Re: USB device just moves

phil-news-nospam@xxxxxxxx wrote:

So tell me how it is that "udev" can do better than the kernel itself to
make sure that when the USB device is re-attached that it will always get
exactly the same major/minor device number? I thought that what "udev"
did was automatically make a device node in the name space to refer to
the new major/minor. Remember, this involves an already mounted filesystem
with files still open.

Well, perhaps I misunderstood (or underestimated) the issue. Your
description of udev is correct. If the major/minor number is critical,
than perhaps udev doesn't help.

The real culprit in this is the poor design of USB, which follows the poor
design of PC. There should be a hardware layer consistency of addresses
based on where something is plugged in (bus number, controller number, port
number, hub port number, hubbed hub port number, etc). Then on top of that
there should be consistent device ID numbers much like ethernet MAC (but at
least 64 bits). If the same device is plugged back into the same port, no
address should change. Nothing should need to be run to "change it back"
as it should just _be_ the same.

There's nothing wrong with the design of USB. As long as the device has a
serial number, the combination of VID, PID, and serial number is unique,
and Windows (at least) will recognize it as the same device no matter what
port of which hub it is plugged into.
--
Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.
.

Relevant Pages

  • [PATCH] usb/core/hub.c: fix sparse warnings
    ... *udev, int pipe) ... usb_device *udev, int port1, ... "unable to enumerate USB device on port ...
    (Linux-Kernel)
  • Re: [SLE] setting /dev/ttyS0 permissions at boot in Suse 10?
    ... set the permissions on ttyS0 via udev. ... The generic serial port device driver is, well, generic. ... there is a GPS attached. ...
    (SuSE)
  • Re: Cups
    ... port on my machine. ... I would conclude then that udev is nto the problem ... we are getting conflicting reports on this matter. ...
    (Fedora)
  • Power Surge Error Message
    ... Power Surge on Hub Port ... A USB device has exceeded the power limits of its hub ... continue to get the same error message popping up. ...
    (microsoft.public.windowsxp.hardware)
  • Goofy Neighbor Causes Hub Port Error
    ... A goofy neighbor of mine turned off the power to my apartment briefly ... "Power surge on port hub. ... "A USB device has malfunctioned and exceeded the ... power limits of its hub port. ...
    (microsoft.public.windowsxp.help_and_support)
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