mirror of
https://github.com/sheumann/hush.git
synced 2024-12-30 20:29:21 +00:00
69 lines
2.5 KiB
Plaintext
69 lines
2.5 KiB
Plaintext
|
-------------
|
||
|
|
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".
|