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linux/drivers/tty/Kconfig
Greg Kroah-Hartman 7c0cca7c84 tty: ldisc: add sysctl to prevent autoloading of ldiscs 
By default, the kernel will automatically load the module of any line
dicipline that is asked for.  As this sometimes isn't the safest thing
to do, provide a sysctl to disable this feature.

By default, we set this to 'y' as that is the historical way that Linux
has worked, and we do not want to break working systems.  But in the
future, perhaps this can default to 'n' to prevent this functionality.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-01-30 09:31:30 +01:00

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config TTY
bool "Enable TTY" if EXPERT
default y
---help---
Allows you to remove TTY support which can save space, and
blocks features that require TTY from inclusion in the kernel.
TTY is required for any text terminals or serial port
communication. Most users should leave this enabled.
if TTY
config VT
bool "Virtual terminal" if EXPERT
depends on !UML
select INPUT
default y
---help---
If you say Y here, you will get support for terminal devices with
display and keyboard devices. These are called "virtual" because you
can run several virtual terminals (also called virtual consoles) on
one physical terminal. This is rather useful, for example one
virtual terminal can collect system messages and warnings, another
one can be used for a text-mode user session, and a third could run
an X session, all in parallel. Switching between virtual terminals
is done with certain key combinations, usually Alt-<function key>.
The setterm command ("man setterm") can be used to change the
properties (such as colors or beeping) of a virtual terminal. The
man page console_codes(4) ("man console_codes") contains the special
character sequences that can be used to change those properties
directly. The fonts used on virtual terminals can be changed with
the setfont ("man setfont") command and the key bindings are defined
with the loadkeys ("man loadkeys") command.
You need at least one virtual terminal device in order to make use
of your keyboard and monitor. Therefore, only people configuring an
embedded system would want to say N here in order to save some
memory; the only way to log into such a system is then via a serial
or network connection.
If unsure, say Y, or else you won't be able to do much with your new
shiny Linux system :-)
config CONSOLE_TRANSLATIONS
depends on VT
default y
bool "Enable character translations in console" if EXPERT
---help---
This enables support for font mapping and Unicode translation
on virtual consoles.
config VT_CONSOLE
bool "Support for console on virtual terminal" if EXPERT
depends on VT
default y
---help---
The system console is the device which receives all kernel messages
and warnings and which allows logins in single user mode. If you
answer Y here, a virtual terminal (the device used to interact with
a physical terminal) can be used as system console. This is the most
common mode of operations, so you should say Y here unless you want
the kernel messages be output only to a serial port (in which case
you should say Y to "Console on serial port", below).
If you do say Y here, by default the currently visible virtual
terminal (/dev/tty0) will be used as system console. You can change
that with a kernel command line option such as "console=tty3" which
would use the third virtual terminal as system console. (Try "man
bootparam" or see the documentation of your boot loader (lilo or
loadlin) about how to pass options to the kernel at boot time.)
If unsure, say Y.
config VT_CONSOLE_SLEEP
def_bool y
depends on VT_CONSOLE && PM_SLEEP
config HW_CONSOLE
bool
depends on VT && !UML
default y
config VT_HW_CONSOLE_BINDING
bool "Support for binding and unbinding console drivers"
depends on HW_CONSOLE
default n
---help---
The virtual terminal is the device that interacts with the physical
terminal through console drivers. On these systems, at least one
console driver is loaded. In other configurations, additional console
drivers may be enabled, such as the framebuffer console. If more than
1 console driver is enabled, setting this to 'y' will allow you to
select the console driver that will serve as the backend for the
virtual terminals.
See <file:Documentation/console/console.txt> for more
information. For framebuffer console users, please refer to
<file:Documentation/fb/fbcon.txt>.
config UNIX98_PTYS
bool "Unix98 PTY support" if EXPERT
default y
---help---
A pseudo terminal (PTY) is a software device consisting of two
halves: a master and a slave. The slave device behaves identical to
a physical terminal; the master device is used by a process to
read data from and write data to the slave, thereby emulating a
terminal. Typical programs for the master side are telnet servers
and xterms.
