Next Previous Contents

---

2. Syntax used

2.1 Function Syntax

When speaking about a function, we write:

"function_name  [ file location . extension ]"

For example:

"schedule [kernel/sched.c]" 

tells us that we talk about

"schedule"

function retrievable from file

[ kernel/sched.c ]

Note: We also assume /usr/src/linux as the starting directory.

2.2 Indentation

Indentation in source code is 3 blank characters.

2.3 InterCallings Analysis

Overview

We use the"InterCallings Analysis "(ICA) to see (in an indented fashion) how kernel functions call each other.

For example, the sleep_on command is described in ICA below:

|sleep_on
|init_waitqueue_entry      --
|__add_wait_queue            |   enqueuing request  
   |list_add                 |
      |__list_add          -- 
   |schedule              ---     waiting for request to be executed
      |__remove_wait_queue --   
      |list_del              |   dequeuing request
         |__list_del       -- 
 
                          sleep_on ICA

The indented ICA is followed by functions' locations:

• sleep_on [kernel/sched.c]
• init_waitqueue_entry [include/linux/wait.h]
• __add_wait_queue
• list_add [include/linux/list.h]
• __list_add
• schedule [kernel/sched.c]
• __remove_wait_queue [include/linux/wait.h]
• list_del [include/linux/list.h]
• __list_del

Note: We don't specify anymore file location, if specified just before.

Details

In an ICA a line like looks like the following

 function1 -> function2

means that < function1 > is a generic pointer to another function. In this case < function1 > points to < function2 >.

When we write:

  function:

it means that < function > is not a real function. It is a label (typically assembler label).

In many sections we may report a ''C'' code or a ''pseudo-code''. In real source files, you could use ''assembler'' or ''not structured'' code. This difference is for learning purposes.

PROs of using ICA

The advantages of using ICA (InterCallings Analysis) are many:

• You get an overview of what happens when you call a kernel function
• Function locations are indicated after the function, so ICA could also be considered as a little ''function reference''
• InterCallings Analysis (ICA) is useful in sleep/awake mechanisms, where we can view what we do before sleeping, the proper sleeping action, and what we'll do after waking up (after schedule).

CONTROs of using ICA

• Some of the disadvantages of using ICA are listed below:

As all theoretical models, we simplify reality avoiding many details, such as real source code and special conditions.

• Additional diagrams should be added to better represent stack conditions, data values, and so on.

---

Next Previous Contents
Linux HOWTO full list