drivers/usb/mon/mon_text.c - LeafOS-Devices/android_kernel_samsung_exynos9820 - Gitiles

 /*
  * 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 <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  (2*PAGE_SIZE / sizeof(struct mon_event_text))

 #define PRINTF_DFL  160

 struct mon_event_text {
 	struct list_head e_link;
 	int type;		/* submit, complete, etc. */
 	unsigned int pipe;	/* Pipe */
 	unsigned long id;	/* From pointer, most of the time */
 	unsigned int tstamp;
 	int length;		/* Depends on type: xfer length or act length */
 	int status;
 	char setup_flag;
 	char data_flag;
 	unsigned char setup[SETUP_MAX];
 	unsigned char data[DATA_MAX];
 };

 #define SLAB_NAME_SZ  30
 struct mon_reader_text {
 	kmem_cache_t *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 void mon_text_ctor(void *, kmem_cache_t *, unsigned long);

 /*
  * 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 (!usb_pipecontrol(urb->pipe) || ev_type != 'S')
 		return '-';

 	if (mbus->uses_dma && (urb->transfer_flags & URB_NO_SETUP_DMA_MAP))
 		return mon_dmapeek(ep->setup, urb->setup_dma, SETUP_MAX);
 	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)
 {
 	int pipe = urb->pipe;

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

 	if (usb_pipein(pipe)) {
 		if (ev_type == 'S')
 			return '<';
 	} else {
 		if (ev_type == 'C')
 			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 (mbus->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)
 {
 	struct mon_event_text *ep;
 	unsigned int stamp;

 	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->pipe = urb->pipe;
 	ep->id = (unsigned long) 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 = urb->status;

 	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');
 }

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

 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->pipe = urb->pipe;
 	ep->id = (unsigned long) 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 usb_bus *ubus;
 	struct mon_reader_text *rp;
 	int rc;

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

 	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%dt_%lx", ubus->busnum,
 	    (long)rp);
 	rp->e_slab = kmem_cache_create(rp->slab_name,
 	    sizeof(struct mon_event_text), sizeof(long), 0,
 	    mon_text_ctor, NULL);
 	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(struct file *file, char __user *buf,
 				size_t nbytes, loff_t *ppos)
 {
 	struct mon_reader_text *rp = file->private_data;
 	struct mon_bus *mbus = rp->r.m_bus;
 	DECLARE_WAITQUEUE(waita, current);
 	struct mon_event_text *ep;
 	int cnt, limit;
 	char *pbuf;
 	char udir, utype;
 	int data_len, i;

 	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 -EWOULDBLOCK;	/* Same as EAGAIN in Linux */
 		}
 		/*
 		 * 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 -EINTR;
 		}
 		set_current_state(TASK_INTERRUPTIBLE);
 	}
 	set_current_state(TASK_RUNNING);
 	remove_wait_queue(&rp->wait, &waita);

 	mutex_lock(&rp->printf_lock);
 	cnt = 0;
 	pbuf = rp->printf_buf;
 	limit = rp->printf_size;

 	udir = usb_pipein(ep->pipe) ? 'i' : 'o';
 	switch (usb_pipetype(ep->pipe)) {
 	case PIPE_ISOCHRONOUS:	utype = 'Z'; break;
 	case PIPE_INTERRUPT:	utype = 'I'; break;
 	case PIPE_CONTROL:	utype = 'C'; break;
 	default: /* PIPE_BULK */  utype = 'B';
 	}
 	cnt += snprintf(pbuf + cnt, limit - cnt,
 	    "%lx %u %c %c%c:%03u:%02u",
 	    ep->id, ep->tstamp, ep->type,
 	    utype, udir, usb_pipedevice(ep->pipe), usb_pipeendpoint(ep->pipe));

 	if (ep->setup_flag == 0) {   /* Setup packet is present and captured */
 		cnt += snprintf(pbuf + cnt, limit - 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 */
 		cnt += snprintf(pbuf + cnt, limit - cnt,
 		    " %c __ __ ____ ____ ____", ep->setup_flag);
 	} else {                     /* No setup for this kind of URB */
 		cnt += snprintf(pbuf + cnt, limit - cnt, " %d", ep->status);
 	}
 	cnt += snprintf(pbuf + cnt, limit - cnt, " %d", ep->length);

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

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

 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;
 }

 const struct file_operations mon_fops_text = {
 	.owner =	THIS_MODULE,
 	.open =		mon_text_open,
 	.llseek =	no_llseek,
 	.read =		mon_text_read,
 	/* .write =	mon_text_write, */
 	/* .poll =		mon_text_poll, */
 	/* .ioctl =	mon_text_ioctl, */
 	.release =	mon_text_release,
 };

