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? > > + /* 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. > > /* > * 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. > #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? > + } > + > + 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? 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