#include <kalloc.h>
#include <memory.h>
#include <panic.h>
#include <riscv.h>
#include <spinlock.h>
#include <string.h>
#include <types.h>

// Physical memory allocator, for user processes,
// kernel stacks, page-table pages,
// and pipe buffers. Allocates whole 4096-byte pages.

/** Free list of physical pages. */
void freerange(void *physaddr_start, void *physaddr_end);

/** First address after kernel. Provided kernel.ld */
extern char kernel_end[];

/** A run is a node in the free list. */
struct Run {
    struct Run *next;
};

/** Kernel memory allocator. */
struct {
    struct Spinlock lock;
    struct Run     *freelist;
} kmem;

void kalloc_init() {
    initlock(&kmem.lock, "kmem");
    freerange(kernel_end, (void *)PHYSTOP);
}

void freerange(void *physaddr_start, void *physaddr_end) {
    char *p;
    p = (char *)PGROUNDUP((u64)physaddr_start);
    for (; p + PGSIZE <= (char *)physaddr_end; p += PGSIZE) kfree(p);
}

void kfree(void *pa) {
    struct Run *r;

    // Assert that page is a ligned to a page boundary and that its correctly
    // sized
    if (((u64)pa % PGSIZE) != 0 || (char *)pa < kernel_end ||
        (u64)pa >= PHYSTOP)
        panic("kfree");

    // Fill with junk to catch dangling refs.
    memset(pa, 1, PGSIZE);

    r = (struct Run *)pa;

    acquire(&kmem.lock);
    r->next = kmem.freelist;
    kmem.freelist = r;
    release(&kmem.lock);
}

void *kalloc(void) {
    struct Run *r;

    acquire(&kmem.lock);

    r = kmem.freelist;

    if (r)
        kmem.freelist = r->next;
    release(&kmem.lock);
    if (r)
        memset((char *)r, 5, PGSIZE); // fill with junk

    return (void *)r;
}