 /*
  * Slab interface: constructor.
  */
 static void mon_text_ctor(void *mem, kmem_cache_t *slab, unsigned long sflags)
 {
 	/*
 	 * Nothing to initialize. No, really!
 	 * So, we fill it with garbage to emulate a reused object.
 	 */
 	memset(mem, 0xe5, sizeof(struct mon_event_text));
 }
	/*
	* 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 <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 (2*PAGE_SIZE / sizeof(struct mon_event_text))

	#define PRINTF_DFL 160

	struct mon_event_text {
	struct list_head e_link;
	int type; /* submit, complete, etc. */
	unsigned int pipe; /* Pipe */
	unsigned long id; /* From pointer, most of the time */
	unsigned int tstamp;
	int length; /* Depends on type: xfer length or act length */
	int status;
	char setup_flag;
	char data_flag;
	unsigned char setup[SETUP_MAX];
	unsigned char data[DATA_MAX];
	};

	#define SLAB_NAME_SZ 30
	struct mon_reader_text {
	kmem_cache_t *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 void mon_text_ctor(void , kmem_cache_t , unsigned long);

	/*
	* 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 (!usb_pipecontrol(urb->pipe) \|\| ev_type != 'S')
	return '-';

	if (mbus->uses_dma && (urb->transfer_flags & URB_NO_SETUP_DMA_MAP))
	return mon_dmapeek(ep->setup, urb->setup_dma, SETUP_MAX);
	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)
	{
	int pipe = urb->pipe;

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

	if (usb_pipein(pipe)) {
	if (ev_type == 'S')
	return '<';
	} else {
	if (ev_type == 'C')
	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 (mbus->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)
	{
	struct mon_event_text *ep;
	unsigned int stamp;

	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->pipe = urb->pipe;
	ep->id = (unsigned long) 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 = urb->status;

	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');
	}

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

	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->pipe = urb->pipe;
	ep->id = (unsigned long) 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 usb_bus *ubus;
	struct mon_reader_text *rp;
	int rc;

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

	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%dt_%lx", ubus->busnum,
	(long)rp);
	rp->e_slab = kmem_cache_create(rp->slab_name,
	sizeof(struct mon_event_text), sizeof(long), 0,
	mon_text_ctor, NULL);
	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(struct file file, char __user buf,
	size_t nbytes, loff_t *ppos)
	{
	struct mon_reader_text *rp = file->private_data;
	struct mon_bus *mbus = rp->r.m_bus;
	DECLARE_WAITQUEUE(waita, current);
	struct mon_event_text *ep;
	int cnt, limit;
	char *pbuf;
	char udir, utype;
	int data_len, i;

	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 -EWOULDBLOCK; /* Same as EAGAIN in Linux */
	}
	/*
	* 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 -EINTR;
	}
	set_current_state(TASK_INTERRUPTIBLE);
	}
	set_current_state(TASK_RUNNING);
	remove_wait_queue(&rp->wait, &waita);

	mutex_lock(&rp->printf_lock);
	cnt = 0;
	pbuf = rp->printf_buf;
	limit = rp->printf_size;

	udir = usb_pipein(ep->pipe) ? 'i' : 'o';
	switch (usb_pipetype(ep->pipe)) {
	case PIPE_ISOCHRONOUS: utype = 'Z'; break;
	case PIPE_INTERRUPT: utype = 'I'; break;
	case PIPE_CONTROL: utype = 'C'; break;
	default: /* PIPE_BULK */ utype = 'B';
	}
	cnt += snprintf(pbuf + cnt, limit - cnt,
	"%lx %u %c %c%c:%03u:%02u",
	ep->id, ep->tstamp, ep->type,
	utype, udir, usb_pipedevice(ep->pipe), usb_pipeendpoint(ep->pipe));

	if (ep->setup_flag == 0) { /* Setup packet is present and captured */
	cnt += snprintf(pbuf + cnt, limit - 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 */
	cnt += snprintf(pbuf + cnt, limit - cnt,
	" %c __ __ ____ ____ ____", ep->setup_flag);
	} else { /* No setup for this kind of URB */
	cnt += snprintf(pbuf + cnt, limit - cnt, " %d", ep->status);
	}
	cnt += snprintf(pbuf + cnt, limit - cnt, " %d", ep->length);

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

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

	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;
	}

	const struct file_operations mon_fops_text = {
	.owner = THIS_MODULE,
	.open = mon_text_open,
	.llseek = no_llseek,
	.read = mon_text_read,
	/* .write = mon_text_write, */
	/* .poll = mon_text_poll, */
	/* .ioctl = mon_text_ioctl, */
	.release = mon_text_release,
	};

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