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         unsigned long flags;
  74
  75         spin_lock_irqsave(&oprofilefs_lock, flags);
  76         buffer_size = fs_buffer_size;
  77         buffer_watershed = fs_buffer_watershed;
  78         spin_unlock_irqrestore(&oprofilefs_lock, flags);
  79
  80         if (buffer_watershed >= buffer_size)
  81                 return -EINVAL;
  82
  83         event_buffer = vmalloc(sizeof(unsigned long) * buffer_size);
  84         if (!event_buffer)
  85                 goto out;
  86
  87         err = 0;
  88 out:
  89         return err;
  90 }
  91
  92
  93 void free_event_buffer(void)
  94 {
  95         vfree(event_buffer);
  96
  97         event_buffer = NULL;
  98 }
  99
 100
 101 static int event_buffer_open(struct inode *inode, struct file *file)
 102 {
 103         int err = -EPERM;
 104
 105         if (!capable(CAP_SYS_ADMIN))
 106                 return -EPERM;
 107
 108         if (test_and_set_bit_lock(0, &buffer_opened))
 109                 return -EBUSY;
 110
 111         /* Register as a user of dcookies
 112          * to ensure they persist for the lifetime of
 113          * the open event file
 114          */
 115         err = -EINVAL;
 116         file->private_data = dcookie_register();
 117         if (!file->private_data)
 118                 goto out;
 119
 120         if ((err = oprofile_setup()))
 121                 goto fail;
 122
 123         /* NB: the actual start happens from userspace
 124          * echo 1 >/dev/oprofile/enable
 125          */
 126
 127         return 0;
 128
 129 fail:
 130         dcookie_unregister(file->private_data);
 131 out:
 132         __clear_bit_unlock(0, &buffer_opened);
 133         return err;
 134 }
 135
 136
 137 static int event_buffer_release(struct inode *inode, struct file *file)
 138 {
 139         oprofile_stop();
 140         oprofile_shutdown();
 141         dcookie_unregister(file->private_data);
 142         buffer_pos = 0;
 143         atomic_set(&buffer_ready, 0);
 144         __clear_bit_unlock(0, &buffer_opened);
 145         return 0;
 146 }
 147
 148
 149 static ssize_t event_buffer_read(struct file *file, char __user *buf,
 150                                  size_t count, loff_t *offset)
 151 {
 152         int retval = -EINVAL;
 153         size_t const max = buffer_size * sizeof(unsigned long);
 154
 155         /* handling partial reads is more trouble than it's worth */
 156         if (count != max || *offset)
 157                 return -EINVAL;
 158
 159         wait_event_interruptible(buffer_wait, atomic_read(&buffer_ready));
 160
 161         if (signal_pending(current))
 162                 return -EINTR;
 163
 164         /* can't currently happen */
 165         if (!atomic_read(&buffer_ready))
 166                 return -EAGAIN;
 167
 168         mutex_lock(&buffer_mutex);
 169
 170         atomic_set(&buffer_ready, 0);
 171
 172         retval = -EFAULT;
 173
 174         count = buffer_pos * sizeof(unsigned long);
 175
 176         if (copy_to_user(buf, event_buffer, count))
 177                 goto out;
 178
 179         retval = count;
 180         buffer_pos = 0;
 181
 182 out:
 183         mutex_unlock(&buffer_mutex);
 184         return retval;
 185 }
 186
 187 const struct file_operations event_buffer_fops = {
 188         .open           = event_buffer_open,
 189         .release        = event_buffer_release,
 190         .read           = event_buffer_read,
 191 };