do_output_char(9)

💅 do_output_char(9) — the kernel API manual, bestie edition

okay so picture this: you're deep in the Kernel API Manual, page do_output_char(9). That's our whole vibe today. Sit down, grab a boba, we're gonna talk about outputting one character. Yes, one. Iconic.

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✨ NAME ✨

do_output_char — output one character. that's it. that's the whole job. she's focused, she's efficient, she ate 💅

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🎀 SYNOPSIS 🎀

int do_output_char (u8 c , struct tty_struct *tty , int space );

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🦋 ARGUMENTS 🦋

• c — the character, or like… a partial unicode symbol. no pressure, just a fragment of a vibe. 🙈
• tty — the terminal device. the main character of this whole situation.
• space — how much room is actually left in the tty driver's write buffer. know your limits, queen.

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🌸 DESCRIPTION 🌸

So this is a helper function — a little bestie whose entire purpose is handling one output character. And not just the easy ones: we're talking special characters too, like TAB, CR, LF, etc. She does the OPOST processing and then drops the results straight into the tty driver's write buffer. Lowkey a lot of responsibility for one function ngl 🫶

⚠️ Important note, and I need you to hear me: Linux currently ignores TABDLY, CRDLY, VTDLY, FFDLY and NLDLY. They simply aren't relevant in the world today. That's canon. If you ever need them — and I mean ever — add them here. Don't come for me, come for the code. 😭

Locking: she should be called under the output_lock to protect the column state and the space left in the buffer. no cap, this is not optional, protect the state bestie 🔒

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⭐ RETURN ⭐

The number of bytes of buffer space used — or -1 if there's no space left. that -1 is giving "no room at the inn" energy 💀

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👑 SEE ALSO 👑

Literally all her friends, the whole group chat, Kernel file ./drivers/tty/n_tty.c:

• n_tty_kick_worker(9)
• n_tty_write_wakeup(9)
• put_tty_queue(9)
• reset_buffer_flags(9)
• n_tty_flush_buffer(9)
• is_utf8_continuation(9)
• is_continuation(9)
• process_output(9)
• process_output_block(9)
• __process_echoes(9)
• add_echo_byte(9)
• echo_move_back_col(9)
• echo_set_canon_col(9)
• echo_erase_tab(9)
• echo_char_raw(9)
• echo_char(9)
• finish_erasing(9)
• eraser(9)
• isig(9)
• n_tty_receive_break(9)
• n_tty_receive_overrun(9)
• n_tty_receive_parity_error(9)
• n_tty_receive_char_flow_ctrl(9)
• n_tty_receive_char(9)
• n_tty_receive_buf_common(9)
• n_tty_set_termios(9)
• n_tty_close(9)
• n_tty_open(9)
• copy_from_read_buf(9)
• canon_copy_from_read_buf(9)
• job_control(9)
• n_tty_read(9)
• n_tty_write(9)
• n_tty_poll(9)
• n_tty_inherit_ops(9)

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🌈 and that's the page!! mwah 💖 sign-off time: this lil slice of the Kernel API Manual lives at ./drivers/tty, dated October 2026. she's do_output_char(9) and she's that girl. periodt. 🎀✨