X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=c188506b53cd0f6ae77645552351b83f44a5857a;hp=1a46a3c1eebf6b0d96d7b21bee77326badecb83c;hb=4809b49e4100e35b0dfb5d93cf501e020366de0b;hpb=d2ce1817117daa9523b1572523f1e7684bae779f diff --git a/README b/README index 1a46a3c1e..c188506b5 100644 --- a/README +++ b/README @@ -1,39 +1,106 @@ +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 is a whole lot of work, has complex dependencies + and differs a lot from distro to distro. All reasonable distros depend on udev + these days and the system will not work without it. -To use: + The upstream udev project does not support or recomend to replace a distro's udev + installation with the upstream version. The installation of a unmodified upstream + version may render your system unusable! There is no "default" setup or a set + of "default" rules provided by the upstream udev version. -- Edit the udev.h file and replace the following variables with values - that make sense for your system: - #define SYSFS_ROOT "/sys" - #define UDEV_ROOT "/home/greg/linux/udev/" - #define DEV_FILE "/dev" - #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 :) +Requirements: + - 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. -- Run make to build the project. + - 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.) -- Make sure sysfs is mounted. + - The proc filesystem must be mounted on /proc. -- 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. + - The sysfs filesystem must be mounted at /sys. No other location + will be supported by udev. -- Watch as the nodes get created and removed. +Operation: + Udev creates and removes device nodes in /dev, based on events the kernel + sends out on device discovery or removal. -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. + - Early in the boot process, /dev 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. -Any comment/questions/concerns please let me know. + - 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. + + - The udevd daemon must be started by an init script to receive netlink + uevents 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 actions like loading kernel + modules are taken, which may cause a lot of events. + + - 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. + + +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. + USE_KLIBC + If set to 'true', udev is built and linked against klibc. + Default value is 'false'. KLCC specifies the klibc compiler + wrapper, usually located at /usr/bin/klcc. + EXTRAS + 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 programs: + 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 /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 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 -greg k-h -greg@kroah.com