should be right?

src/arch/x86/syscall.c

@@ -4,15 +4,84 @@
  * @license GPL-3.0-only
  */
 
+#include "config.h"
 #include "sched/scheduler.h"
 #include <arch/x86.h>
 #include <kernel.h>
 #include <stddef.h>
 #include <io/term/term.h>
 #include <sched/process.h>
+#include <io/kbd/ps2.h>
+#include <fs/initfs.h>
+#include <string/string.h>
 
 extern struct process* current_process;
 
+// Return fd on success, -errno on error
+int sys_open(const char* filename, int flags)
+{
+    if (tar_exists(filename) < 0) {
+        return -ENOENT; // file doesn't exist..
+    }
+    // file exists here!
+    if (current_process->next_free_fd >= FDT_MAX) {
+        return -EMFILE;
+    }
+    int fd = current_process->next_free_fd++;
+    current_process->fdt[fd].fd = fd;
+    current_process->fdt[fd].open = true;
+    current_process->fdt[fd].cursor = 0;
+    strncpy(current_process->fdt[fd].filename, filename, PROCESS_NAME_MAX - 1);
+    return fd;
+}
+
+// Return 0 on success, -EBADFD if invalid FD
+int sys_close(int fd)
+{
+    if (fd < 0 || fd >= FDT_MAX) {
+        return -EBADFD;
+    }
+
+    if (!current_process->fdt[fd].open) {
+        return -EBADFD; // FD not opened in the first place
+    }
+
+    current_process->fdt[fd].open = false;
+    current_process->fdt[fd].filename[0] = '\0';
+    current_process->fdt[fd].cursor = 0;
+    return 0;
+}
+
+// Should return the number of bytes read
+int sys_read(unsigned int fd, char* buf, size_t count)
+{
+    size_t i;
+    switch (fd) {
+        case 0: //read from stdin (keyboard)
+            for (i=0; i<count; i++) {
+                buf[i] = keyboard_getchar();
+            }
+            return i;
+        case 1: // from stdout
+        case 2: // from stderr
+            return -EBADFD;
+        default: // from an open file?
+            if (current_process->fdt[fd].open == false) {
+                return -EBADFD; // File descriptor wasn't open
+            }
+            // Here fd refers to a valid opened file..
+            int sz = tar_read(current_process->fdt[fd].filename,&buf);
+            if (sz == 0) {
+                return -ENOENT;
+            } else {
+                return sz;
+            }
+    }
+
+    return -EBADFD;
+}
+
+// TODO: Should have a return value: number of bytes written on success, -1 on error (errno set) 
 void sys_write(unsigned int fd, const char* buf, size_t count)
 {
     switch (fd) {
@@ -61,14 +130,21 @@ struct cpu_status* syscall_handler(struct cpu_status* regs)
     switch (regs->rax)
     {
         case 0: //sys_read
+            regs->rax = sys_read(regs->rdi, (char*)regs->rsi, regs->rdx);
             break;
         case 1: //sys_write
             sys_write(regs->rdi, (char*)regs->rsi, regs->rdx);
             break;
+        case 2:
+            regs->rax = sys_open((const char*)regs->rdi, regs->rsi);
+            break;
+        case 3:
+            regs->rax = sys_close(regs->rdi);
+            break;
         case 60: //sys_exit
             sys_exit(regs->rdi);
             break;
-        default:
+        default: // bad syscall
             regs->rax = 0xbad515ca11;
             break;
     }