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a91bd6223e
This reverts commit757055ae8d. The commit caused that ttynull was used as the default console on several systems[1][2][3]. As a result, the console was blank even when a better alternative existed. It happened when there was no console configured on the command line and ttynull_init() was the first initcall calling register_console(). Or it happened when /dev/ did not exist when console_on_rootfs() was called. It was not able to open /dev/console even though a console driver was registered. It tried to add ttynull console but it obviously did not help. But ttynull became the preferred console and was used by /dev/console when it was available later. The commit tried to fix a historical problem that have been there for ages. The primary motivation was the commit3cffa06aee("printk/console: Allow to disable console output by using console="" or console=null"). It provided a clean solution for a workaround that was widely used and worked only by chance. This revert causes that the console="" or console=null command line options will again work only by chance. These options will cause that a particular console will be preferred and the default (tty) ones will not get enabled. There will be no console registered at all. As a result there won't be stdin, stdout, and stderr for the init process. But it worked exactly this way even before. The proper solution has to fulfill many conditions: + Register ttynull only when explicitly required or as the ultimate fallback. + ttynull should get associated with /dev/console but it must not become preferred console when used as a fallback. Especially, it must still be possible to replace it by a better console later. Such a change requires clean up of the register_console() code. Otherwise, it would be even harder to follow. Especially, the use of has_preferred_console and CON_CONSDEV flag is tricky. The clean up is risky. The ordering of consoles is not well defined. And any changes tend to break existing user settings. Do the revert at the least risky solution for now. [1] https://lore.kernel.org/linux-kselftest/20201221144302.GR4077@smile.fi.intel.com/ [2] https://lore.kernel.org/lkml/d2a3b3c0-e548-7dd1-730f-59bc5c04e191@synopsys.com/ [3] https://patchwork.ozlabs.org/project/linux-um/patch/20210105120128.10854-1-thomas@m3y3r.de/ Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Reported-by: Vineet Gupta <vgupta@synopsys.com> Reported-by: Thomas Meyer <thomas@m3y3r.de> Signed-off-by: Petr Mladek <pmladek@suse.com> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
459 lines
16 KiB
Plaintext
459 lines
16 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0
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config TTY
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bool "Enable TTY" if EXPERT
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default y
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help
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Allows you to remove TTY support which can save space, and
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blocks features that require TTY from inclusion in the kernel.
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TTY is required for any text terminals or serial port
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communication. Most users should leave this enabled.
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if TTY
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config VT
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bool "Virtual terminal" if EXPERT
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depends on !UML
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select INPUT
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default y
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help
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If you say Y here, you will get support for terminal devices with
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display and keyboard devices. These are called "virtual" because you
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can run several virtual terminals (also called virtual consoles) on
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one physical terminal. This is rather useful, for example one
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virtual terminal can collect system messages and warnings, another
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one can be used for a text-mode user session, and a third could run
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an X session, all in parallel. Switching between virtual terminals
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is done with certain key combinations, usually Alt-<function key>.
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The setterm command ("man setterm") can be used to change the
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properties (such as colors or beeping) of a virtual terminal. The
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man page console_codes(4) ("man console_codes") contains the special
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character sequences that can be used to change those properties
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directly. The fonts used on virtual terminals can be changed with
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the setfont ("man setfont") command and the key bindings are defined
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with the loadkeys ("man loadkeys") command.
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You need at least one virtual terminal device in order to make use
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of your keyboard and monitor. Therefore, only people configuring an
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embedded system would want to say N here in order to save some
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memory; the only way to log into such a system is then via a serial
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or network connection.
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If unsure, say Y, or else you won't be able to do much with your new
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shiny Linux system :-)
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config CONSOLE_TRANSLATIONS
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depends on VT
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default y
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bool "Enable character translations in console" if EXPERT
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help
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This enables support for font mapping and Unicode translation
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on virtual consoles.
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config VT_CONSOLE
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bool "Support for console on virtual terminal" if EXPERT
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depends on VT
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default y
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help
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The system console is the device which receives all kernel messages
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and warnings and which allows logins in single user mode. If you
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answer Y here, a virtual terminal (the device used to interact with
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a physical terminal) can be used as system console. This is the most
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common mode of operations, so you should say Y here unless you want
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the kernel messages be output only to a serial port (in which case
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you should say Y to "Console on serial port", below).
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If you do say Y here, by default the currently visible virtual
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terminal (/dev/tty0) will be used as system console. You can change
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that with a kernel command line option such as "console=tty3" which
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would use the third virtual terminal as system console. (Try "man
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bootparam" or see the documentation of your boot loader (lilo or
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loadlin) about how to pass options to the kernel at boot time.)
