Accessing usb devices with USBDEVFS

Accessing usb devices with USBDEVFS

[Danny Budik]

I have a question that may or may not be related to hotplugging. I have 
noticed that when I plug in a USB device, it takes about 5 seconds for 
it to show up in /proc/bus/usb/001/xxx. I am using HAL to recognize when 
a USB device is plugged in and USBDEVFS to communicate with my device.

When I plug it in, dbus/HAL instantly recognizes it and sends me a 
message.  But when I make the function call to open it (using fopen on 
the file above) I get an error that the device is not found. In fact, it 
takes about 5 seconds for the device to show up in the /proc/bus/usb/ 
directory so I have to place a sleep(5) line in my C code before I am 
able to open the device.

My test machine is a PIII 733 with FC4, latest kernel, so it is a 
relatively slow machine. Is there a way to predict the time that it 
takes for the device to be accessible with USBDEVFS so that I don't have 
to hardcode the sleep statement?

Thanks,
Danny Budik


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Re: Accessing usb devices with USBDEVFS

[Greg KH]

On Fri, Apr 28, 2006 at 01:44:08PM -0400, Danny Budik wrote:
> I have a question that may or may not be related to hotplugging. I have 
> noticed that when I plug in a USB device, it takes about 5 seconds for 
> it to show up in /proc/bus/usb/001/xxx.

What kind of USB device is this?

> I am using HAL to recognize when 
> a USB device is plugged in and USBDEVFS to communicate with my device.

You mean "usbfs" right?  The old "usbdevfs" name went away about 3-4
years ago :)

> When I plug it in, dbus/HAL instantly recognizes it and sends me a 
> message.  But when I make the function call to open it (using fopen on 
> the file above) I get an error that the device is not found. In fact, it 
> takes about 5 seconds for the device to show up in the /proc/bus/usb/ 
> directory so I have to place a sleep(5) line in my C code before I am 
> able to open the device.

Can you enable CONFIG_USB_DEBUG, rebuild the kernel, and post the kernel
log messages for when you plug in the device?

Also, what kernel version is this?

thanks,

greg k-h


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Re: Accessing usb devices with USBDEVFS

[Kay Sievers]

On Fri, Apr 28, 2006 at 01:44:08PM -0400, Danny Budik wrote:
> I have a question that may or may not be related to hotplugging. I have 
> noticed that when I plug in a USB device, it takes about 5 seconds for 
> it to show up in /proc/bus/usb/001/xxx. I am using HAL to recognize when 
> a USB device is plugged in and USBDEVFS to communicate with my device.
> 
> When I plug it in, dbus/HAL instantly recognizes it and sends me a 
> message.  But when I make the function call to open it (using fopen on 
> the file above) I get an error that the device is not found. In fact, it 
> takes about 5 seconds for the device to show up in the /proc/bus/usb/ 
> directory so I have to place a sleep(5) line in my C code before I am 
> able to open the device.
> 
> My test machine is a PIII 733 with FC4, latest kernel, so it is a 
> relatively slow machine. Is there a way to predict the time that it 
> takes for the device to be accessible with USBDEVFS so that I don't have 
> to hardcode the sleep statement?

Recent systems don't use /proc for usb access anymore and real device
nodes in /dev/bus/usb instead. HAL sends "usbraw" device anouncements with
"linux.device_file" as a property when the device is created.

Kay


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Re: Accessing usb devices with USBDEVFS

[Danny Budik]

