Quoting Serge E. Hallyn ([email protected]): > One practical problem I've found with cgroup namespaces is that there > is no way to disambiguate between a cgroupfs mount which was done in > a cgroup namespace, and a bind mount of a cgroupfs directory. So > whether I do > > unshare --cgroup -- bash -c "mount -t cgroup -o freezer f /mnt; cat > /proc/self/mountinfo" > > or whether I just > > mount --bind /sys/fs/cgroup/freezer/$(awk -F: '/freezer/ { print $3 }' > /proc/self/cgroup) /mnt > > 'mount root' field (field 3) in /proc/self/mountinfo will show the > same thing, the result of awk -F: '/freezer/ { print $3 }' /proc/self/cgroup. > > This patch adds a 'nsroot=' field to cgroup mountinfo entries, so that > userspace can distinguish a mount made in a cgroup namespace from a bind > mount from a cgroup subdirectory.
Hi Tejun, no rush on the patch itself, I don't mind if i have to rewrite it from scratch, but I'd like to get the patch into docker/libcontainer using it, so can we decide on whether the syntax as shown here is ok? thanks, -serge > Signed-off-by: Serge Hallyn <[email protected]> > --- > fs/kernfs/mount.c | 2 +- > include/linux/kernfs.h | 3 ++- > kernel/cgroup.c | 29 ++++++++++++++++++++++++++++- > 3 files changed, 31 insertions(+), 3 deletions(-) > > diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c > index b67dbcc..58f59fd 100644 > --- a/fs/kernfs/mount.c > +++ b/fs/kernfs/mount.c > @@ -36,7 +36,7 @@ static int kernfs_sop_show_options(struct seq_file *sf, > struct dentry *dentry) > struct kernfs_syscall_ops *scops = root->syscall_ops; > > if (scops && scops->show_options) > - return scops->show_options(sf, root); > + return scops->show_options(sf, dentry, root); > return 0; > } > > diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h > index c06c442..3124b91 100644 > --- a/include/linux/kernfs.h > +++ b/include/linux/kernfs.h > @@ -145,7 +145,8 @@ struct kernfs_node { > */ > struct kernfs_syscall_ops { > int (*remount_fs)(struct kernfs_root *root, int *flags, char *data); > - int (*show_options)(struct seq_file *sf, struct kernfs_root *root); > + int (*show_options)(struct seq_file *sf, struct dentry *dentry, > + struct kernfs_root *root); > > int (*mkdir)(struct kernfs_node *parent, const char *name, > umode_t mode); > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index 671dc05..806d1e7 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -1593,7 +1593,32 @@ static int rebind_subsystems(struct cgroup_root > *dst_root, u16 ss_mask) > return 0; > } > > -static int cgroup_show_options(struct seq_file *seq, > +static void cgroup_show_nsroot(struct seq_file *seq, struct dentry *dentry, > + struct kernfs_root *kf_root) > +{ > + struct kernfs_node *d_kn = dentry->d_fsdata; > + char *nsroot; > + int len, ret; > + > + if (!kf_root) > + return; > + len = kernfs_path_from_node(d_kn, kf_root->kn, NULL, 0); > + if (len <= 0) > + return; > + nsroot = kzalloc(len + 1, GFP_ATOMIC); > + if (!nsroot) > + return; > + ret = kernfs_path_from_node(d_kn, kf_root->kn, nsroot, len + 1); > + if (ret <= 0 || ret > len) > + goto out; > + > + seq_show_option(seq, "nsroot", nsroot); > + > +out: > + kfree(nsroot); > +} > + > +static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry, > struct kernfs_root *kf_root) > { > struct cgroup_root *root = cgroup_root_from_kf(kf_root); > @@ -1619,6 +1644,8 @@ static int cgroup_show_options(struct seq_file *seq, > seq_puts(seq, ",clone_children"); > if (strlen(root->name)) > seq_show_option(seq, "name", root->name); > + cgroup_show_nsroot(seq, dentry, kf_root); > + > return 0; > } > > -- > 2.7.3 >
