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 DECLARE_MUTEX(buffer_sem);
  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_sem */
  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         down(&buffer_sem);
  64         atomic_set(&buffer_ready, 1);
  65         wake_up(&buffer_wait);
  66         up(&buffer_sem);
  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         down(&buffer_sem);
 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         up(&buffer_sem);
 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 };