mon_text.c

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/*
 * The USB Monitor, inspired by Dave Harding's USBMon.
 *
 * This is a text format reader.
 */

#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/usb.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/debugfs.h>
#include <linux/scatterlist.h>
#include <asm/uaccess.h>

#include "usb_mon.h"

/*
 * No, we do not want arbitrarily long data strings.
 * Use the binary interface if you want to capture bulk data!
 */
#define DATA_MAX  32

/*
 * Defined by USB 2.0 clause 9.3, table 9.2.
 */
#define SETUP_MAX  8

/*
 * This limit exists to prevent OOMs when the user process stops reading.
 * If usbmon were available to unprivileged processes, it might be open
 * to a local DoS. But we have to keep to root in order to prevent
 * password sniffing from HID devices.
 */
#define EVENT_MAX  (4*PAGE_SIZE / sizeof(struct mon_event_text))

/*
 * Potentially unlimited number; we limit it for similar allocations.
 * The usbfs limits this to 128, but we're not quite as generous.
 */
#define ISODESC_MAX   5

#define PRINTF_DFL  250   /* with 5 ISOs segs */

struct mon_iso_desc {
    int status;
    unsigned int offset;
    unsigned int length;    /* Unsigned here, signed in URB. Historic. */
};

struct mon_event_text {
    struct list_head e_link;
    int type;       /* submit, complete, etc. */
    unsigned long id;   /* From pointer, most of the time */
    unsigned int tstamp;
    int busnum;
    char devnum;
    char epnum;
    char is_in;
    char xfertype;
    int length;     /* Depends on type: xfer length or act length */
    int status;
    int interval;
    int start_frame;
    int error_count;
    char setup_flag;
    char data_flag;
    int numdesc;        /* Full number */
    struct mon_iso_desc isodesc[ISODESC_MAX];
    unsigned char setup[SETUP_MAX];
    unsigned char data[DATA_MAX];
};

#define SLAB_NAME_SZ  30
struct mon_reader_text {
    struct kmem_cache *e_slab;
    int nevents;
    struct list_head e_list;
    struct mon_reader r;    /* In C, parent class can be placed anywhere */

    wait_queue_head_t wait;
    int printf_size;
    char *printf_buf;
    struct mutex printf_lock;

    char slab_name[SLAB_NAME_SZ];
};

static struct dentry *mon_dir;      /* Usually /sys/kernel/debug/usbmon */

static void mon_text_ctor(void *);

struct mon_text_ptr {
    int cnt, limit;
    char *pbuf;
};

static struct mon_event_text *
    mon_text_read_wait(struct mon_reader_text *rp, struct file *file);
static void mon_text_read_head_t(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep);
static void mon_text_read_head_u(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep);
static void mon_text_read_statset(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep);
static void mon_text_read_intstat(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep);
static void mon_text_read_isostat(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep);
static void mon_text_read_isodesc(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep);
static void mon_text_read_data(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep);

/*
 * mon_text_submit
 * mon_text_complete
 *
 * May be called from an interrupt.
 *
 * This is called with the whole mon_bus locked, so no additional lock.
 */

static inline char mon_text_get_setup(struct mon_event_text *ep,
    struct urb *urb, char ev_type, struct mon_bus *mbus)
{

    if (ep->xfertype != USB_ENDPOINT_XFER_CONTROL || ev_type != 'S')
        return '-';

    if (urb->setup_packet == NULL)
        return 'Z'; /* '0' would be not as pretty. */

    memcpy(ep->setup, urb->setup_packet, SETUP_MAX);
    return 0;
}

static inline char mon_text_get_data(struct mon_event_text *ep, struct urb *urb,
    int len, char ev_type, struct mon_bus *mbus)
{
    void *src;

    if (len <= 0)
        return 'L';
    if (len >= DATA_MAX)
        len = DATA_MAX;

    if (ep->is_in) {
        if (ev_type != 'C')
            return '<';
    } else {
        if (ev_type != 'S')
            return '>';
    }

    if (urb->num_sgs == 0) {
        src = urb->transfer_buffer;
        if (src == NULL)
            return 'Z'; /* '0' would be not as pretty. */
    } else {
        struct scatterlist *sg = urb->sg;

        if (PageHighMem(sg_page(sg)))
            return 'D';

