stos: pmm: Add physical frame allocation

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

paw/stos/head/mm/pmm.h

@@ -11,9 +11,20 @@
 
 #include <stdef.h>
 
+/* Page frame number */
+typedef UQUAD MM_PFN;
+
 /*
  * Initialize the physical memory management
  */
 VOID MmInitPmm(VOID);
 
+/*
+ * Request a single frame of memory
+ *
+ * Returns the page frame number on success, otherwise
+ * zero on failure e.g., out of memory
+ */
+MM_PFN MmRequestFrame(VOID);
+
 #endif  /* !_MM_PMM_H_ */

paw/stos/mm/pmm.c

@@ -13,6 +13,7 @@
 #include <hal/page.h>
 #include <units.h>
 #include <stdef.h>
+#include <string.h>
 
 #define LOAD_DELAY 128
 
@@ -159,6 +160,22 @@ MmLoadUpdate(VOID)
     LoadIdx %= LoadMax;
 }
 
+MM_PFN
+MmRequestFrame(VOID)
+{
+    MM_PFD *Pfd;
+    UPTR Pma;
+
+    Pfd = MmPfdPop(&PfdList);
+    if (Pfd == NULL) {
+        return 0;
+    }
+
+    RtlMemSet(Pfd, 0, PAGESIZE);
+    Pma = VMA_TO_PMA(Pfd);
+    return Pma >> LOG2_PAGESIZE;
+}
+
 static VOID
 MmProbeMemory(VOID)
 {