Function proc_rwmem

freebsd/kern/sys_process.c:207–293

}

int
proc_rwmem(struct proc *p, struct uio *uio)
{
	vm_map_t map;
	vm_offset_t pageno;		/* page number */
	vm_prot_t reqprot;
	int error, fault_flags, page_offset, writing;

	/*
	 * Assert that someone has locked this vmspace.  (Should be
	 * curthread but we can't assert that.)  This keeps the process
	 * from exiting out from under us until this operation completes.
	 */
	PROC_ASSERT_HELD(p);
	PROC_LOCK_ASSERT(p, MA_NOTOWNED);

	/*
	 * The map we want...
	 */
	map = &p->p_vmspace->vm_map;

	/*
	 * If we are writing, then we request vm_fault() to create a private
	 * copy of each page.  Since these copies will not be writeable by the
	 * process, we must explicity request that they be dirtied.
	 */
	writing = uio->uio_rw == UIO_WRITE;
	reqprot = writing ? VM_PROT_COPY | VM_PROT_READ : VM_PROT_READ;
	fault_flags = writing ? VM_FAULT_DIRTY : VM_FAULT_NORMAL;

	/*
	 * Only map in one page at a time.  We don't have to, but it
	 * makes things easier.  This way is trivial - right?
	 */
	do {
		vm_offset_t uva;
		u_int len;
		vm_page_t m;

		uva = (vm_offset_t)uio->uio_offset;

		/*
		 * Get the page number of this segment.
		 */
		pageno = trunc_page(uva);
		page_offset = uva - pageno;

		/*
		 * How many bytes to copy
		 */
		len = min(PAGE_SIZE - page_offset, uio->uio_resid);

		/*
		 * Fault and hold the page on behalf of the process.
		 */
		error = vm_fault(map, pageno, reqprot, fault_flags, &m);
		if (error != KERN_SUCCESS) {
			if (error == KERN_RESOURCE_SHORTAGE)