Commit eedf265a authored by Committed by Linus Torvalds
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" <firstname.lastname@example.org> Cc: Greg KH <email@example.com> Cc: Peter Hurley <firstname.lastname@example.org> Cc: Peter Anvin <email@example.com> Cc: Andy Lutomirski <firstname.lastname@example.org> Cc: Al Viro <email@example.com> Cc: Serge Hallyn <firstname.lastname@example.org> Cc: Willy Tarreau <email@example.com> Cc: Aurelien Jarno <firstname.lastname@example.org> Cc: One Thousand Gnomes <email@example.com> Cc: Jann Horn <firstname.lastname@example.org> Cc: Jiri Slaby <email@example.com> Cc: Florian Weimer <firstname.lastname@example.org> Cc: Konstantin Khlebnikov <email@example.com> Signed-off-by: Linus Torvalds <firstname.lastname@example.org>
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