如何自動創建設備節點

Ⅰ LINUX設備節點

是這樣的，之所以復有的制時候不需要你自己創建節點，因為有程序自動創建。
class_create和device_create，具體用法很簡單，你自己查查就知道了。

還有，mknod都是在剛開始學習的時候用到，難道你以後寫驅動都要手動建立設備節點嗎？

Ⅱ 如何在udev自動創建設備節點

創建設備文件的方法：
第一種是使用mknod手工創建：mknod filename type major minor
第二種是自動創建設備節點：利用udev（mdev）來實現設備文件的自動創建，首先應保證支持udev（嵌入式系統用mdev），由busybox配置。
udev介紹
udev 運行在用戶模式，而非內核中。udev 的初始化腳本在系統啟動時創建設備節點，並且當插入新設備——加入驅動模塊——在sysfs上注冊新的數據後，udev會創新新的設備節點。
udev 是一個工作在用戶空間的工具，它能根據系統中硬體設備的狀態動態的更新設備文件，包括設備文件的創建，刪除，許可權等。這些文件通常都定義在/dev 目錄下，但也可以在配置文件中指定。udev 必須內核中的sysfs和tmpfs支持，sysfs 為udev 提供設備入口和uevent 通道，tmpfs 為udev 設備文件提供存放空間。
注意，udev 是通過對內核產生的設備文件修改，或增加別名的方式來達到自定義設備文件的目的。但是，udev 是用戶模式程序，其不會更改內核行為。也就是說，內核仍然會創建sda，sdb等設備文件，而udev可根據設備的唯一信息來區分不同的設備，並產生新的設備文件（或鏈接）。而在用戶的應用中，只要使用新產生的設備文件

Ⅲ Android怎麼生成設備節點

Android如何生成設備節點
在Android中，由於沒有mdev和udev，所以它沒有辦法動態的生成設備節點，那麼它是如何做的呢？
我們可以在system/core/init/下的init.c和devices.c中找到答案：
init.c中
int main(int argc, char **argv)
{
...
/* Get the basic filesystem setup we need put
* together in the initramdisk on / and then we'll
* let the rc file figure out the rest.
*/
mkdir("/dev", 0755);
mkdir("/proc", 0755);
mkdir("/sys", 0755);

mount("tmpfs", "/dev", "tmpfs", 0, "mode=0755");
mkdir("/dev/pts", 0755);
mkdir("/dev/socket", 0755);
mount("devpts", "/dev/pts", "devpts", 0, NULL);
mount("proc", "/proc", "proc", 0, NULL);
mount("sysfs", "/sys", "sysfs", 0, NULL);

for(;;) {
...
if (ufds[0].revents == POLLIN)
handle_device_fd(device_fd);

if (ufds[1].revents == POLLIN)
handle_property_set_fd(property_set_fd);
if (ufds[3].revents == POLLIN)
handle_keychord(keychord_fd);
}

return 0;
}

我們再來看看handle_device_fd()，該函數定義在devices.c中
void handle_device_fd(int fd)
{
...
handle_device_event(&uevent);
handle_firmware_event(&uevent);
}
}

而handle_device_event定義如下：
static void handle_device_event(struct uevent *uevent)
{
...
if(!strcmp(uevent->action, "add")) {
make_device(devpath, block, uevent->major, uevent->minor);
return;
}
...
}

make_device定義如下：
static void make_device(const char *path, int block, int major, int minor)
{
...
mode = get_device_perm(path, &uid, &gid) | (block S_IFBLK : S_IFCHR);
dev = (major $amp; ...
setegid(gid);
mknod(path, mode, dev);
chown(path, uid, -1);
setegid(AID_ROOT);
}

我們看看get_device_perm如下實現：
static mode_t get_device_perm(const char *path, unsigned *uid, unsigned *gid)
{
mode_t perm;

if (get_device_perm_inner(qemu_perms, path, uid, gid, &perm) == 0) {
return perm;
} else if (get_device_perm_inner(devperms, path, uid, gid, &perm) == 0) {
return perm;
} else {
struct listnode *node;
struct perm_node *perm_node;
struct perms_ *dp;

/* Check partners list. */
list_for_each(node, &devperms_partners) {
perm_node = node_to_item(node, struct perm_node, plist);
dp = &perm_node->dp;

if (dp->prefix) {
if (strncmp(path, dp->name, strlen(dp->name)))
continue;
} else {
if (strcmp(path, dp->name))
continue;
}
/* Found perm in partner list. */
*uid = dp->uid;
*gid = dp->gid;
return dp->perm;
}
/* Default if nothing found. */
*uid = 0;
*gid = 0;
return 0600;
}
}

我們最後可以看到在devperms中定義了要生成的設備節點：
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 },

