Messages in this thread Patch in this message |  | | Date | Tue, 8 Apr 2008 14:59:32 -0700 | From | sukadev@us ... | Subject | [RFC][PATCH 4/7]: Allow mknod of ptmx and tty in devpts |
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From: Sukadev Bhattiprolu <sukadev@us.ibm.com> Subject: [RFC][PATCH 4/7]: Allow mknod of ptmx and tty in devpts
We want to allow administrators to access PTYs in descendant pts-namespaces, for instance "echo foo > /vserver/vserver1/dev/pts/0". To enable such access we must hold a reference to the pts-ns in which the device (ptmx or slave pty) exists.
Note that we cannot use the pts-ns of the 'current' process since that pts-ns could be different from the pts-ns in which the PTY device was created. So we find the pts-ns from the inode of the PTY (inode->i_sb->s_fs_info).
While this would work for the slave PTY devices like /dev/pts/0, it would not work for either the master PTY device (/dev/ptmx) or controlling terminal (/dev/tty).
To uniformly handle the master, slave and controlling ttys, we allow creation of 'ptmx' and 'tty' devices in /dev/pts. When creating containers, the administrator can then:
In init-pts-ns:
$ mknod /dev/pts/ptmx c 5 2 $ mknod /dev/pts/tty c 5 0 $ rm /dev/ptmx /dev/tty $ ln -s /dev/pts/ptmx /dev/ptmx $ ln -s /dev/pts/tty /dev/tty
In child-pts-ns:
$ umount /dev/pts $ mount -t devpts lxcpts /dev/pts $ mknod /dev/pts/ptmx c 5 2 $ mknod /dev/pts/tty c 5 0
With this, even if the 'ptmx' is accessed from parent pts-ns we still find and hold the pts-ns in which 'ptmx' actually belongs.
This patch merely allows creation of /dev/pts/ptmx and /dev/pts/tty. Follow-on patches will enable cloning the pts namespace and using the pts-ns from the inode.
TODO: - Ability to unlink the /dev/pts/ptmx and /dev/pts/tty nodes.
Note: - If /dev/ptmx is a symlink to /vserver/vserver1/dev/pts/ptmx, open("/dev/ptmx") in init-pts-ns will create a PTY in 'vserver1' !
Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com> --- fs/devpts/inode.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 51 insertions(+), 4 deletions(-)
Index: 2.6.25-rc8-mm1/fs/devpts/inode.c =================================================================== --- 2.6.25-rc8-mm1.orig/fs/devpts/inode.c 2008-04-08 09:18:23.000000000 -0700 +++ 2.6.25-rc8-mm1/fs/devpts/inode.c 2008-04-08 13:35:43.000000000 -0700 @@ -58,7 +58,6 @@ struct pts_namespace init_pts_ns = { .mnt = NULL, }; - static int devpts_remount(struct super_block *sb, int *flags, char *data) { char *p; @@ -122,6 +121,54 @@ static const struct super_operations dev .show_options = devpts_show_options, }; + +static int devpts_mknod(struct inode *dir, struct dentry *dentry, + int mode, dev_t rdev) +{ + int inum; + struct inode *inode; + struct super_block *sb = dir->i_sb; + + if (dentry->d_inode) + return -EEXIST; + + if (!S_ISCHR(mode)) + return -EPERM; + + if (rdev == MKDEV(TTYAUX_MAJOR, 0)) + inum = 2; + else if (rdev == MKDEV(TTYAUX_MAJOR, 2)) + inum = 3; + else + return -EPERM; + + inode = new_inode(sb); + if (!inode) + return -ENOMEM; + + inode->i_ino = inum; + inode->i_uid = inode->i_gid = 0; + inode->i_blocks = 0; + inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME; + + init_special_inode(inode, mode, rdev); + + d_instantiate(dentry, inode); + /* + * Get a reference to the dentry so the device-nodes persist + * even when there are no active references to them. We use + * kill_litter_super() to remove this entry when unmounting + * devpts. + */ + dget(dentry); + return 0; +} + +const struct inode_operations devpts_dir_inode_operations = { + .lookup = simple_lookup, + .mknod = devpts_mknod, +}; + static int devpts_fill_super(struct super_block *s, void *data, int silent) { @@ -141,7 +188,7 @@ devpts_fill_super(struct super_block *s, inode->i_blocks = 0; inode->i_uid = inode->i_gid = 0; inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR; - inode->i_op = &simple_dir_inode_operations; + inode->i_op = &devpts_dir_inode_operations; inode->i_fop = &simple_dir_operations; inode->i_nlink = 2; @@ -214,7 +261,7 @@ static int devpts_get_sb(struct file_sys static void devpts_kill_sb(struct super_block *sb) { sb->s_fs_info = NULL; - kill_anon_super(sb); + kill_litter_super(sb); } static struct file_system_type devpts_fs_type = { @@ -303,7 +350,7 @@ int devpts_pty_new(struct tty_struct *tt if (!inode) return -ENOMEM; - inode->i_ino = number+2; + inode->i_ino = number+4; inode->i_uid = config.setuid ? config.uid : current->fsuid; inode->i_gid = config.setgid ? config.gid : current->fsgid; inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
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