mdev.c (1.char,block的区分2.mdev.conf配置文件中=,>)

busybox/util-linux/mdev.c

/* http://kernel.org/doc/pending/hotplug.txt says that only

* "/sys/block/..." is for block devices. "/sys/bus" etc is not.
* But since 2.6.25 block devices are also in /sys/class/block.
* We use strstr("/block/") to forestall future surprises. */
type = S_IFCHR;
if (strstr(path, "/block/") || (G.subsystem && strncmp(G.subsystem, "block", 5) == 0))
type = S_IFBLK;


在/sys目录下，除了/sys/block,/sys/class/block目录中保存的块设备，其他/sys/class/*目录都是字符设备，所以mdev应用程序是通过判断DEVPATH中是否包含/block/子字符串来判断是block device 还是 char device，
所以，驱动程序要实现mdev，只要在/sys/block或者/sys/class/block（块设备），/sys/class目录下创建名字为设备名的目录，并包含dev（格式为major:minor\n）文件

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在mdev.conf配置文件中 = >的作用

 * When line matches, the device node is created, chmod'ed and chown'ed,
 * moved to path, and if >path, a symlink to moved node is created,
 * all this if /sys/class/.../dev exists.
 *    Examples:
 *    =loop/      - moves to /dev/loop

 *    >disk/sda%1 - moves to /dev/disk/sdaN, makes /dev/sdaN a symlink

 *

自己的理解：=相当于mv，>相当于先mv，在ln -s创建软连接