請問有關撰寫/proc時所用的proc_read函式 - Linux

根據trace到原始的source code部分 proc/fs/generic.c

作者寫到的使用說明：

/*
* 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.

這種方法意思是指將要讀出的資料放在第一個參數欄buffer，

而將第二個參數(自訂buffer空間)設為NULL。不過因為buffer

參數的空間大小為PAGE_SIZE，亦即4096KB，所以若我超過此數

值並不適用。

* 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 [email protected])

這個方式我就不太明白了，*start通常放的是我的自訂buffer

位置，此部分所指的unsigned long value less than the buffer

address意思是？


不知是否有使用過的前輩舉個例子說明，感謝。


* 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.
*/

※ 引述《supermin (　)》之銘言：
: 我使用kernel-2.6.17，撰寫kernel modules來記錄一些系統資訊，
: 使用與user space溝通的機制是/proc，在開完檔案之後指定read function大致如下：
: int procfile_read(char *buffer, char **buffer_location,
: off_t offset, int buffer_length, int *eof, void *data)
: {
: if (offset > 0) {
: ret = 0;
: } else {
: *buffer_location = my_buffer;
: }
: bufferLength = 0;
: return bufferLength;
: }
: 其中my_buffer以及bufferLength為全域變數，
: 我想在記錄完一堆東西之後使用cat /proc/myfile來看我記錄的東西
: 不過由於bufferLength頗大，超過10000bytes，而cat的結果被切掉了，
: 只能顯示部分內容，顯然應該是buffer overflow的問題，
: 這時候該怎麼解決才能看到全部內容呢？

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