xv6-cs450/kalloc.c
Frans Kaashoek 547c28fc1e Don't map IO space in the user part of the address space
Passes all tests now (but need to update usertests to allow for more than 640k)
2011-07-31 21:27:02 -04:00

87 lines
1.7 KiB
C

// Physical memory allocator, intended to allocate
// memory for user processes, kernel stacks, page table pages,
// and pipe buffers. Allocates 4096-byte pages.
#include "types.h"
#include "defs.h"
#include "param.h"
#include "memlayout.h"
#include "mmu.h"
#include "spinlock.h"
struct run {
struct run *next;
};
struct {
struct spinlock lock;
struct run *freelist;
} kmem;
extern char end[]; // first address after kernel loaded from ELF file
char *newend;
// simple page allocator to get off the ground during boot
char *
pgalloc(void)
{
if (newend == 0)
newend = end;
void *p = (void*)PGROUNDUP((uint)newend);
memset(p, 0, PGSIZE);
newend = newend + PGSIZE;
return p;
}
// Initialize free list of physical pages.
void
kinit(void)
{
char *p;
initlock(&kmem.lock, "kmem");
p = (char*)PGROUNDUP((uint)newend);
for(; p + PGSIZE <= (char*)p2v(PHYSTOP); p += PGSIZE)
kfree(p);
}
//PAGEBREAK: 21
// Free the page of physical memory pointed at by v,
// which normally should have been returned by a
// call to kalloc(). (The exception is when
// initializing the allocator; see kinit above.)
void
kfree(char *v)
{
struct run *r;
if((uint)v % PGSIZE || v < end || v2p(v) >= PHYSTOP)
panic("kfree");
// Fill with junk to catch dangling refs.
memset(v, 1, PGSIZE);
acquire(&kmem.lock);
r = (struct run*)v;
r->next = kmem.freelist;
kmem.freelist = r;
release(&kmem.lock);
}
// Allocate one 4096-byte page of physical memory.
// Returns a pointer that the kernel can use.
// Returns 0 if the memory cannot be allocated.
char*
kalloc(void)
{
struct run *r;
acquire(&kmem.lock);
r = kmem.freelist;
if(r)
kmem.freelist = r->next;
release(&kmem.lock);
return (char*)r;
}