浅析dev目录下设备文件mknod节点gid,uid和mode的如何方便设置

init
= > handle_device_fd 收到uevent信息
= > handle_device_event
= >

static void handle_device_event(struct uevent *uevent) { ... /* are we block or char? where should we live? */ if(!strncmp(uevent->path, "/block", 6)) { block = 1; base = "/dev/block/";//根据uevent路径改变该节点路径 mkdir(base, 0755); } else { block = 0; /* this should probably be configurable somehow */ if(!strncmp(uevent->path, "/class/graphics/", 16)) { base = "/dev/graphics/";//根据uevent路径改变该uevent需要创建节点的路径 mkdir(base, 0755); } else if (!strncmp(uevent->path, "/class/oncrpc/", 14)) { base = "/dev/oncrpc/"; mkdir(base, 0755); } else if (!strncmp(uevent->path, "/class/adsp/", 12)) { base = "/dev/adsp/"; mkdir(base, 0755); } else if(!strncmp(uevent->path, "/class/input/", 13)) { base = "/dev/input/";//根据uevent路径改变该uevent需要创建节点的路径 mkdir(base, 0755); } else if(!strncmp(uevent->path, "/class/sensors/", 15)) { base = "/dev/sensors/"; mkdir(base, 0755); } else if(!strncmp(uevent->path, "/class/mtd/", 11)) { base = "/dev/mtd/";//根据uevent路径改变该uevent需要创建节点的路径 mkdir(base, 0755); } else if(!strncmp(uevent->path, "/class/misc/", 12) && !strncmp(name, "log_", 4)) { base = "/dev/log/";//根据uevent路径改变该uevent需要创建节点的路径 mkdir(base, 0755); name += 4; } else if(!strncmp(uevent->path, "/class/sound/", 13)) { base = "/dev/snd/"; mkdir(base, 0755); } else base = "/dev/"; } snprintf(devpath, sizeof(devpath), "%s%s", base, name); if(!strcmp(uevent->action, "add")) { make_device(devpath, block, uevent->major, uevent->minor);//创建节点文件文件devpath return; } ... } static void make_device(const char *path, int block, int major, int minor) { unsigned uid; unsigned gid; mode_t mode; dev_t dev; if(major > 255 || minor > 255) return; mode = get_device_perm(path, &uid, &gid) | (block ? S_IFBLK : S_IFCHR);//获取将要创建的节点是否需要重设它的mode数值 dev = (major << 8) | minor; mknod(path, mode, dev); chown(path, uid, gid); }

get_device_perm函数会比较path路径是否和下面的devperms[ ] 数组中的inode路径相一致, 如果一致, 那么返回devperms[ ] 数组中指定的uid, gid和mode数值, 这样make_device就会向/ dev这个tmpfs'内存虚拟物理盘' 创建inode节点, 同时改变该inode的uid和gid.
于是在devperms[ ] 数组中我们就可以方便的控制生成的/ dev文件的uid, gid和mode了.

static struct perms_ devperms[] = { { "/dev/null", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/zero", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/full", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/ptmx", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/tty", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/random", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/urandom", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/ashmem", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/binder", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/m2d", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/bmm", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/innodev", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/innodev0", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/innodev1", 0666, AID_ROOT, AID_ROOT, 0 }, { "/dev/innodev2", 0666, AID_ROOT, AID_ROOT, 0 }, /* logger should be world writable (for logging) but not readable */ { "/dev/log/", 0662, AID_ROOT, AID_LOG, 1 }, /* these should not be world writable */ { "/dev/android_adb", 0660, AID_ADB, AID_ADB, 0 }, { "/dev/android_adb_enable", 0660, AID_ADB, AID_ADB, 0 }, { "/dev/ttyMSM0", 0660, AID_BLUETOOTH, AID_BLUETOOTH, 0 }, { "/dev/alarm", 0664, AID_SYSTEM, AID_RADIO, 0 }, { "/dev/tty0", 0666, AID_ROOT, AID_SYSTEM, 0 }, { "/dev/graphics/", 0666, AID_ROOT, AID_GRAPHICS, 1 }, { "/dev/hw3d", 0660, AID_SYSTEM, AID_GRAPHICS, 0 }, { "/dev/input/", 0660, AID_ROOT, AID_INPUT, 1 }, { "/dev/eac", 0660, AID_ROOT, AID_AUDIO, 0 }, { "/dev/cam", 0660, AID_ROOT, AID_CAMERA, 0 }, { "/dev/video0", 0660, AID_ROOT, AID_CAMERA, 0 }, { "/dev/mved", 0660, AID_SYSTEM, AID_CAMERA, 0 }, { "/dev/pmem", 0660, AID_SYSTEM, AID_GRAPHICS, 0 }, { "/dev/pmem_gpu", 0660, AID_SYSTEM, AID_GRAPHICS, 1 }, { "/dev/pmem_adsp", 0660, AID_SYSTEM, AID_AUDIO, 1 }, { "/dev/pmem_camera", 0660, AID_SYSTEM, AID_CAMERA, 1 }, { "/dev/oncrpc/", 0660, AID_ROOT, AID_SYSTEM, 1 }, { "/dev/adsp/", 0660, AID_SYSTEM, AID_AUDIO, 1 }, { "/dev/sensors/", 0666, AID_SYSTEM, AID_SYSTEM, 1 }, { "/dev/mt9t013", 0660, AID_SYSTEM, AID_SYSTEM, 0 }, { "/dev/akm8976_daemon",0640, AID_COMPASS, AID_SYSTEM, 0 }, { "/dev/akm8976_aot", 0640, AID_COMPASS, AID_SYSTEM, 0 }, { "/dev/akm8976_pffd", 0640, AID_COMPASS, AID_SYSTEM, 0 }, { "/dev/msm_pcm_out", 0660, AID_SYSTEM, AID_AUDIO, 1 }, { "/dev/msm_pcm_in", 0660, AID_SYSTEM, AID_AUDIO, 1 }, { "/dev/msm_pcm_ctl", 0660, AID_SYSTEM, AID_AUDIO, 1 }, { "/dev/msm_mp3", 0660, AID_SYSTEM, AID_AUDIO, 1 }, { "/dev/smd0", 0640, AID_RADIO, AID_RADIO, 0 }, { "/dev/qmi", 0640, AID_RADIO, AID_RADIO, 0 }, { "/dev/qmi0", 0640, AID_RADIO, AID_RADIO, 0 }, { "/dev/qmi1", 0640, AID_RADIO, AID_RADIO, 0 }, { "/dev/qmi2", 0640, AID_RADIO, AID_RADIO, 0 }, { "/dev/htc-acoustic", 0640, AID_RADIO, AID_RADIO, 0 }, { "/dev/snd/", 0666, AID_ROOT, AID_AUDIO, 1 }, { NULL, 0, 0, 0, 0 }, };

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