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If unsure, say Y.
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config VT_CONSOLE_SLEEP
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def_bool y
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depends on VT_CONSOLE && PM_SLEEP
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config HW_CONSOLE
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bool
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depends on VT && !UML
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default y
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config VT_HW_CONSOLE_BINDING
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bool "Support for binding and unbinding console drivers"
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depends on HW_CONSOLE
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help
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The virtual terminal is the device that interacts with the physical
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terminal through console drivers. On these systems, at least one
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console driver is loaded. In other configurations, additional console
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drivers may be enabled, such as the framebuffer console. If more than
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1 console driver is enabled, setting this to 'y' will allow you to
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select the console driver that will serve as the backend for the
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virtual terminals.
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See <file:Documentation/driver-api/console.rst> for more
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information. For framebuffer console users, please refer to
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<file:Documentation/fb/fbcon.rst>.
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config UNIX98_PTYS
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bool "Unix98 PTY support" if EXPERT
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default y
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help
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A pseudo terminal (PTY) is a software device consisting of two
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halves: a master and a slave. The slave device behaves identical to
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a physical terminal; the master device is used by a process to
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read data from and write data to the slave, thereby emulating a
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terminal. Typical programs for the master side are telnet servers
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and xterms.
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Linux has traditionally used the BSD-like names /dev/ptyxx for
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masters and /dev/ttyxx for slaves of pseudo terminals. This scheme
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has a number of problems. The GNU C library glibc 2.1 and later,
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however, supports the Unix98 naming standard: in order to acquire a
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pseudo terminal, a process opens /dev/ptmx; the number of the pseudo
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terminal is then made available to the process and the pseudo
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terminal slave can be accessed as /dev/pts/<number>. What was
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traditionally /dev/ttyp2 will then be /dev/pts/2, for example.
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All modern Linux systems use the Unix98 ptys. Say Y unless
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you're on an embedded system and want to conserve memory.
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config LEGACY_PTYS
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bool "Legacy (BSD) PTY support"
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default y
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help
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A pseudo terminal (PTY) is a software device consisting of two
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halves: a master and a slave. The slave device behaves identical to
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a physical terminal; the master device is used by a process to
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read data from and write data to the slave, thereby emulating a
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terminal. Typical programs for the master side are telnet servers
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and xterms.
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Linux has traditionally used the BSD-like names /dev/ptyxx
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for masters and /dev/ttyxx for slaves of pseudo
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terminals. This scheme has a number of problems, including
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security. This option enables these legacy devices; on most
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systems, it is safe to say N.
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config LEGACY_PTY_COUNT
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int "Maximum number of legacy PTY in use"
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depends on LEGACY_PTYS
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range 0 256
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default "256"
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help
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The maximum number of legacy PTYs that can be used at any one time.
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The default is 256, and should be more than enough. Embedded
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systems may want to reduce this to save memory.
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When not in use, each legacy PTY occupies 12 bytes on 32-bit
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architectures and 24 bytes on 64-bit architectures.
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config LDISC_AUTOLOAD
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bool "Automatically load TTY Line Disciplines"
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default y
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help
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Historically the kernel has always automatically loaded any
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line discipline that is in a kernel module when a user asks
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for it to be loaded with the TIOCSETD ioctl, or through other
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means. This is not always the best thing to do on systems
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where you know you will not be using some of the more
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"ancient" line disciplines, so prevent the kernel from doing
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this unless the request is coming from a process with the
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CAP_SYS_MODULE permissions.
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Say 'Y' here if you trust your userspace users to do the right
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thing, or if you have only provided the line disciplines that
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you know you will be using, or if you wish to continue to use
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the traditional method of on-demand loading of these modules
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by any user.
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This functionality can be changed at runtime with the
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dev.tty.ldisc_autoload sysctl, this configuration option will
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only set the default value of this functionality.
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source "drivers/tty/serial/Kconfig"
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config SERIAL_NONSTANDARD
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bool "Non-standard serial port support"
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depends on HAS_IOMEM
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help
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Say Y here if you have any non-standard serial boards -- boards
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which aren't supported using the standard "dumb" serial driver.
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This includes intelligent serial boards such as Cyclades,
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Digiboards, etc. These are usually used for systems that need many
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serial ports because they serve many terminals or dial-in
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connections.
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Note that the answer to this question won't directly affect the
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kernel: saying N will just cause the configurator to skip all
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the questions about non-standard serial boards.
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Most people can say N here.
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config ROCKETPORT
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tristate "Comtrol RocketPort support"
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depends on SERIAL_NONSTANDARD && (ISA || EISA || PCI)
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help
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This driver supports Comtrol RocketPort and RocketModem PCI boards.