Kay Sievers wrote:
> On Fri, Apr 28, 2006 at 01:44:08PM -0400, Danny Budik wrote:
>   
>> I have a question that may or may not be related to hotplugging. I have 
>> noticed that when I plug in a USB device, it takes about 5 seconds for 
>> it to show up in /proc/bus/usb/001/xxx. I am using HAL to recognize when 
>> a USB device is plugged in and USBDEVFS to communicate with my device.
>>
>> When I plug it in, dbus/HAL instantly recognizes it and sends me a 
>> message.  But when I make the function call to open it (using fopen on 
>> the file above) I get an error that the device is not found. In fact, it 
>> takes about 5 seconds for the device to show up in the /proc/bus/usb/ 
>> directory so I have to place a sleep(5) line in my C code before I am 
>> able to open the device.
>>
>> My test machine is a PIII 733 with FC4, latest kernel, so it is a 
>> relatively slow machine. Is there a way to predict the time that it 
>> takes for the device to be accessible with USBDEVFS so that I don't have 
>> to hardcode the sleep statement?
>>     
>
> Recent systems don't use /proc for usb access anymore and real device
> nodes in /dev/bus/usb instead. HAL sends "usbraw" device anouncements with
> "linux.device_file" as a property when the device is created.
>
> Kay
So is there a way then to read from the /dev/bus/usb? Like I mentioned 
in the parent post, I am just using fopen, and the functions provided in 
usbdevice_fs.h and usb.h to read data from the usb device. The device is 
a proprietary sensor that my company makes. Is there a 
manual/documentation about how to do this the more "modern" way?

Thanks,
Danny


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Re: Accessing usb devices with USBDEVFS

[Greg KH]

On Mon, May 01, 2006 at 11:39:11AM -0400, Danny Budik wrote:
> Kay Sievers wrote:
> >On Fri, Apr 28, 2006 at 01:44:08PM -0400, Danny Budik wrote:
> >  
> >>I have a question that may or may not be related to hotplugging. I have 
> >>noticed that when I plug in a USB device, it takes about 5 seconds for 
> >>it to show up in /proc/bus/usb/001/xxx. I am using HAL to recognize when 
> >>a USB device is plugged in and USBDEVFS to communicate with my device.
> >>
> >>When I plug it in, dbus/HAL instantly recognizes it and sends me a 
> >>message.  But when I make the function call to open it (using fopen on 
> >>the file above) I get an error that the device is not found. In fact, it 
> >>takes about 5 seconds for the device to show up in the /proc/bus/usb/ 
> >>directory so I have to place a sleep(5) line in my C code before I am 
> >>able to open the device.
> >>
> >>My test machine is a PIII 733 with FC4, latest kernel, so it is a 
> >>relatively slow machine. Is there a way to predict the time that it 
> >>takes for the device to be accessible with USBDEVFS so that I don't have 
> >>to hardcode the sleep statement?
> >>    
> >
> >Recent systems don't use /proc for usb access anymore and real device
> >nodes in /dev/bus/usb instead. HAL sends "usbraw" device anouncements with
> >"linux.device_file" as a property when the device is created.
> >
> >Kay
> So is there a way then to read from the /dev/bus/usb? Like I mentioned 
> in the parent post, I am just using fopen, and the functions provided in 
> usbdevice_fs.h and usb.h to read data from the usb device. The device is 
> a proprietary sensor that my company makes. Is there a 
> manual/documentation about how to do this the more "modern" way?

No, that's still the correct way.  If you use libusb, none of your code
changes at all.   If you are using "raw" usbfs, then just open a
different file.

Hope this helps,

greg k-h


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Re: Accessing usb devices with USBDEVFS

[Danny Budik]

>> So is there a way then to read from the /dev/bus/usb? Like I  
>> mentioned
>> in the parent post, I am just using fopen, and the functions  
>> provided in
>> usbdevice_fs.h and usb.h to read data from the usb device. The  
>> device is
>> a proprietary sensor that my company makes. Is there a
>> manual/documentation about how to do this the more "modern" way?
>
> No, that's still the correct way.  If you use libusb, none of your  
> code
> changes at all.   If you are using "raw" usbfs, then just open a
> different file.
>
> Hope this helps,
>
> greg k-h
>
So that brings me to my next question. I guess I didn't know that  
libusb existed and wrote my own interface functions. Is it because of  
this that whenever I access the USB device, I must be root? Obviously  
that's a security issue. In other words, can I read/write to my USB  
device as a user using libusb?

