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Linux Kernel Programming

You're reading from  Linux Kernel Programming

Product type Book
Published in Mar 2021
Publisher Packt
ISBN-13 9781789953435
Pages 754 pages
Edition 1st Edition
Languages
Author (1):
Kaiwan N. Billimoria Kaiwan N. Billimoria
Profile icon Kaiwan N. Billimoria
Toc

Table of Contents (19) Chapters close

Preface 1. Section 1: The Basics
2. Kernel Workspace Setup 3. Building the 5.x Linux Kernel from Source - Part 1 4. Building the 5.x Linux Kernel from Source - Part 2 5. Writing Your First Kernel Module - LKMs Part 1 6. Writing Your First Kernel Module - LKMs Part 2 7. Section 2: Understanding and Working with the Kernel
8. Kernel Internals Essentials - Processes and Threads 9. Memory Management Internals - Essentials 10. Kernel Memory Allocation for Module Authors - Part 1 11. Kernel Memory Allocation for Module Authors - Part 2 12. The CPU Scheduler - Part 1 13. The CPU Scheduler - Part 2 14. Section 3: Delving Deeper
15. Kernel Synchronization - Part 1 16. Kernel Synchronization - Part 2 17. About Packt 18. Other Books You May Enjoy

Writing a kernel module to demo using the page allocator APIs

Let's now get hands on with the low-level page allocator and free APIs that we've learned about so far. In this section, we will show relevant code snippets, followed by an explanation where warranted, from our demo kernel module (ch8/lowlevel_mem/lowlevel_mem.c).

In the primary worker routine, bsa_alloc()of our small LKM, we highlighted (in bold font) the code comments that show what we are trying to achieve. A few points to note:

  1. First, we do something very interesting: we use our small kernel "library" function klib_llkd.c:show_phy_pages() to literally show you how physical RAM page frames are identity mapped to kernel virtual pages in the kernel lowmem region! (The exact working of the show_phy_pages() routine is discussed very shortly):
// ch8/lowlevel_mem/lowlevel_mem.c
[...]
static int bsa_alloc(void)
{
int stat = -ENOMEM;
u64 numpg2alloc = 0;
const struct page *pg_ptr1;

/*...
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