• Eric W. Biederman's avatar
    devpts: Make each mount of devpts an independent filesystem. · eedf265a
    Eric W. Biederman authored
    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: 's avatar"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: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
    eedf265a
devpts_fs.h 1.02 KB