Quoting sukadev@xxxxxxxxxxxxxxxxxx (sukadev@xxxxxxxxxxxxxxxxxx): > Thanks for detailed review Serge. > > Sorry was unexpectedly off most of this week. Have some responses below > will review/address other comments over the next few days. > > > Serge E. Hallyn [serue@xxxxxxxxxx] wrote: > | Quoting sukadev@xxxxxxxxxx (sukadev@xxxxxxxxxx): > | > > | > >From 4567a37856205a04cc0617e3fcc8ede36b25bcf5 Mon Sep 17 00:00:00 2001 > | > From: Sukadev Bhattiprolu <sukadev@xxxxxxxxxx> > | > Date: Tue, 9 Sep 2008 18:52:56 -0700 > | > Subject: [PATCH 09/10] Enable multiple instances of devpts > | > > | > To support containers, allow multiple instances of devpts filesystem, such > | > that indices of ptys allocated in one instance are independent of ptys > | > allocated in other instances of devpts. > | > > | > But to preserve backward compatibility, enable this support for multiple > | > instances only if: > | > > | > - CONFIG_DEVPTS_MULTIPLE_INSTANCES is set to Y, and > | > - '-o newinstance' mount option is specified while mounting devpts > | > > | > See Documentation/fs/devpts.txt (next patch in series) for details. > | > > | > To use multi-instance mount, a container startup script could: > | > > | > $ ns_exec -cm /bin/bash > | > $ umount /dev/pts > | > $ mount -t devpts -o newinstance lxcpts /dev/pts > | > $ mount -o bind /dev/pts/ptmx /dev/ptmx > | > $ sshd -p 1234 > | > > | > where 'ns_exec -cm /bin/bash' is calls clone() with CLONE_NEWNS flag and execs > | > /bin/bash in the child process. A pty created by the sshd is not visible in > | > the original mount of /dev/pts. > | > > | > USER-SPACE-IMPACT: > | > > | > See Documentation/fs/devpts.txt (included in next patch) for user-space > | > impact in multi-instance and mixed-mode operation. > | > TODO: > | > - Update mount(8), pts(4) man pages. Highlight impact of not > | > redirecting /dev/ptmx to /dev/pts/ptmx after a multi-instance mount. > | > > | > Implementation note: > | > > | > See comments in new get_sb_ref() function in fs/super.c on why > | > get_sb_single() cannot be directly used. > | > > | > Changelog[v5]: > | > - Move get_sb_ref() definition to earlier patch > | > > | > - Move usage info to Documentation/filesystems/devpts.txt (next patch) > | > > | > - Make ptmx node even in init_pts_ns, now that default mode is 0000 > | > (defined in earlier patch, enabled here). > | > > | > - Cache ptmx dentry and use to update mode during remount > | > (defined in earlier patch, enabled here). > | > > | > - Bugfix: explicitly ignore newinstance on remount (if newinstance was > | > specified on remount of initial mount, it would be ignored but > | > /proc/mounts would imply that the option was set) > | > > | > Changelog[v4]: > | > > | > - Update patch description to address H. Peter Anvin's comments > | > > | > - Consolidate multi-instance mode code under new config token, > | > CONFIG_DEVPTS_MULTIPLE_INSTANCE. > | > > | > - Move usage-details from patch description to > | > Documentation/fs/devpts.txt > | > > | > Changelog[v3]: > | > - Rename new mount option to 'newinstance' > | > > | > - Create ptmx nodes only in 'newinstance' mounts > | > > | > - Bugfix: parse_mount_options() modifies @data but since we need to > | > parse the @data twice (once in devpts_get_sb() and once during > | > do_remount_sb()), parse a local copy of @data in devpts_get_sb(). > | > (restructured code in devpts_get_sb() to fix this) > | > > | > Changelog[v2]: > | > - Support both single-mount and multiple-mount semantics and > | > provide '-onewmnt' option to select the semantics. > | > > | > Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxx> > | > --- > | > fs/devpts/inode.c | 168 +++++++++++++++++++++++++++++++++++++++++++++++++++-- > | > 1 files changed, 163 insertions(+), 5 deletions(-) > | > > | > diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c > | > index 6b56255..c54b010 100644 > | > --- a/fs/devpts/inode.c > | > +++ b/fs/devpts/inode.c > | > @@ -48,10 +48,11 @@ struct pts_mount_opts { > | > gid_t