linux/drivers/tty
Eric W. Biederman eedf265aa0 devpts: Make each mount of devpts an independent filesystem.
The /dev/ptmx device node is changed to lookup the directory entry "pts"
in the same directory as the /dev/ptmx device node was opened in.  If
there is a "pts" entry and that entry is a devpts filesystem /dev/ptmx
uses that filesystem.  Otherwise the open of /dev/ptmx fails.

The DEVPTS_MULTIPLE_INSTANCES configuration option is removed, so that
userspace can now safely depend on each mount of devpts creating a new
instance of the filesystem.

Each mount of devpts is now a separate and equal filesystem.

Reserved ttys are now available to all instances of devpts where the
mounter is in the initial mount namespace.

A new vfs helper path_pts is introduced that finds a directory entry
named "pts" in the directory of the passed in path, and changes the
passed in path to point to it.  The helper path_pts uses a function
path_parent_directory that was factored out of follow_dotdot.

In the implementation of devpts:
 - devpts_mnt is killed as it is no longer meaningful if all mounts of
   devpts are equal.
 - pts_sb_from_inode is replaced by just inode->i_sb as all cached
   inodes in the tty layer are now from the devpts filesystem.
 - devpts_add_ref is rolled into the new function devpts_ptmx.  And the
   unnecessary inode hold is removed.
 - devpts_del_ref is renamed devpts_release and reduced to just a
   deacrivate_super.
 - The newinstance mount option continues to be accepted but is now
   ignored.

In devpts_fs.h definitions for when !CONFIG_UNIX98_PTYS are removed as
they are never used.

Documentation/filesystems/devices.txt is updated to describe the current
situation.

This has been verified to work properly on openwrt-15.05, centos5,
centos6, centos7, debian-6.0.2, debian-7.9, debian-8.2, ubuntu-14.04.3,
ubuntu-15.10, fedora23, magia-5, mint-17.3, opensuse-42.1,
slackware-14.1, gentoo-20151225 (13.0?), archlinux-2015-12-01.  With the
caveat that on centos6 and on slackware-14.1 that there wind up being
two instances of the devpts filesystem mounted on /dev/pts, the lower
copy does not end up getting used.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Greg KH <greg@kroah.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Peter Anvin <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Serge Hallyn <serge.hallyn@ubuntu.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Cc: Jann Horn <jann@thejh.net>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Florian Weimer <fw@deneb.enyo.de>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-06-05 10:36:01 -07:00
..
hvc tty: hvc_console: silence unintialized variable warning 2016-04-30 09:26:55 -07:00
ipwireless tty: ipwireless: fix possible NULL dereference 2016-04-30 09:26:55 -07:00
serial remove lots of IS_ERR_VALUE abuses 2016-05-27 15:26:11 -07:00
vt tty: vt, finish looping on duplicate 2016-05-03 15:59:15 -07:00
Kconfig devpts: Make each mount of devpts an independent filesystem. 2016-06-05 10:36:01 -07:00
Makefile TTY: Add MIPS EJTAG Fast Debug Channel TTY driver 2015-03-31 12:04:12 +02:00
amiserial.c tty: Replace ASYNC_INITIALIZED bit and update atomically 2016-04-30 09:26:55 -07:00
bfin_jtag_comm.c TTY: bfin_jtag_comm: remove incorrect wait_until_sent operation 2015-03-07 03:44:14 +01:00
cyclades.c tty: Replace ASYNC_INITIALIZED bit and update atomically 2016-04-30 09:26:55 -07:00
ehv_bytechan.c drivers/tty: make ehv_bytechan.c explicitly non-modular 2016-02-06 23:26:43 -08:00
goldfish.c tty: goldfish: support platform_device with id -1 2016-03-07 16:11:14 -08:00
isicom.c tty: Replace ASYNC_INITIALIZED bit and update atomically 2016-04-30 09:26:55 -07:00
metag_da.c tty/metag_da: Avoid module_init/module_exit in non-modular code 2015-06-16 14:12:31 -04:00
mips_ejtag_fdc.c ttyFDC: Fix build problems due to use of module_{init,exit} 2015-10-17 21:29:21 -07:00
moxa.c tty: Replace ASYNC_INITIALIZED bit and update atomically 2016-04-30 09:26:55 -07:00
moxa.h
mxser.c tty: mxser: Remove unused ASYNC_SHARE_IRQ flag 2016-04-30 09:26:55 -07:00
mxser.h
n_gsm.c TTY and Serial driver update for 4.7-rc1 2016-05-20 20:57:27 -07:00
n_hdlc.c Fix OpenSSH pty regression on close 2016-05-01 13:22:54 -07:00
n_r3964.c tty: r3964: Replace/remove bogus tty lock use 2015-10-17 21:11:29 -07:00
n_tracerouter.c n_tracerouter: stop including <asm-generic/bug> 2015-10-15 00:21:10 +02:00
n_tracesink.c n_tracesink: stop including <asm-generic/bug> 2015-10-15 00:21:11 +02:00
n_tracesink.h
n_tty.c Fix OpenSSH pty regression on close 2016-05-01 13:22:54 -07:00
nozomi.c tty: Replace TTY_THROTTLED bit tests with tty_throttled() 2016-04-30 09:26:55 -07:00
pty.c devpts: Make each mount of devpts an independent filesystem. 2016-06-05 10:36:01 -07:00
rocket.c TTY: add __init attribute 2016-04-30 09:26:55 -07:00
rocket.h tty: rocket: fix comment of ROCKET_SPD_HI 2015-05-24 12:49:16 -07:00
rocket_int.h tty: rocket: Remove private close_wait 2016-01-28 14:13:44 -08:00
synclink.c TTY and Serial driver update for 4.7-rc1 2016-05-20 20:57:27 -07:00
synclink_gt.c TTY and Serial driver update for 4.7-rc1 2016-05-20 20:57:27 -07:00
synclinkmp.c TTY and Serial driver update for 4.7-rc1 2016-05-20 20:57:27 -07:00
sysrq.c sysrq: Fix warning in sysrq generated crash. 2015-12-29 16:29:18 -08:00
tty_audit.c tty: audit: remove unused variable 2016-03-07 16:11:14 -08:00
tty_buffer.c Fix OpenSSH pty regression on close 2016-05-01 13:22:54 -07:00
tty_io.c Merge 4.6-rc7 into tty-next 2016-05-09 09:39:13 +02:00
tty_ioctl.c tty: Replace TTY_THROTTLED bit tests with tty_throttled() 2016-04-30 09:26:55 -07:00
tty_ldisc.c tty: Eliminate global symbol tty_ldisc_N_TTY 2016-01-27 15:13:28 -08:00
tty_ldsem.c tty: Deinline __ldsem_down_write_nested, save 128 bytes 2015-12-13 19:59:48 -08:00
tty_mutex.c Merge 4.5-rc4 into tty-next 2016-02-14 14:36:04 -08:00
tty_port.c tty: Replace ASYNC_INITIALIZED bit and update atomically 2016-04-30 09:26:55 -07:00