Quoting Ram Pai (linuxram@us.ibm.com):
> On Mon, 2007-04-16 at 12:34 +0200, Miklos Szeredi wrote:
> > Currently one of the difficulties with mount propagations is that
> > there's no way to know the current state of the propagation tree.
> > 
> > Has anyone thought about how this info could be queried from
> > userspace?
> 
> I am attaching two patches that I had done way back in Oct 2006 
> with Al Viro. I had sent these patches to Al Viro. But I forgot to
> follow them up, I guess so did Al Viro.
> 
> The first patch disambiguates multiple mount-instances of the same
> filesystem (or part of the same filesystem), by introducing a new
> interface /proc/mounts_new. 
> 
> The second patch introduces a new proc interface that exposes all the
> propagation trees within a namespace.  It does not show propagated
> mounts residing in a different namespace (for privacy reasons). Maybe
> one could modify the patch a little, to allow it; if the user has
> root priviledges. 
> 
> RP
> 
> PS: Sorry these are attachments instead of inline patches. I am scared
> of inlining in evolution. If needed I can send inline patches through
> mutt.
> 
> > 
> > Thanks,
> > Miklos

> This patch disambiguates multiple mount-instances of the same
> filesystem (or part of the same filesystem), by introducing a new
> interface /proc/mounts_new. The interface has the following format.
> 
> ------------------------------------------------------------
> FSID  mntpt  root-dentry  fstype fs-options
> ------------------------------------------------------------
> 
> NOTE: root-dentry is the path to the dentry w.r.t to the root dentry of the
> same filesystem.
> 
> for example: lets say we attempt the following commands
> mount --bind /var /mnt
> mount --bind /mnt/tmp /tmp1
> 
> 'cat /proc/mounts' shows the following:
> /dev/root /mnt ext2 rw 0 0
> /dev/root /tmp1 ext2 rw 0 0
> 
> NOTE: The above mount entries, do not indicate that /tmp1 contains the same
> directory tree as /var/tmp.
> 
> But 'cat /proc/mounts_new' shows us the following:
> 0x6200 /mnt /var ext2 rw 0 0
> 0x6200 /tmp1 /var/tmp ext2 rw 0 0
> 
> The above entries clearly indicates that /var/tmp directory of the ext2
> filesystem with fsid=0x6200 is the directory tree that resides under /tmp1
> 
> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> 
> ---
>  fs/dcache.c              |   53 ++++++++++++++++++++++++++++++++
>  fs/namespace.c           |   35 ++++++++++++++++++---
>  fs/proc/base.c           |   32 +++++++++++++++++--
>  fs/proc/proc_misc.c      |    1 
>  fs/seq_file.c            |   77 ++++++++++++++++++++++++++++++++++-------------
>  include/linux/dcache.h   |    1 
>  include/linux/seq_file.h |    1 
>  7 files changed, 172 insertions(+), 28 deletions(-)
> 
> Index: linux-2.6.17.10/fs/proc/base.c
> ===================================================================
> --- linux-2.6.17.10.orig/fs/proc/base.c
> +++ linux-2.6.17.10/fs/proc/base.c
> @@ -104,6 +104,7 @@ enum pid_directory_inos {
>  	PROC_TGID_MAPS,
>  	PROC_TGID_NUMA_MAPS,
>  	PROC_TGID_MOUNTS,
> +	PROC_TGID_MOUNTS_NEW,
>  	PROC_TGID_MOUNTSTATS,
>  	PROC_TGID_WCHAN,
>  #ifdef CONFIG_MMU
> @@ -145,6 +146,7 @@ enum pid_directory_inos {
>  	PROC_TID_MAPS,
>  	PROC_TID_NUMA_MAPS,
>  	PROC_TID_MOUNTS,
> +	PROC_TID_MOUNTS_NEW,
>  	PROC_TID_MOUNTSTATS,
>  	PROC_TID_WCHAN,
>  #ifdef CONFIG_MMU
> @@ -203,6 +205,7 @@ static struct pid_entry tgid_base_stuff[
>  	E(PROC_TGID_ROOT,      "root",    S_IFLNK|S_IRWXUGO),
>  	E(PROC_TGID_EXE,       "exe",     S_IFLNK|S_IRWXUGO),
>  	E(PROC_TGID_MOUNTS,    "mounts",  S_IFREG|S_IRUGO),
> +	E(PROC_TGID_MOUNTS_NEW,"mounts_new",  S_IFREG|S_IRUGO),
>  	E(PROC_TGID_MOUNTSTATS, "mountstats", S_IFREG|S_IRUSR),
>  #ifdef CONFIG_MMU
>  	E(PROC_TGID_SMAPS,     "smaps",   S_IFREG|S_IRUGO),
> @@ -246,6 +249,7 @@ static struct pid_entry tid_base_stuff[]
>  	E(PROC_TID_ROOT,       "root",    S_IFLNK|S_IRWXUGO),
>  	E(PROC_TID_EXE,        "exe",     S_IFLNK|S_IRWXUGO),
>  	E(PROC_TID_MOUNTS,     "mounts",  S_IFREG|S_IRUGO),
> +	E(PROC_TID_MOUNTS_NEW, "mounts_new",  S_IFREG|S_IRUGO),
>  #ifdef CONFIG_MMU
>  	E(PROC_TID_SMAPS,      "smaps",   S_IFREG|S_IRUGO),
>  #endif
> @@ -692,13 +696,13 @@ static struct file_operations proc_smaps
>  };
>  #endif
> 
> -extern struct seq_operations mounts_op;
>  struct proc_mounts {
>  	struct seq_file m;
>  	int event;
>  };
> 
> -static int mounts_open(struct inode *inode, struct file *file)
