mdev

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如何使用mdev
之前都是使用udev，為了減少使用空間，採用busybox的mdev

更新記錄

item note
20170118 第一版

目錄

mdev

mdev功能：根據kernel訊息來建立dev目錄內容
mdev使用方式：

  1. /bin/mdev >/proc/sys/kernel/hotplug
  2. 設定/etc/mdev.conf
    [-]DEVNAME UID:GID PERM [>|=PATH] [@|$|*PROG]

當有週邊載入時，kernel由此(/proc/sys/kernel/hotplug)通知mdev
mdev在根據sys相關訊息，來產生dev目錄
在建立dev目錄或移除時會都參考mdev.conf設定

  • mdev.conf
    修改/etc/mdev.conf配置文件
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    格式: <device regex> <uid>:<gid> <octal permissions>  [<@|$|*> <command>]
    @ 创建了设备之后运行
    $   删除设备之前运行
    *    在创建设备之后和删除设备之前运行

mdev 板子設定

/proc/sys/kernel/hotplug :

  • /rootfs/etc/rcS設定

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    mount -a
    echo /sbin/mdev > /proc/sys/kernel/hotplug
    mdev -s

  • fstab

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    proc            /proc           proc    defaults        0       0
    sysfs           /sys            sysfs   defaults        0       0
    tmpfs           /dev            tmpfs   defaults        0       0
    tmpfs           /var            tmpfs   defaults,size=16M       0       0

  • hi3536上面的kernel(3.10.0), 記得要移除devtmpfs,此時mdev才會正常工作

mdev test

  • /etc/mdev.conf

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    sd.* 0:0 0600 */etc/add_remove_log.sh

  • add_remove_log.sh

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    #/bin/sh

    echo "======" >> /tmp/mdev.log
    env >> /tmp/mdev.log

  • log

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    ~ # cat /tmp/mdev.log 
    ======
    ======
    DEVNAME=sda
    ACTION=add
    NPARTS=1
    HOME=/
    SEQNUM=627
    MAJOR=8
    MDEV=sda
    DEVPATH=/devices/platform/hiusb-ehci.0/usb1/1-2/1-2:1.0/host4/target4:0:0/4:0:0:0/block/sda
    SUBSYSTEM=block
    PATH=/sbin:/bin:/usr/sbin:/usr/bin
    MINOR=0
    PWD=/dev
    DEVTYPE=disk
    DEVNAME=sda1
    ACTION=add
    HOME=/
    SEQNUM=628
    PARTNAME=Linux filesystem
    MAJOR=8
    MDEV=sda1
    DEVPATH=/devices/platform/hiusb-ehci.0/usb1/1-2/1-2:1.0/host4/target4:0:0/4:0:0:0/block/sda/sda1
    SUBSYSTEM=block
    PATH=/sbin:/bin:/usr/sbin:/usr/bin
    MINOR=1
    PARTN=1
    PWD=/dev
    DEVTYPE=partition
    ======
    DEVNAME=sda1
    ACTION=remove
    HOME=/
    SEQNUM=633
    PARTNAME=Linux filesystem
    MAJOR=8
    MDEV=sda1
    DEVPATH=/devices/platform/hiusb-ehci.0/usb1/1-2/1-2:1.0/host4/target4:0:0/4:0:0:0/block/sda/sda1
    SUBSYSTEM=block
    PATH=/sbin:/bin:/usr/sbin:/usr/bin
    MINOR=1
    PARTN=1
    PWD=/dev
    DEVTYPE=partition
    ======
    DEVNAME=sda
    ACTION=remove
    NPARTS=0
    HOME=/
    SEQNUM=635
    MAJOR=8
    MDEV=sda
    DEVPATH=/devices/platform/hiusb-ehci.0/usb1/1-2/1-2:1.0/host4/target4:0:0/4:0:0:0/block/sda
    SUBSYSTEM=block
    PATH=/sbin:/bin:/usr/sbin:/usr/bin
    MINOR=0
    PWD=/dev
    DEVTYPE=disk

mdev help

  • mdev
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    ~ # mdev --help
    BusyBox v1.20.2 (2017-01-09 05:57:30 UTC) multi-call binary.

    Usage: mdev [-s]

    mdev -s is to be run during boot to scan /sys and populate /dev.

    Bare mdev is a kernel hotplug helper. To activate it:
            echo /sbin/mdev >/proc/sys/kernel/hotplug

    It uses /etc/mdev.conf with lines
            [-]DEVNAME UID:GID PERM [>|=PATH]|[!] [@|$|*PROG]
    where DEVNAME is device name regex, @major,minor[-minor2], or
    environment variable regex. A common use of the latter is
    to load modules for hotplugged devices:
            $MODALIAS=.* 0:0 660 @modprobe "$MODALIAS"

    If /dev/mdev.seq file exists, mdev will wait for its value
    to match $SEQNUM variable. This prevents plug/unplug races.
    To activate this feature, create empty /dev/mdev.seq at boot.

參考