ioctl (nr 16)

Linux Signature

int ioctl(int fd, unsigned long request, ...);

Description

Manipulates the underlying device parameters of special files. Commonly used to query terminal attributes (TCGETS, TIOCGWINSZ, etc.).

Current Implementation

Always returns -ENOTTY (-25), indicating the file descriptor does not refer to a terminal. All arguments are ignored.

This is sufficient for musl’s stdio, which calls ioctl(fd, TIOCGWINSZ, ...) to check if stdout is a terminal for line buffering decisions. Receiving -ENOTTY causes musl to treat the fd as a non-terminal and use full buffering.

Source: osl/src/syscalls/mod.rs — inline stub in syscall_dispatch

Future Work

• Return TIOCGWINSZ data for the VGA console (80x25) so musl recognises it as a terminal.
• Implement TCGETS/TCSETS for basic terminal attribute support.
• Dispatch based on fd to different device drivers.