vm: object: implement vm_object_put_page to add existing pages to a vmo

include/kernel/vm-object.h

@@ -89,6 +89,10 @@ extern struct vm_page *vm_object_get_page(
 	off_t offset,
 	enum vm_object_flags flags,
 	unsigned long *irq_flags);
+extern kern_status_t vm_object_put_page(
+	struct vm_object *vo,
+	off_t offset,
+	struct vm_page *pg);
 
 extern kern_status_t vm_object_read(
 	struct vm_object *vo,

vm/vm-object.c

@@ -1,4 +1,5 @@
 #include <kernel/address-space.h>
+#include <kernel/panic.h>
 #include <kernel/printk.h>
 #include <kernel/sched.h>
 #include <kernel/util.h>
@@ -342,6 +343,54 @@ static struct vm_page *alloc_page(struct vm_object *vo, off_t offset)
 	return NULL;
 }
 
+kern_status_t vm_object_put_page(
+	struct vm_object *vo,
+	off_t offset,
+	struct vm_page *pg)
+{
+	struct btree_node *cur = vo->vo_pages.b_root;
+	if (!vo->vo_pages.b_root) {
+		vo->vo_pages.b_root = &pg->p_bnode;
+		return KERN_OK;
+	}
+
+	while (cur) {
+		struct vm_page *page
+			= BTREE_CONTAINER(struct vm_page, p_bnode, cur);
+		struct btree_node *next = NULL;
+
+		off_t base = page->p_vmo_offset;
+		off_t limit = base + vm_page_get_size_bytes(page);
+		if (offset < base) {
+			next = btree_left(cur);
+		} else if (offset >= limit) {
+			next = btree_right(cur);
+		} else {
+			panic("vm_object_put_page: page already exists");
+			return KERN_NAME_EXISTS;
+		}
+
+		if (next) {
+			cur = next;
+			continue;
+		}
+
+		pg->p_vmo_offset = offset;
+
+		if (offset < base) {
+			btree_put_left(cur, &pg->p_bnode);
+		} else {
+			btree_put_right(cur, &pg->p_bnode);
+		}
+
+		btree_insert_fixup(&vo->vo_pages, &pg->p_bnode);
+
+		return KERN_OK;
+	}
+
+	return KERN_FATAL_ERROR;
+}
+
 static struct vm_page *get_page(struct vm_object *vo, off_t offset)
 {
 	struct btree_node *cur = vo->vo_pages.b_root;