From e1ada1ac8a50fd814c8868e97f977f3544d4929d Mon Sep 17 00:00:00 2001
From: Achilleas Anagnostopoulos <achilleas.imap.mbox@gmail.com>
Date: Wed, 10 May 2017 22:24:03 +0100
Subject: [PATCH] Allow mem region visitors to abort the scan by returning
 false

---
 kernel/hal/multiboot/multiboot.go      |  9 ++++++---
 kernel/hal/multiboot/multiboot_test.go | 17 +++++++++++++++--
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/kernel/hal/multiboot/multiboot.go b/kernel/hal/multiboot/multiboot.go
index 1dd6e9f..6f7de4a 100644
--- a/kernel/hal/multiboot/multiboot.go
+++ b/kernel/hal/multiboot/multiboot.go
@@ -119,8 +119,9 @@ var (
 )
 
 // MemRegionVisitor defies a visitor function that gets invoked by VisitMemRegions
-// for each memory region provided by the boot loader.
-type MemRegionVisitor func(entry *MemoryMapEntry)
+// for each memory region provided by the boot loader. The visitor must return true
+// to continue or false to abort the scan.
+type MemRegionVisitor func(entry *MemoryMapEntry) bool
 
 // SetInfoPtr updates the internal multiboot information pointer to the given
 // value. This function must be invoked before invoking any other function
@@ -151,7 +152,9 @@ func VisitMemRegions(visitor MemRegionVisitor) {
 			entry.Type = MemReserved
 		}
 
-		visitor(entry)
+		if !visitor(entry) {
+			return
+		}
 
 		curPtr += uintptr(ptrMapHeader.entrySize)
 	}
diff --git a/kernel/hal/multiboot/multiboot_test.go b/kernel/hal/multiboot/multiboot_test.go
index 62193b3..9b8a963 100644
--- a/kernel/hal/multiboot/multiboot_test.go
+++ b/kernel/hal/multiboot/multiboot_test.go
@@ -59,8 +59,9 @@ func TestVisitMemRegion(t *testing.T) {
 	var visitCount int
 
 	SetInfoPtr(uintptr(unsafe.Pointer(&emptyInfoData[0])))
-	VisitMemRegions(func(_ *MemoryMapEntry) {
+	VisitMemRegions(func(_ *MemoryMapEntry) bool {
 		visitCount++
+		return true
 	})
 
 	if visitCount != 0 {
@@ -71,7 +72,7 @@ func TestVisitMemRegion(t *testing.T) {
 	SetInfoPtr(uintptr(unsafe.Pointer(&multibootInfoTestData[0])))
 	multibootInfoTestData[128] = 0xFF
 
-	VisitMemRegions(func(entry *MemoryMapEntry) {
+	VisitMemRegions(func(entry *MemoryMapEntry) bool {
 		if entry.PhysAddress != specs[visitCount].expPhys {
 			t.Errorf("[visit %d] expected physical address to be %x; got %x", visitCount, specs[visitCount].expPhys, entry.PhysAddress)
 		}
@@ -82,11 +83,23 @@ func TestVisitMemRegion(t *testing.T) {
 			t.Errorf("[visit %d] expected region type to be %d; got %d", visitCount, specs[visitCount].expType, entry.Type)
 		}
 		visitCount++
+		return true
 	})
 
 	if visitCount != len(specs) {
 		t.Errorf("expected the visitor func to be invoked %d times; got %d", len(specs), visitCount)
 	}
+
+	// Test that the visitor function can abort the scan by returning false
+	visitCount = 0
+	VisitMemRegions(func(entry *MemoryMapEntry) bool {
+		visitCount++
+		return false
+	})
+
+	if visitCount != 1 {
+		t.Errorf("expected the visitor func to be invoked %d times; got %d", 1, visitCount)
+	}
 }
 
 func TestGetFramebufferInfo(t *testing.T) {