linux-kernel - 3 version of MKDEV: kernel, uapi, libc, why?

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Date:   Wed, 11 Apr 2018 08:51:03 +0000
From:   "Zhang, Ning A" <ning.a.zhang@...el.com>
To:     "pombredanne@...b.com" <pombredanne@...b.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "kstewart@...uxfoundation.org" <kstewart@...uxfoundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: 3 version of MKDEV: kernel, uapi, libc, why?

Hi, Greg, Thomas

I find 3 version of MKDEV (actually 2 + makedev)

in include/linux/kdev_t.h

    #define MINORBITS    	    20
    #define MKDEV(ma,mi)    	    (((ma) << MINORBITS) | (mi))

in inlcude/uapi/linux/kdev_t.h

    #define MKDEV(ma,mi)    	    ((ma)<<8 | (mi))

in Android bionic

    #define makedev(__major, __minor) \
      ( \
        (((__major) & 0xfffff000ULL) << 32) | (((__major) & 0xfffULL) <<
    8) | \
        (((__minor) & 0xffffff00ULL) << 12) | (((__minor) & 0xffULL)) \
      )

if I use mknod("renderD128", S_IFCHR|0666, MKDEV(226, 128));
I get wrong device:
crw-rw-rw- 1 root graphics 0, 57984 2011-11-11 11:20 renderD128


if I use ("renderD128",S_IFCHR|0666, makedev(226, 128));
I get right device.

but, when I use: mknod("card0", S_IFCHR|0666, MKDEV(226, 0));
I can get right device.

BR.
Ning.