Commit 01478b83 authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab Committed by Jonathan Corbet
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docs: filesystems: convert devpts.txt to ReST 



- Add a SPDX header;
- Add a document title;
- Some whitespace fixes and new line breaks;
- Mark literal blocks as such;
- Add it to filesystems/index.rst.

Signed-off-by: default avatarMauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/4ac8f3a7edd4d817acf0d173ead7ef74fe010c6c.1588021877.git.mchehab+huawei@kernel.org


Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent f476c6ed

Documentation/admin-guide/sysctl/kernel.rst

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pty

===



See Documentation/filesystems/devpts.txt.

See Documentation/filesystems/devpts.rst.





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Documentation/filesystems/devpts.rst

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.. SPDX-License-Identifier: GPL-2.0



=====================

The Devpts Filesystem

=====================



Each mount of the devpts filesystem is now distinct such that ptys

and their indicies allocated in one mount are independent from ptys

and their indicies in all other mounts.



All mounts of the devpts filesystem now create a ``/dev/pts/ptmx`` node

with permissions ``0000``.



To retain backwards compatibility the a ptmx device node (aka any node

created with ``mknod name c 5 2``) when opened will look for an instance

of devpts under the name ``pts`` in the same directory as the ptmx device

node.



As an option instead of placing a ``/dev/ptmx`` device node at ``/dev/ptmx``

it is possible to place a symlink to ``/dev/pts/ptmx`` at ``/dev/ptmx`` or

to bind mount ``/dev/ptx/ptmx`` to ``/dev/ptmx``.  If you opt for using

the devpts filesystem in this manner devpts should be mounted with

the ``ptmxmode=0666``, or ``chmod 0666 /dev/pts/ptmx`` should be called.



Total count of pty pairs in all instances is limited by sysctls::



    kernel.pty.max = 4096	- global limit

    kernel.pty.reserve = 1024	- reserved for filesystems mounted from the initial mount namespace

    kernel.pty.nr		- current count of ptys



Per-instance limit could be set by adding mount option ``max=<count>``.



This feature was added in kernel 3.4 together with

``sysctl kernel.pty.reserve``.



In kernels older than 3.4 sysctl ``kernel.pty.max`` works as per-instance limit.

Documentation/filesystems/devpts.txt

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Each mount of the devpts filesystem is now distinct such that ptys

and their indicies allocated in one mount are independent from ptys

and their indicies in all other mounts.



All mounts of the devpts filesystem now create a /dev/pts/ptmx node

with permissions 0000.



To retain backwards compatibility the a ptmx device node (aka any node

created with "mknod name c 5 2") when opened will look for an instance

of devpts under the name "pts" in the same directory as the ptmx device

node.



As an option instead of placing a /dev/ptmx device node at /dev/ptmx

it is possible to place a symlink to /dev/pts/ptmx at /dev/ptmx or

to bind mount /dev/ptx/ptmx to /dev/ptmx.  If you opt for using

the devpts filesystem in this manner devpts should be mounted with

the ptmxmode=0666, or chmod 0666 /dev/pts/ptmx should be called.



Total count of pty pairs in all instances is limited by sysctls:

kernel.pty.max = 4096		- global limit

kernel.pty.reserve = 1024	- reserved for filesystems mounted from the initial mount namespace

kernel.pty.nr			- current count of ptys



Per-instance limit could be set by adding mount option "max=<count>".

This feature was added in kernel 3.4 together with sysctl kernel.pty.reserve.

In kernels older than 3.4 sysctl kernel.pty.max works as per-instance limit.

Documentation/filesystems/index.rst

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   splice

   locking

   directory-locking

   devpts



   automount-support