Linux has traditionally used the BSD-like names /dev/ptyxx for
masters and /dev/ttyxx for slaves of pseudo terminals. This scheme
has a number of problems. The GNU C library glibc 2.1 and later,
however, supports the Unix98 naming standard: in order to acquire a
pseudo terminal, a process opens /dev/ptmx; the number of the pseudo
terminal is then made available to the process and the pseudo
terminal slave can be accessed as /dev/pts/<number>. What was
traditionally /dev/ttyp2 will then be /dev/pts/2, for example.
All modern Linux systems use the Unix98 ptys. Say Y unless
you're on an embedded system and want to conserve memory.
config LEGACY_PTYS
bool "Legacy (BSD) PTY support"
default y
---help---
A pseudo terminal (PTY) is a software device consisting of two
halves: a master and a slave. The slave device behaves identical to
a physical terminal; the master device is used by a process to
read data from and write data to the slave, thereby emulating a
terminal. Typical programs for the master side are telnet servers
and xterms.
Linux has traditionally used the BSD-like names /dev/ptyxx
for masters and /dev/ttyxx for slaves of pseudo
terminals. This scheme has a number of problems, including
security. This option enables these legacy devices; on most
systems, it is safe to say N.
config LEGACY_PTY_COUNT
int "Maximum number of legacy PTY in use"
depends on LEGACY_PTYS
range 0 256
default "256"
---help---
The maximum number of legacy PTYs that can be used at any one time.
The default is 256, and should be more than enough. Embedded
systems may want to reduce this to save memory.
When not in use, each legacy PTY occupies 12 bytes on 32-bit
architectures and 24 bytes on 64-bit architectures.
config SERIAL_NONSTANDARD
bool "Non-standard serial port support"
depends on HAS_IOMEM
---help---
Say Y here if you have any non-standard serial boards -- boards
which aren't supported using the standard "dumb" serial driver.
This includes intelligent serial boards such as Cyclades,
Digiboards, etc. These are usually used for systems that need many
serial ports because they serve many terminals or dial-in
connections.
Note that the answer to this question won't directly affect the
kernel: saying N will just cause the configurator to skip all
the questions about non-standard serial boards.
Most people can say N here.
config ROCKETPORT
tristate "Comtrol RocketPort support"
depends on SERIAL_NONSTANDARD && (ISA || EISA || PCI)
help
This driver supports Comtrol RocketPort and RocketModem PCI boards.
These boards provide 2, 4, 8, 16, or 32 high-speed serial ports or
modems. For information about the RocketPort/RocketModem boards
and this driver read <file:Documentation/serial/rocket.txt>.
To compile this driver as a module, choose M here: the
module will be called rocket.
If you want to compile this driver into the kernel, say Y here. If
you don't have a Comtrol RocketPort/RocketModem card installed, say N.
config CYCLADES
tristate "Cyclades async mux support"
depends on SERIAL_NONSTANDARD && (PCI || ISA)
select FW_LOADER
---help---
This driver supports Cyclades Z and Y multiserial boards.
You would need something like this to connect more than two modems to
your Linux box, for instance in order to become a dial-in server.
For information about the Cyclades-Z card, read
<file:Documentation/serial/README.cycladesZ>.
To compile this driver as a module, choose M here: the
module will be called cyclades.
If you haven't heard about it, it's safe to say N.
config CYZ_INTR
bool "Cyclades-Z interrupt mode operation"
depends on CYCLADES && PCI
help
The Cyclades-Z family of multiport cards allows 2 (two) driver op
modes: polling and interrupt. In polling mode, the driver will check
the status of the Cyclades-Z ports every certain amount of time
(which is called polling cycle and is configurable). In interrupt
mode, it will use an interrupt line (IRQ) in order to check the
status of the Cyclades-Z ports. The default op mode is polling. If
unsure, say N.
config MOXA_INTELLIO
tristate "Moxa Intellio support"
depends on SERIAL_NONSTANDARD && (ISA || EISA || PCI)
select FW_LOADER
help
Say Y here if you have a Moxa Intellio multiport serial card.
