On Mon, 2007-04-16 at 14:16 -0500, Serge E. Hallyn wrote:
> > This patch introduces a new proc interface that exposes all the
> propagation
> > trees within the namespace.
> >
> > It walks through each off the mounts in the namespace, and prints
> the following information.
> >
> > mount-id: a unique mount identifier
> > dev-id : the unique device used to identify the device containing
> the filesystem
> > path-from-root: mount point of the mount from /
> > path-from-root-of-its-sb: path from its own root dentry.
> > propagation-flag: SHARED, SLAVE, UNBINDABLE, PRIVATE
> > peer-mount-id: the mount-id of its peer mount (if this mount is
> shared)
> > master-mount-id: the mount-id of its master mount (if this mount is
> slave)
> >
> > Using the above information one could easily write a script that can
> > draw all the propagation trees in the namespace.
> >
> >
> > Example:
> > Here is a sample output of cat /proc/$$/mounts_propagation
> >
> > 0xa917800 0x1 / / PRIVATE
> > 0xa917200 0x6200 / / PRIVATE
> > 0xa917180 0x3 /proc / PRIVATE
> > 0xa917f80 0xa /dev/pts / PRIVATE
> > 0xa917100 0x6210 /mnt / SHARED peer:0xa917100
> > 0xa917f00 0x6210 /tmp /1 SLAVE master:0xa917100
> > 0xa917900 0x6220 /mnt/2 / SHARED peer:0xa917900
> >
> > line 5 indicates that the mount with id 0xa917100 is mounted at /mnt
> is shared
> > and it is the only mount in its peer group.
> >
> > line 6 indicates that the mount with id 0xa917f00 is mounted
> at /tmp, its
> > root is the dentry 1 present under its root directory. This mount is
> a
> > slave mount and its master is the mount with id 0xa917100.
> >
> > line 7 indicates that the mount with id 0xa917900 is mounted
> at /mnt/2, its
> > root is the dentry / of its filesystem. This mount is a
> > shared and it is the only mount in its peer group.
> >
> > one could write a script which runs through these lines and draws 4
> > individual satellite mounts and two propagation trees, the first
> propagation
> > tree has a shared mount and a slave mount. and the second
> propagation tree has
> > just one shared mount.
> >
> >
> > Signed-off-by: Ram Pai <linuxram@xxxxxxxxxx>
> > ---
> > fs/namespace.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> > fs/pnode.c | 6 ------
> > fs/pnode.h | 6 ++++++
> > fs/proc/base.c | 22 +++++++++++++++++++++-
> > 4 files changed, 69 insertions(+), 7 deletions(-)
> >
> > Index: linux-2.6.17.10/fs/namespace.c
> > ===================================================================
> > --- linux-2.6.17.10.orig/fs/namespace.c
> > +++ linux-2.6.17.10/fs/namespace.c
> > @@ -410,6 +410,41 @@ static int show_vfsmnt_new(struct seq_fi
> > return show_options(m, v);
> > }
> >
> > +static int show_vfsmnt_propagation(struct seq_file *m, void *v)
> > +{
> > + struct vfsmount *mnt = v;
> > + seq_printf(m, "0x%x", (int)mnt);
> > + seq_putc(m, ' ');
> > + seq_printf(m, "0x%x", new_encode_dev(mnt->mnt_sb->s_dev));
> > + seq_putc(m, ' ');
> > + seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
> > + seq_putc(m, ' ');
> > + seq_dentry(m, mnt->mnt_root, " \t\n\\");
> > + seq_putc(m, ' ');
> > +
> > + if (IS_MNT_SHARED(mnt)) {
> > + seq_printf(m, "%s ", "SHARED");
> > + if (IS_MNT_SLAVE(mnt)) {
> > + seq_printf(m, "%s ", "SLAVE");
> > + }
> > + } else if (IS_MNT_SLAVE(mnt)) {
> > + seq_printf(m, "%s ", "SLAVE");
> > + } else if (IS_MNT_UNBINDABLE(mnt)) {
> > + seq_printf(m, "%s ", "UNBINDABLE");
> > + } else {
> > + seq_printf(m, "%s ", "PRIVATE");
> > + }
> > +
> > + if (IS_MNT_SHARED(mnt)) {
> > + seq_printf(m, "peer:0x%x ", (int)next_peer(mnt));
>
> Ok, so if the sequence of events was
>
> mount --make-shared /mnt
> (some user logs in and gets a cloned namespace, so his /mnt
> becomes the next peer of /mnt)
> mount --bind /mnt /tmp
> (some other user logs in and gets cloned namespace...)
>
> or some such sequence of events, we could lose all information
> about /mnt and /tmp being peers, right? Should a new
> next_peer_in_same_namespace(mnt) be used rather than next_peer()?
you are right. it should print next_peer(mnt) only if CAP_SYS_ADMIN,
else print next_peer_in_same_namespace(mnt).
>
> Somewhat similarly,
>
> > + }
> > + if (IS_MNT_SLAVE(mnt)) {
> > + seq_printf(m, "master:0x%x ", (int)mnt->mnt_master);
>
> Should we for privacy reasons not print out the address
> mnt->mnt_master
> is in a different namespace (perhaps if !CAP_SYS_ADMIN)?
right. it should print mnt->mnt_master if (CAP_SYS_ADMIN), otherwise
print master_in_same_namespace(mnt).
RP
>
> Otherwise I like this.
>
> thanks,
> -serge
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