[PATCH 10/11] Introduce single user mode

[PATCH 10/11] Introduce single user mode

[stefani]

From: Stefani Seibold <stefani@seibold.net>

Most USB devices can only used in a single usage mode. This patch
prevents a reopening on an already opened device.

Signed-off-by: Stefani Seibold <stefani@seibold.net>
---
 drivers/usb/usb-skeleton.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/drivers/usb/usb-skeleton.c b/drivers/usb/usb-skeleton.c
index 11cc97b..81d256f 100644
--- a/drivers/usb/usb-skeleton.c
+++ b/drivers/usb/usb-skeleton.c
@@ -61,6 +61,7 @@ struct usb_skel {
 	int			errors;			/* the last request tanked */
 	bool			ongoing_read;		/* a read is going on */
 	bool			connected;		/* connected flag */
+	bool			in_use;			/* in use flag */
 	spinlock_t		err_lock;		/* lock for errors */
 	struct kref		kref;
 	struct mutex		io_mutex;		/* synchronize with disconnect */
@@ -104,6 +105,11 @@ static int skel_open(struct inode *inode, struct file *file)
 		goto exit;
 	}
 
+	if (dev->in_use) {
+		retval = -EBUSY;
+		goto exit;
+	}
+
 	retval = usb_autopm_get_interface(interface);
 	if (retval)
 		goto exit;
@@ -111,6 +117,7 @@ static int skel_open(struct inode *inode, struct file *file)
 	/* increment our usage count for the device */
 	kref_get(&dev->kref);
 
+	dev->in_use = true;
 	mutex_unlock(&sync_mutex);
 
 	/* save our object in the file's private structure */
@@ -131,6 +138,7 @@ static int skel_release(struct inode *inode, struct file *file)
 	if (dev->connected)
 		usb_autopm_put_interface(
 			usb_find_interface(&skel_driver, iminor(inode)));
+	dev->in_use = false;
 
 	/* decrement the count on our device */
 	kref_put(&dev->kref, skel_delete);
@@ -529,6 +537,7 @@ static int skel_probe(struct usb_interface *interface,
 
 	dev->udev = usb_get_dev(interface_to_usbdev(interface));
 	dev->connected = true;
+	dev->in_use = false;
 
 	/* set up the endpoint information */
 	/* use only the first bulk-in and bulk-out endpoints */
-- 
1.7.8.6

[PATCH 11/11] Bump version number and add aditional author

[stefani]

From: Stefani Seibold <stefani@seibold.net>

Signed-off-by: Stefani Seibold <stefani@seibold.net>
---
 drivers/usb/usb-skeleton.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/drivers/usb/usb-skeleton.c b/drivers/usb/usb-skeleton.c
index 81d256f..c93841c 100644
--- a/drivers/usb/usb-skeleton.c
+++ b/drivers/usb/usb-skeleton.c
@@ -1,7 +1,8 @@
 /*
- * USB Skeleton driver - 2.2
+ * USB Skeleton driver - 2.3
  *
  * Copyright (C) 2001-2004 Greg Kroah-Hartman (greg@kroah.com)
+ * fixes by Stefani Seibold (stefani@seibold.net)
  *
  *	This program is free software; you can redistribute it and/or
  *	modify it under the terms of the GNU General Public License as
-- 
1.7.8.6

Re: [PATCH 10/11] Introduce single user mode

[Andi Kleen]

stefani@seibold.net writes:
>  	}
>  
> +	if (dev->in_use) {
> +		retval = -EBUSY;
> +		goto exit;
> +	}

This plus setting the flag has to be inside the mutex, otherwise you
have an obvious race.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only

[PATCH] fix usb skeleton driver

[stefani]

From: Stefani Seibold <stefani@seibold.net>

This is a fix for the USB skeleton driver to bring it in shape.

- The usb_interface structure pointer will be no longer stored 
- Every access to the USB will be handled trought the usb_interface pointer
- Add a new bool 'connected' for signaling a disconnect (== false)
- Handle a non blocking read without blocking
- Code cleanup
- Synchronize disconnect() handler with open() and release(), to fix races
- Introduced fsync
- Single user mode
- Eliminated dead code
- Save some bytes in the dev structure

Some word about the open()/release() races with disconnect() of an USB device
(which can happen any time):
- The return interface pointer from usb_find_interface() could be already owned
  by an other driver and no more longer handle by the skeleton driver.
- Or the dev pointer return by usb_get_intfdata() could point to an already
  release memory.

This races can not handled by a per device mutex. Only a driver global mutex
could do this job, since the kref_put() in the skel_disconnect() must be
protected, otherwise skel_open() could access an already released memory.

I know that this races are very small, but on heavy load or misdesigned or buggy
hardware this could lead in a OOPS or unpredictable behavior.

The patch is against linux 3.5.0 commit eea5b5510fc5545d15b69da8e485a7424ae388cf

Hope this helps

Signed-off-by: Stefani Seibold <stefani@seibold.net>

[PATCH 10/11] Introduce single user mode

[stefani]

From: Stefani Seibold <stefani@seibold.net>

Most USB devices can only used in a single usage mode. This patch
prevents a reopening on an already opened device.

Signed-off-by: Stefani Seibold <stefani@seibold.net>
---
 drivers/usb/usb-skeleton.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/drivers/usb/usb-skeleton.c b/drivers/usb/usb-skeleton.c
index 11cc97b..81d256f 100644
--- a/drivers/usb/usb-skeleton.c
+++ b/drivers/usb/usb-skeleton.c
@@ -61,6 +61,7 @@ struct usb_skel {
 	int			errors;			/* the last request tanked */
 	bool			ongoing_read;		/* a read is going on */
 	bool			connected;		/* connected flag */
+	bool			in_use;			/* in use flag */
 	spinlock_t		err_lock;		/* lock for errors */
 	struct kref		kref;
 	struct mutex		io_mutex;		/* synchronize with disconnect */
@@ -104,6 +105,11 @@ static int skel_open(struct inode *inode, struct file *file)
 		goto exit;
 	}
 
+	if (dev->in_use) {
+		retval = -EBUSY;
+		goto exit;
+	}
+
 	retval = usb_autopm_get_interface(interface);
 	if (retval)
 		goto exit;
@@ -111,6 +117,7 @@ static int skel_open(struct inode *inode, struct file *file)
 	/* increment our usage count for the device */
 	kref_get(&dev->kref);
 
+	dev->in_use = true;
 	mutex_unlock(&sync_mutex);
 
 	/* save our object in the file's private structure */
@@ -131,6 +138,7 @@ static int skel_release(struct inode *inode, struct file *file)
 	if (dev->connected)
 		usb_autopm_put_interface(
 			usb_find_interface(&skel_driver, iminor(inode)));
+	dev->in_use = false;
 
 	/* decrement the count on our device */
 	kref_put(&dev->kref, skel_delete);
@@ -529,6 +537,7 @@ static int skel_probe(struct usb_interface *interface,
 
 	dev->udev = usb_get_dev(interface_to_usbdev(interface));
 	dev->connected = true;
+	dev->in_use = false;
 
 	/* set up the endpoint information */
 	/* use only the first bulk-in and bulk-out endpoints */
-- 
1.7.8.6