ae30210d9
Mike Frysinger
2007-02-14
Subject
create a document for mdev so people dont have to rtfs
Binary
No binary (build failed)
Architecture & Compiler Flags
—
Build Log
(log yok)
Commit Diff GitHub →
docs/mdev.txt+68 -0
| @@ -0,0 +1,68 @@ | |
| + | ------------- |
| + | MDEV Primer |
| + | ------------- |
| + | |
| + | For those of us who know how to use mdev, a primer might seem lame. For |
| + | everyone else, mdev is a weird black box that they hear is awesome, but can't |
| + | seem to get their head around how it works. Thus, a primer. |
| + | |
| + | ----------- |
| + | Basic Use |
| + | ----------- |
| + | |
| + | Mdev has two primary uses: initial population and dynamic updates. Both |
| + | require sysfs support in the kernel and have it mounted at /sys. For dynamic |
| + | updates, you also need to have hotplugging enabled in your kernel. |
| + | |
| + | Here's a typical code snippet from the init script: |
| + | [1] mount -t sysfs sysfs /sys |
| + | [2] echo /bin/mdev > /proc/sys/kernel/hotplug |
| + | [3] mdev -s |
| + | |
| + | Of course, a more "full" setup would entail executing this before the previous |
| + | code snippet: |
| + | [4] mount -t tmpfs mdev /dev |
| + | [5] mkdir /dev/pts |
| + | [6] mount -t devpts devpts /dev/pts |
| + | |
| + | The simple explanation here is that [1] you need to have /sys mounted before |
| + | executing mdev. Then you [2] instruct the kernel to execute /bin/mdev whenever |
| + | a device is added or removed so that the device node can be created or |
| + | destroyed. Then you [3] seed /dev with all the device nodes that were created |
| + | while the system was booting. |
| + | |
| + | For the "full" setup, you want to [4] make sure /dev is a tmpfs filesystem |
| + | (assuming you're running out of flash). Then you want to [5] create the |
| + | /dev/pts mount point and finally [6] mount the devpts filesystem on it. |
| + | |
| + | ------------- |
| + | MDEV Config (/etc/mdev.conf) |
| + | ------------- |
| + | |
| + | Mdev has an optional config file for controlling ownership/permissions of |
| + | device nodes if your system needs something more than the default root/root |
| + | 660 permissions. |
| + | |
| + | The file has the format: |
| + | <device regex> <uid>:<gid> <octal permissions> |
| + | For example: |
| + | hd[a-z][0-9]* 0:3 660 |
| + | |
| + | The config file parsing stops at the first matching line. If no line is |
| + | matched, then the default of 0:0 660 is used. To set your own default, simply |
| + | create your own total match like so: |
| + | .* 1:1 777 |
| + | |
| + | If you also enable support for executing your own commands, then the file has |
| + | the format: |
| + | <device regex> <uid>:<gid> <octal permissions> [<@|$|*> <command>] |
| + | The special characters have the meaning: |
| + | @ Run after creating the device. |
| + | $ Run before removing the device. |
| + | * Run both after creating and before removing the device. |
| + | |
| + | The command is executed via the system() function (which means you're giving a |
| + | command to the shell), so make sure you have a shell installed at /bin/sh. |
| + | |
| + | For your convenience, the shell env var $MDEV is set to the device name. So if |
| + | the device 'hdc' was matched, MDEV would be set to "hdc". |
util-linux/Config.in+10 -26
| @@ -269,46 +269,30 @@ config MDEV | |
| bool "mdev" | |
| default n | |
| help | |
| - | mdev is a mini-udev implementation: call it with -s to populate |
| - | /dev from /sys, then "echo /sbin/mdev > /proc/sys/kernel/hotplug" to |
| - | have it handle hotplug events afterwards. Device names are taken |
| - | from sysfs. |
| + | mdev is a mini-udev implementation for dynamically creating device |
| + | nodes in the /dev directory. |
| + | |
| + | For more information, please see docs/mdev.txt |
| config FEATURE_MDEV_CONF | |
| bool "Support /etc/mdev.conf" | |
| default n | |
| depends on MDEV | |
| help | |
| - | The mdev config file contains lines that look like: |
| - | |
| - | hd[a-z][0-9]* 0:3 660 |
| - | |
| - | That's device name (with regex match), uid:gid, and permissions. |
| + | Add support for the mdev config file to control ownership and |
| + | permissions of the device nodes. |
| - | Config file parsing stops on the first matching line. If no config |
| - | entry is matched, devices are created with default 0:0 660. (Make |
| - | the last line match .* to override this.) |
| + | For more information, please see docs/mdev.txt |
| config FEATURE_MDEV_EXEC | |
| bool "Support command execution at device addition/removal" | |
| default n | |
| depends on FEATURE_MDEV_CONF | |
| help | |
| - | This adds support for an optional field to /etc/mdev.conf, consisting |
| - | of a special character and a command line to run after creating the |
| - | corresponding device(s) and before removing, ala: |
| - | |
| - | hdc root:cdrom 660 *ln -s $MDEV cdrom |
| - | |
| - | The $MDEV environment variable is set to the name of the device. |
| - | |
| - | The special characters and their meanings are: |
| - | @ Run after creating the device. |
| - | $ Run before removing the device. |
| - | * Run both after creating and before removing the device. |
| + | This adds support for an optional field to /etc/mdev.conf for |
| + | executing commands when devices are created/removed. |
| - | Commands are executed via system() so you need /bin/sh, meaning you |
| - | probably want to select a default shell in the Shells menu. |
| + | For more information, please see docs/mdev.txt |
| config MKSWAP | |
| bool "mkswap" | |