1/**
2 * @file event_buffer.c
3 *
4 * @remark Copyright 2002 OProfile authors
5 * @remark Read the file COPYING
6 *
7 * @author John Levon <levon@movementarian.org>
8 *
9 * This is the global event buffer that the user-space
10 * daemon reads from. The event buffer is an untyped array
11 * of unsigned longs. Entries are prefixed by the
12 * escape value ESCAPE_CODE followed by an identifying code.
13 */
14
15#include <linux/vmalloc.h>
16#include <linux/oprofile.h>
17#include <linux/sched/signal.h>
18#include <linux/capability.h>
19#include <linux/dcookies.h>
20#include <linux/fs.h>
21#include <linux/uaccess.h>
22
23#include "oprof.h"
24#include "event_buffer.h"
25#include "oprofile_stats.h"
26
27DEFINE_MUTEX(buffer_mutex);
28
29static unsigned long buffer_opened;
30static DECLARE_WAIT_QUEUE_HEAD(buffer_wait);
31static unsigned long *event_buffer;
32static unsigned long buffer_size;
33static unsigned long buffer_watershed;
34static size_t buffer_pos;
35/* atomic_t because wait_event checks it outside of buffer_mutex */
36static atomic_t buffer_ready = ATOMIC_INIT(0);
37
38/*
39 * Add an entry to the event buffer. When we get near to the end we
40 * wake up the process sleeping on the read() of the file. To protect
41 * the event_buffer this function may only be called when buffer_mutex
42 * is set.
43 */
44void add_event_entry(unsigned long value)
45{
46 /*
47 * This shouldn't happen since all workqueues or handlers are
48 * canceled or flushed before the event buffer is freed.
49 */
50 if (!event_buffer) {
51 WARN_ON_ONCE(1);
52 return;
53 }
54
55 if (buffer_pos == buffer_size) {
56 atomic_inc(&oprofile_stats.event_lost_overflow);
57 return;
58 }
59
60 event_buffer[buffer_pos] = value;
61 if (++buffer_pos == buffer_size - buffer_watershed) {
62 atomic_set(&buffer_ready, 1);
63 wake_up(&buffer_wait);
64 }
65}
66
67
68/* Wake up the waiting process if any. This happens
69 * on "echo 0 >/dev/oprofile/enable" so the daemon
70 * processes the data remaining in the event buffer.
71 */
72void wake_up_buffer_waiter(void)
73{
74 mutex_lock(&buffer_mutex);
75 atomic_set(&buffer_ready, 1);
76 wake_up(&buffer_wait);
77 mutex_unlock(&buffer_mutex);
78}
79
80
81int alloc_event_buffer(void)
82{
83 unsigned long flags;
84
85 raw_spin_lock_irqsave(&oprofilefs_lock, flags);
86 buffer_size = oprofile_buffer_size;
87 buffer_watershed = oprofile_buffer_watershed;
88 raw_spin_unlock_irqrestore(&oprofilefs_lock, flags);
89
90 if (buffer_watershed >= buffer_size)
91 return -EINVAL;
92
93 buffer_pos = 0;
94 event_buffer = vmalloc(array_size(buffer_size, sizeof(unsigned long)));
95 if (!event_buffer)
96 return -ENOMEM;
97
98 return 0;
99}
100
101
102void free_event_buffer(void)
103{
104 mutex_lock(&buffer_mutex);
105 vfree(event_buffer);
106 buffer_pos = 0;
107 event_buffer = NULL;
108 mutex_unlock(&buffer_mutex);
109}
110
111
112static int event_buffer_open(struct inode *inode, struct file *file)
113{
114 int err = -EPERM;
115
116 if (!capable(CAP_SYS_ADMIN))
117 return -EPERM;
118
119 if (test_and_set_bit_lock(0, &buffer_opened))
120 return -EBUSY;
121
122 /* Register as a user of dcookies
123 * to ensure they persist for the lifetime of
124 * the open event file
125 */
126 err = -EINVAL;
127 file->private_data = dcookie_register();
128 if (!file->private_data)
129 goto out;
130
131 if ((err = oprofile_setup()))
132 goto fail;
133
134 /* NB: the actual start happens from userspace
135 * echo 1 >/dev/oprofile/enable
136 */
137
138 return nonseekable_open(inode, file);
139
140fail:
141 dcookie_unregister(file->private_data);
142out:
143 __clear_bit_unlock(0, &buffer_opened);
144 return err;
145}
146
147
148static int event_buffer_release(struct inode *inode, struct file *file)
149{
150 oprofile_stop();
151 oprofile_shutdown();
152 dcookie_unregister(file->private_data);
153 buffer_pos = 0;
154 atomic_set(&buffer_ready, 0);
155 __clear_bit_unlock(0, &buffer_opened);
156 return 0;
157}
158
159
160static ssize_t event_buffer_read(struct file *file, char __user *buf,
161 size_t count, loff_t *offset)
162{
163 int retval = -EINVAL;
164 size_t const max = buffer_size * sizeof(unsigned long);
165
166 /* handling partial reads is more trouble than it's worth */
167 if (count != max || *offset)
168 return -EINVAL;
169
170 wait_event_interruptible(buffer_wait, atomic_read(&buffer_ready));
171
172 if (signal_pending(current))
173 return -EINTR;
174
175 /* can't currently happen */
176 if (!atomic_read(&buffer_ready))
177 return -EAGAIN;
178
179 mutex_lock(&buffer_mutex);
180
181 /* May happen if the buffer is freed during pending reads. */
182 if (!event_buffer) {
183 retval = -EINTR;
184 goto out;
185 }
186
187 atomic_set(&buffer_ready, 0);
188
189 retval = -EFAULT;
190
191 count = buffer_pos * sizeof(unsigned long);
192
193 if (copy_to_user(buf, event_buffer, count))
194 goto out;
195
196 retval = count;
197 buffer_pos = 0;
198
199out:
200 mutex_unlock(&buffer_mutex);
201 return retval;
202}
203
204const struct file_operations event_buffer_fops = {
205 .open = event_buffer_open,
206 .release = event_buffer_release,
207 .read = event_buffer_read,
208 .llseek = no_llseek,
209};
210