/proc/filesystem读取称为三次

Question

这是我的第一个内核，在下面的示例程序中，我创建了一个简单的proc/filesystem。我看到阅读时，每当我猫的内核猫都被称为3次。想知道为什么这样做。

out，代码在下面。

cat /proc/myKernel
dmesg | grep -i myKernel
myKernel: Read (/proc/myKernel) called
myKernel: Read (/proc/myKernel) called
myKernel: Read (/proc/myKernel) called
int myKernel_read( char *buffer, char **bufferLocation, off_t offset, int bufferLength, int *eof, void *data )
{
    int ret = 0;
    u64 msrvalue;
    printk(KERN_INFO "myKernel: Read (/proc/%s) calledn", procFile_name);
    ret = sprintf(buffer, "Hello Worldn");
    return ret;
}
static int __init myKernel_init(void)
{
    entry = create_proc_entry(procFile_name, 0644, NULL);
    if(!entry)
        printk(KERN_INFO "myKernel: error registering proc control filen");
    else 
    {
        entry->read_proc = myKernel_read;
    }
    return 0;
}

Answer 1

问题与RET值有关。我仍然不知道为什么这三次被称为三次，但是当偏移小于零时，我必须进行实际读数。

int myKernel_read( char *buffer, char **bufferLocation, off_t offset, int bufferLength, int *eof, void *data )
{
    int ret;
    u64 msrvalue;
    if (offset > 0) 
    {
        /* we have finished to read, return 0 */
        ret  = 0;
    } else 
    {
        /* fill the buffer, return the buffer size */
                // DO THE READ HERE. NOT OUTSIDE
                //
                printk(KERN_INFO "myKernel: Read (/proc/%s) calledn", procFile_name);
        ret = sprintf(buffer, "MyKernel = %xn", 0);
    }
    return ret;
}