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