata,
+				   size_t udatalen, void *tpdata);
+
+static int register_user_event(char *name, char *args,
+			       struct user_event **newuser);
+
+/*
+ * Parses a register command for user_events
+ * Format: event_name[;field1;field2;...]
+ *
+ * Example event named test with a 20 char msg field at offset 0 with a unsigned int at offset 20:
+ * test;char[]\tmsg\t20\t0;unsigned int\tid\t4\t20;
+ *
+ * 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. Types of __data_loc must trace a value that
+ * is offset by the value of the DIAG_IOCQLOCOFFSET ioctl to decode properly.
+ * This makes it easy for the common cases via the terminal, as only __data_loc
+ * types require an awareness by the user of the common property offsets.
+ */
+static int user_event_parse_cmd(char *raw_command, struct user_event **newuser)
+{
+	char *name = raw_command;
+	char *args = strpbrk(name, ";");
+
+	if (args)
+		*args++ = 0;
+
+	return register_user_event(name, args, newuser);
+}
+
+/*
+ * Parses the values of a field within the description
+ * Format: type\tname\tsize\toffset\t[future additions\t]
+ */
+static int user_event_parse_field(char *field, struct user_event *user)
+{
+	char *part, *type, *name;
+	u32 size, offset;
+	int depth = 0;
+
+	while ((part = strsep(&field, "\t")) != NULL) {
+		switch (depth++) {
+		case FIELD_DEPTH_TYPE:
+			type = part;
+			break;
+		case FIELD_DEPTH_NAME:
+			name = part;
+			break;
+		case FIELD_DEPTH_SIZE:
+			if (kstrtou32(part, 10, &size))
+				return -EINVAL;
+			break;
+		case FIELD_DEPTH_OFFSET:
+			if (kstrtou32(part, 10, &offset))
+				return -EINVAL;
+			/*
+			 * User does not know what trace_entry size is
+			 * so we have to add to the offset. For data loc
+			 * scenarios, user mode applications must be aware
+			 * of this size when emitting the data location.
+			 * The DIAG_IOCQLOCOFFSET ioctl can be used to get this.
+			 */
+			offset += sizeof(struct trace_entry);
+			break;
+		default:
+			/* Forward compatibility, ignore */
+			goto end;
+		}
+	}
+end:
+	if (depth < FIELD_DEPTH_OFFSET)
+		return -EINVAL;
+
+	if (!strcmp(type, "print_fmt")) {
+		user->call.print_fmt = name;
+		return 0;
+	}
+
+	return trace_define_field(&user->call, type, name, offset, size,
+				  type[0] != 'u', FILTER_OTHER);
+}
+
+/*
+ * Parses the fields that were described for the event
+ */
+static int user_event_parse_fields(struct user_event *user)
+{
+	char *field;
+	int ret = -EINVAL;
+
+	while ((field = strsep(&user->args, ";")) != NULL) {
+		ret = user_event_parse_field(field, user);
+
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
+
+static int user_event_define_fields(struct trace_event_call *call)
+{
+	struct user_event *user = (struct user_event *)call->data;
+
+	/* User chose to not disclose arguments */
+	if (user->args == NULL)
+		return 0;
+
+	return user_event_parse_fields(user);
+}
+
+static struct trace_event_fields user_event_fields_array[] = {
+	{ .type = TRACE_FUNCTION_TYPE,
+	  .define_fields = user_event_define_fields },
+	{}
+};
+
+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;
+
+	/*
+	 * trace_remove_event_call invokes unregister_trace_event:
+	 * Pick the correct one based on if we set the data or not
+	 */
+	if (user->index != 0) {
+		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);
+	} else {
+		unregister_trace_event(&user->call.event);
+	}
+
+	kfree(EVENT_NAME(user));
+	kfree(user);
+
+	return ret;
+}
+
+static struct user_event *find_user_event(u32 key, char *name)
+{
+	struct user_event *user;
+
+	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, const char __user *udata,
+			      size_t udatalen, 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) + udatalen);
+
+	if (!entry)
+		return;
+
+	if (!copy_from_user(entry + 1, udata, udatalen))
+		trace_event_buffer_commit(&event_buffer);
+}
+
+#ifdef CONFIG_PERF_EVENTS
+/*
+ * Writes the user supplied payload out to perf ring buffer or eBPF program.
