[PATCH 06/10] Define mknod_ptmx()
Serge E. Hallyn
serue at us.ibm.com
Wed Sep 24 11:21:25 PDT 2008
Quoting sukadev at us.ibm.com (sukadev at us.ibm.com):
>
> >From df5d5863f8601baa25237b60c3fcd614ee0b34aa Mon Sep 17 00:00:00 2001
> From: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> Date: Tue, 9 Sep 2008 10:23:07 -0700
> Subject: [PATCH 06/10] Define mknod_ptmx()
>
> /dev/ptmx is closely tied to the devpts filesystem. An open of /dev/ptmx,
> allocates the next pty index and the associated device shows up in the
> devpts fs as /dev/pts/n.
>
> Wih multiple instancs of devpts filesystem, during an open of /dev/ptmx
> we would be unable to determine which instance of the devpts is being
> accessed.
>
> So we move the 'ptmx' node into /dev/pts and use the inode of the 'ptmx'
> node to identify the superblock and hence the devpts instance. This patch
> adds ability for the kernel to internally create the [ptmx, c, 5:2] device
> when mounting devpts filesystem. Since the ptmx node in devpts is new and
> may surprise some userspace scripts, the default permissions for the new
> node is 0000. These permissions can be changed either using chmod or by
> remounting with the new '-o ptmxmode=0666' mount option.
>
> Changelog[v4]:
> - Change default permissions of pts/ptmx node to 0000.
> - Move code for ptmxmode under #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES.
>
> Changelog[v3]:
> - Rename ptmx_mode to ptmxmode (for consistency with 'newinstance')
>
> Changelog[v2]:
> - [H. Peter Anvin] Remove mknod() system call support and create the
> ptmx node internally.
>
> Changelog[v1]:
> - Earlier version of this patch enabled creating /dev/pts/tty as
> well. As pointed out by Al Viro and H. Peter Anvin, that is not
> really necessary.
>
> Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> ---
> fs/devpts/inode.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 files changed, 74 insertions(+), 2 deletions(-)
>
> diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
> index 7ae60aa..17e14f5 100644
> --- a/fs/devpts/inode.c
> +++ b/fs/devpts/inode.c
> @@ -27,6 +27,13 @@
> #define DEVPTS_SUPER_MAGIC 0x1cd1
>
> #define DEVPTS_DEFAULT_MODE 0600
> +/*
> + * ptmx is a new node in /dev/pts and will be unused in legacy (single-
> + * instance) mode. To prevent surprises in user space, set permissions of
> + * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
> + * permissions.
> + */
> +#define DEVPTS_DEFAULT_PTMX_MODE 0000
> #define PTMX_MINOR 2
>
> extern int pty_limit; /* Config limit on Unix98 ptys */
> @@ -40,10 +47,11 @@ struct pts_mount_opts {
> uid_t uid;
> gid_t gid;
> umode_t mode;
> + umode_t ptmxmode;
> };
>
> enum {
> - Opt_uid, Opt_gid, Opt_mode,
> + Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode,
> Opt_err
> };
>
> @@ -51,6 +59,9 @@ static match_table_t tokens = {
> {Opt_uid, "uid=%u"},
> {Opt_gid, "gid=%u"},
> {Opt_mode, "mode=%o"},
> +#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
> + {Opt_ptmxmode, "ptmxmode=%o"},
> +#endif
> {Opt_err, NULL}
> };
>
> @@ -81,6 +92,7 @@ static int parse_mount_options(char *data, struct pts_mount_opts *opts)
> opts->uid = 0;
> opts->gid = 0;
> opts->mode = DEVPTS_DEFAULT_MODE;
> + opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
>
> while ((p = strsep(&data, ",")) != NULL) {
> substring_t args[MAX_OPT_ARGS];
> @@ -109,6 +121,13 @@ static int parse_mount_options(char *data, struct pts_mount_opts *opts)
> return -EINVAL;
> opts->mode = option & S_IALLUGO;
> break;
> +#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
> + case Opt_ptmxmode:
> + if (match_octal(&args[0], &option))
> + return -EINVAL;
> + opts->ptmxmode = option & S_IALLUGO;
> + break;
> +#endif
> default:
> printk(KERN_ERR "devpts: called with bogus options\n");
> return -EINVAL;
> @@ -118,6 +137,55 @@ static int parse_mount_options(char *data, struct pts_mount_opts *opts)
> return 0;
> }
>
> +#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
> +static int mknod_ptmx(struct super_block *sb)
> +{
> + struct dentry *root;
> + struct dentry *dentry;
> + struct inode *inode;
> + struct pts_fs_info *fsi = DEVPTS_SB(sb);
> + struct pts_mount_opts *opts = &fsi->mount_opts;
> + int mode;
> +
> + root = sb->s_root;
> + dentry = lookup_one_len("ptmx", root, 4);
I realize you intend for this to only be used before mount is completed,
but it still seems like a good idea to have this grab the root inode
mutex.
> + if (IS_ERR(dentry)) {
> + printk(KERN_ERR "Unable to alloc dentry for ptmx node\n");
> + return -ENOMEM;
> + }
> +
> + if (dentry->d_inode) {
> + printk(KERN_ERR "'ptmx' (ino %lu) exists in this devpts\n",
> + dentry->d_inode->i_ino);
> + return 0;
> + }
> +
> + /*
> + * Create a new 'ptmx' node in this mount of devpts.
> + */
> + inode = new_inode(sb);
> + if (!inode) {
> + printk(KERN_ERR "Unable to alloc inode for ptmx node\n");
> + dput(dentry);
> + return -ENOMEM;
> + }
> +
> + inode->i_uid = inode->i_gid = 0;
As we've discussed, you need to reserve inode number 2 for ptmx, set
inode->i_ino to 2 here, and then set inode->i_ino to the pty_index+3
when creating a new pty.
> + inode->i_blocks = 0;
> + inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
> +
> + mode = S_IFCHR|opts->ptmxmode;
> + init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
> +
> + d_add(dentry, inode);
> +
> + printk(KERN_DEBUG "Created ptmx node in devpts ino %lu\n",
> + inode->i_ino);
> +
> + return 0;
> +}
> +#endif
> +
> static int devpts_remount(struct super_block *sb, int *flags, char *data)
> {
> struct pts_fs_info *fsi = DEVPTS_SB(sb);
> @@ -136,6 +204,9 @@ static int devpts_show_options(struct seq_file *seq, struct vfsmount *vfs)
> if (opts->setgid)
> seq_printf(seq, ",gid=%u", opts->gid);
> seq_printf(seq, ",mode=%03o", opts->mode);
> +#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
> + seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
> +#endif
>
> return 0;
> }
> @@ -156,6 +227,7 @@ static void *new_pts_fs_info(void)
>
> ida_init(&fsi->allocated_ptys);
> fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
> + fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
>
> return fsi;
> }
> @@ -211,7 +283,7 @@ static void devpts_kill_sb(struct super_block *sb)
> struct pts_fs_info *fsi = DEVPTS_SB(sb);
>
> kfree(fsi);
> - kill_anon_super(sb);
> + kill_litter_super(sb);
> }
>
> static struct file_system_type devpts_fs_type = {
> --
> 1.5.2.5
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