net: hns3: Resolved the issue that the debugfs query result is inconsistent.

This patch modifies the implementation of debugfs:
When the user process stops unexpectedly, not all data of the file system
is read. In this case, the save_buf pointer is not released. When the user
process is called next time, save_buf is used to copy the cached data
to the user space. As a result, the queried data is inconsistent. To solve
this problem, determine whether the function is invoked for the first time
based on the value of *ppos. If *ppos is 0, obtain the actual data.

Fixes: 5e69ea7 ("net: hns3: refactor the debugfs process")
Signed-off-by: Hao Lan <[email protected]>
Signed-off-by: Guangwei Zhang <[email protected]>
Signed-off-by: Jijie Shao <[email protected]>
Signed-off-by: Paolo Abeni <[email protected]>

Author: Hao Lan

drivers/net/ethernet/hisilicon/hns3/hns3_debugfs.c

@@ -1293,8 +1293,10 @@ static ssize_t hns3_dbg_read(struct file *filp, char __user *buffer,
 
 		/* save the buffer addr until the last read operation */
 		*save_buf = read_buf;
+	}
 
-		/* get data ready for the first time to read */
+	/* get data ready for the first time to read */
+	if (!*ppos) {
 		ret = hns3_dbg_read_cmd(dbg_data, hns3_dbg_cmd[index].cmd,
 					read_buf, hns3_dbg_cmd[index].buf_len);
 		if (ret)