kABI简介
kABI: Kernel Application Binary Interface，是内核为用户空间程序提供的稳定的二进制接口。kABI兼容，即内核与驱动的二进制兼容。如果驱动用到的内核接口都是兼容的，那么驱动就可以不用重新编译就可以在新版本安装使用。当然，kABI兼容也会带来架构腐化、维护时间长、维护成本高等问题。
kABI白名单
kABI白名单是内核提供的对外接口的子集。kernel研发过程中各个版本之间kABI白名单内的接口保持不变，那么只使用白名单内的内核函数的驱动就无需重新编译，即可在新版本内核中使用。
如何创建kABI白名单
拟出需兼容的驱动列表，通过modprobe等工具得到驱动所设计的函数，筛选出其中的内核函数。

$ modprobe --dump-modversions megaraid_sas.ko
0x79d6acc4      module_layout
0x6bc3fbc0      __unregister_chrdev
0x2d3385d3      system_wq
0x99b8fd62      kmalloc_caches          # 内核函数
...

再从驱动编译版本内核的Modules.symvers筛选出函数信息即可得到kABI白名单Module.kabi

$ cat Module.symvers | grep kmalloc_caches
0x00000000	kmalloc_caches	vmlinux	EXPORT_SYMBOL

检查kABI兼容性
此处使用CentOS 7.x的开源工具check-kabi，进行kABI兼容性检查。

#!/usr/bin/python
# 
# check-kabi - Red Hat kABI reference checking tool
# 
# We use this script to check against reference Module.kabi files.
# 
# Author: Jon Masters <jcm@redhat.com>
# Copyright (C) 2007-2009 Red Hat, Inc.
# 
# This software may be freely redistributed under the terms of the GNU# General Public License (GPL).
# Changelog:
# 
# 2009/08/15 - Updated for use in RHEL6.
# 2007/06/13 - Initial rewrite in python by Jon Masters.

__author__ = "Jon Masters <jcm@redhat.com>"
__version__ = "2.0"
__date__ = "2009/08/15"
__copyright__ = "Copyright (C) 2007-2009 Red Hat, Inc"
__license__ = "GPL"

import getopt
import os
import re
import string
import sys

true = 1
false = 0

def load_symvers(symvers,filename):
    """Load a Module.symvers file."""

    symvers_file = open(filename,"r")

    while true:
        in_line = symvers_file.readline()
        if in_line == "":
            break
        if in_line == "\n":
            continue
        checksum,symbol,directory,type = string.split(in_line)

        symvers[symbol] = in_line[0:-1]
def load_kabi(kabi,filename):
    """Load a Module.kabi file."""

    kabi_file = open(filename,"r")

    while true:
        in_line = kabi_file.readline()
        if in_line == "":
            break
        if in_line == "\n":
            continue
        checksum,symbol,directory,type = string.split(in_line)

        kabi[symbol] = in_line[0:-1]
def check_kabi(symvers,kabi):
    """Check Module.kabi and Module.symvers files."""

    fail=0
    warn=0
    lost=0
    changed_symbols=[]
    moved_symbols=[]
    losted_symbols=[]

    for symbol in kabi:
        abi_hash,abi_sym,abi_dir,abi_type = string.split(kabi[symbol])
        if symvers.has_key(symbol):
            sym_hash,sym_sym,sym_dir,sym_type = string.split(symvers[symbol])
        if abi_hash != sym_hash:
            fail=1
            changed_symbols.append(symbol)

        if abi_dir != sym_dir:
            warn=1
            moved_symbols.append(symbol)
        else:
            lost=1
            losted_symbols.append(symbol)

    if fail:
        print "*** ERROR - ABI BREAKAGE WAS DETECTED ***"
        print ""
        print "The following symbols have been changed (this will cause an ABI breakage):"
        print "new kabi:"
        for symbol in changed_symbols:
            print symvers[symbol]
        print "old kabi:"
        for symbol in changed_symbols:
            print kabi[symbol]
        print ""

    if lost:
        print "*** ERROR - ABI BREAKAGE WAS DETECTED ***"
        print ""
        print "The following symbols have been losted (this will cause an ABI breakage):"
        print "old kabi:"
        for symbol in losted_symbols:
            print kabi[symbol]
        print ""

    if warn:
        print "*** WARNING - ABI SYMBOLS MOVED ***"
        print ""
        print "The following symbols moved (typically caused by moving a symbol from being"
        print "provided by the kernel vmlinux out to a loadable module):"
        print "new kabi:"
        for symbol in moved_symbols:
            print symvers[symbol]
        print "old kabi"
        for symbol in moved_symbols:
            print kabi[symbol]

        print ""

    """Halt the build, if we got errors and/or warnings. In either case,
       double-checkig is required to avoid introducing / concealing
       KABI inconsistencies."""
    if fail or warn or lost:
        sys.exit(1)
        sys.exit(0)

def usage():
    print """
check-kabi: check Module.kabi and Module.symvers files.

    check-kabi [ -k Module.kabi ] [ -s Module.symvers ]

"""

if __name__ == "__main__":

    symvers_file = ""
    kabi_file = ""

    opts, args = getopt.getopt(sys.argv[1:], 'hk:s:')

    for o, v in opts:
        if o == "-s":
            symvers_file = v
        if o == "-h":
            usage()
            sys.exit(0)
        if o == "-k":
            kabi_file = v

    if (symvers_file == "") or (kabi_file == ""):
        usage()
        sys.exit(1)

    symvers={}
    kabi={}

    load_symvers(symvers,symvers_file)
    load_kabi(kabi,kabi_file)
    check_kabi(symvers,kabi)

依据kABI兼容性实现原理，此python脚本将当前符号表中函数信息与kABI白名单中的函数信息进行对比。如果相关函数发生变化，将输出对应信息且需要相对应的kabi fix进行修复；无打印信息则表示kABI验证通过。check-kabi脚本使用方法如下。

python2 check-kabi -k Module.kabi -s Module.symvers