        /* For the text interface we copy only the first sg buffer */
        len = min_t(int, sg->length, len);
        src = sg_virt(sg);
    }

    memcpy(ep->data, src, len);
    return 0;
}

static inline unsigned int mon_get_timestamp(void)
{
    struct timeval tval;
    unsigned int stamp;

    do_gettimeofday(&tval);
    stamp = tval.tv_sec & 0xFFF;    /* 2^32 = 4294967296. Limit to 4096s. */
    stamp = stamp * 1000000 + tval.tv_usec;
    return stamp;
}

static void mon_text_event(struct mon_reader_text *rp, struct urb *urb,
    char ev_type, int status)
{
    struct mon_event_text *ep;
    unsigned int stamp;
    struct usb_iso_packet_descriptor *fp;
    struct mon_iso_desc *dp;
    int i, ndesc;

    stamp = mon_get_timestamp();

    if (rp->nevents >= EVENT_MAX ||
        (ep = kmem_cache_alloc(rp->e_slab, GFP_ATOMIC)) == NULL) {
        rp->r.m_bus->cnt_text_lost++;
        return;
    }

    ep->type = ev_type;
    ep->id = (unsigned long) urb;
    ep->busnum = urb->dev->bus->busnum;
    ep->devnum = urb->dev->devnum;
    ep->epnum = usb_endpoint_num(&urb->ep->desc);
    ep->xfertype = usb_endpoint_type(&urb->ep->desc);
    ep->is_in = usb_urb_dir_in(urb);
    ep->tstamp = stamp;
    ep->length = (ev_type == 'S') ?
        urb->transfer_buffer_length : urb->actual_length;
    /* Collecting status makes debugging sense for submits, too */
    ep->status = status;

    if (ep->xfertype == USB_ENDPOINT_XFER_INT) {
        ep->interval = urb->interval;
    } else if (ep->xfertype == USB_ENDPOINT_XFER_ISOC) {
        ep->interval = urb->interval;
        ep->start_frame = urb->start_frame;
        ep->error_count = urb->error_count;
    }
    ep->numdesc = urb->number_of_packets;
    if (ep->xfertype == USB_ENDPOINT_XFER_ISOC &&
            urb->number_of_packets > 0) {
        if ((ndesc = urb->number_of_packets) > ISODESC_MAX)
            ndesc = ISODESC_MAX;
        fp = urb->iso_frame_desc;
        dp = ep->isodesc;
        for (i = 0; i < ndesc; i++) {
            dp->status = fp->status;
            dp->offset = fp->offset;
            dp->length = (ev_type == 'S') ?
                fp->length : fp->actual_length;
            fp++;
            dp++;
        }
        /* Wasteful, but simple to understand: ISO 'C' is sparse. */
        if (ev_type == 'C')
            ep->length = urb->transfer_buffer_length;
    }

    ep->setup_flag = mon_text_get_setup(ep, urb, ev_type, rp->r.m_bus);
    ep->data_flag = mon_text_get_data(ep, urb, ep->length, ev_type,
            rp->r.m_bus);

    rp->nevents++;
    list_add_tail(&ep->e_link, &rp->e_list);
    wake_up(&rp->wait);
}

static void mon_text_submit(void *data, struct urb *urb)
{
    struct mon_reader_text *rp = data;
    mon_text_event(rp, urb, 'S', -EINPROGRESS);
}

static void mon_text_complete(void *data, struct urb *urb, int status)
{
    struct mon_reader_text *rp = data;
    mon_text_event(rp, urb, 'C', status);
}

static void mon_text_error(void *data, struct urb *urb, int error)
{
    struct mon_reader_text *rp = data;
    struct mon_event_text *ep;

