Clarification on pt_t struct

[Ronald Mathias]

Hello,

I was going over the Minix 3.2 source code, especially the Virtual
Memory Server part.

I had a doubt about this struct at minix/minix/servers/vm/pt.h

/* A pagetable. */
typedef struct
{
u32_t *pt_dir; /* page aligned (ARCH_VM_DIR_ENTRIES) */
u32_t pt_dir_phys; /* physical address of pt_dir */
u32_t *pt_pt[ARCH_VM_DIR_ENTRIES]; /* Pointers to page tables in
VM address space. */
.......
} pt_t;

What is the need for having both u32_t *pt_pt and u32_t
*pt_pt[ARCH_VM_DIR_ENTRIES] pointers ?

I am thinking only one pointer pt_dir was sufficient as from this
pointer, we can get the Page table entries also right.

Regards,
Ronald Mathias

[Peter Shkenev]

Hello Ronald,

Sorry for not answering too long.

Looks like you are working with AST's "Operating Systems: Design and Implementation" book. Does it give any information on this structure.

Also, you can look at this struct in current version of Minix, it is located at /minix/servers/vm/pt.h . It is more documented there. I had a quick look at this and I suppose that there are many parts of the page table.

Best regards,

Peter

понедельник, 19 апреля 2021 г. в 21:07:17 UTC+3, RM:

[Ronald Mathias]

Hi Peter,

Thanks for your help. Yes. I am referring to the latest version of
Minix. I am also reading the book.

So far I have managed to get the 3.2.1 version of Minix cross compiled
on my Ubuntu box.

I have also created a boot CD with grub as my bootloader and installed
the kernel for debugging with GDB.

I might need to read the code some more times to make sense of it.

Regards,
Ronald Mathias

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