如果构建为外部模块，Linux Char设备驱动程序不起作用，但如果构建为运行内核，则工作。但为什么？
问题描述：
OS：Fedora的26阿尔法如果构建为外部模块，Linux Char设备驱动程序不起作用，但如果构建为运行内核，则工作。但为什么？
内核：Linux的4.11
内核手动通过以下命令编译：
1）使oldconfig这个
2）的make menuconfig
3）使所有
4）make module_install
5）使安装
在成功编译和安装最新的内核， 我建立了一些模块，但为通过make -C /root/linux-4.11/ M=$(pwd) modules一个外部模块不是针对运行的内核。 我开发的所有基本模块都是按照预期编译，安装和工作的，但后来我编写了基本的字符设备驱动程序，但后来发现了一些奇怪的问题。也就是说，在通过insmod成功编译和插入模块之后，我没有收到关于此模块的任何内核消息，也没有在/ dev /目录中生成char设备，然后我也搜索了有关此问题但没有得到任何更好的回答这个问题。
然后，突然我试图将其编译并通过make -C /lib/modules/$(uname -r)/build/ M=$(pwd) modules作为运行内核，然后插入模块后，我得到了我的预期结果。 但是现在，我想知道为什么会发生这种情况，因为其他简单模块在构建为外部模块时工作正常，但为什么不是这个？
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/device.h>
#include <linux/kdev_t.h>
#include <linux/uaccess.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/version.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Neeraj Pal <[email protected]>");
MODULE_DESCRIPTION("Sample Character Driver");
static dev_t first;
static struct device *dev_ret;
static struct cdev c_dev;
static struct class *cl;
static int dev_open(struct inode *,struct file *);
static int dev_release(struct inode *,struct file *);
static ssize_t dev_read(struct file *, char __user *,size_t count, loff_t *);
static ssize_t dev_write(struct file *, const char __user *,size_t count, loff_t *);
static struct file_operations fops = {
.owner = THIS_MODULE,
.open = dev_open,
.read = dev_read,
.write = dev_write,
.release = dev_release
};
static int __init chardev_init(void)
{
int ret;
printk(KERN_ALERT "char device registered\n");
if ((ret = alloc_chrdev_region(&first,0,1,"Namastey")) < 0)
{
return ret;
}
if (IS_ERR(cl = class_create(THIS_MODULE,"hello")))
{
unregister_chrdev_region(first,1);
return PTR_ERR(cl);
}
if (IS_ERR(dev_ret = device_create(cl,NULL,first,NULL,"mychar")))
{
class_destroy(cl);
unregister_chrdev_region(first,1);
return PTR_ERR(dev_ret);
}
cdev_init(&c_dev,&fops);
if ((ret = cdev_add(&c_dev, first, 1)) < 0)
{
device_destroy(cl, first);
class_destroy(cl);
unregister_chrdev_region(first, 1);
return ret;
}
return 0;
}
static void __exit chardev_exit(void)
{
cdev_del(&c_dev);
device_destroy(cl, first);
class_destroy(cl);
unregister_chrdev_region(first, 1);
printk(KERN_INFO " Unloaded \n");
}
static int dev_open(struct inode *i, struct file *f)
{
printk(KERN_INFO "Driver: open()\n");
return 0;
}
static int dev_release(struct inode *i, struct file *f)
{
printk(KERN_INFO "Driver: close()\n");
return 0;
}
static ssize_t dev_read(struct file *f, char __user *buf, size_t len, loff_t *off)
{
printk(KERN_INFO "Driver: read()\n");
return 0;
}
static ssize_t dev_write(struct file *f, const char __user *buf, size_t len,
loff_t *off)
{
printk(KERN_INFO "Driver: write()\n");
return len;
}
module_init(chardev_init);
module_exit(chardev_exit);
编译&内核日志&内核，操作系统详细资料（既是外部模块，然后作为对运行内核）：
[[email protected] ldd]# uname -a
Linux localhost.localdomain 4.11.0 #1 SMP Tue May 2 14:34:09 IST 2017 x86_64 x86_64 x86_64 GNU/Linux
[[email protected] ldd]#
#NOW,BUILD as external module
[[email protected] ldd]# make -C /root/linux-4.11/ M=$(pwd) modules
make: Entering directory '/root/linux-4.11'
WARNING: Symbol version dump ./Module.symvers
is missing; modules will have no dependencies and modversions.
Building modules, stage 2.
MODPOST 1 modules
make: Leaving directory '/root/linux-4.11'
[[email protected] ldd]# insmod char
char_driver/ char.ko char.mod.o char.o
[[email protected] ldd]# insmod char.ko
insmod: ERROR: could not insert module char.ko: File exists
[[email protected] ldd]# rmmod char
[[email protected] ldd]# insmod char.ko
[[email protected] ldd]# journalctl -n 10
-- Logs begin at Tue 2017-05-02 11:28:36 IST, end at Fri 2017-05-05 12:14:01 IST. --
May 05 12:12:11 localhost.localdomain systemd[1]: Started Network Manager Script Dispatcher Service.
May 05 12:12:11 localhost.localdomain nm-dispatcher[1356]: req:1 'dhcp4-change' [ens3]: new request (4 scripts)
May 05 12:12:11 localhost.localdomain nm-dispatcher[1356]: req:1 'dhcp4-change' [ens3]: start running ordered scripts...
May 05 12:12:11 localhost.localdomain dhclient[564]: bound to xxx.xxx.xxx.xx-- renewal in 1401 seconds.