    if (rp->nevents >= EVENT_MAX ||
        (ep = kmem_cache_alloc(rp->e_slab, GFP_ATOMIC)) == NULL) {
        rp->r.m_bus->cnt_text_lost++;
        return;
    }

    ep->type = 'E';
    ep->id = (unsigned long) urb;
    ep->busnum = urb->dev->bus->busnum;
    ep->devnum = urb->dev->devnum;
    ep->epnum = usb_endpoint_num(&urb->ep->desc);
    ep->xfertype = usb_endpoint_type(&urb->ep->desc);
    ep->is_in = usb_urb_dir_in(urb);
    ep->tstamp = mon_get_timestamp();
    ep->length = 0;
    ep->status = error;

    ep->setup_flag = '-';
    ep->data_flag = 'E';

    rp->nevents++;
    list_add_tail(&ep->e_link, &rp->e_list);
    wake_up(&rp->wait);
}

/*
 * Fetch next event from the circular buffer.
 */
static struct mon_event_text *mon_text_fetch(struct mon_reader_text *rp,
    struct mon_bus *mbus)
{
    struct list_head *p;
    unsigned long flags;

    spin_lock_irqsave(&mbus->lock, flags);
    if (list_empty(&rp->e_list)) {
        spin_unlock_irqrestore(&mbus->lock, flags);
        return NULL;
    }
    p = rp->e_list.next;
    list_del(p);
    --rp->nevents;
    spin_unlock_irqrestore(&mbus->lock, flags);
    return list_entry(p, struct mon_event_text, e_link);
}

/*
 */
static int mon_text_open(struct inode *inode, struct file *file)
{
    struct mon_bus *mbus;
    struct mon_reader_text *rp;
    int rc;

    mutex_lock(&mon_lock);
    mbus = inode->i_private;

    rp = kzalloc(sizeof(struct mon_reader_text), GFP_KERNEL);
    if (rp == NULL) {
        rc = -ENOMEM;
        goto err_alloc;
    }
    INIT_LIST_HEAD(&rp->e_list);
    init_waitqueue_head(&rp->wait);
    mutex_init(&rp->printf_lock);

    rp->printf_size = PRINTF_DFL;
    rp->printf_buf = kmalloc(rp->printf_size, GFP_KERNEL);
    if (rp->printf_buf == NULL) {
        rc = -ENOMEM;
        goto err_alloc_pr;
    }

    rp->r.m_bus = mbus;
    rp->r.r_data = rp;
    rp->r.rnf_submit = mon_text_submit;
    rp->r.rnf_error = mon_text_error;
    rp->r.rnf_complete = mon_text_complete;

    snprintf(rp->slab_name, SLAB_NAME_SZ, "mon_text_%p", rp);
    rp->e_slab = kmem_cache_create(rp->slab_name,
        sizeof(struct mon_event_text), sizeof(long), 0,
        mon_text_ctor);
    if (rp->e_slab == NULL) {
        rc = -ENOMEM;
        goto err_slab;
    }

    mon_reader_add(mbus, &rp->r);

    file->private_data = rp;
    mutex_unlock(&mon_lock);
    return 0;

// err_busy:
//  kmem_cache_destroy(rp->e_slab);
err_slab:
    kfree(rp->printf_buf);
err_alloc_pr:
    kfree(rp);
err_alloc:
    mutex_unlock(&mon_lock);
    return rc;
}

/*
 * For simplicity, we read one record in one system call and throw out
 * what does not fit. This means that the following does not work:
 *   dd if=/dbg/usbmon/0t bs=10
 * Also, we do not allow seeks and do not bother advancing the offset.
 */
static ssize_t mon_text_read_t(struct file *file, char __user *buf,
                size_t nbytes, loff_t *ppos)
{
    struct mon_reader_text *rp = file->private_data;
    struct mon_event_text *ep;
    struct mon_text_ptr ptr;

    if (IS_ERR(ep = mon_text_read_wait(rp, file)))
        return PTR_ERR(ep);
    mutex_lock(&rp->printf_lock);
    ptr.cnt = 0;
    ptr.pbuf = rp->printf_buf;
    ptr.limit = rp->printf_size;

