Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 773 insertions, 0 deletions

diff --git a/drivers/usb/mon/mon_text.c b/drivers/usb/mon/mon_text.c
new file mode 100644
index 000000000..39cb14164
--- /dev/null
+++ b/drivers/usb/mon/mon_text.c
@@ -0,0 +1,773 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * 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/sched/signal.h>
+#include <linux/time.h>
+#include <linux/ktime.h>
+#include <linux/export.h>
+#include <linux/mutex.h>
+#include <linux/debugfs.h>
+#include <linux/scatterlist.h>
+#include <linux/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;
+	size_t printf_offset;
+	size_t printf_togo;
+	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 timespec64 now;
+	unsigned int stamp;
+
+	ktime_get_ts64(&now);
+	stamp = now.tv_sec & 0xFFF;  /* 2^32 = 4294967296. Limit to 4096s. */
+	stamp = stamp * USEC_PER_SEC + now.tv_nsec / NSEC_PER_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;
+}
+
+static ssize_t mon_text_copy_to_user(struct mon_reader_text *rp,
+    char __user * const buf, const size_t nbytes)
+{
+	const size_t togo = min(nbytes, rp->printf_togo);
+
+	if (copy_to_user(buf, &rp->printf_buf[rp->printf_offset], togo))
+		return -EFAULT;
+	rp->printf_togo -= togo;
+	rp->printf_offset += togo;
+	return togo;
+}
+
+/* ppos is not advanced since the llseek operation is not permitted. */
+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;
+	ssize_t ret;
+
+	mutex_lock(&rp->printf_lock);
+
+	if (rp->printf_togo == 0) {
+
+		ep = mon_text_read_wait(rp, file);
+		if (IS_ERR(ep)) {
+			mutex_unlock(&rp->printf_lock);
+			return PTR_ERR(ep);
+		}
+		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 += scnprintf(ptr.pbuf + ptr.cnt, ptr.limit - ptr.cnt,
+		    " %d", ep->length);
+		mon_text_read_data(rp, &ptr, ep);
+
+		rp->printf_togo = ptr.cnt;
+		rp->printf_offset = 0;
+
+		kmem_cache_free(rp->e_slab, ep);
+	}
+
+	ret = mon_text_copy_to_user(rp, buf, nbytes);
+	mutex_unlock(&rp->printf_lock);
+	return ret;
+}
+
+/* ppos is not advanced since the llseek operation is not permitted. */
+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;
+	ssize_t ret;
+
+	mutex_lock(&rp->printf_lock);
+
+	if (rp->printf_togo == 0) {
+
+		ep = mon_text_read_wait(rp, file);
+		if (IS_ERR(ep)) {
+			mutex_unlock(&rp->printf_lock);
+			return PTR_ERR(ep);
+		}
+		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 += scnprintf(ptr.pbuf + ptr.cnt, ptr.limit - ptr.cnt,
+		    " %d", ep->length);
+		mon_text_read_data(rp, &ptr, ep);
+
+		rp->printf_togo = ptr.cnt;
+		rp->printf_offset = 0;
+
+		kmem_cache_free(rp->e_slab, ep);
+	}
+
+	ret = mon_text_copy_to_user(rp, buf, nbytes);
+	mutex_unlock(&rp->printf_lock);
+	return ret;
+}
+
+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 += scnprintf(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 += scnprintf(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 += scnprintf(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 += scnprintf(p->pbuf + p->cnt, p->limit - p->cnt,
+		    " %c __ __ ____ ____ ____", ep->setup_flag);
+	} else {                     /* No setup for this kind of URB */
+		p->cnt += scnprintf(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 += scnprintf(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 += scnprintf(p->pbuf + p->cnt, p->limit - p->cnt,
+		    " %d:%d:%d", ep->status, ep->interval, ep->start_frame);
+	} else {
+		p->cnt += scnprintf(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 += scnprintf(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 += scnprintf(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 += scnprintf(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 += scnprintf(p->pbuf + p->cnt,
+					    p->limit - p->cnt,
+					    " ");
+				}
+				p->cnt += scnprintf(p->pbuf + p->cnt,
+				    p->limit - p->cnt,
+				    "%02x", ep->data[i]);
+			}
+			p->cnt += scnprintf(p->pbuf + p->cnt, p->limit - p->cnt,
+			    "\n");
+		} else {
+			p->cnt += scnprintf(p->pbuf + p->cnt, p->limit - p->cnt,
+			    " %c\n", ep->data_flag);
+		}
+	} else {
+		p->cnt += scnprintf(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)
+{
+	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;
+		mbus->dent_t = debugfs_create_file(name, 0600, mon_dir, mbus,
+							     &mon_fops_text_t);
+	}
+
+	rc = snprintf(name, NAMESZ, "%du", busnum);
+	if (rc <= 0 || rc >= NAMESZ)
+		goto err_print_u;
+	mbus->dent_u = debugfs_create_file(name, 0600, mon_dir, mbus,
+					   &mon_fops_text_u);
+
+	rc = snprintf(name, NAMESZ, "%ds", busnum);
+	if (rc <= 0 || rc >= NAMESZ)
+		goto err_print_s;
+	mbus->dent_s = debugfs_create_file(name, 0600, mon_dir, mbus,
+					   &mon_fops_stat);
+
+	return 1;
+
+err_print_s:
+	debugfs_remove(mbus->dent_u);
+	mbus->dent_u = NULL;
+err_print_u:
+	if (ubus != NULL) {
+		debugfs_remove(mbus->dent_t);
+		mbus->dent_t = NULL;
+	}
+err_print_t:
+	return 0;
+}
+
+void mon_text_del(struct mon_bus *mbus)
+{
+	debugfs_remove(mbus->dent_u);
+	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)
+{
+	mon_dir = debugfs_create_dir("usbmon", usb_debug_root);
+	return 0;
+}
+
+void mon_text_exit(void)
+{
+	debugfs_remove(mon_dir);
+}