[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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