gid; > | > umode_t mode; > | > umode_t ptmxmode; > | > + int newinstance; > | > }; > | > > | > enum { > | > - Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, > | > + Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, > | > Opt_err > | > }; > | > > | > @@ -61,6 +62,7 @@ static match_table_t tokens = { > | > {Opt_mode, "mode=%o"}, > | > #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES > | > {Opt_ptmxmode, "ptmxmode=%o"}, > | > + {Opt_newinstance, "newinstance"}, > | > #endif > | > {Opt_err, NULL} > | > }; > | > @@ -78,13 +80,15 @@ static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb) > | > > | > static inline struct super_block *pts_sb_from_inode(struct inode *inode) > | > { > | > +#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES > | > if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC) > | > return inode->i_sb; > | > - > | > +#endif > | > return devpts_mnt->mnt_sb; > | > } > | > > | > -static int parse_mount_options(char *data, struct pts_mount_opts *opts) > | > +static int parse_mount_options(char *data, int remount, > | > + struct pts_mount_opts *opts) > | > { > | > char *p; > | > > | > @@ -95,6 +99,10 @@ static int parse_mount_options(char *data, struct pts_mount_opts *opts) > | > opts->mode = DEVPTS_DEFAULT_MODE; > | > opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE; > | > | So does this mean that if I do a remount, the mode and ptmxmode will get > | reset to the defaults unless I specify them again? > > Yes. > > I think I pointed out this behavior earlier but don't think I received any > comments and stuck to current behavior (which for instance resets the mode > to default). > > Besides, this behavior may help in the transition - initial kernel mount > would set ptmx-mode to 0 (default) and admin can update /etc/fstab to set > ptmx mode meaningfully. > > | > | > > | > + /* ignore newinstance on remount to avoid confusing show_options */ > | > + if (!remount) > | > + opts->newinstance = 0; > | > + > | > while ((p = strsep(&data, ",")) != NULL) { > | > substring_t args[MAX_OPT_ARGS]; > | > int token; > | > @@ -128,6 +136,10 @@ static int parse_mount_options(char *data, struct pts_mount_opts *opts) > | > return -EINVAL; > | > opts->ptmxmode = option & S_IALLUGO; > | > break; > | > + case Opt_newinstance: > | > + if (!remount) > | > + opts->newinstance = 1; > | > + break; > | > #endif > | > default: > | > printk(KERN_ERR "devpts: called with bogus options\n"); > | > @@ -180,6 +192,8 @@ static int mknod_ptmx(struct super_block *sb) > | > > | > d_add(dentry, inode); > | > > | > + fsi->ptmx_dentry = dentry; > | > + > | > printk(KERN_DEBUG "Created ptmx node in devpts ino %lu\n", > | > inode->i_ino); > | > > | > @@ -207,7 +221,7 @@ static int devpts_remount(struct super_block *sb, int *flags, char *data) > | > struct pts_fs_info *fsi = DEVPTS_SB(sb); > | > struct pts_mount_opts *opts = &fsi->mount_opts; > | > > | > - err = parse_mount_options(data, opts); > | > + err = parse_mount_options(data, 1, opts); > | > | A guess a #define rather than '1' would be better here. > > Ok. > > | > | > > | > /* > | > * parse_mount_options() restores options to default values > | > @@ -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 ? 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. > Does it mislead or confuse ? > > | > | > #endif > | > > | > return 0; > | > @@ -298,12 +314,153 @@ fail: > | > return -ENOMEM; > | > } > | > > | > +#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES > | > +/* > | > + * Safely parse the mount options in @data and update @opts. > | > + * > | > + * devpts ends up parsing options two times during mount, due to the > | > + * two modes of operation it supports. The first parse occurs in > | > + * devpts_get_sb() when determining the mode (single-instance or > | > + * multi-instance mode). The second parse happens in devpts_remount() > | > + * or new_pts_mount() depending on the mode. > | > + * > | > + * Parsing of options modifies the @data making subsequent parsing > | > + * incorrect. So make a local copy of @data and parse it. > | > + * > | > + * Return: 0 On success, -errno on error > | > + */ > | > +static int safe_parse_mount_options(void *data, struct pts_mount_opts *opts) > | > +{ > | > + int rc; > | > + void *datacp; > | > + > | > + if (!data) > | > + return 0; > | > + > | > + /* Use kstrdup() ? */ > | > + datacp = kmalloc(PAGE_SIZE, GFP_KERNEL); > | > + if (!datacp) > | > + return -ENOMEM; > | > + > | > + memcpy(datacp, data, PAGE_SIZE); > | > + rc = parse_mount_options((char *)datacp, 0, opts); > | > + kfree(datacp); > | > + > | > + return rc; > | > +} > | > + > | > +/* > | > + * Mount a new (private) instance of devpts. PTYs created in this > | > + * instance are independent of the PTYs in other devpts instances. > | > + */ > | > +static int new_pts_mount(struct file_system_type *fs_type, int flags, > | > + void *data, struct vfsmount *mnt) > | > +{ > | > + int err; > | > + struct pts_fs_info *fsi; > | > + struct pts_mount_opts *opts; > | > + > | > + printk(KERN_NOTICE "devpts: newinstance mount\n"); > | > + > | > + err = get_sb_nodev(fs_type, flags, data, devpts_fill_super, mnt); > | > + if (err) > | > + return err; > | > + > | > + fsi = DEVPTS_SB(mnt->mnt_sb); > | > + opts = &fsi->mount_opts; > | > + > | > + err = parse_mount_options(data, 0, opts); > | > + if (err) > | > + goto fail; > | > + > | > + err = mknod_ptmx(mnt->mnt_sb); > | > + if (err) > | > + goto fail; > | > + > | > + return 0; > | > + > | > +fail: > | > + dput(mnt->mnt_sb->s_root); > | > + deactivate_super(mnt->mnt_sb); > | > + return err; > | > +} > | > + > | > +/* > | > + * Check if 'newinstance' mount option was specified in @data. > | > + * > | > + * Return: -errno on error (eg: invalid mount options specified) > | > + * : 1 if 'newinstance' mount option was specified > | > + * : 0 if 'newinstance' mount option was NOT specified > | > + */ > | > +static int is_new_instance_mount(void *data) > | > +{ > | > + int rc; > | > + struct pts_mount_opts opts; > | > + > | > + if (!data) > | > + return 0; > | > + > | > + rc = safe_parse_mount_options(data, &opts); > | > + if (!rc) > | > + rc = opts.newinstance; > | > + > | > + return rc; > | > +} > | > + > | > +/* > | > + * Mount or remount the initial kernel mount of devpts. This type of > | > + * mount maintains the legacy, single-instance semantics, while the > | > + * kernel still allows multiple-instances. > | > + */ > | > +static int init_pts_mount(struct file_system_type *fs_type, int flags, > | > + void *data, struct vfsmount *mnt) > | > +{ > | > + int err; > | > + > | > + if (!devpts_mnt) { > | > + err = get_sb_single(fs_type, flags, data, devpts_fill_super, > | > + mnt); > | > + > | > + 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. > | > | > + } > | > + > | > + 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'? > | > | Yup, just confirmed, using: > | > | ns_exec -cmiup /bin/sh > | mount -t devpts -o newinstance -n none /dev/pts > | mount -t devpts -n none /mnt > | ls /dev/pts > | ptmx > | ls /mnt > | 0 ptmx > | That's weird. > | > +} > | > +#else > | > +/* > | > + * This supports only the legacy single-instance semantics (no > | > + * multiple-instance semantics) > | > + */ > | > +static int devpts_get_sb(struct file_system_type *fs_type, int flags, > | > + const char *dev_name, void *data, struct vfsmount *mnt) > | > +{ > | > return get_sb_single(fs_type, flags, data, devpts_fill_super, mnt); > | > } > | > > | > +#endif > | > + > | > static void devpts_kill_sb(struct super_block *sb) > | > { > | > struct pts_fs_info *fsi = DEVPTS_SB(sb); > | > @@ -431,8 +588,9 @@ void devpts_pty_kill(struct tty_struct *tty) > | > if (dentry && !IS_ERR(dentry)) { > | > inode->i_nlink--; > | > d_delete(dentry); > | > - dput(dentry); > | > + dput(dentry); // d_lookup in devpts_pty_new > | > } > | > + dput(dentry); // d_find_alias above > | > > | > mutex_unlock(&root->d_inode->i_mutex); > | > } > | > -- > | > 1.5.2.5 _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers