kalloc.[ch] from xv6, memory.[ch] containing memory probing algorithm and constants

kern/kalloc.c

@@ -0,0 +1,75 @@
+#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;
+}