Danny Budik
Inductive Signature Technologies
Systems Engineer




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Re: Accessing usb devices with USBDEVFS

[Greg KH]

On Mon, May 01, 2006 at 03:00:17PM -0400, Danny Budik wrote:
> 
> >>So is there a way then to read from the /dev/bus/usb? Like I  
> >>mentioned
> >>in the parent post, I am just using fopen, and the functions  
> >>provided in
> >>usbdevice_fs.h and usb.h to read data from the usb device. The  
> >>device is
> >>a proprietary sensor that my company makes. Is there a
> >>manual/documentation about how to do this the more "modern" way?
> >
> >No, that's still the correct way.  If you use libusb, none of your  
> >code
> >changes at all.   If you are using "raw" usbfs, then just open a
> >different file.
> >
> >Hope this helps,
> >
> >greg k-h
> >
> So that brings me to my next question. I guess I didn't know that  
> libusb existed and wrote my own interface functions. Is it because of  
> this that whenever I access the USB device, I must be root? Obviously  
> that's a security issue. In other words, can I read/write to my USB  
> device as a user using libusb?

No, that is what this change in moving the usbfs files from
/proc/bus/usb/ to /dev/bus/usb enables now.  You can create a simple
udev rule to give your device the proper owner:group permissions and
then you will not have to be root to use your program.

Or you could have mounted usbfs with the proper options, but that would
make all usbfs files with that owner:group permissions.

libusb just tries to make writing to usbfs devices easier than handling
the "raw" usb commands.

Hope this helps,

greg k-h


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Re: Accessing usb devices with USBDEVFS

[Kay Sievers]

On Mon, May 01, 2006 at 03:00:17PM -0400, Danny Budik wrote:
> 
> >>So is there a way then to read from the /dev/bus/usb? Like I  
> >>mentioned
> >>in the parent post, I am just using fopen, and the functions  
> >>provided in
> >>usbdevice_fs.h and usb.h to read data from the usb device. The  
> >>device is
> >>a proprietary sensor that my company makes. Is there a
> >>manual/documentation about how to do this the more "modern" way?
> >
> >No, that's still the correct way.  If you use libusb, none of your  
> >code
> >changes at all.   If you are using "raw" usbfs, then just open a
> >different file.
> >
> >Hope this helps,
> >
> >greg k-h
> >
> So that brings me to my next question. I guess I didn't know that  
> libusb existed and wrote my own interface functions. Is it because of  
> this that whenever I access the USB device, I must be root? Obviously  
> that's a security issue. In other words, can I read/write to my USB  
> device as a user using libusb?

That has nothing to do with the way you access the device it's not
different for libusb or a simple open(). The usual way is to change
the owner/group of the device node or add an user ACL to the
node when it appears and grant access that way to normal users.
There are several solutions out there like pam_console, resmgr, or just
putting the users in a special group.

Kay


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Re: Accessing usb devices with USBDEVFS

[Danny Budik]

>>>Recent systems don't use /proc for usb access anymore and real device
>>>nodes in /dev/bus/usb instead. HAL sends "usbraw" device anouncements with
>>>"linux.device_file" as a property when the device is created.
>>>
>>>Kay

I looked at the hal properties of my device and there is no 
linux.device_file property. Does this mean that my device is not 
"usbraw" enabled?

>>So is there a way then to read from the /dev/bus/usb? Like I mentioned 
>>in the parent post, I am just using fopen, and the functions provided in 
>>usbdevice_fs.h and usb.h to read data from the usb device. The device is 
>>a proprietary sensor that my company makes. Is there a 
>>manual/documentation about how to do this the more "modern" way?
> 
> 
> No, that's still the correct way.  If you use libusb, none of your code
> changes at all.   If you are using "raw" usbfs, then just open a
> different file.
> 
> Hope this helps,
> 
> greg k-h
> 
> 

How do I use the "raw" usbfs? I tried reading from the /dev/bus/usb file 
and got a bind - address already in use error.

Danny


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Re: Accessing usb devices with USBDEVFS

[Greg KH]

On Fri, May 05, 2006 at 04:45:30PM -0400, Danny Budik wrote:
> How do I use the "raw" usbfs? I tried reading from the /dev/bus/usb file 
> and got a bind - address already in use error.

Look at how libusb is implemented for a good example of how to do this.
The source code to 'lsusb' will also help you out here.

good luck,

greg k-h


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