introduce SECTION_NULL

3 files changed, 20 insertions, 16 deletions

diff --git a/demo_functionality.c b/demo_functionality.c
index 366edd7..3cf5b8f 100644
--- a/demo_functionality.c
+++ b/demo_functionality.c
@@ -79,7 +79,7 @@ void demo_setup_PL0(void)
   uint16_t physical_section_number = claim_and_map_section
     ((void*) 5, PL0_SECTION_NUMBER, AP_2_0_MODEL_RW_ALL);
   
-  if (physical_section_number == CLAIM_FAILURE)
+  if (physical_section_number == SECTION_NULL)
     {
       puts("Couldn't claim memory section for unprivileged code :(");
       while(1);
diff --git a/paging.c b/paging.c
index 6560047..771c681 100644
--- a/paging.c
+++ b/paging.c
@@ -122,7 +122,7 @@ struct section_node
   void *owner; // 0 if free, 1 if used by kernel, 2 if split to pages
 
   // it's actually a 2-directional lists;
-  // end of list is marked by reference to itself;
+  // end of list is marked by reference to SECTION_NULL;
   // we use offsets into sections_list array instead of pointers;
   uint16_t prev, next;
 };
@@ -133,7 +133,7 @@ static uint16_t
   all_sections_count, kernel_sections_count,
   split_sections_count, free_sections_count;
 
-// those are undefined when the corresponding count is 0;
+// those are SECTION_NULL when the corresponding count is 0;
 static uint16_t
   first_free_section, first_kernel_section, first_split_section;
 
@@ -146,11 +146,13 @@ void setup_pager_structures(uint32_t available_mem)
   
   sections_list = (struct section_node*) SECTIONS_LIST_START;
 
+  first_split_section = SECTION_NULL;
+  
   for (uint16_t i = 0; i < kernel_sections_count; i++)
     sections_list[i] = (struct section_node) {
       .owner = OWNER_KERNEL,
-      .prev = i == 0 ? i : i - 1,
-      .next = i == kernel_sections_count - 1 ? i : i + 1
+      .prev = i == 0 ? SECTION_NULL : i - 1,
+      .next = i == kernel_sections_count - 1 ? SECTION_NULL : i + 1
     };
 
   first_kernel_section = 0;
@@ -159,8 +161,8 @@ void setup_pager_structures(uint32_t available_mem)
        i < all_sections_count; i++)
     sections_list[i] = (struct section_node) {
       .owner = OWNER_FREE,
-      .prev = i == kernel_sections_count ? i : i - 1,
-      .next = i == all_sections_count - 1 ? i : i + 1
+      .prev = i == kernel_sections_count ? SECTION_NULL : i - 1,
+      .next = i == all_sections_count - 1 ? SECTION_NULL : i + 1
     };
 
   first_free_section = kernel_sections_count;
@@ -170,11 +172,11 @@ void setup_pager_structures(uint32_t available_mem)
   puts(" free sections left for use");
 }
 
-// return section number or CLAIM_FAILURE in case of failure
+// return section number or SECTION_NULL in case of failure
 static uint16_t claim_section(void *owner)
 {
   if (!free_sections_count)
-    return CLAIM_FAILURE; // failure
+    return SECTION_NULL; // failure
 
   uint16_t section = first_free_section;
   
@@ -183,10 +185,12 @@ static uint16_t claim_section(void *owner)
       uint16_t next;
       
       next = sections_list[section].next;
-      sections_list[next].prev = next;
+      sections_list[next].prev = SECTION_NULL;
 
       first_free_section = next;
     }
+  else
+    first_free_section = SECTION_NULL;
 
   if (owner == OWNER_KERNEL)
     {
@@ -194,7 +198,7 @@ static uint16_t claim_section(void *owner)
 
       sections_list[section] = (struct section_node) {
 	.owner = owner,
-	.prev = section,
+	.prev = SECTION_NULL,
 	.next = first_kernel_section
       };
 
@@ -205,8 +209,8 @@ static uint16_t claim_section(void *owner)
   else
     sections_list[section] = (struct section_node) {
       .owner = owner,
-      .prev = section,
-      .next = section
+      .prev = SECTION_NULL,
+      .next = SECTION_NULL
     };
 
   return section;
@@ -218,7 +222,7 @@ uint16_t claim_and_map_section
 {
   uint16_t section = claim_section(owner);
   
-  if (section == CLAIM_FAILURE)
+  if (section == SECTION_NULL)
     return section;
   
   short_section_descriptor_t volatile *section_entry =
diff --git a/paging.h b/paging.h
index 1715a6e..4ac8efa 100644
--- a/paging.h
+++ b/paging.h
@@ -5,9 +5,9 @@ void setup_flat_map(void);
 
 void setup_pager_structures(uint32_t available_mem);
 
-#define CLAIM_FAILURE 0xffff
+#define SECTION_NULL 0xffff
 
-// returns section number or CLAIM_FAILURE in case of failure
+// returns section number or SECTION_NULL in case of failure
 uint16_t claim_and_map_section
 (void *owner, uint16_t where_to_map, uint8_t access_permissions);