STRUCT TTY_PORT(9)

🌈 struct tty_port(9) 🌈

okay bestie, welcome to the struct tty_port(9) page from the Kernel API Manual ✨ this is the port-level information situation, and it is literally main character energy for TTY drivers. no cap.

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🌸 NAME 🌸

struct tty_port — port level information. periodt 💅

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✨ SYNOPSIS ✨

struct tty_port {
    struct tty_bufhead      buf;
    struct tty_struct       *tty;
    struct tty_struct       *itty;
    const struct tty_port_operations *ops;
    const struct tty_port_client_operations *client_ops;
    spinlock_t lock;
    int blocked_open;
    int count;
    wait_queue_head_t open_wait;
    wait_queue_head_t delta_msr_wait;
    unsigned long           flags;
    unsigned long           iflags;
    unsigned char           console:1;
    struct mutex            mutex;
    struct mutex            buf_mutex;
    u8 *xmit_buf;
    u8 *xmit_fifo;
    unsigned int            close_delay;
    unsigned int            closing_wait;
    int drain_delay;
    struct kref             kref;
    void *client_data;
 };

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🎀 MEMBERS 🎀

vibe check on every single member, no skips, no cap 🫶

• buf — buffer for this port, locked internally.
• tty — back pointer to struct tty_struct, valid only if the tty is open. Use tty_port_tty_get to obtain it (and tty_kref_put to release).
• itty — internal back pointer to struct tty_struct. Avoid this. It should be eliminated in the long term. not me warning you bestie 😭
• ops — tty port operations (like activate, shutdown), see struct tty_port_operations.
• client_ops — tty port client operations (like receive_buf, write_wakeup). By default, tty_port_default_client_ops is used.
• lock — lock protecting tty.
• blocked_open — # of procs waiting for open in tty_port_block_til_ready.
• count — usage count.
• open_wait — open waiters queue (waiting e.g. for a carrier).
• delta_msr_wait — modem status change queue (waiting for MSR changes).
• flags — user TTY flags (ASYNC_).
• iflags — internal flags (TTY_PORT_).
• console — when set, the port is a console.
• mutex — locking, for open, shutdown and other port operations.
• buf_mutex — xmit_buf alloc lock.
• xmit_buf — optional xmit buffer used by some drivers.
• xmit_fifo — optional xmit buffer used by some drivers.
• close_delay — delay in jiffies to wait when closing the port.
• closing_wait — delay in jiffies for output to be sent before closing.
• drain_delay — set to zero if no pure time based drain is needed else set to size of fifo.
• kref — references counter. Reaching zero calls ops->destruct if non-NULL or frees the port otherwise.
• client_data — pointer to private data, for client_ops.

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🦋 DESCRIPTION 🦋

Each device keeps its own port level information. struct tty_port was introduced as a common structure for such information. As every TTY device shall have a backing tty_port structure, every driver can use these members. iconic behavior, honestly 💖

⚠️ The tty port has a different lifetime to the tty so must be kept apart. In addition be careful as tty -> port mappings are valid for the life of the tty object but in many cases port -> tty mappings are valid only until a hangup so don’t use the wrong path. fr fr, this is the danger zone 💀

Tty port shall be initialized by tty_port_init and shut down either by tty_port_destroy (refcounting not used), or tty_port_put (refcounting).

There is a lot of helpers around struct tty_port too. To name the most significant ones: tty_port_open, tty_port_close (or tty_port_close_start and tty_port_close_end separately if need be), and tty_port_hangup. These call ops->activate and ops->shutdown as needed. slay 🔥

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💜 SEE ALSO 💜

• Kernel file ./include/linux/tty_port.h
• struct tty_port_operations(9)

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and that’s the whole page, bestie 🫶 source/version situation: ./include/linux, dated October 2026, page struct tty_port(9) — mwah 💋✨