event_buffer.c

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#include <linux/vmalloc.h>
#include <linux/oprofile.h>
#include <linux/sched.h>
#include <linux/capability.h>
#include <linux/dcookies.h>
#include <linux/fs.h>
#include <asm/uaccess.h>

#include "oprof.h"
#include "event_buffer.h"
#include "oprofile_stats.h"

DEFINE_MUTEX(buffer_mutex);

static unsigned long buffer_opened;
static DECLARE_WAIT_QUEUE_HEAD(buffer_wait);
static unsigned long *event_buffer;
static unsigned long buffer_size;
static unsigned long buffer_watershed;
static size_t buffer_pos;
/* atomic_t because wait_event checks it outside of buffer_mutex */
static atomic_t buffer_ready = ATOMIC_INIT(0);

/*
 * Add an entry to the event buffer. When we get near to the end we
 * wake up the process sleeping on the read() of the file. To protect
 * the event_buffer this function may only be called when buffer_mutex
 * is set.
 */
void add_event_entry(unsigned long value)
{
    /*
     * This shouldn't happen since all workqueues or handlers are
     * canceled or flushed before the event buffer is freed.
     */
    if (!event_buffer) {
        WARN_ON_ONCE(1);
        return;
    }

    if (buffer_pos == buffer_size) {
        atomic_inc(&oprofile_stats.event_lost_overflow);
        return;
    }

    event_buffer[buffer_pos] = value;
    if (++buffer_pos == buffer_size - buffer_watershed) {
        atomic_set(&buffer_ready, 1);
        wake_up(&buffer_wait);
    }
}


/* Wake up the waiting process if any. This happens
 * on "echo 0 >/dev/oprofile/enable" so the daemon
 * processes the data remaining in the event buffer.
 */
void wake_up_buffer_waiter(void)
{
    mutex_lock(&buffer_mutex);
    atomic_set(&buffer_ready, 1);
    wake_up(&buffer_wait);
    mutex_unlock(&buffer_mutex);
}


int alloc_event_buffer(void)
{
    unsigned long flags;

    raw_spin_lock_irqsave(&oprofilefs_lock, flags);
    buffer_size = oprofile_buffer_size;
    buffer_watershed = oprofile_buffer_watershed;
    raw_spin_unlock_irqrestore(&oprofilefs_lock, flags);

    if (buffer_watershed >= buffer_size)
        return -EINVAL;

    buffer_pos = 0;
    event_buffer = vmalloc(sizeof(unsigned long) * buffer_size);
    if (!event_buffer)
        return -ENOMEM;

    return 0;
}


void free_event_buffer(void)
{
    mutex_lock(&buffer_mutex);
    vfree(event_buffer);
    buffer_pos = 0;
    event_buffer = NULL;
    mutex_unlock(&buffer_mutex);
}


static int event_buffer_open(struct inode *inode, struct file *file)
{
    int err = -EPERM;

    if (!capable(CAP_SYS_ADMIN))
        return -EPERM;

    if (test_and_set_bit_lock(0, &buffer_opened))
        return -EBUSY;

    /* Register as a user of dcookies
     * to ensure they persist for the lifetime of
     * the open event file
     */
    err = -EINVAL;
    file->private_data = dcookie_register();
    if (!file->private_data)
        goto out;

    if ((err = oprofile_setup()))
        goto fail;

    /* NB: the actual start happens from userspace
     * echo 1 >/dev/oprofile/enable
     */

    return nonseekable_open(inode, file);

fail:
    dcookie_unregister(file->private_data);
out:
    __clear_bit_unlock(0, &buffer_opened);
    return err;
}


static int event_buffer_release(struct inode *inode, struct file *file)
{
    oprofile_stop();
    oprofile_shutdown();
    dcookie_unregister(file->private_data);
    buffer_pos = 0;
    atomic_set(&buffer_ready, 0);
    __clear_bit_unlock(0, &buffer_opened);
    return 0;
}


static ssize_t event_buffer_read(struct file *file, char __user *buf,
                 size_t count, loff_t *offset)
{
    int retval = -EINVAL;
    size_t const max = buffer_size * sizeof(unsigned long);

    /* handling partial reads is more trouble than it's worth */
    if (count != max || *offset)
        return -EINVAL;

    wait_event_interruptible(buffer_wait, atomic_read(&buffer_ready));

    if (signal_pending(current))
        return -EINTR;

    /* can't currently happen */
    if (!atomic_read(&buffer_ready))
        return -EAGAIN;

    mutex_lock(&buffer_mutex);

    /* May happen if the buffer is freed during pending reads. */
    if (!event_buffer) {
        retval = -EINTR;
        goto out;
    }

    atomic_set(&buffer_ready, 0);

    retval = -EFAULT;

    count = buffer_pos * sizeof(unsigned long);

    if (copy_to_user(buf, event_buffer, count))
        goto out;

    retval = count;
    buffer_pos = 0;

out:
    mutex_unlock(&buffer_mutex);
    return retval;
}

const struct file_operations event_buffer_fops = {
    .open       = event_buffer_open,
    .release    = event_buffer_release,
    .read       = event_buffer_read,
    .llseek     = no_llseek,
};