munmap() and do_munmap(): Removing an Address Interval

The do_munmap() function removes an address interval from a specified process address space. The function is declared in <linux/mm.h>:

int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)

The first parameter specifies the address space from which the interval starting at address start of length len bytes is removed. On success, zero is returned. Otherwise, a negative error code is returned.

The munmap() System Call

The munmap() system call is exported to user-space as a means to allow processes to remove address intervals from their address space; it is the complement of the mmap() system call:

int munmap(void *start, size_t length)

The system call is defined in mm/mmap.c and acts as a very simple wrapper to do_munmap():

asmlinkage long sys_munmap(unsigned long addr, size_t len)
{
        int ret;
        struct mm_struct *mm;

        mm = current->mm;
        down_write(&mm->mmap_sem);
        ret = do_munmap(mm, addr, len);
        up_write(&mm->mmap_sem);
        return ret;
}