vma-funcs.md

VMA Functions

Contents

Memory Descriptor

• allocate_mm() - Allocates a new struct mm_struct from the slab allocator.
• free_mm() - Frees a struct mm_struct from the slab allocator.
• copy_mm() - Initialises the specified struct task_struct with a copy of the current task's struct mm_struct.

VMA Helpers

• vma_is_anonymous() - Determines if the specified VMA is anonymous (i.e. does not map a file.)

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Function Descriptions

allocate_mm()

void *allocate_mm(void)

allocate_mm() simply allocates a new struct mm_struct from the slab allocator via kmem_cache_alloc().

NOTE: Macro, inferring function signature.

Arguments

N/A

Returns

A pointer to the newly allocated struct mm_struct.

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free_mm()

void free_mm(struct mm_struct *mm)

free_mm() frees the specified struct mm_struct from the slab allocator via kmem_cache_free().

NOTE: Macro, inferring function signature.

Arguments

• mm - A pointer to the struct mm_struct which is to be freed.

Returns

N/A

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copy_mm()

int copy_mm(unsigned long clone_flags, struct task_struct *tsk)

copy_mm() copies the current task's struct mm_struct to the specified struct task_struct, resetting statistics as it does so.

The bulk of the actual duplication is performed by dup_mm() and dup_mmap() which copy the page tables too.

There are some exceptions:

1. If clone_flags & CLONE_VM then the current task's struct mm_struct is shared rather than copied.

2. If this is a kernel thread, i.e. there is no current->mm available, the copy is aborted.

Arguments

• clone_flags - The clone flags associated with the copy, if it's the case that clone_flags & CLONE_VM, then the struct mm_struct is not copied and is instead shared.

• tsk - The task whose mm field we want to assign a copy of the current task's struct mm_struct to.

Returns

0 if successful, error code otherwise.

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vma_is_anonymous()

bool vma_is_anonymous(struct vm_area_struct *vma)

vma_is_anonymous() determines whether the specified VMA (i.e. struct vm_area_struct) is anonymous - an anonymous VMA is one that does not map a file but rather simply represents an area of memory unassociated with any file.

The function simply tests whether the VMA's vm_ops fields is null - if so, no operations are specified and so the VMA is anonymous, otherwise it is not.

Arguments

• vma - The VMA whose anonymity we wish to determine.

Returns

true if the VMA is anonymous, otherwise false.

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