Implement dup3 syscall (#162)

pk/file.c

@@ -53,6 +53,20 @@ int file_dup(file_t* f)
   return -1;
 }
 
+int file_dup3(file_t* f, int newfd)
+{
+  if (newfd < 0 || newfd >= MAX_FDS)
+      return -1;
+
+  if (atomic_cas(&fds[newfd], 0, f) == 0)
+  {
+      file_incref(f);
+      return newfd;
+  }
+
+  return -1;
+}
+
 void file_init()
 {
   // create stdin, stdout, stderr and FDs 0-2

pk/file.h

@@ -23,6 +23,7 @@ file_t* file_open(const char* fn, int flags, int mode);
 void file_decref(file_t*);
 void file_incref(file_t*);
 int file_dup(file_t*);
+int file_dup3(file_t*, int newfd);
 
 file_t* file_openat(int dirfd, const char* fn, int flags, int mode);
 ssize_t file_pwrite(file_t* f, const void* buf, size_t n, off_t off);

pk/syscall.c

@@ -181,6 +181,21 @@ int sys_dup(int fd)
   return r;
 }
 
+int sys_dup3(int fd, int newfd, int flags)
+{
+  kassert(flags == 0);
+  int r = -EBADF;
+  file_t* f = file_get(fd);
+
+  if (f)
+  {
+    r = file_dup3(f, newfd);
+    file_decref(f);
+  }
+
+  return r;
+}
+
 ssize_t sys_lseek(int fd, size_t ptr, int dir)
 {
   ssize_t r = -EBADF;
@@ -462,6 +477,7 @@ long do_syscall(long a0, long a1, long a2, long a3, long a4, long a5, unsigned l
     [SYS_ftruncate] = sys_ftruncate,
     [SYS_getdents] = sys_getdents,
     [SYS_dup] = sys_dup,
+    [SYS_dup3] = sys_dup3,
     [SYS_readlinkat] = sys_stub_nosys,
     [SYS_rt_sigprocmask] = sys_stub_success,
     [SYS_ioctl] = sys_stub_nosys,

pk/syscall.h

@@ -43,6 +43,7 @@
 #define SYS_ftruncate 46
 #define SYS_getdents 61
 #define SYS_dup 23
+#define SYS_dup3 24
 #define SYS_readlinkat 78
 #define SYS_rt_sigprocmask 135
 #define SYS_ioctl 29