ptos: ex: Add pool allocator header groundwork

Signed-off-by: Chloe M. <chloe@mensia.org>

service/ptos/head/ex/pool.h

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: Pool allocator
+ * Author:      Chloe M.
+ */
+
+#ifndef _EX_POOL_H_
+#define _EX_POOL_H_ 1
+
+#include <ptdef.h>
+
+/* Maximum levels per region */
+#define POOL_LEVEL_MAX 8
+
+/* Minimum log2 granularity */
+#define POOL_MIN_LOG2  3
+
+/* Compute the granularity at a specific level */
+#define POOL_LEVEL_GRAN(X) \
+    (1 << ((X) + POOL_MIN_LOG2))
+
+/*
+ * A pool page represents a single allocatable
+ * unit within a pool segment.
+ *
+ * @Bitmap: Bitmap within pool page
+ * @Next:   Next page within list
+ */
+typedef struct _POOL_PAGE {
+    UQUAD Bitmap;
+    struct _POOL_PAGE *Next;
+} POOL_PAGE;
+
+/*
+ * A pool segment represents a list of pages at a specific
+ * granularity.
+ *
+ * @LastPage:  Last page in segment
+ * @PageCount: Number of pages in this segment
+ */
+typedef struct {
+    POOL_PAGE *LastPage;
+    USIZE PageCount;
+} POOL_SEGMENT;
+
+/*
+ * A pool region represents a whole area in which several
+ * pool levels can reside.
+ *
+ * @Level: Segment levels
+ */
+typedef struct {
+    POOL_SEGMENT Level[POOL_LEVEL_MAX];
+} POOL_REGION;
+
+#endif  /* !_EX_POOL_H_ */