user/electric-fence/page.c

/* For email below, drop spaces and <spam-buster> tag.
 * MODIFIED:  March 20, 2014 (jric<spam-buster> @ <spam-buster> chegg DOT com)
 */
#include "efence.h"
#include <fcntl.h>
#include <parlib/uthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>

static caddr_t startAddr = (caddr_t)0;

/*
 * Create memory.
 */
void *Page_Create(size_t size)
{
	caddr_t allocation;

	/*
	 * In this version, "startAddr" is a _hint_, not a demand.
	 * When the memory I map here is contiguous with other
	 * mappings, the allocator can coalesce the memory from two
	 * or more mappings into one large contiguous chunk, and thus
	 * might be able to find a fit that would not otherwise have
	 * been possible. I could _force_ it to be contiguous by using
	 * the MMAP_FIXED flag, but I don't want to stomp on memory mappings
	 * generated by other software, etc.
	 */
	allocation = (caddr_t)mmap(startAddr, size, PROT_READ | PROT_WRITE,
	                           MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

	/*
	 * Set the "address hint" for the next mmap() so that it will abut
	 * the mapping we just created.
	 *
	 * HP/UX 9.01 has a kernel bug that makes mmap() fail sometimes
	 * when given a non-zero address hint, so we'll leave the hint set
	 * to zero on that system. HP recently told me this is now fixed.
	 * Someone please tell me when it is probable to assume that most
	 * of those systems that were running 9.01 have been upgraded.
	 */
	startAddr = allocation + size;

	if (allocation == (caddr_t)-1)
		EF_Exit("mmap() failed: %r");

	return (void *)allocation;
}

static void mprotectFailed(void)
{
	EF_Exit("mprotect() failed: %r");
}

void Page_AllowAccess(void *address, size_t size)
{
	if (mprotect((caddr_t)address, size, PROT_READ | PROT_WRITE) < 0)
		mprotectFailed();
}

void Page_DenyAccess(void *address, size_t size)
{
	if (mprotect((caddr_t)address, size, PROT_NONE) < 0)
		mprotectFailed();
}

void Page_Delete(void *address, size_t size)
{
	Page_DenyAccess(address, size);
}

size_t Page_Size(void)
{
	return PGSIZE;
}