+ */
+static void user_event_perf(struct user_event *user, const char __user *udata,
+			    size_t udatalen, void *tpdata)
+{
+	struct hlist_head *perf_head;
+
+	if (bpf_prog_array_valid(&user->call)) {
+		struct user_bpf_context context = {0};
+
+		context.udatalen = udatalen;
+		context.udata = udata;
+
+		trace_call_bpf(&user->call, &context);
+	}
+
+	perf_head = this_cpu_ptr(user->call.perf_events);
+
+	if (perf_head && !hlist_empty(perf_head)) {
+		struct trace_entry *perf_entry;
+		struct pt_regs *regs;
+		size_t size = sizeof(*perf_entry) + udatalen;
+		int context;
+
+		perf_entry = perf_trace_buf_alloc(ALIGN(size, 8),
+						  &regs, &context);
+
+		if (!perf_entry)
+			return;
+
+		perf_fetch_caller_regs(regs);
+
+		if (copy_from_user(perf_entry + 1,
+				   udata,
+				   udatalen))
+			return;
+
+		perf_trace_buf_submit(perf_entry, size, context,
+				      user->call.event.type, 1, regs,
+				      perf_head, NULL);
+	}
+}
+#endif
+
+/*
+ * 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;
+
+		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;
+#ifdef CONFIG_PERF_EVENTS
+				else if (probe_func == user_event_perf)
+					status |= EVENT_STATUS_PERF;
+#endif
+				else
+					status |= EVENT_STATUS_OTHER;
+			} while ((++probe_func_ptr)->func);
+		}
+	}
+
+	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:
+		ret = tracepoint_probe_register(call->tp,
+						call->class->perf_probe,
+						data);
+		if (!ret)
+			goto inc;
+		break;
+
+	case TRACE_REG_PERF_UNREGISTER:
+		tracepoint_probe_unregister(call->tp,
+					    call->class->perf_probe,
+					    data);
+		goto dec;
+
+	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->refs);
+	update_reg_page_for(user);
+	return 0;
+dec:
+	update_reg_page_for(user);
+	atomic_dec(&user->refs);
+	return 0;
+}
+
+static u32 user_event_key(char *name)
+{
+	return jhash(name, strlen(name), 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;
+
+	name = kstrdup(raw_command + USER_EVENTS_PREFIX_LEN, GFP_KERNEL);
+
+	if (!name)
+		return -ENOMEM;
+
+	mutex_lock(&event_mutex);
+	ret = user_event_parse_cmd(name, &user);
+	mutex_unlock(&event_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;
+	char status;
+
+	seq_printf(m, "%s%s", USER_EVENTS_PREFIX, EVENT_NAME(user));
+
+	head = trace_get_fields(&user->call);
+
+	list_for_each_entry_safe(field, next, head, link)
+		seq_printf(m, ";%s %s", field->type, field->name);
+
+	status = register_page_data[user->index];
+
+	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");
+		seq_puts(m, ")");
+	}
+
+	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->refs) != 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,
+};
+
+/*
+ * Register a trace_event into the system, either find or create.
+ */
+static int register_user_event(char *name, char *args,
+			       struct user_event **newuser)
+{
+	int ret;
+	int index;
+	u32 key = user_event_key(name);
+	struct user_event *user = find_user_event(key, name);
+
+	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);
+
+	user->tracepoint.name = name;
+	user->args = args;
+
+	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.reg = user_event_reg;
+	user->class.probe = user_event_ftrace;
+#ifdef CONFIG_PERF_EVENTS
+	user->class.perf_probe = user_event_perf;
+#endif
+
+	ret = register_trace_event(&user->call.event);
+
+	if (!ret) {
+		ret = -ENODEV;
+		goto put_user;
+	}
+
+	ret = trace_add_event_call(&user->call);
+
+	if (ret) {
+		destroy_user_event(user);
+		goto out;
+	}
+
+	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:
+	kfree(user);
+put_name:
+	kfree(name);
+out:
+	return ret;
+}
+
+/*
+ * Deletes a previously created event if it is no longer being used.
