add modprobe-like capability and automatic ueventd loading

add modprobe-like capability and automatic ueventd loading

Author: Jianxun Zhang <jianxun.zhang@intel.com>
Author: Daniel Leung <daniel.leung@intel.com>
Author: Andrew Boie <andrew.p.boie@intel.com>

- insmod_by_dep() added to libcutils; loads a module into kernel.
Modules the target module depends on will be loaded first. Loading
will be stopped when an error occurs.

- rmmod_by_dep() added to libcutils; removes a module from kernel.
It also tries to remove other modules the target module depends
on until an error occurs.

- Implement wildcard matching for ueventd rules.
The PCI and USB addresses for devices can change from devices
from devices for a particular class of peripheral, for example,
bluetooth. The ueventd rules created with these addresses are
then device-specific.

This changes the way ueventd rules with wildcard are handled.
Instead of matching just the prefix with a trailing wildcard,
now these rules can have wildcard anywhere in the rule.
The wildcard matching is implemented using fnmatch(), where
its matching is simliar to shell pathname expansion. It suits
this particular usage model well.

For example, instead of creating a rule to match:

  /sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.3/2-1.3:1.0/bluetooth/hci0/rfkill*

, this would suffice:

  /sys/devices/*/bluetooth/hci0/rfkill*

- Let ueventd auto-load kernel modules. Implements the functionality
for ueventd to auto-load kernel modules when uevents are triggered.
Since /system may not be mounted when uevents are fired,
a deferred loading mechanism is implemented. Once mapping of
module and alias is available, these modules are then loaded.
Modules can also be blacklisted so they will not be loaded
automatically. One example would be the Wifi driver, as
Android's has to control its loading and unloading.

- add 'probemod' builtin command. This command accepts the name of a
kernel module plus a set of command line arguments. The module will
be loaded, along with all its dependencies, using the libcutils
insmod_by_dep() API.

- Drivers in kernel can request modules by launching a program in
user space, the program's path by default is "/sbin/modprobe".
Because Android system has no modprobe and ueventd is the only
program handling the module aliases so far, This patch provides a
cheap approach to handle kernel's requests in ueventd executable.

- Add new builtin init command "coldboot". The main purpose is to
provide an approach in init.*.rc files to fire uevents for devices
under the path which is passed as the the argument. This should be
called after /system is mounted so any queued events that need to
load a module can be fired.