    mon_text_read_head_t(rp, &ptr, ep);
    mon_text_read_statset(rp, &ptr, ep);
    ptr.cnt += snprintf(ptr.pbuf + ptr.cnt, ptr.limit - ptr.cnt,
        " %d", ep->length);
    mon_text_read_data(rp, &ptr, ep);

    if (copy_to_user(buf, rp->printf_buf, ptr.cnt))
        ptr.cnt = -EFAULT;
    mutex_unlock(&rp->printf_lock);
    kmem_cache_free(rp->e_slab, ep);
    return ptr.cnt;
}

static ssize_t mon_text_read_u(struct file *file, char __user *buf,
                size_t nbytes, loff_t *ppos)
{
    struct mon_reader_text *rp = file->private_data;
    struct mon_event_text *ep;
    struct mon_text_ptr ptr;

    if (IS_ERR(ep = mon_text_read_wait(rp, file)))
        return PTR_ERR(ep);
    mutex_lock(&rp->printf_lock);
    ptr.cnt = 0;
    ptr.pbuf = rp->printf_buf;
    ptr.limit = rp->printf_size;

    mon_text_read_head_u(rp, &ptr, ep);
    if (ep->type == 'E') {
        mon_text_read_statset(rp, &ptr, ep);
    } else if (ep->xfertype == USB_ENDPOINT_XFER_ISOC) {
        mon_text_read_isostat(rp, &ptr, ep);
        mon_text_read_isodesc(rp, &ptr, ep);
    } else if (ep->xfertype == USB_ENDPOINT_XFER_INT) {
        mon_text_read_intstat(rp, &ptr, ep);
    } else {
        mon_text_read_statset(rp, &ptr, ep);
    }
    ptr.cnt += snprintf(ptr.pbuf + ptr.cnt, ptr.limit - ptr.cnt,
        " %d", ep->length);
    mon_text_read_data(rp, &ptr, ep);

    if (copy_to_user(buf, rp->printf_buf, ptr.cnt))
        ptr.cnt = -EFAULT;
    mutex_unlock(&rp->printf_lock);
    kmem_cache_free(rp->e_slab, ep);
    return ptr.cnt;
}

static struct mon_event_text *mon_text_read_wait(struct mon_reader_text *rp,
    struct file *file)
{
    struct mon_bus *mbus = rp->r.m_bus;
    DECLARE_WAITQUEUE(waita, current);
    struct mon_event_text *ep;

    add_wait_queue(&rp->wait, &waita);
    set_current_state(TASK_INTERRUPTIBLE);
    while ((ep = mon_text_fetch(rp, mbus)) == NULL) {
        if (file->f_flags & O_NONBLOCK) {
            set_current_state(TASK_RUNNING);
            remove_wait_queue(&rp->wait, &waita);
            return ERR_PTR(-EWOULDBLOCK);
        }
        /*
         * We do not count nwaiters, because ->release is supposed
         * to be called when all openers are gone only.
         */
        schedule();
        if (signal_pending(current)) {
            remove_wait_queue(&rp->wait, &waita);
            return ERR_PTR(-EINTR);
        }
        set_current_state(TASK_INTERRUPTIBLE);
    }
    set_current_state(TASK_RUNNING);
    remove_wait_queue(&rp->wait, &waita);
    return ep;
}

static void mon_text_read_head_t(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep)
{
    char udir, utype;

    udir = (ep->is_in ? 'i' : 'o');
    switch (ep->xfertype) {
    case USB_ENDPOINT_XFER_ISOC:    utype = 'Z'; break;
    case USB_ENDPOINT_XFER_INT: utype = 'I'; break;
    case USB_ENDPOINT_XFER_CONTROL: utype = 'C'; break;
    default: /* PIPE_BULK */  utype = 'B';
    }
    p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
        "%lx %u %c %c%c:%03u:%02u",
        ep->id, ep->tstamp, ep->type,
        utype, udir, ep->devnum, ep->epnum);
}

