[Devel] [RFC][PATCH 3/4]: Enable multiple mounts of /dev/pts

Serge E. Hallyn serue at us.ibm.com
Wed Feb 6 08:16:08 PST 2008


Quoting Pavel Emelyanov (xemul at openvz.org):
> sukadev at us.ibm.com wrote:
> > From: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> > Subject: [RFC][PATCH 3/4]: Enable multiple mounts of /dev/pts
> > 
> > To support multiple PTY namespaces, we should be allow multiple mounts of
> > /dev/pts, once within each PTY namespace.
> > 
> > This patch removes the get_sb_single() in devpts_get_sb() and uses test and
> > set sb interfaces to allow remounting /dev/pts.  The patch also removes the
> > globals, 'devpts_root' and uses current_pts_mnt() to access 'devpts_mnt'
> > 
> > Changelog:
> > 	- Version 0: Based on earlier versions from Serge Hallyn and
> > 	  Matt Helsley.
> > 
> > Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> > ---
> >  fs/devpts/inode.c |  120 +++++++++++++++++++++++++++++++++++++++++++++---------
> >  1 file changed, 101 insertions(+), 19 deletions(-)
> > 
> > Index: linux-2.6.24/fs/devpts/inode.c
> > ===================================================================
> > --- linux-2.6.24.orig/fs/devpts/inode.c	2008-02-05 17:30:52.000000000 -0800
> > +++ linux-2.6.24/fs/devpts/inode.c	2008-02-05 19:16:39.000000000 -0800
> > @@ -34,7 +34,10 @@ static inline struct idr *current_pts_ns
> >  }
> >  
> >  static struct vfsmount *devpts_mnt;
> > -static struct dentry *devpts_root;
> > +static inline struct vfsmount *current_pts_ns_mnt(void)
> > +{
> > +	return devpts_mnt;
> > +}
> >  
> >  static struct {
> >  	int setuid;
> > @@ -130,7 +133,7 @@ devpts_fill_super(struct super_block *s,
> >  	inode->i_fop = &simple_dir_operations;
> >  	inode->i_nlink = 2;
> >  
> > -	devpts_root = s->s_root = d_alloc_root(inode);
> > +	s->s_root = d_alloc_root(inode);
> >  	if (s->s_root)
> >  		return 0;
> >  	
> > @@ -140,10 +143,53 @@ fail:
> >  	return -ENOMEM;
> >  }
> >  
> > +/*
> > + * We use test and set super-block operations to help determine whether we
> > + * need a new super-block for this namespace. get_sb() walks the list of
> > + * existing devpts supers, comparing them with the @data ptr. Since we
> > + * passed 'current's namespace as the @data pointer we can compare the
> > + * namespace pointer in the super-block's 's_fs_info'.  If the test is
> > + * TRUE then get_sb() returns a new active reference to the super block.
> > + * Otherwise, it helps us build an active reference to a new one.
> > + */
> > +
> > +static int devpts_test_sb(struct super_block *sb, void *data)
> > +{
> > +	return sb->s_fs_info == data;
> > +}
> > +
> > +static int devpts_set_sb(struct super_block *sb, void *data)
> > +{
> > +	sb->s_fs_info = data;
> > +	return set_anon_super(sb, NULL);
> > +}
> > +
> >  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);
> > +	struct super_block *sb;
> > +	int err;
> > +
> > +	/* hereafter we're very simlar to get_sb_nodev */
> > +	sb = sget(fs_type, devpts_test_sb, devpts_set_sb, data);
> > +	if (IS_ERR(sb))
> > +		return PTR_ERR(sb);
> > +
> > +	if (sb->s_root)
> > +		return simple_set_mnt(mnt, sb);
> > +
> > +	sb->s_flags = flags;
> > +	err = devpts_fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
> > +	if (err) {
> > +		up_write(&sb->s_umount);
> > +		deactivate_super(sb);
> > +		return err;
> > +	}
> > +
> 
> That stuff becomes very very similar to that in proc :)
> Makes sense to consolidate. Maybe...

Yeah, and the mqns that Cedric sent too.  I think Cedric said he'd
started an a patch implementing a helper.  Cedric?

Pavel, not long ago you said you were starting to look at tty and pty
stuff - did you have any different ideas on devpts virtualization, or
are you ok with this minus your comments thus far?

