X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=f37c12a8e06b65008481afb5b2bc66220237e6a8;hp=07fa162bbd87d6f26e561f51b59d3fe4bac76d1e;hb=98520be72f9a0167df1da3c7b1a4ca2e88c3c831;hpb=cee360d32efd8392f7e342dcaeda1de50a2c1bcf

diff --git a/README b/README
index 07fa162bb..f37c12a8e 100644
--- a/README
+++ b/README
@@ -1,37 +1,94 @@
+udev - userspace device management
 
-udev - a userspace implementation of devfs
+For more information see the files in the docs/ directory.
 
-For more information on the design, and structure of this project, see the
-files in the docs/ directory.
+Important Note:
+  Integrating udev in the system has complex dependencies and differs from distro
+  to distro. All major distros depend on udev these days and the system may not
+  work without a properly installed version. The upstream udev project does not
+  recommend to replace a distro's udev installation with the upstream version.
 
-To use:
+Requirements:
+  - Version 2.6.15 of the Linux kernel for reliable operation of this release of
+    udev. The kernel may have a requirement on udev too, see Documentation/Changes
+    in the kernel source tree for the actual dependency.
 
-- Edit the udev.h file and replace the following variables with values
-  that make sense for your system:
-	#define UDEV_ROOT       "/udev/"
-	#define MKNOD           "/bin/mknod"
-  The only value most people will have to change is the UDEV_ROOT
-  variable, as I doubt you really want device nodes to be created in my
-  home directory :)
+  - The kernel must have sysfs, unix domain sockets and networking 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.)
 
-- Run make to build the project.
+  - The proc filesystem must be mounted on /proc, the sysfs filesystem must
+    be mounted at /sys. No other location is supported by udev.
 
-- Make sure sysfs is mounted.
 
-- Point /proc/sys/kernel/hotplug at the location of the udev binary that
-  is created.  Then plug some block devices in, or other types of
-  devices that create dev files in sysfs.  An easy way to do this,
-  without any hardware is to use the scsi_debug module to create virtual
-  scsi devices.
+Operation:
+  Udev creates and removes device nodes in /dev, based on events the kernel
+  sends out on device discovery or removal.
 
-- Watch as the nodes get created and removed.
+  - Very early in the boot process, the /dev directory should get a 'tmpfs'
+    filesystem mounted, which is populated from scratch by udev. Created nodes
+    or changed permissions will not survive a reboot, which is intentional.
 
+  - The content of /lib/udev/devices directory which contains the nodes,
+    symlinks and directories, which are always expected to be in /dev, should
+    be copied over to the tmpfs mounted /dev, to provide the required nodes
+    to initialize udev and continue booting.
 
-Yes this is a really rough first cut, I know.  It's mostly a proof of
-concept that this can actually work.  See the TODO file for a list of
-things left to be done.
+  - The old hotplug helper /sbin/hotplug should be disabled on bootup, before
+    actions like loading kernel modules are taken, which may cause a lot of
+    events.
 
-Any comment/questions/concerns please let me know.
+  - The udevd daemon must be started on bootup to receive netlink uevents
+    from the kernel driver core.
+
+  - 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 exports a major/minor number, udev will create a
+    device node with the default kernel name or the one specified by a
+    matching udev rule.
+
+
+Compile Options:
+  DESTDIR
+  	Prefix of 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, 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
+  	in the udev config file.
+  USE_SELINUX
+  	If set to 'true', udev will be built with SELinux support
+  	enabled.  This is disabled by default.
+  EXTRAS
+  	list of helper programs in extras/ to build.
+        make EXTRAS="extras/cdrom_id extras/scsi_id extras/volume_id"
+
+
+Installation:
+  - The install target intalls the udev binaries in the default locations,
+    All at boot time reqired binaries will be installed in /lib/udev or /sbin.
+
+  - The default location for scripts and binaries that are called from
+    rules is /lib/udev. Other packages who install udev rules, should use
+    that directory 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.
+
+  - Copies of the rules files for the major distros are provided as examples
+    in the etc/udev directory.
+
+  - The persistent device naming links in /dev/disk/ are required by other
+    software that depends on the data udev has collected from the devices
+    and should be installed by default with every udev installation.
+
+Please direct any comment/question/concern to the linux-hotplug-devel mailing list at:
+  linux-hotplug@vger.kernel.org
 
-greg k-h
-greg@kroah.com