libc: Implement fcntl(F_DUPFD) and dup()

apps/src/init.c

@@ -141,5 +141,23 @@ int main()
 
     printf("Press any key to restart.\n\n");
 
+    int ferr = fileno(stderr);
+    int newerr = dup(ferr);
+    if (newerr < 0)
+    {
+        perror("dup");
+        return 1;
+    }
+    FILE* new_stderr = fdopen(newerr, "rw");
+    if (!new_stderr)
+    {
+        perror("fdopen");
+        return 1;
+    }
+
+    fprintf(new_stderr, "Bye!\n");
+
+    fclose(new_stderr);
+
     return 0;
 }

kernel/src/sys/stdio.cpp

@@ -20,7 +20,7 @@
 
 #define FNCTL_DUPFD 0
 
-void sys_fcntl(Context* context, int fd, int command, uintptr_t arg)
+void sys_fcntl(Context* context, int fd, int command, [[maybe_unused]] uintptr_t arg)
 {
     if (fd >= TASK_MAX_FDS || fd < 0)
     {
@@ -34,7 +34,8 @@ void sys_fcntl(Context* context, int fd, int command, uintptr_t arg)
         return;
     }
     Descriptor& file = current_task->files[fd];
-    if (command == FNCTL_DUPFD)
+    if (command == FNCTL_DUPFD) // FIXME: If arg is greater than 0, return the lowest numbered available file descriptor
+                                // greater than or equal to arg.
     {
         int dupfd = current_task->alloc_fd();
         if (dupfd < 0)

libs/libc/include/fcntl.h

@@ -8,6 +8,9 @@
 /* Open for reading and writing. */
 #define O_RDWR 3
 
+/* Duplicate a file descriptor. */
+#define F_DUPFD 0
+
 #ifdef __cplusplus
 extern "C"
 {
@@ -16,6 +19,9 @@ extern "C"
     /* Opens the file specified by pathname. Returns a file descriptor on success, or -1 on error. */
     int open(const char* pathname, int flags);
 
+    /* Performs an operation on the file descriptor fd determined by cmd. */
+    int fcntl(int fd, int cmd, ...);
+
 #ifdef __cplusplus
 }
 #endif

libs/libc/include/luna/syscall.h

@@ -15,6 +15,7 @@
 #define SYS_close 11
 #define SYS_seek 12
 #define SYS_exec 13
+#define SYS_fcntl 14
 
 #ifndef __want_syscalls
 #ifdef __cplusplus

libs/libc/include/unistd.h

@@ -45,6 +45,9 @@ extern "C"
     /* Moves the read/write file offset for fd to offset, depending on whence. */
     off_t lseek(int fd, off_t offset, int whence);
 
+    /* Returns a copy of the file descriptor fd. */
+    int dup(int fd);
+
 #ifdef __cplusplus
 }
 #endif

libs/libc/src/fcntl.cpp

@@ -1,4 +1,5 @@
 #include <fcntl.h>
+#include <stdarg.h>
 #include <sys/syscall.h>
 #include <unistd.h>
 
@@ -8,4 +9,18 @@ extern "C"
     {
         return (int)syscall(SYS_open, pathname, flags);
     }
+
+    int fcntl(int fd, int cmd, ...)
+    {
+        va_list ap;
+        va_start(ap, cmd);
+        long result;
+        switch (cmd)
+        {
+        case F_DUPFD: result = syscall(SYS_fcntl, fd, cmd, va_arg(ap, int)); break;
+        default: result = syscall(SYS_fcntl, fd, cmd, 0); break;
+        }
+        va_end(ap);
+        return (int)result;
+    }
 }

libs/libc/src/unistd.cpp

@@ -1,4 +1,5 @@
 #include <bits/error.h>
+#include <fcntl.h>
 #include <luna.h>
 #include <luna/syscall.h>
 #include <stdarg.h>
@@ -45,6 +46,7 @@ extern "C"
             result = __luna_syscall2(number, arg0, arg1);
             break;
         }
+        case SYS_fcntl:
         case SYS_seek:
         case SYS_write:
         case SYS_read:
@@ -101,4 +103,9 @@ extern "C"
         syscall(SYS_exit, status);
         __builtin_unreachable();
     }
+
+    int dup(int fd)
+    {
+        return fcntl(fd, F_DUPFD, 0);
+    }
 }