From mboxrd@z Thu Jan 1 00:00:00 1970 From: sukadev-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org Subject: Re: [PATCH 09/10] Enable multiple instances of devpts Date: Mon, 29 Sep 2008 08:18:28 -0700 Message-ID: <20080929151828.GA10202@us.ibm.com> References: <20080912174845.GA17350@us.ibm.com> <20080912175322.GJ17350@us.ibm.com> <20080924202616.GB31664@us.ibm.com> <20080926210347.GB31505@us.ibm.com> <20080929130131.GA12531@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20080929130131.GA12531-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: "Serge E. Hallyn" Cc: kyle-hoO6YkzgTuCM0SS3m2neIg@public.gmane.org, bastian-yyjItF7Rl6lg9hUCZPvPmw@public.gmane.org, ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org, hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org, containers-qjLDD68F18O7TbgM5vRIOg@public.gmane.org, xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, alan-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org List-Id: containers.vger.kernel.org Serge E. Hallyn [serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org] wrote: | Quoting sukadev-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org (sukadev-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org): | > | > @@ -232,6 +246,8 @@ static int devpts_show_options(struct seq_file *seq, struct vfsmount *vfs) | > | > seq_printf(seq, ",mode=%03o", opts->mode); | > | > #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES | > | > seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode); | > | > + if (opts->newinstance) | > | > + seq_printf(seq, ",newinstance"); | > | | > | Is actually that something we want to show? It doesn't seem | > | informative. | > | > Without this users have no easy way of knowing whether they have a | > private mount specially if they mounted from command line ? You mean in a nested container ? I agree that it does not help then. | | If they were in a container to begin with, then they still don't know. | | Now if you were to keep a unique per-instance id and have show_options | list 'instance=%x', that would be helpful. Either that or just | dropping the info altogether make sense. This 'newinstance' listing | is meaningless. | Another way to look at it is that it is a mount option that was specified and we just report it. It may not be useful always but might help in some cases. But I am fine either way. | > | > + | > | > + err = mknod_ptmx(mnt->mnt_sb); | > | > + if (err) { | > | > + dput(mnt->mnt_sb->s_root); | > | > + deactivate_super(mnt->mnt_sb); | > | > + } else | > | > + devpts_mnt = mnt; | > | > + | > | > + return err; | > | | > | There is no locking here, so in early-userspace two competing processes | > | could both try to set devpts_mnt, right? | > | > Hmm. I was thinking there would be only one thread calling the | > vfs_kern_mount() in init_devpts_fs. | | But what if init happens to (perhaps mistakenly) lead to 2 racing ones? | | Sure it's just a small memory leak, but why not just prevent it. Ok. | | > | | > | > + } | > | > + | > | > + return get_sb_ref(devpts_mnt->mnt_sb, flags, data, mnt); | > | > +} | > | > + | > | > static int devpts_get_sb(struct file_system_type *fs_type, | > | > int flags, const char *dev_name, void *data, struct vfsmount *mnt) | > | > { | > | > + int new; | > | > + | > | > + new = is_new_instance_mount(data); | > | > + if (new < 0) | > | > + return new; | > | > + | > | > + if (new) | > | > + return new_pts_mount(fs_type, flags, data, mnt); | > | > + | > | > + return init_pts_mount(fs_type, flags, data, mnt); | > | | > | Wait a sec - so if a container does | > | | > | mount -t devpts -o newinstance none /dev/pts | > | and then later on just does | > | mount -t devpts none /dev/pts | > | | > | it'll get the init_pts_ns, not the one it had created? | > | > Yes. Should we treat the latter as remount of the private instance ? | > If so, user could add '-oremount' ? | > | > The logic seems simple: With newinstance create a private namespace. | > Without newinstance, bind to initial ns. | | But if I'm in a container in a new mounts ns and somehow managed | to umount -l /dev/pts, shouldn't i be able to remount my container's | devpts by just doing 'mount -t devpts devpts /dev/pts'? Now wouldn't that require us to associate the devpts mount with some notion of a container ? (a namespace object in nsproxy of container-init like we do with /proc). Yes, after 'umount -l' we have lost _that_ devpts ns and we may have to 'redo' the relevant container-init parts