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These boards provide 2, 4, 8, 16, or 32 high-speed serial ports or
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modems. For information about the RocketPort/RocketModem boards
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and this driver read <file:Documentation/driver-api/serial/rocket.rst>.
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To compile this driver as a module, choose M here: the
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module will be called rocket.
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If you want to compile this driver into the kernel, say Y here. If
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you don't have a Comtrol RocketPort/RocketModem card installed, say N.
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config CYCLADES
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tristate "Cyclades async mux support"
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depends on SERIAL_NONSTANDARD && (PCI || ISA)
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select FW_LOADER
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help
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This driver supports Cyclades Z and Y multiserial boards.
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You would need something like this to connect more than two modems to
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your Linux box, for instance in order to become a dial-in server.
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For information about the Cyclades-Z card, read
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<file:Documentation/driver-api/serial/cyclades_z.rst>.
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To compile this driver as a module, choose M here: the
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module will be called cyclades.
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If you haven't heard about it, it's safe to say N.
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config CYZ_INTR
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bool "Cyclades-Z interrupt mode operation"
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depends on CYCLADES && PCI
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help
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The Cyclades-Z family of multiport cards allows 2 (two) driver op
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modes: polling and interrupt. In polling mode, the driver will check
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the status of the Cyclades-Z ports every certain amount of time
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(which is called polling cycle and is configurable). In interrupt
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mode, it will use an interrupt line (IRQ) in order to check the
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status of the Cyclades-Z ports. The default op mode is polling. If
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unsure, say N.
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config MOXA_INTELLIO
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tristate "Moxa Intellio support"
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depends on SERIAL_NONSTANDARD && (ISA || EISA || PCI)
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select FW_LOADER
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help
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Say Y here if you have a Moxa Intellio multiport serial card.
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To compile this driver as a module, choose M here: the
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module will be called moxa.
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config MOXA_SMARTIO
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tristate "Moxa SmartIO support v. 2.0"
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depends on SERIAL_NONSTANDARD && (PCI || EISA || ISA)
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help
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Say Y here if you have a Moxa SmartIO multiport serial card and/or
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want to help develop a new version of this driver.
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This is upgraded (1.9.1) driver from original Moxa drivers with
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changes finally resulting in PCI probing.
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This driver can also be built as a module. The module will be called
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mxser. If you want to do that, say M here.
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config SYNCLINK_GT
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tristate "SyncLink GT/AC support"
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depends on SERIAL_NONSTANDARD && PCI
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help
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Support for SyncLink GT and SyncLink AC families of
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synchronous and asynchronous serial adapters
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manufactured by Microgate Systems, Ltd. (www.microgate.com)
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config ISI
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tristate "Multi-Tech multiport card support"
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depends on SERIAL_NONSTANDARD && PCI
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select FW_LOADER
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help
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This is a driver for the Multi-Tech cards which provide several
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serial ports. The driver is experimental and can currently only be
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built as a module. The module will be called isicom.
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If you want to do that, choose M here.
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config N_HDLC
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tristate "HDLC line discipline support"
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depends on SERIAL_NONSTANDARD
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help
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Allows synchronous HDLC communications with tty device drivers that
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support synchronous HDLC such as the Microgate SyncLink adapter.
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This driver can be built as a module ( = code which can be
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inserted in and removed from the running kernel whenever you want).
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The module will be called n_hdlc. If you want to do that, say M
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here.
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config PPC_EPAPR_HV_BYTECHAN
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bool "ePAPR hypervisor byte channel driver"
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depends on PPC
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select EPAPR_PARAVIRT
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help
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This driver creates /dev entries for each ePAPR hypervisor byte
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channel, thereby allowing applications to communicate with byte
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channels as if they were serial ports.
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config PPC_EARLY_DEBUG_EHV_BC
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bool "Early console (udbg) support for ePAPR hypervisors"
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depends on PPC_EPAPR_HV_BYTECHAN=y
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help
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Select this option to enable early console (a.k.a. "udbg") support
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via an ePAPR byte channel. You also need to choose the byte channel
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handle below.
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config PPC_EARLY_DEBUG_EHV_BC_HANDLE
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int "Byte channel handle for early console (udbg)"
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depends on PPC_EARLY_DEBUG_EHV_BC
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default 0
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help
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If you want early console (udbg) output through a byte channel,
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specify the handle of the byte channel to use.
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For this to work, the byte channel driver must be compiled
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in-kernel, not as a module.
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Note that only one early console driver can be enabled, so don't
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enable any others if you enable this one.
