From eedf265aa003b4781de24cfed40a655a664457e6 Mon Sep 17 00:00:00 2001 From: Eric W. Biederman Date: Thu, 2 Jun 2016 10:29:47 -0500 Subject: 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" Cc: Greg KH Cc: Peter Hurley Cc: Peter Anvin Cc: Andy Lutomirski Cc: Al Viro Cc: Serge Hallyn Cc: Willy Tarreau Cc: Aurelien Jarno Cc: One Thousand Gnomes Cc: Jann Horn Cc: Jiri Slaby Cc: Florian Weimer Cc: Konstantin Khlebnikov Signed-off-by: Linus Torvalds --- drivers/tty/Kconfig | 11 ----------- drivers/tty/pty.c | 15 ++++++++------- 2 files changed, 8 insertions(+), 18 deletions(-) (limited to 'drivers') diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig index 82c4d2e45319..95103054c0e4 100644 --- a/drivers/tty/Kconfig +++ b/drivers/tty/Kconfig @@ -120,17 +120,6 @@ config UNIX98_PTYS All modern Linux systems use the Unix98 ptys. Say Y unless you're on an embedded system and want to conserve memory. -config DEVPTS_MULTIPLE_INSTANCES - bool "Support multiple instances of devpts" - depends on UNIX98_PTYS - default n - ---help--- - Enable support for multiple instances of devpts filesystem. - If you want to have isolated PTY namespaces (eg: in containers), - say Y here. Otherwise, say N. If enabled, each mount of devpts - filesystem with the '-o newinstance' option will create an - independent PTY namespace. - config LEGACY_PTYS bool "Legacy (BSD) PTY support" default y diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c index dd4b8417e7f4..f856c4544eea 100644 --- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -668,7 +668,7 @@ static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty) else fsi = tty->link->driver_data; devpts_kill_index(fsi, tty->index); - devpts_put_ref(fsi); + devpts_release(fsi); } static const struct tty_operations ptm_unix98_ops = { @@ -733,10 +733,11 @@ static int ptmx_open(struct inode *inode, struct file *filp) if (retval) return retval; - fsi = devpts_get_ref(inode, filp); - retval = -ENODEV; - if (!fsi) + fsi = devpts_acquire(filp); + if (IS_ERR(fsi)) { + retval = PTR_ERR(fsi); goto out_free_file; + } /* find a device that is not in use. */ mutex_lock(&devpts_mutex); @@ -745,7 +746,7 @@ static int ptmx_open(struct inode *inode, struct file *filp) retval = index; if (index < 0) - goto out_put_ref; + goto out_put_fsi; mutex_lock(&tty_mutex); @@ -789,8 +790,8 @@ err_release: return retval; out: devpts_kill_index(fsi, index); -out_put_ref: - devpts_put_ref(fsi); +out_put_fsi: + devpts_release(fsi); out_free_file: tty_free_file(filp); return retval; -- cgit v1.2.3