static void mon_text_read_head_u(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep)
{
    char udir, utype;

    udir = (ep->is_in ? 'i' : 'o');
    switch (ep->xfertype) {
    case USB_ENDPOINT_XFER_ISOC:    utype = 'Z'; break;
    case USB_ENDPOINT_XFER_INT: utype = 'I'; break;
    case USB_ENDPOINT_XFER_CONTROL: utype = 'C'; break;
    default: /* PIPE_BULK */  utype = 'B';
    }
    p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
        "%lx %u %c %c%c:%d:%03u:%u",
        ep->id, ep->tstamp, ep->type,
        utype, udir, ep->busnum, ep->devnum, ep->epnum);
}

static void mon_text_read_statset(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep)
{

    if (ep->setup_flag == 0) {   /* Setup packet is present and captured */
        p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
            " s %02x %02x %04x %04x %04x",
            ep->setup[0],
            ep->setup[1],
            (ep->setup[3] << 8) | ep->setup[2],
            (ep->setup[5] << 8) | ep->setup[4],
            (ep->setup[7] << 8) | ep->setup[6]);
    } else if (ep->setup_flag != '-') { /* Unable to capture setup packet */
        p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
            " %c __ __ ____ ____ ____", ep->setup_flag);
    } else {                     /* No setup for this kind of URB */
        p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
            " %d", ep->status);
    }
}

static void mon_text_read_intstat(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep)
{
    p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
        " %d:%d", ep->status, ep->interval);
}

static void mon_text_read_isostat(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep)
{
    if (ep->type == 'S') {
        p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
            " %d:%d:%d", ep->status, ep->interval, ep->start_frame);
    } else {
        p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
            " %d:%d:%d:%d",
            ep->status, ep->interval, ep->start_frame, ep->error_count);
    }
}

static void mon_text_read_isodesc(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep)
{
    int ndesc;  /* Display this many */
    int i;
    const struct mon_iso_desc *dp;

    p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
        " %d", ep->numdesc);
    ndesc = ep->numdesc;
    if (ndesc > ISODESC_MAX)
        ndesc = ISODESC_MAX;
    if (ndesc < 0)
        ndesc = 0;
    dp = ep->isodesc;
    for (i = 0; i < ndesc; i++) {
        p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
            " %d:%u:%u", dp->status, dp->offset, dp->length);
        dp++;
    }
}

static void mon_text_read_data(struct mon_reader_text *rp,
    struct mon_text_ptr *p, const struct mon_event_text *ep)
{
    int data_len, i;

    if ((data_len = ep->length) > 0) {
        if (ep->data_flag == 0) {
            p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
                " =");
            if (data_len >= DATA_MAX)
                data_len = DATA_MAX;
            for (i = 0; i < data_len; i++) {
                if (i % 4 == 0) {
                    p->cnt += snprintf(p->pbuf + p->cnt,
                        p->limit - p->cnt,
                        " ");
                }
                p->cnt += snprintf(p->pbuf + p->cnt,
                    p->limit - p->cnt,
                    "%02x", ep->data[i]);
            }
            p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
                "\n");
        } else {
            p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt,
                " %c\n", ep->data_flag);
        }
    } else {
        p->cnt += snprintf(p->pbuf + p->cnt, p->limit - p->cnt, "\n");
    }
}

static int mon_text_release(struct inode *inode, struct file *file)
{
    struct mon_reader_text *rp = file->private_data;
    struct mon_bus *mbus;
    /* unsigned long flags; */
    struct list_head *p;
    struct mon_event_text *ep;

    mutex_lock(&mon_lock);
    mbus = inode->i_private;

    if (mbus->nreaders <= 0) {
        printk(KERN_ERR TAG ": consistency error on close\n");
        mutex_unlock(&mon_lock);
        return 0;
    }
    mon_reader_del(mbus, &rp->r);

