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1da177e4 LT |
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/dcookies.h> | |
19 | #include <linux/fs.h> | |
20 | #include <asm/uaccess.h> | |
21 | ||
22 | #include "oprof.h" | |
23 | #include "event_buffer.h" | |
24 | #include "oprofile_stats.h" | |
25 | ||
26 | DECLARE_MUTEX(buffer_sem); | |
27 | ||
28 | static unsigned long buffer_opened; | |
29 | static DECLARE_WAIT_QUEUE_HEAD(buffer_wait); | |
30 | static unsigned long * event_buffer; | |
31 | static unsigned long buffer_size; | |
32 | static unsigned long buffer_watershed; | |
33 | static size_t buffer_pos; | |
34 | /* atomic_t because wait_event checks it outside of buffer_sem */ | |
35 | static atomic_t buffer_ready = ATOMIC_INIT(0); | |
36 | ||
37 | /* Add an entry to the event buffer. When we | |
38 | * get near to the end we wake up the process | |
39 | * sleeping on the read() of the file. | |
40 | */ | |
41 | void add_event_entry(unsigned long value) | |
42 | { | |
43 | if (buffer_pos == buffer_size) { | |
44 | atomic_inc(&oprofile_stats.event_lost_overflow); | |
45 | return; | |
46 | } | |
47 | ||
48 | event_buffer[buffer_pos] = value; | |
49 | if (++buffer_pos == buffer_size - buffer_watershed) { | |
50 | atomic_set(&buffer_ready, 1); | |
51 | wake_up(&buffer_wait); | |
52 | } | |
53 | } | |
54 | ||
55 | ||
56 | /* Wake up the waiting process if any. This happens | |
57 | * on "echo 0 >/dev/oprofile/enable" so the daemon | |
58 | * processes the data remaining in the event buffer. | |
59 | */ | |
60 | void wake_up_buffer_waiter(void) | |
61 | { | |
62 | down(&buffer_sem); | |
63 | atomic_set(&buffer_ready, 1); | |
64 | wake_up(&buffer_wait); | |
65 | up(&buffer_sem); | |
66 | } | |
67 | ||
68 | ||
69 | int alloc_event_buffer(void) | |
70 | { | |
71 | int err = -ENOMEM; | |
72 | ||
73 | spin_lock(&oprofilefs_lock); | |
74 | buffer_size = fs_buffer_size; | |
75 | buffer_watershed = fs_buffer_watershed; | |
76 | spin_unlock(&oprofilefs_lock); | |
77 | ||
78 | if (buffer_watershed >= buffer_size) | |
79 | return -EINVAL; | |
80 | ||
81 | event_buffer = vmalloc(sizeof(unsigned long) * buffer_size); | |
82 | if (!event_buffer) | |
83 | goto out; | |
84 | ||
85 | err = 0; | |
86 | out: | |
87 | return err; | |
88 | } | |
89 | ||
90 | ||
91 | void free_event_buffer(void) | |
92 | { | |
93 | vfree(event_buffer); | |
94 | } | |
95 | ||
96 | ||
97 | static int event_buffer_open(struct inode * inode, struct file * file) | |
98 | { | |
99 | int err = -EPERM; | |
100 | ||
101 | if (!capable(CAP_SYS_ADMIN)) | |
102 | return -EPERM; | |
103 | ||
104 | if (test_and_set_bit(0, &buffer_opened)) | |
105 | return -EBUSY; | |
106 | ||
107 | /* Register as a user of dcookies | |
108 | * to ensure they persist for the lifetime of | |
109 | * the open event file | |
110 | */ | |
111 | err = -EINVAL; | |
112 | file->private_data = dcookie_register(); | |
113 | if (!file->private_data) | |
114 | goto out; | |
115 | ||
116 | if ((err = oprofile_setup())) | |
117 | goto fail; | |
118 | ||
119 | /* NB: the actual start happens from userspace | |
120 | * echo 1 >/dev/oprofile/enable | |
121 | */ | |
122 | ||
123 | return 0; | |
124 | ||
125 | fail: | |
126 | dcookie_unregister(file->private_data); | |
127 | out: | |
128 | clear_bit(0, &buffer_opened); | |
129 | return err; | |
130 | } | |
131 | ||
132 | ||
133 | static int event_buffer_release(struct inode * inode, struct file * file) | |
134 | { | |
135 | oprofile_stop(); | |
136 | oprofile_shutdown(); | |
137 | dcookie_unregister(file->private_data); | |
138 | buffer_pos = 0; | |
139 | atomic_set(&buffer_ready, 0); | |
140 | clear_bit(0, &buffer_opened); | |
141 | return 0; | |
142 | } | |
143 | ||
144 | ||
145 | static ssize_t event_buffer_read(struct file * file, char __user * buf, | |
146 | size_t count, loff_t * offset) | |
147 | { | |
148 | int retval = -EINVAL; | |
149 | size_t const max = buffer_size * sizeof(unsigned long); | |
150 | ||
151 | /* handling partial reads is more trouble than it's worth */ | |
152 | if (count != max || *offset) | |
153 | return -EINVAL; | |
154 | ||
155 | wait_event_interruptible(buffer_wait, atomic_read(&buffer_ready)); | |
156 | ||
157 | if (signal_pending(current)) | |
158 | return -EINTR; | |
159 | ||
160 | /* can't currently happen */ | |
161 | if (!atomic_read(&buffer_ready)) | |
162 | return -EAGAIN; | |
163 | ||
164 | down(&buffer_sem); | |
165 | ||
166 | atomic_set(&buffer_ready, 0); | |
167 | ||
168 | retval = -EFAULT; | |
169 | ||
170 | count = buffer_pos * sizeof(unsigned long); | |
171 | ||
172 | if (copy_to_user(buf, event_buffer, count)) | |
173 | goto out; | |
174 | ||
175 | retval = count; | |
176 | buffer_pos = 0; | |
177 | ||
178 | out: | |
179 | up(&buffer_sem); | |
180 | return retval; | |
181 | } | |
182 | ||
183 | struct file_operations event_buffer_fops = { | |
184 | .open = event_buffer_open, | |
185 | .release = event_buffer_release, | |
186 | .read = event_buffer_read, | |
187 | }; |