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
...