    /*
     * In theory, e_list is protected by mbus->lock. However,
     * after mon_reader_del has finished, the following is the case:
     *  - we are not on reader list anymore, so new events won't be added;
     *  - whole mbus may be dropped if it was orphaned.
     * So, we better not touch mbus.
     */
    /* spin_lock_irqsave(&mbus->lock, flags); */
    while (!list_empty(&rp->e_list)) {
        p = rp->e_list.next;
        ep = list_entry(p, struct mon_event_text, e_link);
        list_del(p);
        --rp->nevents;
        kmem_cache_free(rp->e_slab, ep);
    }
    /* spin_unlock_irqrestore(&mbus->lock, flags); */

    kmem_cache_destroy(rp->e_slab);
    kfree(rp->printf_buf);
    kfree(rp);

    mutex_unlock(&mon_lock);
    return 0;
}

static const struct file_operations mon_fops_text_t = {
    .owner =    THIS_MODULE,
    .open =     mon_text_open,
    .llseek =   no_llseek,
    .read =     mon_text_read_t,
    .release =  mon_text_release,
};

static const struct file_operations mon_fops_text_u = {
    .owner =    THIS_MODULE,
    .open =     mon_text_open,
    .llseek =   no_llseek,
    .read =     mon_text_read_u,
    .release =  mon_text_release,
};

int mon_text_add(struct mon_bus *mbus, const struct usb_bus *ubus)
{
    struct dentry *d;
    enum { NAMESZ = 10 };
    char name[NAMESZ];
    int busnum = ubus? ubus->busnum: 0;
    int rc;

    if (mon_dir == NULL)
        return 0;

    if (ubus != NULL) {
        rc = snprintf(name, NAMESZ, "%dt", busnum);
        if (rc <= 0 || rc >= NAMESZ)
            goto err_print_t;
        d = debugfs_create_file(name, 0600, mon_dir, mbus,
                                 &mon_fops_text_t);
        if (d == NULL)
            goto err_create_t;
        mbus->dent_t = d;
    }

    rc = snprintf(name, NAMESZ, "%du", busnum);
    if (rc <= 0 || rc >= NAMESZ)
        goto err_print_u;
    d = debugfs_create_file(name, 0600, mon_dir, mbus, &mon_fops_text_u);
    if (d == NULL)
        goto err_create_u;
    mbus->dent_u = d;

    rc = snprintf(name, NAMESZ, "%ds", busnum);
    if (rc <= 0 || rc >= NAMESZ)
        goto err_print_s;
    d = debugfs_create_file(name, 0600, mon_dir, mbus, &mon_fops_stat);
    if (d == NULL)
        goto err_create_s;
    mbus->dent_s = d;

    return 1;

err_create_s:
err_print_s:
    debugfs_remove(mbus->dent_u);
    mbus->dent_u = NULL;
err_create_u:
err_print_u:
    if (ubus != NULL) {
        debugfs_remove(mbus->dent_t);
        mbus->dent_t = NULL;
    }
err_create_t:
err_print_t:
    return 0;
}

void mon_text_del(struct mon_bus *mbus)
{
    debugfs_remove(mbus->dent_u);
    if (mbus->dent_t != NULL)
        debugfs_remove(mbus->dent_t);
    debugfs_remove(mbus->dent_s);
}

/*
 * Slab interface: constructor.
 */
static void mon_text_ctor(void *mem)
{
    /*
     * Nothing to initialize. No, really!
     * So, we fill it with garbage to emulate a reused object.
     */
    memset(mem, 0xe5, sizeof(struct mon_event_text));
}

int __init mon_text_init(void)
{
    struct dentry *mondir;

    mondir = debugfs_create_dir("usbmon", usb_debug_root);
    if (IS_ERR(mondir)) {
        /* debugfs not available, but we can use usbmon without it */
        return 0;
    }
    if (mondir == NULL) {
        printk(KERN_NOTICE TAG ": unable to create usbmon directory\n");
        return -ENOMEM;
    }
    mon_dir = mondir;
    return 0;
}

void mon_text_exit(void)
{
    debugfs_remove(mon_dir);
}