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[linux-2.6/mini2440.git] / drivers / usb / mon / mon_text.c

/*
 * 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/time.h>
#include <linux/mutex.h>
#include <linux/debugfs.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)
{
        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 '>';
        }

        /*
         * The check to see if it's safe to poke at data has an enormous
         * number of corner cases, but it seems that the following is
         * more or less safe.
         *
         * We do not even try to look at transfer_buffer, because it can
         * contain non-NULL garbage in case the upper level promised to
         * set DMA for the HCD.
         */
        if (urb->dev->bus->uses_dma &&
            (urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
                return mon_dmapeek(ep->data, urb->transfer_dma, len);
        }

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

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

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

        do_gettimeofday(&tval);
        stamp = tval.tv_sec & 0xFFFF;   /* 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++;
                }
        }

        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 = 0;
        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 = 0;
        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 (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", NULL);
        if (IS_ERR(mondir)) {
                printk(KERN_NOTICE TAG ": debugfs is not available\n");
                return -ENODEV;
        }
        if (mondir == NULL) {
                printk(KERN_NOTICE TAG ": unable to create usbmon directory\n");
                return -ENODEV;
        }
        mon_dir = mondir;
        return 0;
}

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