Linux TTY function tracking

1. Introduction

This article describes the function tracking procedures for TTY open, TTY read, and TTY write operations

2. Example

Here is a simple Linux TTY open and read-write process

3. Open

When the device node/dev/ttys0 is opened, the kernel calls Vfs_open and then calls to Tty_open, and Tty_open analyzes the following

Tty_open Tty_alloc_file/*assign Tty_file_private and assign to file::p rivate_data*/Tty_open_current_tty/*If the current device is/dev/tty, try to reopen it, usually returning null*/Tty_open_by_driver/*If the function above returns null by finding the TTY driver to open the TTY device*/Tty_lookup_driver/*find the corresponding TTY driver based on the device number*/Tty_driver_lookup_tty/*Find out if tty_struct exists based on tty_driver::tty_operations::lookup/tty_driver::tty_struct*/Tty_reopen/*if Tty_struct is assigned, open the TTY*/Tty_ldisc_reinit/*wiring procedures for initializing TTY devices*/Tty_ldisc_get/*obtain the corresponding line code for registration according to the category (default is N_tty) and assign the corresponding Tty_ldisc instance*/Tty_set_termios_ldisc/*wiring procedures for setting up the TTY*/Tty_ldisc_open/*call Tty_ldisc::tty_ldisc_ops::open, for N_tty to N_tty_open*/Tty_init_dev/*if Tty_struct is not assigned, it is allocated (!!! The UART is SO!!!) */alloc_tty_struct/*assigning and initializing a tty_struct, including driver, OPS, index, etc.*/Tty_ldisc_init/*wiring procedures for initializing tty_struct*/Tty_ldisc_get/*obtain n_tty corresponding circuit code and assign corresponding Tty_ldisc instance*/tty_struct::tty_operations=tty_driver::tty_operations/*sets the set of function actions for Tty_struct*/Tty_driver_install_tty/*install portals for TTY devices via Tty_driver::tty_operations::install or Tty_standard_install*/Tty_ldisc_setup/*Open Line Procedure*/Tty_ldisc_open/*call Tty_ldisc::tty_ldisc_ops::open, for N_tty to N_tty_open*/Tty_add_file/*associating files to Tty_struce*/Tty_struct::tty_operations::open/*with Tty_driver::tty_operations::open, for the serial port is Uart_open*/

4. Write

Write calls Tty_write, which is parsed as follows:

Tty_write File_tty/*get the corresponding tty_struct by File::tty_file_private::tty_struct*/Do_tty_write/*Call Tty_struct::tty_ldisc::tty_ldisc_ops::write*/N_tty_write/*for line codes of type N_tty, write is N_tty_write*/process_echoes/*handle all pending echoed characters*/__process_echoes/*write the echo character to be processed*/Tty_write_room/*Call Tty_struct::tty_operations::write_room*/echo_buf Tty_put_char/** Call Tty_struct::tty_operations::p Ut_char * or call Tty_struct::tty_operations::write*/Do_output_char/*Call Tty_struct::tty_operations::write*/Tty_struct::tty_operations::flush_chars/*  */process_output_block process_output tty_struct::tty_operations::flush_chars Tty_struct::tty_opera Tions::write

5. Read

Read invokes Tty_read, which is parsed as follows:

tty_read  tty_struct::tty_ldisc::tty_ldisc_ops::read  /**/    N _tty_read      tty_buffer_flush_work        flush_work

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Linux TTY function tracking