X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=f6d1ab525756f0175a470f6f305a77277bdf0bda;hp=773bc5508d3bdf513b29e622b9067789abf36b06;hb=71b4b701b1c5261de0dba5b071ec10089361de0e;hpb=67c89548d112e3d00ccdbad399720458b8289117

diff --git a/README b/README
index 773bc5508..f6d1ab525 100644
--- a/README
+++ b/README
@@ -1,23 +1,40 @@
 udev - userspace device management
 
-For more information see the files in the docs/ directory.
+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.
 
-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.
+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.
 
 Requirements:
-  - Version 2.6.22 of the Linux kernel for reliable operation of this release of
-    udev. The kernel must not use the CONFIG_SYSFS_DEPRECATED* option.
+  - Version 2.6.25 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=y
+      CONFIG_SIGNALFD=y
+      CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes)
+      CONFIG_BLK_DEV_BSG=y (SCSI devices)
 
-  - The kernel must have sysfs, unix domain sockets and networking enabled.
-    Unix domain sockets (CONFIG_UNIX) as a loadable kernel module is not
-    supported.
+  - For reliable operations, the kernel must not use the CONFIG_SYSFS_DEPRECATED*
+    option.
 
-  - The proc filesystem must be mounted on /proc/, the sysfs filesystem must
-    be mounted at /sys/. No other locations are supported by udev.
+  - Unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work,
+    but it is not supported.
+
+  - The proc filesystem must be mounted on /proc, the sysfs filesystem must
+    be mounted at /sys. No other locations are supported by udev.
 
   - The system must have the following group names resolvable at udev startup:
       disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, kmem.
@@ -25,33 +42,35 @@ Requirements:
     these group names with only the rootfs mounted, and while no network is
     available.
 
+  - To build all udev extras, libacl, libglib2, libusb, usbutils, pciutils,
+    gperf are needed. These dependencies can be disabled with the
+    --disable-extras option.
+
 Operation:
-  Udev creates and removes device nodes in /dev/, based on events the kernel
+  Udev creates and removes device nodes in /dev, based on events the kernel
   sends out on device discovery or removal.
 
-  - 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.
+  - Early in the boot process, the /dev directory should get a 'tmpfs'
+    filesystem mounted, which is maintained 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,
+  - 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 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.
-
-  - The udevd daemon must be started on bootup to receive netlink uevents
-    from the kernel driver core.
+  - 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.
 
   - All kernel events are matched against a set of specified rules in
-    /lib/udev/rules.d/ which make it possible to hook into the event
+    /lib/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.
 
-Please direct any comment/question/concern to the linux-hotplug mailing list at:
+Please direct any comment/question to the linux-hotplug mailing list at:
   linux-hotplug@vger.kernel.org