To compile this driver as a module, choose M here: the
module will be called moxa.
config MOXA_SMARTIO
tristate "Moxa SmartIO support v. 2.0"
depends on SERIAL_NONSTANDARD && (PCI || EISA || ISA)
help
Say Y here if you have a Moxa SmartIO multiport serial card and/or
want to help develop a new version of this driver.
This is upgraded (1.9.1) driver from original Moxa drivers with
changes finally resulting in PCI probing.
This driver can also be built as a module. The module will be called
mxser. If you want to do that, say M here.
config SYNCLINK
tristate "Microgate SyncLink card support"
depends on SERIAL_NONSTANDARD && PCI && ISA_DMA_API
help
Provides support for the SyncLink ISA and PCI multiprotocol serial
adapters. These adapters support asynchronous and HDLC bit
synchronous communication up to 10Mbps (PCI adapter).
This driver can only be built as a module ( = code which can be
inserted in and removed from the running kernel whenever you want).
The module will be called synclink. If you want to do that, say M
here.
config SYNCLINKMP
tristate "SyncLink Multiport support"
depends on SERIAL_NONSTANDARD && PCI
help
Enable support for the SyncLink Multiport (2 or 4 ports)
serial adapter, running asynchronous and HDLC communications up
to 2.048Mbps. Each ports is independently selectable for
RS-232, V.35, RS-449, RS-530, and X.21
This driver may be built as a module ( = code which can be
inserted in and removed from the running kernel whenever you want).
The module will be called synclinkmp. If you want to do that, say M
here.
config SYNCLINK_GT
tristate "SyncLink GT/AC support"
depends on SERIAL_NONSTANDARD && PCI
help
Support for SyncLink GT and SyncLink AC families of
synchronous and asynchronous serial adapters
manufactured by Microgate Systems, Ltd. (www.microgate.com)
config NOZOMI
tristate "HSDPA Broadband Wireless Data Card - Globe Trotter"
depends on PCI
help
If you have a HSDPA driver Broadband Wireless Data Card -
Globe Trotter PCMCIA card, say Y here.
To compile this driver as a module, choose M here, the module
will be called nozomi.
config ISI
tristate "Multi-Tech multiport card support"
depends on SERIAL_NONSTANDARD && PCI
select FW_LOADER
help
This is a driver for the Multi-Tech cards which provide several
serial ports. The driver is experimental and can currently only be
built as a module. The module will be called isicom.
If you want to do that, choose M here.
config N_HDLC
tristate "HDLC line discipline support"
depends on SERIAL_NONSTANDARD
help
Allows synchronous HDLC communications with tty device drivers that
support synchronous HDLC such as the Microgate SyncLink adapter.
This driver can be built as a module ( = code which can be
inserted in and removed from the running kernel whenever you want).
The module will be called n_hdlc. If you want to do that, say M
here.
config N_GSM
tristate "GSM MUX line discipline support (EXPERIMENTAL)"
depends on NET
help
This line discipline provides support for the GSM MUX protocol and
presents the mux as a set of 61 individual tty devices.
config TRACE_ROUTER
tristate "Trace data router for MIPI P1149.7 cJTAG standard"
depends on TRACE_SINK
default n
help
The trace router uses the Linux tty line discipline framework to
route trace data coming from a tty port (say UART for example) to
the trace sink line discipline driver and to another tty port (say
USB). This is part of a solution for the MIPI P1149.7, compact JTAG,
standard, which is for debugging mobile devices. The PTI driver in
drivers/misc/pti.c defines the majority of this MIPI solution.
You should select this driver if the target kernel is meant for
a mobile device containing a modem. Then you will need to select
"Trace data sink for MIPI P1149.7 cJTAG standard" line discipline
driver.
config TRACE_SINK
tristate "Trace data sink for MIPI P1149.7 cJTAG standard"
default n
help
The trace sink uses the Linux line discipline framework to receive
trace data coming from the trace router line discipline driver
to a user-defined tty port target, like USB.
This is to provide a way to extract modem trace data on
devices that do not have a PTI HW module, or just need modem
trace data to come out of a different HW output port.
This is part of a solution for the P1149.7, compact JTAG, standard.
