Linux Kernel Architecture

Chapter3:MemoryManagement

Table 3-2: Functions for Analyzing Page Table Entries.

Function Description

pgd_val

pud_val

pmd_val

pte_val

pgprot_val

Convert a variable of typepte_tand so on to anunsigned longnumber.

__pgd

__pud

__pmd

__pte

__pgprot

Do the reverse ofpdg_valand so on: They convert anunsigned longnumber into

avariableoftypepdg_tand so on.

pgd_index

pud_index

pmd_index

pte_index

Yield the address of the next-level table starting from a memory pointer and a

page table entry.

pgd_present

pud_present

pmd_present

pte_present

Check whether the_PRESENTbit of the corresponding entry is set. This is the case

when the page or page table addressed is in RAM memory.

pgd_none

pud_none

pmd_none

pte_none

Do the logical reverse of thexxx_presentfunctions. If they return a true value,

the searched page isnotin RAM.

pgd_clear

pud_clear

pmd_clear

pte_clear

Delete the passed page table entry. This is usually done by setting it to zero.

pgd_bad

pud_bad

pmd_bad

Check whether entries of the page middle, upper, and global directories are

invalid. They are used for safety purposes in functions that receive input param-

eters from the outside where it cannot be assumed that the parameters are valid.

pmd_page

pud_page

pte_page

Return the address of thepagestructure holding the data on the page or the

entries of the page middle directories.

How do theoffsetfunctions work? Let us considerpmd_offsetas an example. It requires as parameter
an entry from the page global directory (src_pgd)andanaddressin memory. It returns an element from
one of the page middle directories.

src_pmd = pmd_offset(src_pgd, address);