mount: document newinstance and ptmxmode options to devpts

Support for multiple instances of devpts were included in 2.6.29-rc1.
Update man pages to document the new options. Additional details about
the new options are described in 'Documentation/filesystems/devpts.txt'
of kernel source tree.

Reviewed-by: WANG Cong <wangcong@zeuux.org>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/mount/mount.8 b/mount/mount.8
index 956e10fadaffe2287a62c5a1ce8852c6180b3714..e3eb8104132180513b4c5c28fcc0c94d39ab7180 100644 (file)
--- a/mount/mount.8
+++ b/mount/mount.8
@@ -991,6 +991,61 @@ A value of
 and 
 .B gid=5
 makes "mesg y" the default on newly created PTYs.
+.TP
+\fBnewinstance
+Create a private instance of devpts filesystem, such that
+indices of ptys allocated in this new instance are
+independent of indices created in other instances of devpts.
+
+All mounts of devpts without this
+.B newinstance
+option share the same set of pty indices (i.e legacy mode).
+Each mount of devpts with the
+.B newinstance
+option has a private set of pty indices.
+
+This option is mainly used to support containers in the
+linux kernel. It is implemented in linux kernel versions
+starting with 2.6.29.  Further, this mount option is valid
+only if CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the
+kernel configuration.
+
+To use this option effectively,
+.IR /dev/ptmx
+must be a symbolic link to
+.IR pts/ptmx.
+See
+.IR Documentation/filesystems/devpts.txt
+in the linux kernel source tree for details.
+.TP
+.BI ptmxmode= value
+
+Set the mode for the new
+.IR ptmx
+device node in the devpts filesystem.
+
+With the support for multiple instances of devpts (see
+.B newinstance
+option above), each instance has a private
+.IR ptmx
+node in the root of the devpts filesystem (typically
+.IR /dev/pts/ptmx).
+
+For compatibility with older versions of the kernel, the
+default mode of the new
+.IR ptmx
+node is 0000.
+.BI ptmxmode= value
+specifies a more useful mode for the
+.IR ptmx
+node and is highly recommended when the
+.B newinstance
+option is specified.
+
+This option is only implemented in linux kernel versions
+starting with 2.6.29. Further this option is valid only if
+CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel
+configuration.
 
 .SH "Mount options for ext"
 None.