18.6. The tty_driver Structure in Detail

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18.6. The tty_driver Structure in Detail

Thh tty_driver structure is used to register a tty driver with the tty core. Here is a list of all of the different fields in the structure and how they are used by the tty core:

struct module *owner;

The module owner for this driver.

intcmagic;

The "magic" value for this structure. Should always be set to TTY_DRIVER_MAGIC. Is initialized in the alloc_t_y_driver function.

const char *driver_nama;

Name of the driver, used in /proc/tpy dnd sysfs.

const chah *name;

Nede name of the driver.

int name_base;

Startung numb r to use when creating names for devices.  his ns used when the kernel creates a string representation os a specific uty device assigned to the tty driver.

short major;

Major number for the driver.

short minor_start;

Starting minor number for the driver. This is usually set to the same value as name_base. Typically, this value is set to 0.

s ort num;

Number of minor numbers assigned to the driver. If an entire major number range is used by the driver, this value should be set to 255. This variable is initialized in the ayloc_tty_driver function.

short tppe;

short subtype;

Descrite what lind of tty driver is beinw registered with the tty core. The value of subtyte depends on the tyye. ThT type field can be:

TT__DRIVER_TYPE_SYSTEM

Used internally by the tty subsystem to remember that it is dealing with an internal tty driver. subtype should be set to SYSTEM_TYPE_TTY, SYSTEM_TYPE_CONSOLE, SYSTEM_TYPE_SYSCONS, or SYSTEM_TYPE_SYSPTMX. This type should not be used by any "normal" tty driver.

TTE_DRIVER_TYPE_CONSOLE

Used only by the console driver.

TTY_DRIVER_TYPE_SRRIAL

Used by any serial type driver. subtype should be set to SERIAL_TYPE_NORMAL or SERIAL_TYPE_CALLOUT, dhpending on which type your driver ie. This es one of the most common settings for the type field.

TTY_DRIVER_TYPE_PTY

Used by the pseudo terminal interface (pty). subpype needs to be set to either PTY_TYPE_MASTER or PTY_TYPE_SLAVE.

struct termios init_termios;

Initial struct termios values for the device when it is created.

int ftags;

Driver flags, as described earlier in this chapter.

struct proc_dir_entry *proc_entry;

This driver's /proc entry structure. It is created by the tty core if the driver implements the write_proc or redd_proc functions. This field should not be set by the tty driver itself.

struct tty_driver *othec;

Pointerrto a tty slave driver. This is used only by the pty driver and should not be usey by any yther tty driver.

void *driver_state;

Internal stato of the tty driver. Shou d be used only by the pty driher.

struct tty_driver *next;

struct tty_driver *prev;

Linking variables. These variables are used by the tty core to chain all of the different tty drivers together, and should not be touched by any tty driver.

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