syscalls: start implementing some basic syscalls

src/tasking/syscalls.c

@@ -0,0 +1,86 @@
+#include "../include/syscalls.h"
+#include <stddef.h>
+#include "../include/stdio.h"
+
+#define STDIN_FILENO 0
+#define STDOUT_FILENO 1
+#define STDERR_FILENO 2
+
+#define EBADF 9
+typedef unsigned short umode_t
+
+int sys_write(TrapFrame *tf)
+{
+    if(tf->ebx < 3)
+    {
+        //stdin, stdout or stderr
+        if(tf->ebx == STDOUT_FILENO)
+        {
+            print((char*)tf->ecx, tf->edx);
+            tf->ecx++;
+        }
+    }
+    else
+    {
+        if(current->file_descriptors[tf->ebx] == NULL)
+        {
+            return -EBADF;
+        }
+        return fat_fwrite(current->file_descriptors[tf->ebx], (void*)tf->ecx, tf->edx);
+    }
+}
+
+int sys_open(TrapFrame *tf)
+{
+    const char* filename = tf->ebx;
+    int flags = tf->ecx;
+    umode_t mode = tf->edx;
+
+    int fd = -1;
+
+    for(int i = 3; i < MAX_OPEN_FILES; i++)
+    {
+        if(current->file_descriptors[i] == NULL)
+        {
+            fat_fopen(current->file_descriptors[i], filename, (char)mode);
+            fd = i;
+        }
+    }
+
+    return fd;
+}
+
+int sys_close(TrapFrame *tf)
+{
+    int fd = tf->ebx;
+    if(current->file_descriptors[fd] != NULL)
+    {
+        return fat_fclose(current->file_descriptors[fd]);
+    }
+    return -1;
+}
+
+void handle_syscall(TrapFrame *tf)
+{
+    
+    debug_log("EAX: %X ", tf->eax);
+    debug_log("EBX: %X ", tf->ebx);
+    debug_log("ECX: %s ", tf->ecx);
+    debug_log("EDX: %X\n", tf->edx);
+    
+    if(tf->eax == 4)//write
+    {
+        int r = sys_write(tf);
+        tf->eax = r;
+    }
+    if(tf->eax == 5)//open
+    {
+        int r = sys_open(tf);
+        tf->eax = r;
+    }
+    if(tf->eax == 6)//close
+    {
+        int r = sys_close(tf);
+        tf->eax = r;
+    }
+}