+ */
+static int delete_user_event(char *name)
+{
+	u32 key = user_event_key(name);
+	struct user_event *user = find_user_event(key, name);
+
+	if (!user)
+		return -ENOENT;
+
+	if (atomic_read(&user->refs) != 0)
+		return -EBUSY;
+
+	return destroy_user_event(user);
+}
+
+/*
+ * Validates the user payload and writes to the appropriate sub-system.
+ */
+static ssize_t user_events_write(struct file *file, const char __user *ubuf,
+				 size_t count, loff_t *ppos)
+{
+	struct user_event *user;
+	struct tracepoint *tp;
+
+	if (*ppos != 0 || count <= 0)
+		return -EFAULT;
+
+	user = file->private_data;
+
+	if (!user)
+		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;
+
+		preempt_disable();
+
+		if (unlikely(!(cpu_online(raw_smp_processor_id()))))
+			goto preempt_out;
+
+		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, ubuf, count, tpdata);
+			} while ((++probe_func_ptr)->func);
+		}
+preempt_out:
+		preempt_enable();
+	}
+
+	return count;
+}
+
+/*
+ * 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)
+{
+	void __user *ubuf = (void __user *)uarg;
+	struct user_event *user;
+	char *name;
+	long ret;
+
+	switch (cmd) {
+	case DIAG_IOCSREG:
+		/* Register/lookup on behalf of user process */
+		name = strndup_user(ubuf, MAX_EVENT_DESC);
+
+		if (IS_ERR(name)) {
+			ret = PTR_ERR(name);
+			goto out;
+		}
+
+		mutex_lock(&event_mutex);
+
+		if (file->private_data) {
+			/* Already associated with an event */
+			ret = -EMFILE;
+			kfree(name);
+			goto reg_out;
+		}
+
+		ret = user_event_parse_cmd(name, &user);
+
+		if (!ret) {
+			file->private_data = user;
+			atomic_inc(&user->refs);
+		}
+reg_out:
+		mutex_unlock(&event_mutex);
+
+		if (ret < 0)
+			goto out;
+
+		/* Return page index to check before writes */
+		ret = user->index;
+		break;
+
+	case DIAG_IOCSDEL:
+		/* Delete on behalf of user process */
+		name = strndup_user(ubuf, MAX_EVENT_DESC);
+
+		if (IS_ERR(name)) {
+			ret = PTR_ERR(name);
+			goto out;
+		}
+
+		mutex_lock(&event_mutex);
+		ret = delete_user_event(name);
+		mutex_unlock(&event_mutex);
+
+		kfree(name);
+		break;
+
+	case DIAG_IOCQLOCOFFSET:
+		/*
+		 * Return data offset to use for data locs. This enables
+		 * user mode processes to query the common property sizes.
+		 * If this was not known, the data location values written
+		 * would be incorrect from the user mode side.
+		 */
+		ret = sizeof(struct trace_entry);
+		break;
+
+	default:
+		ret = -ENOTTY;
+		break;
+	}
+out:
+	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 *user = file->private_data;
+
+	if (user)
+		atomic_dec(&user->refs);
+
+	return 0;
+}
+
+static const struct file_operations user_events_data_fops = {
+	.write = user_events_write,
+	.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_events_mmap(struct file *filp, 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, PAGE_READONLY);
+}
+
+static const struct file_operations user_events_mmap_fops = {
+	.mmap = user_events_mmap,
+};
+
+/*
+ * 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_events_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_mmap", 0644, NULL,
+				    NULL, &user_events_mmap_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 = kmalloc(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

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