Re: general hotplug/udev questions

[Kay Sievers <kay.sievers@vrfy.org>]

On Fri, Aug 19, 2005 at 09:47:59AM -0700, Greg KH wrote:
> On Fri, Aug 19, 2005 at 10:33:02PM +0600, Alexander E. Patrakov wrote:
> > Greg KH wrote:
> > 
> > >On Fri, Aug 19, 2005 at 03:09:59PM +0600, Alexander E. Patrakov wrote:
> > > 
> > >
> > >>Do I understand correctly that the "crawl through sysfs" approach means 
> > >>bus-specific conversion between sysfs contents (e.g the fact that 
> > >>/sys/bus/usb/devices/1-1/idProduct contains "4002" here) and environment 
> > >>variables (in this case, PRODUCT=...)?
> > >>   
> > >>
> > >
> > >Yes, but it's a world easier now that we have added the 'modalias' sysfs
> > >files so we don't have to reconstruct anything.  All we care about at
> > >coldplug time is loading the modules and creating existing device nodes.
> > > 
> > >
> > Sorry, no. We should also care about providing some hook for packages 
> > like SANE and gPhoto2 to chown/chmod pseudofiles in /proc/bus/usb. This 
> > requires perfect reconstruction of at least $PRODUCT and $DEVICE.
> 
> Like Kay said, /proc/bus/usb/???/ is now dead.  We have sane device nodes for
> those usbfs files now that udev can manipulate the permissions for
> properly.  Run the latest -mm trees to see this.
> 
> Kay, you have a libusb patch to support this, right?  Care to share it?

It requires this crazy udev rule:
  SUBSYSTEM="usb_device", PROGRAM="/bin/sh -c 'X=%k X=$${X#usbdev} B=$${X%%%%.*} D=$${X#*.}; echo bus/usb/$$B/$$D'", SYMLINK+="%c"

and this patch to libusb, that falls back to the real nodes if usbfs is
not mounted.

###
Patch against libusb, to prepare for the upcoming changes in
the Linux usb core, which will create real device nodes in /dev
with udev. The following rule:
  SUBSYSTEM="usb_device", PROGRAM="/bin/sh -c 'X=%k X=$${X#usbdev} B=$${X%%%%.*} D=$${X#*.}; echo bus/usb/$$B/$$D'", SYMLINK="%c"

creates a similar structure in /dev as usbfs creates in /proc to
be picked up by libusb.

I've removed the fallback to /sys/bus/usb cause this is completely
wrong and can and will never work and /dev/usb is used differently
and will also not provide access to the raw usb devices.

Signed-off-by: Kay Sievers <kay.sievers@suse.de>
---

diff -u -r1.73 linux.c
--- linux.c	1 Mar 2005 19:36:42 -0000	1.73
+++ linux.c	9 Aug 2005 00:06:43 -0000
@@ -636,11 +636,8 @@
     if (check_usb_vfs("/proc/bus/usb")) {
       strncpy(usb_path, "/proc/bus/usb", sizeof(usb_path) - 1);
       usb_path[sizeof(usb_path) - 1] = 0;
-    } else if (check_usb_vfs("/sys/bus/usb")) { /* 2.6 Kernel with sysfs */
-      strncpy(usb_path, "/sys/bus/usb", sizeof(usb_path) -1);
-      usb_path[sizeof(usb_path) - 1] = 0;
-    } else if (check_usb_vfs("/dev/usb")) {
-      strncpy(usb_path, "/dev/usb", sizeof(usb_path) - 1);
+    } else if (check_usb_vfs("/dev/bus/usb")) {
+      strncpy(usb_path, "/dev/bus/usb", sizeof(usb_path) -1);
       usb_path[sizeof(usb_path) - 1] = 0;
     } else
       usb_path[0] = 0;	/* No path, no USB support */



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