I.MX6 su.c 测试

/*************************************************************************
 *                        I.MX6 su.c 测试
 * 说明：
 *     今天突然想分析一下su的源代码，看一下其工作机制。
 *
 *                                       2016-8-10 深圳 南山平山村 曾剑锋
 ************************************************************************/

一、su源代码修改：
    /*
    **
    ** Copyright 2008, The Android Open Source Project
    **
    ** Licensed under the Apache License, Version 2.0 (the "License");
    ** you may not use this file except in compliance with the License.
    ** You may obtain a copy of the License at
    **
    **     http://www.apache.org/licenses/LICENSE-2.0
    **
    ** Unless required by applicable law or agreed to in writing, software
    ** distributed under the License is distributed on an "AS IS" BASIS,
    ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    ** See the License for the specific language governing permissions and
    ** limitations under the License.
    */

    #define LOG_TAG "su"

    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <sys/types.h>
    #include <dirent.h>
    #include <errno.h>

    #include <unistd.h>
    #include <time.h>

    #include <pwd.h>

    #include <private/android_filesystem_config.h>

    /*
     * SU can be given a specific command to exec. UID _must_ be
     * specified for this (ie argc => 3).
     *
     * Usage:
     * su 1000
     * su 1000 ls -l
     */
    int main(int argc, char **argv)
    {
        struct passwd *pw;
        int uid, gid, myuid;

        /* Until we have something better, only root and the shell can use su. */
        myuid = getuid();
        // if (myuid != AID_ROOT && myuid != AID_SHELL) {
        //     fprintf(stderr,"su: uid %d not allowed to su\n", myuid);
        //     // return 1;
        // }

        if(argc < 2) {
            uid = gid = 0;
        } else {
            pw = getpwnam(argv[1]);

            if(pw == 0) {
                uid = gid = atoi(argv[1]);
            } else {
                uid = pw->pw_uid;
                gid = pw->pw_gid;
            }
        }

        // if(setgid(gid) || setuid(uid)) {
        //     fprintf(stderr,"su: permission denied\n");
        //     return 1;
        // }

        /* User specified command for exec. */
        if (argc == 3 ) {
            if (execlp(argv[2], argv[2], NULL) < 0) {
                fprintf(stderr, "su: exec failed for %s Error:%s\n", argv[2],
                        strerror(errno));
                return -errno;
            }
        } else if (argc > 3) {
            /* Copy the rest of the args from main. */
            char *exec_args[argc - 1];
            memset(exec_args, 0, sizeof(exec_args));
            memcpy(exec_args, &argv[2], sizeof(exec_args));
            if (execvp(argv[2], exec_args) < 0) {
                fprintf(stderr, "su: exec failed for %s Error:%s\n", argv[2],
                        strerror(errno));
                return -errno;
            }
        }

        /* Default exec shell. */
        execlp("/system/bin/sh", "sh", NULL);

        fprintf(stderr, "su: exec failed\n");
        return 1;
    }

二、权限：
    chmod 4775 /system/xbin/su 

三、调用：
    private static String cmdList[] = {
        "su 0 netcfg can0 down",
        "su 0 ip link set can0 type can bitrate 1000000 triple-sampling on",
        "su 0 netcfg can0 up",
    };