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.
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