sched.h: create_new_process - correct function to create a new process in an available spot

kernel.c

@@ -5,10 +5,12 @@
 #include "io.h"
 #include "malloc.h"
 
-void create_processes_from_bin_table();
+void read_binary_table();
 
 extern ProcessControlBlock processes[PROCESS_COUNT];
 
+// this array is populated when the memory image is built, therefore it should
+// resign in a section which is not overwritten with zeros on startup
 loaded_binary binary_table[NUM_BINARIES] __attribute__ ((section (".data")));
 
 extern void memset(unsigned int, void*, void*);
@@ -19,20 +21,20 @@ extern void init()
 
     dbgln("Kernel started!", 15);
 
-    create_processes_from_bin_table();
+    read_binary_table();
 
     scheduler_run_next();   
 }
 
-void create_processes_from_bin_table()
+void read_binary_table()
 {
     char msg[28] = "found bin with id 0 at pos 0";
-    ProcessControlBlock* next_process = processes;
 
     malloc_info info;
     info.allocate_memory_end = (void*) 0xFF0000;
     info.allocate_memory_start = (void*) 0;
 
+    // calculate the end of loaded binaries
     for (int i = 0; i < NUM_BINARIES; i++) {
         if (binary_table[i].binid == 0)
             break;
@@ -50,21 +52,9 @@ void create_processes_from_bin_table()
         if (binary_table[i].binid == 0)
             break;
 
-
-        optional_voidptr stack_top = malloc_stack(1<<12); // allocate 4Kib stack
-        if (has_error(stack_top)) {
-            dbgln("Error while allocating stack for initial process", 48);
-            continue;
-        }
-
-        next_process->status = PROC_RDY;
-        next_process->pid = binary_table[i].binid;
-        next_process->pc = binary_table[i].entrypoint;
-
-        next_process->regs[1] = (int) stack_top.value; // set stack top, put 32 bytes of zeros there
-        next_process++;
-        dbgln("enabled process from table", 26);
-
+        // create a new process for each binary found
+        // it should have around 4kb stack
+        create_new_process(binary_table+i, 1<<12);
     }
 }
 

kernel.h

@@ -11,23 +11,6 @@
 // scheduler settings
 #define TIME_SLICE_LEN 100          // number of cpu time ticks per slice
 
-
-/* This struct holds information about binaries which are currently loaded into
- * memory. Currently the kernel is not able to load binaries into memory, as
- * no file system layer is implemented. When the memory image is built, the 
- * list of loaded binaries is populated aswell.
- */
-typedef struct loaded_binary {
-    int binid;
-    int entrypoint;
-    void* bounds[2];
-} loaded_binary;
-
-// create a global table holding all loaded binaries.
-// this is either populated at runtime when binaries are loaded dynamically
-// or when a memory image is created.
-extern loaded_binary binary_table[NUM_BINARIES];
-
 // init function
 extern __attribute__((__noreturn__)) void init();
 

kinclude/ktypes.h

@@ -25,6 +25,8 @@ enum process_status {
 
 // process structure:
 typedef struct ProcessControlBlock ProcessControlBlock;
+struct loaded_binary;
+
 struct ProcessControlBlock {
     int pid;
     int pc;
@@ -33,9 +35,23 @@ struct ProcessControlBlock {
     // scheduling information
     enum process_status status;
     ProcessControlBlock* waiting_for_process;
+    struct loaded_binary* binary;
     unsigned long long int asleep_until;
 };
 
+
+/* This struct holds information about binaries which are currently loaded into
+ * memory. Currently the kernel is not able to load binaries into memory, as
+ * no file system layer is implemented. When the memory image is built, the 
+ * list of loaded binaries is populated aswell.
+ */
+typedef struct loaded_binary {
+    int binid;
+    int entrypoint;
+    void* bounds[2];
+} loaded_binary;
+
+
 /*
  *  Optionals
  *

kinclude/sched.c

@@ -2,6 +2,7 @@
 #include "sched.h"
 #include "csr.h"
 #include "io.h"
+#include "malloc.h"
 
 
 // scheduling data:
@@ -9,6 +10,7 @@ ProcessControlBlock processes[PROCESS_COUNT];
 ProcessControlBlock* current_process;
 unsigned long long int scheduling_interrupted_start;
 unsigned long long int next_interrupt_scheduled_for;
+int next_process_id = 1;
 
 void scheduler_run_next ()
 {
@@ -154,3 +156,54 @@ void mark_ecall_entry()
 {
     scheduling_interrupted_start = read_time();
 }
+
+optional_pcbptr find_available_pcb_slot() {
+    static int index = 0;
+    int start_index = index;
+    ProcessControlBlock* pcb = processes + index;
+
+    while (pcb->status != PROC_DEAD) {        
+        index = (index + 1) % PROCESS_COUNT;
+        if (index == start_index)
+            return (optional_pcbptr) { .error = ENOBUFS };
+        pcb = processes + index;
+    }
+    return (optional_pcbptr) { .value = pcb };
+}
+
+int create_new_process(loaded_binary* bin, int stack_size)
+{
+    // try to get a position in the processes list
+    optional_pcbptr slot_or_err = find_available_pcb_slot();
+    // if that failed, we cannot creat a new process
+    if (has_error(slot_or_err)) {
+        dbgln("No more process structs!", 24);
+        return slot_or_err.error;
+    }
+
+    // allocate stack for the new process
+    optional_voidptr stack_top_or_err = malloc_stack(stack_size); // allocate 4Kib stack
+    // if that failed, we also can't create a new process
+    if (has_error(stack_top_or_err)) {
+        dbgln("Error while allocating stack for process", 40);
+        return stack_top_or_err.error;
+    }
+
+    ProcessControlBlock* pcb = slot_or_err.value;
+
+    // determine next pid
+    int pid = next_process_id++;
+
+    // mark process as ready
+    pcb->status = PROC_RDY;
+    pcb->pid = pid;
+    pcb->pc = bin->entrypoint;
+    pcb->binary = bin;
+    // load stack top into stack pointer register
+    pcb->regs[1] = (int) stack_top_or_err.value;
+    // load pid into a0 register
+    pcb->regs[9] = pid;
+
+    dbgln("Created new process!", 20);
+
+}

kinclude/sched.h

@@ -18,4 +18,7 @@ int  scheduler_index_from_pid(int pid);
 int* get_current_process_registers();
 ProcessControlBlock* get_current_process();
 void mark_ecall_entry();
+
+int create_new_process(loaded_binary* bin, int stack_size);
+
 #endif