X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=6e09b3a52da14540adf82a03a650a3df1bd0d750;hp=07fa162bbd87d6f26e561f51b59d3fe4bac76d1e;hb=4c514e31734a704ca58e543fa4330616ba584b39;hpb=cee360d32efd8392f7e342dcaeda1de50a2c1bcf diff --git a/README b/README index 07fa162bb..6e09b3a52 100644 --- a/README +++ b/README @@ -1,37 +1,101 @@ +udev - Linux userspace device management -udev - a userspace implementation of devfs +Integrating udev in the system has complex dependencies and may differ from +distribution to distribution. A system may not be able to boot up or work +reliably without a properly installed udev version. The upstream udev project +does not recommend to replace a distro's udev installation with the upstream +version. -For more information on the design, and structure of this project, see the -files in the docs/ directory. +The upstream udev project's set of default rules may require a most recent +kernel release to work properly. -To use: +Tools and rules shipped by udev are not public API and may change at any time. +Never call any private tool in /lib/udev from any external application, it might +just go away in the next release. Access to udev information is only offered +by udevadm and libudev. Tools and rules in /lib/udev, and the entire content of +the /dev/.udev directory is private to udev and does change whenever needed. -- 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 :) +Requirements: + - Version 2.6.27 of the Linux kernel with sysfs, procfs, signalfd, inotify, + unix domain sockets, networking and hotplug enabled: + CONFIG_HOTPLUG=y + CONFIG_UEVENT_HELPER_PATH="" + CONFIG_NET=y + CONFIG_UNIX=y + CONFIG_SYSFS=y + CONFIG_SYSFS_DEPRECATED*=n + CONFIG_PROC_FS=y + CONFIG_TMPFS=y + CONFIG_INOTIFY_USER=y + CONFIG_SIGNALFD=y + CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes) + CONFIG_BLK_DEV_BSG=y (SCSI devices) -- Run make to build the project. + - Udev will not work with the CONFIG_SYSFS_DEPRECATED* option. -- Make sure sysfs is mounted. + - Unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work, + but it is not supported. -- 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 deprecated hotplug helper /sbin/hotplug should be disabled in the + kernel configuration, it is not needed today, and may render the system + unusable because the kernel may create too many processes in parallel + so that the system runs out-of-memory. -- Watch as the nodes get created and removed. + - The proc filesystem must be mounted on /proc, the sysfs filesystem must + be mounted at /sys. No other locations are supported by a standard + udev installation. + - The system must have the following group names resolvable at udev startup: + disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, kmem. + Especially in LDAP setups, it is required, that getgrnam() is able to resolve + these group names with only the rootfs mounted, and while no network is + available. -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. + - To build all 'udev extras', libacl, libglib2, libusb, usbutils, pciutils, + gperf are needed. These dependencies can be disabled with the + --disable-extras configure option. -Any comment/questions/concerns please let me know. +Setup: + - At bootup, the /dev directory should get the 'devtmpfs' filesystem + mounted. Udev will manage permissions and ownership of the kernel-created + device nodes, and possibly create additional symlinks. If needed, udev also + works on an empty 'tmpfs' filesystem, but some static device nodes like + /dev/null, /dev/console, /dev/kmsg are needed to be able to start udev itself. -greg k-h -greg@kroah.com + - The content of /lib/udev/devices directory which contains static content like + symlinks and directories, which are always expected to be in /dev, should + be copied over to the mounted /dev directory: + cp -axT --remove-destination /lib/udev/devices /dev + + - The udev daemon should be started to handle device events sent by the kernel. + During bootup, the kernel can be asked to send events for all already existing + devices, to apply the configuration to these devices. This is usually done by: + /sbin/udevadm trigger --type=subsystems + /sbin/udevadm trigger --type=devices + + - Restarting the daemon does never apply any rules to existing devices. + + - New/changed rule files are picked up automatically, there is no daemon + restart or signal needed. + +Operation: + - Udev creates/removes device nodes in /dev, based on events the kernel + sends out on device creation/removal. + + - All kernel events are matched against a set of specified rules, which + possibly hook into the event processing and load required kernel + modules to setup devices. For all devices the kernel exports a major/minor + number, if needed, udev will create a device node with the default kernel + name. If specified, udev applies permissions/ownership to the device + node, creates additional symlinks pointing to the node, and executes + programs to handle the device. + + - The events udev handles, and the information udev merges into its device + database, can be accessed with libudev: + http://www.kernel.org/pub/linux/utils/kernel/hotplug/libudev/ + http://www.kernel.org/pub/linux/utils/kernel/hotplug/gudev/ + +For more details about udev and udev rules see the udev(7) man page. + +Please direct any comment/question to the linux-hotplug mailing list at: + linux-hotplug@vger.kernel.org