biggger changes in the next udev version

biggger changes in the next udev version

[Kay Sievers]

We merged now the recent changes for udev to the upstream repository:
  http://kernel.org/git/gitweb.cgi?p=linux/hotplug/udev.git;a=summary

It is a sync-up with the features of the currently shipped SUSE
version along with some new features. The goal is to take over the
complete kernel event processing and provide an efficient way to dispatch
kernel events. Replacing the current shell script logic and the kernel
forked helper with a netlink-daemon and a rule based event handling:

  o udevd listens to netlink events now. The first valid netlink event
    will make udevd ignore any message from udevsend that contains a
    SEQNUM, to avoid duplicate events. SUSE disables the forked events:
      echo "" > /proc/sys/kernel/hotplug
    completely and uses only netlink to receive kernel events. For
    full support, it needs a patch for the broken input subsytem, that
    unfortunately still bypasses the driver core.

  o /etc/dev.d/ + /etc/hotplug.d/ directory multiplexing is completely
    removed from udev itself and must be emulated by calling small
    helper binaries provided in the extras folder:
      make EXTRAS=extras/run_directory/
    will build udev_run_devd and udev_run_hotplugd, which can be called
    from a rule if needed:
      RUN+="/sbin/udev_run_hotplugd"
    The recommended way to handle this is to convert all the calls from
    the directories to explicit udev rules and get completely rid of the
    multiplexing. (To catch a ttyUSB event, you now no longer need to
    fork and exit 300 tty instances you are not interested in, it is just
    one rule that matches exactly that device.)

  o udev handles now _all_ events not just events for class and block
    devices, this way it is possible to control the complete event
    behavior with udev rules. Especially useful for rules like:
      ACTION="add", DEVPATH="/devices/*", MODALIAS="*", RUN+="/sbin/modprobe $modalias"

  o As used in the modalias rule, udev supports now textual
    substitution placeholder along with the usual format chars. This
    needs to be documented some day, for now it's only here:
      http://kernel.org/git/gitweb.cgi?p=linux/hotplug/udev.git;a=blob;f=udev_rules.c#l226

  o The rule keys support now more operations. This is documented in the
    man page. It is possible now to add values to list-keys like the SYMLINK
    and RUN list with KEY+="value", to clear the list by assigning KEY="".
    Also "final"-assignments are supported by using KEY:="value", which will
    prevent changing the key by any later rule.

  o kernel 2.6.12 has the "detached_state" attribute removed from
    sysfs, which was used to recognize sysfs population. We switched that
    to wait for the "bus" link, which is only available in kernels after 2.6.11.
    Running this udev version on older kernels may cause a delay for
    some events and is not recommended.

  o A few binaries are added to the repository, which can be used to replay
    kernel events from initramfs instead of using coldplug. udevd can
    be instructed now to queue only events while the stored events from
    initramfs are filled into the udevd-queue. There is no documentation
    now besides the code itself. The additional binaries get compiled, but
    are not installed by default.


Any testing, feedback and help is appreciated.

Thanks,
Kay


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