Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/Documentation/filesystems/devpts.txt b/Documentation/filesystems/devpts.txt
new file mode 100644
index 000000000..9f94fe276
--- /dev/null
+++ b/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.