/* logger should be world writable (for logging) but not readable */
{ "/dev/log/", 0662, AID_ROOT, AID_LOG, 1 },

/* the msm hw3d client device node is world writable/readable. */
{ "/dev/msm_hw3dc", 0666, AID_ROOT, AID_ROOT, 0 },

/* gpu driver for adreno200 is globally accessible */
{ "/dev/kgsl", 0666, AID_ROOT, AID_ROOT, 0 },

/* these should not be world writable */
{ "/dev/diag", 0660, AID_RADIO, AID_RADIO, 0 },
{ "/dev/diag_arm9", 0660, AID_RADIO, AID_RADIO, 0 },
{ "/dev/android_adb", 0660, AID_ADB, AID_ADB, 0 },
{ "/dev/android_adb_enable", 0660, AID_ADB, AID_ADB, 0 },
{ "/dev/ttyMSM0", 0600, AID_BLUETOOTH, AID_BLUETOOTH, 0 },
{ "/dev/ttyHS0", 0600, AID_BLUETOOTH, AID_BLUETOOTH, 0 },
{ "/dev/uinput", 0660, AID_SYSTEM, AID_BLUETOOTH, 0 },
{ "/dev/alarm", 0664, AID_SYSTEM, AID_RADIO, 0 },
{ "/dev/tty0", 0660, AID_ROOT, AID_SYSTEM, 0 },
{ "/dev/graphics/", 0660, AID_ROOT, AID_GRAPHICS, 1 },
{ "/dev/msm_hw3dm", 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/pmem", 0660, AID_SYSTEM, AID_GRAPHICS, 0 },
{ "/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/snd/", 0660, AID_SYSTEM, AID_AUDIO, 1 },
{ "/dev/mt9t013", 0660, AID_SYSTEM, AID_SYSTEM, 0 },
{ "/dev/msm_camera/", 0660, AID_SYSTEM, AID_SYSTEM, 1 },
{ "/dev/akm8976_daemon",0640, AID_COMPASS, AID_SYSTEM, 0 },
{ "/dev/akm8976_aot", 0640, AID_COMPASS, AID_SYSTEM, 0 },
{ "/dev/akm8973_daemon",0640, AID_COMPASS, AID_SYSTEM, 0 },
{ "/dev/akm8973_aot", 0640, AID_COMPASS, AID_SYSTEM, 0 },
{ "/dev/bma150", 0640, AID_COMPASS, AID_SYSTEM, 0 },
{ "/dev/cm3602", 0640, AID_COMPASS, AID_SYSTEM, 0 },
{ "/dev/akm8976_pffd", 0640, AID_COMPASS, AID_SYSTEM, 0 },
{ "/dev/lightsensor", 0640, AID_SYSTEM, 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_snd", 0660, AID_SYSTEM, AID_AUDIO, 1 },
{ "/dev/msm_mp3", 0660, AID_SYSTEM, AID_AUDIO, 1 },
{ "/dev/audience_a1026", 0660, AID_SYSTEM, AID_AUDIO, 1 },
{ "/dev/tpa2018d1", 0660, AID_SYSTEM, AID_AUDIO, 1 },
{ "/dev/msm_audpre", 0660, AID_SYSTEM, AID_AUDIO, 0 },
{ "/dev/msm_audio_ctl", 0660, AID_SYSTEM, AID_AUDIO, 0 },
{ "/dev/htc-acoustic", 0660, AID_SYSTEM, AID_AUDIO, 0 },
{ "/dev/vdec", 0660, AID_SYSTEM, AID_AUDIO, 0 },
{ "/dev/q6venc", 0660, AID_SYSTEM, AID_AUDIO, 0 },
{ "/dev/snd/dsp", 0660, AID_SYSTEM, AID_AUDIO, 0 },
{ "/dev/snd/dsp1", 0660, AID_SYSTEM, AID_AUDIO, 0 },
{ "/dev/snd/mixer", 0660, AID_SYSTEM, AID_AUDIO, 0 },
{ "/dev/smd0", 0640, AID_RADIO, AID_RADIO, 0 },
{ "/dev/qemu_trace", 0666, AID_SYSTEM, AID_SYSTEM, 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 },
/* CDMA radio interface MUX */
{ "/dev/ts0710mux", 0640, AID_RADIO, AID_RADIO, 1 },
{ "/dev/ppp", 0660, AID_RADIO, AID_VPN, 0 },
{ "/dev/tun", 0640, AID_VPN, AID_VPN, 0 },
{ NULL, 0, 0, 0, 0 },
};

Ⅳ android sensor怎樣創建設備節點

在Android中，由於沒有mdev和udev，所以它沒有辦法動態的生成設備節點，那麼它是如何做的呢？

我們可以在system/core/init/下的init.c和devices.c中找到答案：

init.c中

在Android中，沒有獨立的類似於udev或者mdev的用戶程序，這個功能集成到了init中做了。代碼見：system/core/init/init.c文件，如下：

if (ufds[0].revents == POLLIN)

handle_device_fd(device_fd);

