Question

我一直在为LCD模块编写lcd内核驱动程序。一切顺利，我可以写入显示，创建一个我可以写入的/ dev / lcd节点，它将在屏幕上显示结果。我以为使用llseek fops回调将光标定位在lcd上会很好，这样我就可以使用倒带fseek等。但是它没有按照我的预期工作，下面是我所看到的摘要：

来自司机方的相关代码行是：

loff_t lcd_llseek(struct file *filp, loff_t off, int whence)
{
    switch (whence) {
        case 0: // SEEK_SET
            if (off > 4*LINE_LENGTH || off < 0) {
                printk(KERN_ERR "unsupported SEEK_SET offset %llx\n", off);
                return -EINVAL;
            }
            lcd_gotoxy(&lcd, off, 0, WHENCE_ABS);
            break;
        case 1: // SEEK_CUR 
            if (off > 4*LINE_LENGTH || off < -4*LINE_LENGTH) {
                printk(KERN_ERR "unsupported SEEK_CUR offset %llx\n", off);
                return -EINVAL;
            }
            lcd_gotoxy(&lcd, off, 0, WHENCE_REL);
            break;
        case 2: // SEEK_END (not supported, hence fall though)
        default:
            // how did we get here !
            printk(KERN_ERR "unsupported seek operation\n");
            return -EINVAL;
    }
    filp->f_pos = lcd.pos;
    printk(KERN_INFO "lcd_llseek complete\n");
    return lcd.pos;
}

int lcd_open(struct inode *inode, struct file *filp)
{
    if (!atomic_dec_and_test(&lcd_available)) {
        atomic_inc(&lcd_available);
        return -EBUSY; // already open
    }

    return 0;
}

static struct file_operations fops = {
    .owner = THIS_MODULE,
    .write = lcd_write,
    .llseek = lcd_llseek,
    .open = lcd_open,
    .release = lcd_release,
};

int lcd_init(void)
{
    ...

    // allocate a new dev number (this can be dynamic or
    // static if passed in as a module param)
    if (major) {
        devno = MKDEV(major, 0);
        ret = register_chrdev_region(devno, 1, MODULE_NAME);
    } else {
        ret = alloc_chrdev_region(&devno, 0, 1, MODULE_NAME);
        major = MAJOR(devno);
    }
    if (ret < 0) {
        printk(KERN_ERR "alloc_chrdev_region failed\n");
        goto fail;
    }

    // create a dummy class for the lcd
    cl = class_create(THIS_MODULE, "lcd");
    if (IS_ERR(cl)) {
        printk(KERN_ERR "class_simple_create for class lcd failed\n");
        goto fail1;
    }

    // create cdev interface
    cdev_init(&cdev, &fops);
    cdev.owner = THIS_MODULE;
    ret = cdev_add(&cdev, devno, 1);
    if (ret) {
        printk(KERN_ERR "cdev_add failed\n");
        goto fail2;
    }

    // create /sys/lcd/fplcd/dev so udev will add our device to /dev/fplcd
    device = device_create(cl, NULL, devno, NULL, "lcd");
    if (IS_ERR(device)) {
        printk(KERN_ERR "device_create for fplcd failed\n");
        goto fail3;
    }
    ...
}

为了测试lseek调用我有以下单元测试：

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#define log(msg, ...) fprintf(stdout, __FILE__ ":%s():[%d]:" msg, __func__, __LINE__, __VA_ARGS__)

int lcd;

void test(void)
{
    int k;

    // a lot of hello's
    log("hello world test\n",1);
    if (lseek(lcd, 0, SEEK_CUR) == -1) {
        log("failed to seek\n", 1);
    }
}

int main(int argc, char **argv)
{
    lcd = open("/dev/lcd", O_WRONLY);
    if (lcd == -1) {
        perror("unable to open lcd");
        exit(EXIT_FAILURE);
    }

    test();

    close(lcd);
    return 0;
}

文件交叉编译如下：

~/Workspace/ts4x00/lcd-module$ cat Makefile 
obj-m += fls_lcd.o

all:
    make -C $(KPATH) M=$(PWD) modules
    $(CROSS_COMPILE)gcc -g -fPIC $(CFLAGS) lcd_unit_test.c -o lcd_unit_test

clean:
    make -C $(KPATH) M=$(PWD) clean
    rm -rf lcd_unit_test
~/Workspace/ts4x00/lcd-module$ make CFLAGS+="-march=armv4 -ffunction-sections -fdata-sections"
make -C ~/Workspace/ts4x00/linux-2.6.29 M=~/Workspace/ts4x00/lcd-module modules
make[1]: Entering directory `~/Workspace/ts4x00/linux-2.6.29'
  CC [M]  ~/Workspace/ts4x00/lcd-module/fls_lcd.o
~/Workspace/ts4x00/lcd-module/fls_lcd.c:443: warning: 'lcd_entry_mode' defined but not used
  Building modules, stage 2.
  MODPOST 1 modules
  CC      ~/Workspace/ts4x00/lcd-module/fls_lcd.mod.o
  LD [M]  ~/Workspace/ts4x00/lcd-module/fls_lcd.ko
make[1]: Leaving directory `~/Workspace/ts4x00/linux-2.6.29'
~/Workspace/ts4x00/arm-2008q3/bin/arm-none-linux-gnueabi-gcc -g -fPIC -march=armv4 -ffunction-sections -fdata-sections lcd_unit_test.c -o lcd_unit_test

这是运行驱动程序的输出，单元测试是：

root@ts4700:~/devel# insmod ./fls_lcd.ko 
root@ts4700:~/devel# ./lcd_unit_test 
lcd_unit_test.c:test():[61]:hello world test
lcd_unit_test.c:test():[63]:failed to seek
root@ts4700:~/devel# dmesg
FLS LCD driver started
unsupported SEEK_SET offset bf0a573c

我无法弄清楚为什么参数在内核端被严重破坏，我试图将SEEK_CUR置于0位置并且在驱动程序中我得到了一个SEEK_SET（无论我在单元测试中放置了什么）和一个疯狂的关闭的大数字？

有谁知道发生了什么事？

btw我正在为arm dev kit

编译内核2.6.29

Answer 1

好的对不起伙计们在昨晚尝试调试这个问题后，归结为编译错误的内核（我将KPATH留给了内核的不同配置而不是sdcard）

抱歉浪费每个人的时间，但希望如果有人看到他们的内核驱动程序中看起来像一个疯狂的堆栈，这可能会让他们直截了当。

哦，感谢所有帮助：）

llseek在内核驱动程序中没有表现

1 个答案: