[PATCH] mark struct file_operations const 5
[linux-2.6.git] / drivers / oprofile / event_buffer.c
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 const struct file_operations event_buffer_fops = {
185         .open           = event_buffer_open,
186         .release        = event_buffer_release,
187         .read           = event_buffer_read,
188 };