If you select this option, you need to select
"Trace data router for MIPI P1149.7 cJTAG standard".
config PPC_EPAPR_HV_BYTECHAN
bool "ePAPR hypervisor byte channel driver"
depends on PPC
select EPAPR_PARAVIRT
help
This driver creates /dev entries for each ePAPR hypervisor byte
channel, thereby allowing applications to communicate with byte
channels as if they were serial ports.
config PPC_EARLY_DEBUG_EHV_BC
bool "Early console (udbg) support for ePAPR hypervisors"
depends on PPC_EPAPR_HV_BYTECHAN=y
help
Select this option to enable early console (a.k.a. "udbg") support
via an ePAPR byte channel. You also need to choose the byte channel
handle below.
config PPC_EARLY_DEBUG_EHV_BC_HANDLE
int "Byte channel handle for early console (udbg)"
depends on PPC_EARLY_DEBUG_EHV_BC
default 0
help
If you want early console (udbg) output through a byte channel,
specify the handle of the byte channel to use.
For this to work, the byte channel driver must be compiled
in-kernel, not as a module.
Note that only one early console driver can be enabled, so don't
enable any others if you enable this one.
If the number you specify is not a valid byte channel handle, then
there simply will be no early console output. This is true also
if you don't boot under a hypervisor at all.
config GOLDFISH_TTY
tristate "Goldfish TTY Driver"
depends on GOLDFISH
select SERIAL_CORE
select SERIAL_CORE_CONSOLE
help
Console and system TTY driver for the Goldfish virtual platform.
config GOLDFISH_TTY_EARLY_CONSOLE
bool
default y if GOLDFISH_TTY=y
select SERIAL_EARLYCON
config MIPS_EJTAG_FDC_TTY
bool "MIPS EJTAG Fast Debug Channel TTY"
depends on MIPS_CDMM
help
This enables a TTY and console on the MIPS EJTAG Fast Debug Channels,
if they are present. This can be useful when working with an EJTAG
probe which supports it, to get console output and a login prompt via
EJTAG without needing to connect a serial cable.
TTY devices are named e.g. ttyFDC3c2 (for FDC channel 2 of the FDC on
CPU3).
The console can be enabled with console=fdc1 (for FDC channel 1 on all
CPUs). Do not use the console unless there is a debug probe attached
to drain the FDC TX FIFO.
If unsure, say N.
config MIPS_EJTAG_FDC_EARLYCON
bool "Early FDC console"
depends on MIPS_EJTAG_FDC_TTY
help
This registers a console on FDC channel 1 very early during boot (from
MIPS arch code). This is useful for bring-up and debugging early boot
issues.
Do not enable unless there is a debug probe attached to drain the FDC
TX FIFO.
If unsure, say N.
config MIPS_EJTAG_FDC_KGDB
bool "Use KGDB over an FDC channel"
depends on MIPS_EJTAG_FDC_TTY && KGDB
default y
help
This enables the use of KGDB over an FDC channel, allowing KGDB to be
used remotely or when a serial port isn't available.
config MIPS_EJTAG_FDC_KGDB_CHAN
int "KGDB FDC channel"
depends on MIPS_EJTAG_FDC_KGDB
range 2 15
default 3
help
FDC channel number to use for KGDB.
config VCC
tristate "Sun Virtual Console Concentrator"
depends on SUN_LDOMS
help
Support for Sun logical domain consoles.
config LDISC_AUTOLOAD
bool "Automatically load TTY Line Disciplines"
default y
help
Historically the kernel has always automatically loaded any
line discipline that is in a kernel module when a user asks
for it to be loaded with the TIOCSETD ioctl, or through other
means. This is not always the best thing to do on systems
where you know you will not be using some of the more
"ancient" line disciplines, so prevent the kernel from doing
this unless the request is coming from a process with the
CAP_SYS_MODULE permissions.
Say 'Y' here if you trust your userspace users to do the right
thing, or if you have only provided the line disciplines that
you know you will be using, or if you wish to continue to use
the traditional method of on-demand loading of these modules
by any user.
This functionality can be changed at runtime with the
dev.tty.ldisc_autoload sysctl, this configuration option will
only set the default value of this functionality.
endif # TTY
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