update README

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

README

@@ -13,50 +13,58 @@ Important Note:
   of "default" rules provided by the upstream udev version.
 
 Requirements:
-  - 2.6 version of the Linux kernel.
+  - 2.6.x version of the Linux kernel. See the RELEASE-NOTES file in the
+    udev tree and the Documentation/Changes in the kernel source tree for
+    the actual dependency.
 
-  - The kernel must have sysfs, netlink, and hotplug enabled.
+  - The kernel must have sysfs and unix domain socket enabled.
+    (unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work,
+     but it is completely silly, don't complain if anything goes wrong.)
 
   - The proc filesystem must be mounted on /proc.
 
   - The sysfs filesystem must be mounted at /sys. No other location
-    is supported.
+    will be supported by udev.
 
 
 Operation:
-  - Udev creates and removes device nodes in /dev based on events
-    the kernel sends out on device discovery or removal
+  Udev creates and removes device nodes in /dev, based on events the kernel
+  sends out on device discovery or removal.
 
-  - Directly after mounting the root filesystem, the udevd daemon must be
-    started by an init script.
+  - Directly after mouting the real root filesystem, wherever that
+    happens, in initramfs or with a directly mounted root, /dev should get
+    a tmpfs filesystem mounted, which is populated from scratch by udev.
+    Created nodes or changed permissions don't survive a reboot.
+
+  - The content of /lib/udev/devices directory should be copied over to the
+    tmpfs mounted /dev, to provide the required nodes to initialize udev.
+
+  - The udevd daemon must be started to receive netlink events from the kernel
+    driver core.
 
   - From kernel version 2.6.15 on, the hotplug helper /sbin/hotplug should
-    be disabled with an init script before kernel modules are loaded.
+    be disabled with an init script before the boot scripts are run and
+    kernel modules are loaded.
 
-  - During bootup, /dev usually gets a tmpfs filesystem mounted which is
-    populated from scratch by udev (created nodes don't survive a reboot,
-    the /lib/udev/devices directory should be used for "static nodes").
+  - All kernel events are matched against a set of specified rules in
+    /etc/udev/rules.d/ which make it possible to hook into the event
+    processing to load required kernel modules and setup devices. For all
+    devices the kernel requests a device node, udev will create one with
+    the default name or the one specified by a matching udev rules.
 
-  - Udev replaces the hotplug event management invoked from /sbin/hotplug
-    by the udevd daemon, which receives the kernel events over netlink.
-
-  - All kernel events are matched against a set of specified rules which
-    make it possible to hook into the event processing.
-
-  - Copies of the rules files for all major distros are in the etc/udev
-    directory (you may look there how others distros are doing it).
 
 Compile Options:
   prefix
-  	Set this to the default root that you want to use only override
-  	this if you really know what you are doing even then, you probably
+  	Set this to the default root that you want to use. Only override
+  	this if you really know what you are doing, even then, you probably
   	don't do the right thing.
   DESTDIR
   	Prefix for install target, used for package building.
   USE_LOG
-  	if set to 'true', udev is able to pass errors or debug information
-  	to syslog. This is very useful to see what udev is doing or not doing,
-  	it is enabled by default.
+  	If set to 'true', udev is able to pass errors or debug information
+  	to syslog. This is very useful to see what udev is doing or not doing.
+  	It is enabled by default, don't expect any useful answer, if you
+  	need to hunt a bug, but you can't enable syslog.
   DEBUG
   	If set to 'true', very verbose debugging messages will be compiled
   	into the udev binaries. The actual level of debugging is specified
@@ -75,20 +83,29 @@ Compile Options:
   	If set, will build the "extra" helper programs as specified
   	as listed (see below for an example).
 
-If you want to build the udev helper program cdrom_id and scsi_id:
-  make EXTRAS="extras/cdrom_id extras/scsi_id"
+If you want to build the udev helper programs:
+  make EXTRAS="extras/cdrom_id extras/scsi_id extras/volume_id"
+
 
 Installation:
-  - The install target intall the udev binaries in the default locations,
-    all at boot time reqired binaries will be installed in /sbin.
+  - The install target intalls the udev binaries in the default locations,
+    All at boot time reqired binaries will be installed in /sbin.
 
   - The default location for scripts and binaries that are called from
-    rules is /lib/udev.
+    rules is /lib/udev. Other packages who install udev rules, should use
+    that diretory too.
 
   - It is recommended to use the /lib/udev/devices directory to place
     device nodes and symlinks in, which are copied to /dev at every boot.
     That way, nodes for broken subsystems or devices which can't be
-    detected automatically by the kernel will always be available.
+    detected automatically by the kernel, will always be available.
+
+  - Copies of the rules files for all major distros are in the etc/udev
+    directory (you may look there how others distros are doing it).
+
+  - The persistent disk links in /dev/disk are the de facto standard
+    on Linux and should be installed with every default udev installation.
+    The devfs naming scheme rules are not recommended and not supported.
 
 Please direct any comment/question/concern to the linux-hotplug-devel mailing list at:
   linux-hotplug-devel@lists.sourceforge.net

TODO

@@ -1,9 +1,6 @@
 This is a list of things that needs to be done. They are in no specific
 order.  We will gladly accept patches for any of these items:
 
-- Completely replace the built-in wait_for_sysfs stuff in udev_sysfs.c
-  by rules using the WAIT_FOR_SYSFS key.
-
 - Log the relationship of the kernel name and the persistent disk name
   to syslog, so any error logged from the kernel can be associated with
   any of the links at that time.