Re: udev craze: need /dev/bus/usb rationale

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

On Wed, Jan 25, 2006 at 09:37:09PM +0100, Linus Walleij wrote:
> Having fun making packages for Fedora we have run into a coordination 
> issue between udev and libusb.
> 
> As you know libusb programs (like SANE custom USB backends or my own pet 
> libnjb) use raw device nodes with no kernel drivers attached to them. A 
> suitable udev rule found in this mail:
> 
> http://sourceforge.net/mailarchive/message.php?msg_id\x12695893
> 
> looks like this:
> 
> SUBSYSTEM="usb_device", PROGRAM="/bin/sh -c 'X=%k X=$${X#usbdev} 
> B=$${X%%%%.*}
> D=$${X#*.}; echo bus/usb/$$B/$$D'", SYMLINK="%c"
> 
> has been applied to most distributions set of default rules. (Well Debian 
> and Fedora atleast, I guess SuSE too.)

I use:
  SUBSYSTEM="usb_device", PROGRAM="/bin/sh -c 'K=%k; K=$${K#usbdev}; \
  printf bus/usb/%%03i/%%03i $${K%%%%.*} $${K#*.}'", NAME="%c", MOD E="0644"

> This rule creates a dynamic device hierarchy belowe /dev/bus/usb similar 
> to the good 'ol /proc/bus/usb and everyone is happy. Libusb was patched 
> to support this device hierarchy. But wait. We found an inconsistency: 
> that script will create hex-named nodes:
> 
>   /dev/bus/usb/01AB1/01BCF

Huh, my shell does not do this weird hex stuff and the numbers seems
pretty high for a USB bus :). It's may be caused by the "X"? The rule
above does the leading zeros, like /proc was, which is nicer too.

> However libusb has this code in linux.c row 336 or so:
> 
>   if (!strchr("0123456789", entry->d_name[strlen(entry->d_name) - 1]))
> 
> Of course it could be fixed with a patch:
> 
>   if (!strchr("0123456789ABCDEF", entry->d_name[strlen(entry->d_name) - 1]))
> 
> But we need a clear rationale:
> 
> * How shall /dev/bus/usb subdirs and device files be named?
> 
> * If they shall be all decimal figures, change all rules accordingly and
>   libusb will work fine as it is.
> 
> * If they shall be hex, make the above suggested change to libusb.

No, they should not change and be the same as they have been in /proc.

Thanks,
Kay


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