其中handle_device_fd(device_fd)函數在system/core/init/devices.c中實現，參數device_fd 由函數device_init（）->open_uevent_socket()->socket(PF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT)函數調用返回。

函數handle_device_fd(device_fd)中，根據傳進來的device_fd參數，調用recv(fd, msg, UEVENT_MSG_LEN, 0)函數，將內核探測到的設備並通過NETLINK機制傳過來的socket描述符轉化成消息。接著調用parse_event(msg, &uevent);函數將消息翻譯成uevent事件，並將改事件傳遞給handle_device_event（&uevent）函數。

handle_device_event（&uevent）函數中，依據參數uevent->subsystem類型創建dev下的相應目錄，如：/dev/graphics。緊接著根據uevent->action是"add"還是"remove"來實現設備節點的創建與刪除。如果uevent->action是"add"，則調用make_device(devpath, block, uevent->major, uevent->minor)函數生成設備節點。如果uevent->action是"remove"，則調用unlink(devpath)對設備節點進行刪除。

Ⅳ linux鍔犺澆dts鐨勬椂鍊欎細鍒涘緩璁懼囪妭鐐瑰悧

From:http://m.blog.csdn.net/blog/liliyaya/9188193

1. 鍦\kernel\of\fdt.c 涓鏈夊備笅鍒濆嬪寲鍑芥暟 娉ㄩ噴涓婏細灞曞紑璁懼囨爲錛屽壋寤篸evice_nodes鍒板叏灞鍙橀噺allnodes涓

void __init unflatten_device_tree(void)
{
__unflatten_device_tree(initial_boot_params, &allnodes,
early_init_dt_alloc_memory_arch);

/* Get pointer to "/chosen" and "/aliasas" nodes for use everywhere */
of_alias_scan(early_init_dt_alloc_memory_arch);
}
unflatten_device_tree鍑芥暟琚玸etup_arch鍑芥暟璋冪敤錛
鍥犱負鎴戜滑浣跨敤寰楁槸arm騫沖彴鎵浠ュ瓨鍦\kernel\arch\arm\kernel\setup.c涓
void __init setup_arch(char **cmdline_p)
{
unflatten_device_tree()
}

setup_arch鍑芥暟鍦╧ernel鍚鍔ㄦ槸琚璋冪敤錛屽備笅鍚鍔╧ernel瀛樺湪\kernel\init\main.c涓
asmlinkage void __init start_kernel(void)
{
setup_arch(&command_line);
}

榪欎簺宸ヤ綔瀹屾垚瑙ｆ瀽DTS鏂囦歡銆備繚瀛樺埌鍏ㄥ矓閾捐〃allnodes涓銆

2銆佸湪makefile涓鏈夎繖孌佃瘽鏉ョ紪璇慸ts鏂囦歡錛

$(obj)/A20%.dtb: $(src)/dts/A20%.dts FORCE
$(call if_changed_dep,dtc)

$(obj)/A68M%.dtb: $(src)/dts/A68M%.dts FORCE
$(call if_changed_dep,dtc)

鍜.c鏂囦歡鐢熸垚.o鏂囦歡涓鏍 鍥炵敓鎴.dtb鏂囦歡銆傚湪
/home/liyang/workspace/SZ_JB-mr1-8628-bsp-1012/out/target/proct/msm8226/obj/KERNEL_OBJ/arch/arm/boot
鐩褰曚笅錛屼笌zimage涓涓鐩褰曘

3銆
鍦 board-8226.c涓鏈夊垵濮嬪寲鍑芥暟-->鍚鍔ㄨ嚜鍔ㄦ帀鐢
void __init msm8226_init(void)
{
of_platform_populate(NULL, of_default_bus_match_table, adata, NULL);
}

of_platform_populate鍦╧ernel\driver\of\platform.c涓瀹氫箟錛屽洖鏌ヨ

root = root ? of_node_get(root) : of_find_node_by_path("/");
for_each_child_of_node(root, child)
{
rc = of_platform_bus_create(child, matches, lookup, parent, true);
if (rc)
break;
}
of_node_put(root);

鍦ㄨ繖閲岀敤鍒板緱鍑芥暟of_find_node_by_path浼氭渶緇堣皟鐢ㄥ埌kernel\driver\of\base.c涓寰楀嚱鏁
struct device_node *of_find_node_by_path(const char *path)
{
閬嶅巻絎1姝ヤ腑寰梐llnodes鎵懼埌鏍硅妭鐐
}

of_platform_bus_create()鍑芥暟涓鍒涘緩寰楀唴瀹瑰瓨鍦ㄤ簡 adata涓銆

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