X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?a=blobdiff_plain;f=udev%2Fudev.xml;h=678023c373f444aef087447b9cf9619c0ba70cea;hb=f2291cd07f24d2e1b7c3295ea6570f64b935ba55;hp=41941c820f5e2ed326964e5a1b28da17adfa2fc9;hpb=bfbf65aad06550afcc5b886c1d3acf4c561edb2b;p=elogind.git diff --git a/udev/udev.xml b/udev/udev.xml index 41941c820..678023c37 100644 --- a/udev/udev.xml +++ b/udev/udev.xml @@ -18,23 +18,28 @@ udev - dynamic device management + Linux dynamic device management DESCRIPTION - udev provides a dynamic device directory containing only the files for - actually present devices. It creates or removes device node files in the - /dev directory, or it renames network interfaces. - - Usually udev runs as udevd - 8 and receives uevents directly from the - kernel if a device is added or removed from the system. - - If udev receives a device event, it matches its configured rules - against the available device attributes provided in sysfs to identify the device. - Rules that match may provide additional device information or specify a device - node name and multiple symlink names and instruct udev to run additional programs - as part of the device event handling. + udev supplies the system software with device events, manages permissions + of device nodes and may create additional symlinks in the /dev + directory, or renames network interfaces. The kernel usually just assigns unpredictable + device names based on the order of discovery. Meaningful symlinks or network device + names provide a way to reliably identify devices based on their properties or + current configuration. + + The udev daemon udevd + 8 receives device uevents directly from + the kernel whenever a device is added or removed from the system, or it changes its + state. When udev receives a device event, it matches its configured set of rules + against various device attributes to identify the device. Rules that match, may + provide additional device information to be stored in the udev database, or information + to be used to create meaningful symlink names. + + All device information udev processes, is stored in the udev database and + sent out to possible event subscribers. Access to all stored data and the event + sources are provided by the library libudev. CONFIGURATION @@ -84,9 +89,9 @@ If all match keys are matching against its value, the rule gets applied and the assign keys get the specified value assigned. - A matching rule may specify the name of the device node, add a symlink - pointing to the node, or run a specified program as part of the event handling. - If no matching rule is found, the default device node name is used. + A matching rule may rename a network interface, add symlinks + pointing to the device node, or run a specified program as part of + the event handling. A rule consists of a list of one or more key value pairs separated by a comma. Each key has a distinct operation, depending on the used operator. Valid @@ -237,6 +242,13 @@ + + + + Match against a device tag. + + + @@ -297,8 +309,17 @@ - The name of the node to be created, or the name the network interface - should be renamed to. + The name, a network interface should be renamed to. Or as + a temporary workaraound, the name a device node should be named. + Usually the kernel provides the defined node name, or even creates + and removes the node before udev even receives any event. Changing + the node name from the kernel's default creates inconsistencies + and is not supported. If the kernel and NAME specify different names, + an error will be logged. Udev is only expected to handle device node + permissions and to create additional symlinks, not to change + kernel-provided device node names. Instead of renaming a device node, + SYMLINK should be used. Symlink names must never conflict with + device node names, it will result in unpredictable behavior. @@ -306,9 +327,16 @@ The name of a symlink targeting the node. Every matching rule will add - this value to the list of symlinks to be created along with the device node. - Multiple symlinks may be specified by separating the names by the space - character. + this value to the list of symlinks to be created. Multiple symlinks may be + specified by separating the names by the space character. In case multiple + devices claim the same name, the link will always point to the device with + the highest link_priority. If the current device goes away, the links will + be re-evaluated and the device with the next highest link_priority will own + the link. If no link_priority is specified, the order of the devices, and + which one of them will own the link, is undefined. Claiming the same name for + a symlink, which is or might be used for a device node, may result in + unexpected behavior and is not supported. + @@ -336,6 +364,19 @@ + + + + Attach a tag to a device. This is used to filter events for users + of libudev's monitor functionality, or to enumerate a group of tagged + devices. The implementation can only work efficiently if only a few + tags are attached to a device. It is only meant to be used in + contexts with specific device filter requirements, and not as a + general-purpose flag. Excessive use might result in inefficient event + handling. + + + @@ -347,12 +388,10 @@ is specified, and the executed program returns non-zero, the event will be marked as failed for a possible later handling. - If the specified string starts with - , all current event - values will be passed to the specified socket, as a message in the same - format the kernel sends an uevent. If the first character of the specified path - is an @ character, an abstract namespace socket is used, instead of an existing - socket file. + If no absolute path is given, the program is expected to live in + /lib/udev, otherwise the absolute path must be + specified. Program name and arguments are separated by spaces. Single quotes + can be used to specify arguments with spaces. @@ -380,7 +419,9 @@ Execute an external program specified as the assigned value and - import its output, which must be in environment key format. + import its output, which must be in environment key + format. Path specification, command/argument separation, + and quoting work like in . @@ -390,6 +431,14 @@ environment key format. + + + + Import a single property specified as the assigned value from the + current device database. This works only if the database is already populated + by an earlier event. + + @@ -410,7 +459,8 @@ - Wait for a file to become available. + Wait for a file to become available or until a 10 + seconds timeout expires. @@ -419,19 +469,6 @@ Rule and device options: - - - - Ignore this event completely. - - - - - - Do not remove the device node when the device goes away. This may be - useful as a workaround for broken device drivers. - - @@ -439,14 +476,6 @@ priorities overwrite existing symlinks of other devices. The default is 0. - - - - Create the device nodes for all available partitions of a block device. - This may be useful for removable media devices where media changes are not - detected. - - @@ -466,7 +495,7 @@ Watch the device node with inotify, when closed after being opened for - writing, a change uevent will be synthesised. + writing, a change uevent will be synthesised.