Am Tue, 27 Jan 2009 10:56:35 -0200
schrieb Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxx>:
> On Thu, 22 Jan 2009 22:12:08 +0100
> Thierry Merle <thierry.merle@xxxxxxx> wrote:
>
> > Laurent Pinchart a écrit :
> > > On Thursday 22 January 2009, Carsten Meier wrote:
> > >> Am Thu, 22 Jan 2009 00:20:00 +0100
> > >>
> > >> schrieb Laurent Pinchart <laurent.pinchart@xxxxxxxxx>:
> > >>> Hi Carsten,
> > >>>
> > >>> On Wednesday 21 January 2009, Carsten Meier wrote:
> > >>>> now I want to translate bus_info into a sysfs-path to obtain
> > >>>> device-info like serial numbers. Given a device reports
> > >>>> "usb-0000:00:1d.2-2" as bus_info, then the device-info is
> > >>>> located under "/sys/bus/usb/devices/2-2", which is a symlink
> > >>>> to the appropriate /sys/devices/ directory, right?
> > >>> I'm afraid not. In the above bus_info value, 0000:00:1d.2 is
> > >>> the PCI bus path of your USB controller, and the last digit
> > >>> after the dash is the USB device path.
> > >>>
> > >>>> All I have to do is to compare the first 4 chars of bus_info
> > >>>> against "usb-", get the chars after "." and append it to
> > >>>> "/sys/bus/usb/devices/" to obatin a sysfs-path, right?
> > >>>>
> > >>>> Is there a more elegant solution or already a function for
> > >>>> this? Can the "." appear more than once before the last one?
> > >>> Probably not before, but definitely after.
> > >>>
> > >>> Root hubs get a USB device path set to '0'. Every other device
> > >>> is numbered according to the hub port number it is connected
> > >>> to. If you have an external hub connected on port 2 of your
> > >>> root hub, and have a webcam connected to port 3 of the external
> > >>> hub, usb_make_path() will return "usb-0000:00:1d.2-2.3".
> > >>>
> > >>> Cheers,
> > >>>
> > >>> Laurent Pinchart
> > >> Hi,
> > >>
> > >> On my machine, my pvrusb2 (connected directly to my mini-pc)
> > >> shows up under "/sys/bus/usb/devices/7-2/" which is a symbolic
> > >> link to "../../../devices/pci0000:00/0000:00:1d.7/usb7/7-2"
> > >
> > > You're just lucky that USB bus 7 (usb7/7) is connected to the 7th
> > > function of your USB host controller (1d.7).
> > >
> > > Here's an example of what I get on my computer:
> > >
> > > /sys/bus/usb/devices/4-2
> > > -> ../../../devices/pci0000:00/0000:00:1d.2/usb4/4-2
> > >
> > >> I can't test for the new bus_info-string, because it's not fixed
> > >> yet in the driver. But if I got it correctly it should be
> > >> "usb-0000:00:1d.7-7.2" ?
> > >
> > > I think you will get usb-0000:00:1d.7-2
> > >
> > >> Then I've to simply take the string after the last dash, replace
> > >> "." by "-" and append it to "/sys/bus/usb/devices/" for a
> > >> sysfs-path?
> > >
> > > Unfortunately the mapping is not that direct. The part before the
> > > last dash identifies the USB host controller. The part after the
> > > last dash identifies the device path related to the controller,
> > > expressed as a combination of port numbers.
> > >
> > > The sysfs device path /sys/bus/usb/devices/7-2/ includes a USB
> > > bus number (in this case 7) that is not present in
> > > usb_make_path()'s output.
> > >
> > > To find the sysfs path of your USB peripheral, you will have to
> > > find out which bus number the bus name (0000:00:1d.7) corresponds
> > > to. You might be able to find that by checking each usb[0-9]+
> > > links in /sys/bus/usb/devices and comparing the link's target
> > > with the bus name.
> > >
> > To ease this processing, using libsysfs can be a good idea...
> > On my system, the documentation of libsysfs is here:
> > /usr/doc/sysfsutils-2.1.0/libsysfs.txt
> > Knowing the bus-id, it won't be hard to look at it in data
> > structures. Just my 2 cents.
>
> Hi Thierry,
>
> It may be a good idea to add some code at the v4l2-apps dir for
> retrieving the sysfs place. Maybe we may add it at qv4l2 and at
> v4l2-ctl.
>
> Cheers,
> Mauro
Hi,
here is code which I've written for it. It is in C++ with Boost, but
adaption to C shouldn't be hard. It's not extensively tested and put
into the public domain.
#include <stdexcept>
#include <string>
#include <boost/lexical_cast.hpp>
#include <cstdio>
extern "C" {
#include <sysfs/libsysfs.h>
}
bool obtain_usb_sysfs_path(
const char *busname, const char *usbpath, string &sysfspath_out)
{
bool rc = false;
::sysfs_device *usbctl = NULL;
::sysfs_bus *usb = NULL;
try
{
// open usb host controller
usbctl = ::sysfs_open_device("pci", busname);
if(!usbctl)
throw runtime_error(
"Unable to open usb host controller");
// find matching usb bus
usb = ::sysfs_open_bus("usb");
if(!usb)
throw runtime_error("Unable to open usb");
::dlist *usbdevs = ::sysfs_get_bus_devices(usb);
if(!usbdevs)
throw runtime_error("Unable to get usb devices");
::sysfs_device *usbdev = NULL;
dlist_for_each_data(
usbdevs, usbdev, struct sysfs_device)
{
// compare pathes of usb host controller and
// parent of enumerated usb devices
::sysfs_device *pdev =
::sysfs_get_device_parent(usbdev);
if(!pdev)
continue;
if(strcmp(usbctl->path, pdev->path) == 0)
break;
}
::sysfs_close_device(usbctl);
usbctl = NULL;
// assemble usb device path
if(usbdev)
{
::sysfs_attribute *busnumattr =
::sysfs_get_device_attr(usbdev, "busnum");
if(!busnumattr)
throw runtime_error(
"Unable to get usb bus number");
string str(busnumattr->value, busnumattr->len);
unsigned int busnum;
if(sscanf(str.c_str(), "%u", &busnum) != 1)
throw runtime_error(
"Unable to parse usb bus number");
sysfspath_out = usbdev->path;
sysfspath_out += '/';
sysfspath_out += lexical_cast<string>(busnum);
sysfspath_out += '-';
sysfspath_out += usbpath;
rc = true;
}
::sysfs_close_bus(usb);
usb = NULL;
}
catch(...)
{
if(usb)
::sysfs_close_bus(usb);
if(usbctl)
::sysfs_close_device(usbctl);
throw;
}
return rc;
}
Maybe it is of use for one or another.
Cheers,
Carsten
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