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If the number you specify is not a valid byte channel handle, then
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there simply will be no early console output. This is true also
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if you don't boot under a hypervisor at all.
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config GOLDFISH_TTY
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tristate "Goldfish TTY Driver"
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depends on GOLDFISH
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select SERIAL_CORE
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select SERIAL_CORE_CONSOLE
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help
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Console and system TTY driver for the Goldfish virtual platform.
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config GOLDFISH_TTY_EARLY_CONSOLE
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bool
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default y if GOLDFISH_TTY=y
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select SERIAL_EARLYCON
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config N_GSM
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tristate "GSM MUX line discipline support (EXPERIMENTAL)"
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depends on NET
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help
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This line discipline provides support for the GSM MUX protocol and
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presents the mux as a set of 61 individual tty devices.
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config NOZOMI
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tristate "HSDPA Broadband Wireless Data Card - Globe Trotter"
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depends on PCI
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help
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If you have a HSDPA driver Broadband Wireless Data Card -
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Globe Trotter PCMCIA card, say Y here.
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To compile this driver as a module, choose M here, the module
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will be called nozomi.
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config MIPS_EJTAG_FDC_TTY
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bool "MIPS EJTAG Fast Debug Channel TTY"
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depends on MIPS_CDMM
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help
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This enables a TTY and console on the MIPS EJTAG Fast Debug Channels,
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if they are present. This can be useful when working with an EJTAG
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probe which supports it, to get console output and a login prompt via
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EJTAG without needing to connect a serial cable.
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TTY devices are named e.g. ttyFDC3c2 (for FDC channel 2 of the FDC on
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CPU3).
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The console can be enabled with console=fdc1 (for FDC channel 1 on all
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CPUs). Do not use the console unless there is a debug probe attached
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to drain the FDC TX FIFO.
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If unsure, say N.
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config MIPS_EJTAG_FDC_EARLYCON
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bool "Early FDC console"
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depends on MIPS_EJTAG_FDC_TTY
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help
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This registers a console on FDC channel 1 very early during boot (from
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MIPS arch code). This is useful for bring-up and debugging early boot
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issues.
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Do not enable unless there is a debug probe attached to drain the FDC
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TX FIFO.
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If unsure, say N.
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config MIPS_EJTAG_FDC_KGDB
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bool "Use KGDB over an FDC channel"
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depends on MIPS_EJTAG_FDC_TTY && KGDB
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default y
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help
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This enables the use of KGDB over an FDC channel, allowing KGDB to be
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used remotely or when a serial port isn't available.
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config MIPS_EJTAG_FDC_KGDB_CHAN
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int "KGDB FDC channel"
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depends on MIPS_EJTAG_FDC_KGDB
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range 2 15
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default 3
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help
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FDC channel number to use for KGDB.
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config NULL_TTY
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tristate "NULL TTY driver"
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help
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Say Y here if you want a NULL TTY which simply discards messages.
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This is useful to allow userspace applications which expect a console
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device to work without modifications even when no console is
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available or desired.
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In order to use this driver, you should redirect the console to this
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TTY, or boot the kernel with console=ttynull.
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If unsure, say N.
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config TRACE_ROUTER
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tristate "Trace data router for MIPI P1149.7 cJTAG standard"
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depends on TRACE_SINK
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help
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The trace router uses the Linux tty line discipline framework to
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route trace data coming from a tty port (say UART for example) to
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the trace sink line discipline driver and to another tty port (say
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USB). This is part of a solution for the MIPI P1149.7, compact JTAG,
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standard, which is for debugging mobile devices. The PTI driver in
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drivers/misc/pti.c defines the majority of this MIPI solution.
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You should select this driver if the target kernel is meant for
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a mobile device containing a modem. Then you will need to select
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"Trace data sink for MIPI P1149.7 cJTAG standard" line discipline
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driver.
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config TRACE_SINK
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tristate "Trace data sink for MIPI P1149.7 cJTAG standard"
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help
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The trace sink uses the Linux line discipline framework to receive
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trace data coming from the trace router line discipline driver
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to a user-defined tty port target, like USB.
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This is to provide a way to extract modem trace data on
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devices that do not have a PTI HW module, or just need modem
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trace data to come out of a different HW output port.
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This is part of a solution for the P1149.7, compact JTAG, standard.
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If you select this option, you need to select
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"Trace data router for MIPI P1149.7 cJTAG standard".
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config VCC
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tristate "Sun Virtual Console Concentrator"
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depends on SUN_LDOMS
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help
|
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Support for Sun logical domain consoles.
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source "drivers/tty/hvc/Kconfig"
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endif # TTY
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source "drivers/tty/serdev/Kconfig"
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