> 
> > +	sb->s_flags |= MS_ACTIVE;
> > +	devpts_mnt = mnt;
> > +
> > +	return simple_set_mnt(mnt, sb);
> >  }
> >  
> >  static struct file_system_type devpts_fs_type = {
> > @@ -158,10 +204,9 @@ static struct file_system_type devpts_fs
> >   * to the System V naming convention
> >   */
> >  
> > -static struct dentry *get_node(int num)
> > +static struct dentry *get_node(struct dentry *root, int num)
> >  {
> >  	char s[12];
> > -	struct dentry *root = devpts_root;
> >  	mutex_lock(&root->d_inode->i_mutex);
> >  	return lookup_one_len(s, root, sprintf(s, "%d", num));
> >  }
> > @@ -207,12 +252,28 @@ int devpts_pty_new(struct tty_struct *tt
> >  	struct tty_driver *driver = tty->driver;
> >  	dev_t device = MKDEV(driver->major, driver->minor_start+number);
> >  	struct dentry *dentry;
> > -	struct inode *inode = new_inode(devpts_mnt->mnt_sb);
> > +	struct dentry *root;
> > +	struct vfsmount *mnt;
> > +	struct inode *inode;
> > +
> >  
> >  	/* We're supposed to be given the slave end of a pty */
> >  	BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
> >  	BUG_ON(driver->subtype != PTY_TYPE_SLAVE);
> >  
> > +	mnt = current_pts_ns_mnt();
> > +	if (!mnt)
> > +		return -ENOSYS;
> > +	root = mnt->mnt_root;
> > +
> > +	mutex_lock(&root->d_inode->i_mutex);
> > +	inode = idr_find(current_pts_ns_allocated_ptys(), number);
> > +	mutex_unlock(&root->d_inode->i_mutex);
> > +
> > +	if (inode && !IS_ERR(inode))
> > +		return -EEXIST;
> > +
> > +	inode = new_inode(mnt->mnt_sb);
> >  	if (!inode)
> >  		return -ENOMEM;
> >  
> > @@ -222,23 +283,31 @@ int devpts_pty_new(struct tty_struct *tt
> >  	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
> >  	init_special_inode(inode, S_IFCHR|config.mode, device);
> >  	inode->i_private = tty;
> > +	idr_replace(current_pts_ns_allocated_ptys(), inode, number);
> >  
> > -	dentry = get_node(number);
> > +	dentry = get_node(root, number);
> >  	if (!IS_ERR(dentry) && !dentry->d_inode) {
> >  		d_instantiate(dentry, inode);
> > -		fsnotify_create(devpts_root->d_inode, dentry);
> > +		fsnotify_create(root->d_inode, dentry);
> >  	}
> >  
> > -	mutex_unlock(&devpts_root->d_inode->i_mutex);
> > +	mutex_unlock(&root->d_inode->i_mutex);
> >  
> >  	return 0;
> >  }
> >  
> >  struct tty_struct *devpts_get_tty(int number)
> >  {
> > -	struct dentry *dentry = get_node(number);
> > +	struct vfsmount *mnt;
> > +	struct dentry *dentry;
> >  	struct tty_struct *tty;
> >  
> > +	mnt = current_pts_ns_mnt();
> > +	if (!mnt)
> > +		return NULL;
> > +
> > +	dentry = get_node(mnt->mnt_root, number);
> > +
> >  	tty = NULL;
> >  	if (!IS_ERR(dentry)) {
> >  		if (dentry->d_inode)
> > @@ -246,14 +315,21 @@ struct tty_struct *devpts_get_tty(int nu
> >  		dput(dentry);
> >  	}
> >  
> > -	mutex_unlock(&devpts_root->d_inode->i_mutex);
> > +	mutex_unlock(&mnt->mnt_root->d_inode->i_mutex);
> >  
> >  	return tty;
> >  }
> >  
> >  void devpts_pty_kill(int number)
> >  {
> > -	struct dentry *dentry = get_node(number);
> > +	struct dentry *dentry;
> > +	struct dentry *root;
> > +	struct vfsmount *mnt;
> > +
> > +	mnt = current_pts_ns_mnt();
> > +	root = mnt->mnt_root;
> > +
> > +	dentry = get_node(root, number);
> >  
> >  	if (!IS_ERR(dentry)) {
> >  		struct inode *inode = dentry->d_inode;
> > @@ -264,17 +340,23 @@ void devpts_pty_kill(int number)
> >  		}
> >  		dput(dentry);
> >  	}
> > -	mutex_unlock(&devpts_root->d_inode->i_mutex);
> > +	mutex_unlock(&root->d_inode->i_mutex);
> >  }
> >  
> >  static int __init init_devpts_fs(void)
> >  {
> > -	int err = register_filesystem(&devpts_fs_type);
> > -	if (!err) {
> > -		devpts_mnt = kern_mount(&devpts_fs_type);
> > -		if (IS_ERR(devpts_mnt))
> > -			err = PTR_ERR(devpts_mnt);
> > -	}
> > +	struct vfsmount *mnt;
> > +	int err;
> > +
> > +	err = register_filesystem(&devpts_fs_type);
> > +	if (err)
> > +		return err;
> > +
> > +	mnt = kern_mount_data(&devpts_fs_type, NULL);
> > +	if (IS_ERR(mnt))
> > +		err = PTR_ERR(mnt);
> > +	else
> > +		devpts_mnt = mnt;
> >  	return err;
> >  }
> >  
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