X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=38459c6b226141408e3b7d2d33c32324dd42c822;hp=07fa162bbd87d6f26e561f51b59d3fe4bac76d1e;hb=df4554c333aec1a4bc2c3335aef6e92f2c13bfcd;hpb=cee360d32efd8392f7e342dcaeda1de50a2c1bcf diff --git a/README b/README index 07fa162bb..38459c6b2 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 replacing 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 /usr/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 /usr/lib/udev and the entire contents +of the /run/udev directory are private to udev and do 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 2.6.34 of the Linux kernel with sysfs, procfs, signalfd, inotify, + unix domain sockets, networking and hotplug enabled -- Run make to build the project. + - Some architectures might need a later kernel, that supports accept4(), + or need to backport the accept4() syscall wiring in the kernel. -- Make sure sysfs is mounted. + - These options are required: + CONFIG_DEVTMPFS=y + CONFIG_HOTPLUG=y + CONFIG_INOTIFY_USER=y + CONFIG_NET=y + CONFIG_PROC_FS=y + CONFIG_SIGNALFD=y + CONFIG_SYSFS=y + CONFIG_SYSFS_DEPRECATED*=n + CONFIG_UEVENT_HELPER_PATH="" -- 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. + - These options might be needed: + CONFIG_BLK_DEV_BSG=y (SCSI devices) + CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes) -- Watch as the nodes get created and removed. + - The /dev directory needs the 'devtmpfs' filesystem mounted. + Udev only manages the permissions and ownership of the + kernel-provided device nodes, and possibly creates additional symlinks. + - Udev requires /run to be writable, which is usually done by mounting a + 'tmpfs' filesystem. -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. + - This version of udev does not work properly with the CONFIG_SYSFS_DEPRECATED* + option enabled. -Any comment/questions/concerns please let me know. + - 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. -greg k-h -greg@kroah.com + - The proc filesystem must be mounted on /proc, and the sysfs filesystem must + be mounted at /sys. No other locations are supported by a standard + udev installation. + + - The default rule sset requires the following group names resolvable at udev startup: + disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, and kmem. + Especially in LDAP setups, it is required that getgrnam() be able to resolve + these group names with only the rootfs mounted and while no network is + available. + + - Some udev extras have external dependencies like: + libglib2, usbutils, pciutils, and gperf. + All these extras can be disabled with configure options. + +Setup: + - The udev daemon should be started to handle device events sent by the kernel. + During bootup, the events for already existing devices can be replayed, so + that they are configured by udev. The systemd service files contain the + needed commands to start the udev daemon and the coldplug sequence. + + - Restarting the daemon never applies any rules to existing devices. + + - New/changed rule files are picked up automatically; there is usually no + daemon restart or signal needed. + +Operation: + - Based on events the kernel sends out on device creation/removal, udev + creates/removes device nodes and symlinks in the /dev directory. + + - All kernel events are matched against a set of specified rules, which + possibly hook into the event processing and load required kernel + modules to set up devices. For all devices, the kernel exports a major/minor + number; if needed, udev creates a device node with the default kernel + device 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 man pages: + http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev/ + +Please direct any comment/question to the linux-hotplug mailing list at: + linux-hotplug@vger.kernel.org