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 /*
  39  * Add an entry to the event buffer. When we get near to the end we
  40  * wake up the process sleeping on the read() of the file. To protect
  41  * the event_buffer this function may only be called when buffer_mutex
  42  * is set.
  43  */
  44 void add_event_entry(unsigned long value)
  45 {
  46         /*
  47          * This shouldn't happen since all workqueues or handlers are
  48          * canceled or flushed before the event buffer is freed.
  49          */
  50         if (!event_buffer) {
  51                 WARN_ON_ONCE(1);
  52                 return;
  53         }
  54
  55         if (buffer_pos == buffer_size) {
  56                 atomic_inc(&oprofile_stats.event_lost_overflow);
  57                 return;
  58         }
  59
  60         event_buffer[buffer_pos] = value;
  61         if (++buffer_pos == buffer_size - buffer_watershed) {
  62                 atomic_set(&buffer_ready, 1);
  63                 wake_up(&buffer_wait);
  64         }
  65 }
  66
  67
  68 /* Wake up the waiting process if any. This happens
  69  * on "echo 0 >/dev/oprofile/enable" so the daemon
  70  * processes the data remaining in the event buffer.
  71  */
  72 void wake_up_buffer_waiter(void)
  73 {
  74         mutex_lock(&buffer_mutex);
  75         atomic_set(&buffer_ready, 1);
  76         wake_up(&buffer_wait);
  77         mutex_unlock(&buffer_mutex);
  78 }
  79
  80
  81 int alloc_event_buffer(void)
  82 {
  83         unsigned long flags;
  84
  85         spin_lock_irqsave(&oprofilefs_lock, flags);
  86         buffer_size = oprofile_buffer_size;
  87         buffer_watershed = oprofile_buffer_watershed;
  88         spin_unlock_irqrestore(&oprofilefs_lock, flags);
  89
  90         if (buffer_watershed >= buffer_size)
  91                 return -EINVAL;
  92
  93         buffer_pos = 0;
  94         event_buffer = vmalloc(sizeof(unsigned long) * buffer_size);
  95         if (!event_buffer)
  96                 return -ENOMEM;
  97
  98         return 0;
  99 }
 100
 101
 102 void free_event_buffer(void)
 103 {
 104         mutex_lock(&buffer_mutex);
 105         vfree(event_buffer);
 106         buffer_pos = 0;
 107         event_buffer = NULL;
 108         mutex_unlock(&buffer_mutex);
 109 }
 110
 111
 112 static int event_buffer_open(struct inode *inode, struct file *file)
 113 {
 114         int err = -EPERM;
 115
 116         if (!capable(CAP_SYS_ADMIN))
 117                 return -EPERM;
 118
 119         if (test_and_set_bit_lock(0, &buffer_opened))
 120                 return -EBUSY;
 121
 122         /* Register as a user of dcookies
 123          * to ensure they persist for the lifetime of
 124          * the open event file
 125          */
 126         err = -EINVAL;
 127         file->private_data = dcookie_register();
 128         if (!file->private_data)
 129                 goto out;
 130
 131         if ((err = oprofile_setup()))
 132                 goto fail;
 133
 134         /* NB: the actual start happens from userspace
 135          * echo 1 >/dev/oprofile/enable
 136          */
 137
 138         return nonseekable_open(inode, file);
 139
 140 fail:
 141         dcookie_unregister(file->private_data);
 142 out:
 143         __clear_bit_unlock(0, &buffer_opened);
 144         return err;
 145 }
 146
 147
 148 static int event_buffer_release(struct inode *inode, struct file *file)
 149 {
 150         oprofile_stop();
 151         oprofile_shutdown();
 152         dcookie_unregister(file->private_data);
 153         buffer_pos = 0;
 154         atomic_set(&buffer_ready, 0);
 155         __clear_bit_unlock(0, &buffer_opened);
 156         return 0;
 157 }
 158
 159
 160 static ssize_t event_buffer_read(struct file *file, char __user *buf,
 161                                  size_t count, loff_t *offset)
 162 {
 163         int retval = -EINVAL;
 164         size_t const max = buffer_size * sizeof(unsigned long);
 165
 166         /* handling partial reads is more trouble than it's worth */
 167         if (count != max || *offset)
 168                 return -EINVAL;
 169
 170         wait_event_interruptible(buffer_wait, atomic_read(&buffer_ready));
 171
 172         if (signal_pending(current))
 173                 return -EINTR;
 174
 175         /* can't currently happen */
 176         if (!atomic_read(&buffer_ready))
 177                 return -EAGAIN;
 178
 179         mutex_lock(&buffer_mutex);
 180
 181         /* May happen if the buffer is freed during pending reads. */
 182         if (!event_buffer) {
 183                 retval = -EINTR;
 184                 goto out;
 185         }
 186
 187         atomic_set(&buffer_ready, 0);
 188
 189         retval = -EFAULT;
 190
 191         count = buffer_pos * sizeof(unsigned long);
 192
 193         if (copy_to_user(buf, event_buffer, count))
 194                 goto out;
 195
 196         retval = count;
 197         buffer_pos = 0;
 198
 199 out:
 200         mutex_unlock(&buffer_mutex);
 201         return retval;
 202 }
 203
 204 const struct file_operations event_buffer_fops = {
 205         .open           = event_buffer_open,
 206         .release        = event_buffer_release,
 207         .read           = event_buffer_read,
 208         .llseek         = no_llseek,
 209 };