May 05 12:12:21 localhost.localdomain audit[1]: SERVICE_STOP pid=1 uid=0 auid=4294967295 ses=4294967295 msg='unit=NetworkManager-dispatcher comm="syst
May 05 12:14:01 localhost.localdomain anacron[1345]: Job `cron.daily' started
May 05 12:14:01 localhost.localdomain run-parts[1377]: (/etc/cron.daily) starting logrotate
May 05 12:14:01 localhost.localdomain run-parts[1382]: (/etc/cron.daily) finished logrotate
May 05 12:14:01 localhost.localdomain anacron[1345]: Job `cron.daily' terminated
May 05 12:14:01 localhost.localdomain anacron[1345]: Normal exit (1 job run)
[[email protected] ldd]# uname -a;cat /etc/redhat-release ;cat Makefile
Linux localhost.localdomain 4.11.0 #1 SMP Tue May 2 14:34:09 IST 2017 x86_64 x86_64 x86_64 GNU/Linux
Fedora release 26 (Twenty Six)
obj-m := char.o
[[email protected] ldd]# make -C /lib/modules
modules/ modules-load.d/
[[email protected] ldd]# make -C /lib/modules/4.11.0
4.11.0/ 4.11.0-0.rc3.git0.2.fc26.x86_64/
[[email protected] ldd]# make -C /lib/modules/4.11.0/
build/ kernel/ source/
#Now, Build against running kernel
[[email protected] ldd]# make -C /lib/modules/4.11.0/build/ M=$(pwd) modules
make: Entering directory '/usr/src/linux-4.11'
CC [M] /root/ldd/char.o
Building modules, stage 2.
MODPOST 1 modules
CC /root/ldd/char.mod.o
LD [M] /root/ldd/char.ko
make: Leaving directory '/usr/src/linux-4.11'
[[email protected] ldd]# rmmod char
[[email protected] ldd]# insmod char.ko
[[email protected] ldd]# journalctl -n 10
-- Logs begin at Tue 2017-05-02 11:28:36 IST, end at Fri 2017-05-05 12:33:04 IST. --
May 05 12:12:11 localhost.localdomain nm-dispatcher[1356]: req:1 'dhcp4-change' [ens3]: new request (4 scripts)
May 05 12:12:11 localhost.localdomain nm-dispatcher[1356]: req:1 'dhcp4-change' [ens3]: start running ordered scripts...
May 05 12:12:11 localhost.localdomain dhclient[564]: bound to xxx.xxx.xxx.xx-- renewal in 1401 seconds.
May 05 12:12:21 localhost.localdomain audit[1]: SERVICE_STOP pid=1 uid=0 auid=4294967295 ses=4294967295 msg='unit=NetworkManager-dispatcher comm="syst
May 05 12:14:01 localhost.localdomain anacron[1345]: Job `cron.daily' started
May 05 12:14:01 localhost.localdomain run-parts[1377]: (/etc/cron.daily) starting logrotate
May 05 12:14:01 localhost.localdomain run-parts[1382]: (/etc/cron.daily) finished logrotate
May 05 12:14:01 localhost.localdomain anacron[1345]: Job `cron.daily' terminated
May 05 12:14:01 localhost.localdomain anacron[1345]: Normal exit (1 job run)
May 05 12:33:04 localhost.localdomain kernel: char device registered
[[email protected] ldd]# ls -la /dev/mychar
crw------- 1 root root 244, 0 May 5 12:33 /dev/mychar
[[email protected] ldd]# echo "" > /dev/mychar
[[email protected] ldd]# cat /dev/mychar
[[email protected] ldd]# rmmod char
[[email protected] ldd]# journalctl -n 10
-- Logs begin at Tue 2017-05-02 11:28:36 IST, end at Fri 2017-05-05 12:33:57 IST. --
May 05 12:14:01 localhost.localdomain anacron[1345]: Job `cron.daily' terminated
May 05 12:14:01 localhost.localdomain anacron[1345]: Normal exit (1 job run)
May 05 12:33:04 localhost.localdomain kernel: char device registered
May 05 12:33:40 localhost.localdomain kernel: Driver: open()
May 05 12:33:40 localhost.localdomain kernel: Driver: write()
May 05 12:33:40 localhost.localdomain kernel: Driver: close()
May 05 12:33:51 localhost.localdomain kernel: Driver: open()
May 05 12:33:51 localhost.localdomain kernel: Driver: read()
May 05 12:33:51 localhost.localdomain kernel: Driver: close()
May 05 12:33:57 localhost.localdomain kernel: Unloaded
您还可以看到下面可用上述日志和输出屏幕截图细节（点击链接，如果你不满足于文本信息）：
Build against external module (not working,don't know why and Kernel & OS Details and Makefile
答
有关缺少Module.symvers的警告表明您正在构建的内核缺少CONFIG_MODVERSIONS选项。您需要启用此选项才能够有时针对不同内核构建的加载模块。如果您正在构建的内核源代码没有完全编译并且该文件尚未生成，那么问题也会发生。
构建命令，日志等应该*在问题文章* **中作为文本**，而不是链接为图像。请编辑帖子并修复这些问题。 – Tsyvarev
您收到关于缺少Module.symvers的警告。这就是允许你有时*加载针对不同内核构建的模块。我认为你正在构建的内核不是内置的，或者它已禁用CONFIG_MODVERSIONS（请参阅该选项的帮助文本）。 – fernan
@Tsyvarev以文本格式更新并添加了所有信息，但如果有人不理解文本格式，那么对于这种情况，我还保留截图格式。 –