> +static int __mounts_open(struct inode *inode, struct file *file,
> +			struct seq_operations *mounts_op)
>  {
>  	struct task_struct *task = proc_task(inode);
>  	struct namespace *namespace;
> @@ -716,7 +720,7 @@ static int mounts_open(struct inode *ino
>  		p = kmalloc(sizeof(struct proc_mounts), GFP_KERNEL);
>  		if (p) {
>  			file->private_data = &p->m;
> -			ret = seq_open(file, &mounts_op);
> +			ret = seq_open(file, mounts_op);
>  			if (!ret) {
>  				p->m.private = namespace;
>  				p->event = namespace->event;
> @@ -729,6 +733,16 @@ static int mounts_open(struct inode *ino
>  	return ret;
>  }
> 
> +extern struct seq_operations mounts_op, mounts_new_op;
> +static int mounts_open(struct inode *inode, struct file *file)
> +{
> +	return (__mounts_open(inode, file, &mounts_op));
> +}
> +static int mounts_new_open(struct inode *inode, struct file *file)
> +{
> +	return __mounts_open(inode, file, &mounts_new_op);
> +}
> +
>  static int mounts_release(struct inode *inode, struct file *file)
>  {
>  	struct seq_file *m = file->private_data;
> @@ -763,6 +777,14 @@ static struct file_operations proc_mount
>  	.poll		= mounts_poll,
>  };
> 
> +static struct file_operations proc_mounts_new_operations = {
> +	.open		= mounts_new_open,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.release	= mounts_release,
> +	.poll		= mounts_poll,
> +};
> +
>  extern struct seq_operations mountstats_op;
>  static int mountstats_open(struct inode *inode, struct file *file)
>  {
> @@ -1799,6 +1821,10 @@ static struct dentry *proc_pident_lookup
>  		case PROC_TGID_MOUNTS:
>  			inode->i_fop = &proc_mounts_operations;
>  			break;
> +		case PROC_TID_MOUNTS_NEW:
> +		case PROC_TGID_MOUNTS_NEW:
> +			inode->i_fop = &proc_mounts_new_operations;
> +			break;
>  #ifdef CONFIG_MMU
>  		case PROC_TID_SMAPS:
>  		case PROC_TGID_SMAPS:
> Index: linux-2.6.17.10/fs/dcache.c
> ===================================================================
> --- linux-2.6.17.10.orig/fs/dcache.c
> +++ linux-2.6.17.10/fs/dcache.c
> @@ -1477,6 +1477,59 @@ char * d_path(struct dentry *dentry, str
>  	return res;
>  }
> 
> +static inline int prepend(char **buffer, int *buflen, const char *str,
> +					int namelen)
> +{
> +	if ((*buflen -= namelen) < 0)
> +		return 1;
> +	*buffer -= namelen;
> +	memcpy(*buffer, str, namelen);
> +	return 0;
> +}
> +
> +/*
> + * write full pathname into buffer and return start of pathname.
> + * If @vfsmnt is not specified return the path relative to the
> + * its filesystem's root.
> + */
> +char * dentry_path(struct dentry *dentry, char *buf, int buflen)
> +{
> +	char * end = buf+buflen;
> +	char * retval;
> +
> +	spin_lock(&dcache_lock);
> +	prepend(&end, &buflen, "\0", 1);
> +	if (!IS_ROOT(dentry) && d_unhashed(dentry)) {
> +		if (prepend(&end, &buflen, "//deleted", 10))
> +			goto Elong;
> +	}
> +	/* Get '/' right */
> +	retval = end-1;
> +	*retval = '/';
> +
> +	for (;;) {
> +		struct dentry * parent;
> +		if (IS_ROOT(dentry))
> +			break;
> +
> +		parent = dentry->d_parent;
> +		prefetch(parent);
> +
> +		if (prepend(&end, &buflen, dentry->d_name.name,
> +				dentry->d_name.len) ||
> +	            prepend(&end, &buflen, "/", 1))
> +			goto Elong;
> +
> +		retval = end;
> +		dentry = parent;
> +	}
> +	spin_unlock(&dcache_lock);
> +	return retval;
> +Elong:
> +	spin_unlock(&dcache_lock);
> +	return ERR_PTR(-ENAMETOOLONG);
> +}
> +
>  /*
>   * NOTE! The user-level library version returns a
>   * character pointer. The kernel system call just
> Index: linux-2.6.17.10/fs/seq_file.c
> ===================================================================
> --- linux-2.6.17.10.orig/fs/seq_file.c
> +++ linux-2.6.17.10/fs/seq_file.c
> @@ -338,38 +338,75 @@ int seq_printf(struct seq_file *m, const
>  }
>  EXPORT_SYMBOL(seq_printf);
> 
> -int seq_path(struct seq_file *m,
> -	     struct vfsmount *mnt, struct dentry *dentry,
> +static inline char *mangle_path(char *s, char *p, char *esc)
> +{
> +	while (s <= p) {
> +		char c = *p++;
> +		if (!c) {
> +			return s;
> +		} else if (!strchr(esc, c)) {
> +			*s++ = c;
> +		} else if (s + 4 > p) {
> +			break;
> +		} else {
> +			*s++ = '\\';
> +			*s++ = '0' + ((c & 0300) >> 6);
> +			*s++ = '0' + ((c & 070) >> 3);
> +			*s++ = '0' + (c & 07);
> +		}
> +	}
> +	return NULL;
> +}
> +
> +/*
> + * return the absolute path of 'dentry' residing in mount 'mnt'.
> + */
> +int seq_path(struct seq_file *m, struct vfsmount *mnt, struct dentry