无法理解Linux内核模块中read_proc的工作情况

我在这里回顾内核模块示例

程序中使用的read_proc如下所示：

int fortune_read( char *page, char **start, off_t off,

               int count, int *eof, void *data )

{

    int len;

     if (off > 0) {
         *eof = 1;
          return 0;
     }

     /* Wrap-around */
    if (next_fortune >= cookie_index) next_fortune = 0;

    len = sprintf(page, "%s\n", &cookie_pot[next_fortune]);

    next_fortune += len;

    return len;
}

有人能解释为什么off被检查为大于0吗。此外，是否有人能解释一下“停止”和“计数”论点的重要性

到目前为止，我的理解是我们必须在页面中写入数据，并且必须在数据结束时设置eof

---

谢谢。

关闭是文件中必须从中读取数据的位置。这类似于正常文件的偏移。但是，在proc_read的例子中，它有一些不同之处。例如，如果调用proc文件上的read调用来读取100字节的数据，proc_read中的off和count将如下所示：

第一次，off=0，计数100。例如，在proc_read中，您只返回了10个字节。然后控件无法返回到用户应用程序，内核将再次调用proc_read，off为10，计数为90。同样，如果您在程序读取中返回20，您将再次调用off 30，计数70。像这样，你将被呼叫，直到计数达到0。然后数据被写入给定的用户缓冲区，应用程序read（）调用返回

但是如果您没有100字节的数据，并且只想返回几个字节，那么必须将eof设置为1。然后read（）函数立即返回

首先，下面的评论解释得比我好

      /*
       * How to be a proc read function
       * ------------------------------
                     * Prototype:
                     *    int f(char *buffer, char **start, off_t offset,
                     *          int count, int *peof, void *dat)
                     *
                     * Assume that the buffer is "count" bytes in size.
                     *
                     * If you know you have supplied all the data you
                     * have, set *peof.
                     *
                     * You have three ways to return data:
                     * 0) Leave *start = NULL.  (This is the default.)
                     *    Put the data of the requested offset at that
                     *    offset within the buffer.  Return the number (n)
                     *    of bytes there are from the beginning of the
                     *    buffer up to the last byte of data.  If the
                     *    number of supplied bytes (= n - offset) is 
                     *    greater than zero and you didn't signal eof
                     *    and the reader is prepared to take more data
                     *    you will be called again with the requested
                     *    offset advanced by the number of bytes 
                     *    absorbed.  This interface is useful for files
                     *    no larger than the buffer.
                     * 1) Set *start = an unsigned long value less than
                     *    the buffer address but greater than zero.
                     *    Put the data of the requested offset at the
                     *    beginning of the buffer.  Return the number of
                     *    bytes of data placed there.  If this number is
                     *    greater than zero and you didn't signal eof
                     *    and the reader is prepared to take more data
                     *    you will be called again with the requested
                     *    offset advanced by *start.  This interface is
                     *    useful when you have a large file consisting
                     *    of a series of blocks which you want to count
                     *    and return as wholes.
                     *    (Hack by Paul.Russell@rustcorp.com.au)
                     * 2) Set *start = an address within the buffer.
                     *    Put the data of the requested offset at *start.
                     *    Return the number of bytes of data placed there.
                     *    If this number is greater than zero and you
                     *    didn't signal eof and the reader is prepared to
                     *    take more data you will be called again with the
                     *    requested offset advanced by the number of bytes
                     *    absorbed.
                     */

---

off

（文件内的偏移量）的值大于零意味着调用

fourtune\u read

函数不是第一次。在这种情况下，不需要向用户写入任何内容，因为在第一次调用.AFAIK时有一个数据，因为linux 3.10的机制已经改变，所以您不需要该签名的功能。看见