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.h>
18 #include <linux/capability.h>
19 #include <linux/dcookies.h>
20 #include <linux/fs.h>
21 #include <asm/uaccess.h>
22
23 #include "oprof.h"
24 #include "event_buffer.h"
25 #include "oprofile_stats.h"
26
27 DEFINE_MUTEX(buffer_mutex);
28
29 static unsigned long buffer_opened;
30 static DECLARE_WAIT_QUEUE_HEAD(buffer_wait);
31 static unsigned long * event_buffer;
32 static unsigned long buffer_size;
33 static unsigned long buffer_watershed;
34 static size_t buffer_pos;
35 /* atomic_t because wait_event checks it outside of buffer_mutex */
36 static atomic_t buffer_ready = ATOMIC_INIT(0);
37
38 /* Add an entry to the event buffer. When we
39 * get near to the end we wake up the process
40 * sleeping on the read() of the file.
41 */
42 void add_event_entry(unsigned long value)
43 {
44 if (buffer_pos == buffer_size) {
45 atomic_inc(&oprofile_stats.event_lost_overflow);
46 return;
47 }
48
49 event_buffer[buffer_pos] = value;
50 if (++buffer_pos == buffer_size - buffer_watershed) {
51 atomic_set(&buffer_ready, 1);
52 wake_up(&buffer_wait);
53 }
54 }
55
56
57 /* Wake up the waiting process if any. This happens
58 * on "echo 0 >/dev/oprofile/enable" so the daemon
59 * processes the data remaining in the event buffer.
60 */
61 void wake_up_buffer_waiter(void)
62 {
63 mutex_lock(&buffer_mutex);
64 atomic_set(&buffer_ready, 1);
65 wake_up(&buffer_wait);
66 mutex_unlock(&buffer_mutex);
67 }
68
69
70 int alloc_event_buffer(void)
71 {
72 int err = -ENOMEM;
73
74 spin_lock(&oprofilefs_lock);
75 buffer_size = fs_buffer_size;
76 buffer_watershed = fs_buffer_watershed;
77 spin_unlock(&oprofilefs_lock);
78
79 if (buffer_watershed >= buffer_size)
80 return -EINVAL;
81
82 event_buffer = vmalloc(sizeof(unsigned long) * buffer_size);
83 if (!event_buffer)
84 goto out;
85
86 err = 0;
87 out:
88 return err;
89 }
90
91
92 void free_event_buffer(void)
93 {
94 vfree(event_buffer);
95 }
96
97
98 static int event_buffer_open(struct inode * inode, struct file * file)
99 {
100 int err = -EPERM;
101
102 if (!capable(CAP_SYS_ADMIN))
103 return -EPERM;
104
105 if (test_and_set_bit(0, &buffer_opened))
106 return -EBUSY;
107
108 /* Register as a user of dcookies
109 * to ensure they persist for the lifetime of
110 * the open event file
111 */
112 err = -EINVAL;
113 file->private_data = dcookie_register();
114 if (!file->private_data)
115 goto out;
116
117 if ((err = oprofile_setup()))
118 goto fail;
119
120 /* NB: the actual start happens from userspace
121 * echo 1 >/dev/oprofile/enable
122 */
123
124 return 0;
125
126 fail:
127 dcookie_unregister(file->private_data);
128 out:
129 clear_bit(0, &buffer_opened);
130 return err;
131 }
132
133
134 static int event_buffer_release(struct inode * inode, struct file * file)
135 {
136 oprofile_stop();
137 oprofile_shutdown();
138 dcookie_unregister(file->private_data);
139 buffer_pos = 0;
140 atomic_set(&buffer_ready, 0);
141 clear_bit(0, &buffer_opened);
142 return 0;
143 }
144
145
146 static ssize_t event_buffer_read(struct file * file, char __user * buf,
147 size_t count, loff_t * offset)
148 {
149 int retval = -EINVAL;
150 size_t const max = buffer_size * sizeof(unsigned long);
151
152 /* handling partial reads is more trouble than it's worth */
153 if (count != max || *offset)
154 return -EINVAL;
155
156 wait_event_interruptible(buffer_wait, atomic_read(&buffer_ready));
157
158 if (signal_pending(current))
159 return -EINTR;
160
161 /* can't currently happen */
162 if (!atomic_read(&buffer_ready))
163 return -EAGAIN;
164
165 mutex_lock(&buffer_mutex);
166
167 atomic_set(&buffer_ready, 0);
168
169 retval = -EFAULT;
170
171 count = buffer_pos * sizeof(unsigned long);
172
173 if (copy_to_user(buf, event_buffer, count))
174 goto out;
175
176 retval = count;
177 buffer_pos = 0;
178
179 out:
180 mutex_unlock(&buffer_mutex);
181 return retval;
182 }
183
184 struct file_operations event_buffer_fops = {
185 .open = event_buffer_open,
186 .release = event_buffer_release,
187 .read = event_buffer_read,
188 };
189
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