mon_stat.c

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/*
 * The USB Monitor, inspired by Dave Harding's USBMon.
 *
 * This is the 's' or 'stat' reader which debugs usbmon itself.
 * Note that this code blows through locks, so make sure that
 * /dbg/usbmon/0s is well protected from non-root users.
 *
 */

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/usb.h>
#include <linux/fs.h>
#include <asm/uaccess.h>

#include "usb_mon.h"

#define STAT_BUF_SIZE  80

struct snap {
    int slen;
    char str[STAT_BUF_SIZE];
};

static int mon_stat_open(struct inode *inode, struct file *file)
{
    struct mon_bus *mbus;
    struct snap *sp;

    if ((sp = kmalloc(sizeof(struct snap), GFP_KERNEL)) == NULL)
        return -ENOMEM;

    mbus = inode->i_private;

    sp->slen = snprintf(sp->str, STAT_BUF_SIZE,
        "nreaders %d events %u text_lost %u\n",
        mbus->nreaders, mbus->cnt_events, mbus->cnt_text_lost);

    file->private_data = sp;
    return 0;
}

static ssize_t mon_stat_read(struct file *file, char __user *buf,
                size_t nbytes, loff_t *ppos)
{
    struct snap *sp = file->private_data;

    return simple_read_from_buffer(buf, nbytes, ppos, sp->str, sp->slen);
}

static int mon_stat_release(struct inode *inode, struct file *file)
{
    struct snap *sp = file->private_data;
    file->private_data = NULL;
    kfree(sp);
    return 0;
}

const struct file_operations mon_fops_stat = {
    .owner =    THIS_MODULE,
    .open =     mon_stat_open,
    .llseek =   no_llseek,
    .read =     mon_stat_read,
    /* .write = mon_stat_write, */
    /* .poll =      mon_stat_poll, */
    /* .unlocked_ioctl =    mon_stat_ioctl, */
    .release =  mon_stat_release,
};