On Sun, Apr 17, 2016 at 03:04:32PM -0500, serge.hallyn@xxxxxxxxxx wrote:
> From: Serge Hallyn <serge.hallyn@xxxxxxxxxx>
>
> When showing a cgroupfs entry in mountinfo, show the
> path of the mount root dentry relative to the reader's
> cgroup namespace root.
>
> Signed-off-by: Serge Hallyn <serge.hallyn@xxxxxxxxxx>
> ---
> fs/kernfs/mount.c | 14 ++++++++++++++
> include/linux/kernfs.h | 2 ++
> kernel/cgroup.c | 35 +++++++++++++++++++++++++++++++++++
> 3 files changed, 51 insertions(+)
>
> diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
> index f73541f..3b78724 100644
> --- a/fs/kernfs/mount.c
> +++ b/fs/kernfs/mount.c
> @@ -15,6 +15,7 @@
> #include <linux/slab.h>
> #include <linux/pagemap.h>
> #include <linux/namei.h>
> +#include <linux/seq_file.h>
>
> #include "kernfs-internal.h"
>
> @@ -40,6 +41,18 @@ static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
> return 0;
> }
>
> +static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
> +{
> + struct kernfs_node *node = dentry->d_fsdata;
> + struct kernfs_root *root = kernfs_root(node);
> + struct kernfs_syscall_ops *scops = root->syscall_ops;
> +
> + if (scops && scops->show_path)
> + return scops->show_path(sf, node, root);
> +
> + return seq_dentry(sf, dentry, " \t\n\\");
> +}
> +
> const struct super_operations kernfs_sops = {
> .statfs = simple_statfs,
> .drop_inode = generic_delete_inode,
> @@ -47,6 +60,7 @@ const struct super_operations kernfs_sops = {
>
> .remount_fs = kernfs_sop_remount_fs,
> .show_options = kernfs_sop_show_options,
> + .show_path = kernfs_sop_show_path,
> };
>
> /**
> diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
> index c06c442..30f089e 100644
> --- a/include/linux/kernfs.h
> +++ b/include/linux/kernfs.h
> @@ -152,6 +152,8 @@ struct kernfs_syscall_ops {
> int (*rmdir)(struct kernfs_node *kn);
> int (*rename)(struct kernfs_node *kn, struct kernfs_node *new_parent,
> const char *new_name);
> + int (*show_path)(struct seq_file *sf, struct kernfs_node *kn,
> + struct kernfs_root *root);
> };
>
> struct kernfs_root {
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 671dc05..9a0d7b3 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -1593,6 +1593,40 @@ static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
> return 0;
> }
>
> +static int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
> + struct kernfs_root *kf_root)
> +{
> + int len = 0, ret = 0;
> + char *buf = NULL;
> + struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
> + struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
> + struct cgroup *ns_cgroup;
> +
> + mutex_lock(&cgroup_mutex);
Hm, I can't grab the cgroup mutex here because I already have the
namespace_sem. But that's required by cset_cgroup_from_root(). Can
I just call that under rcu_read_lock() instead? (Not without
changing the lockdep_assert_help()). Is there another way to get the
info needed here?
> + spin_lock_bh(&css_set_lock);
> + ns_cgroup = cset_cgroup_from_root(ns->root_cset, kf_cgroot);
> + len = kernfs_path_from_node(kf_node, ns_cgroup->kn, NULL, 0);
> + if (len > 0)
> + buf = kmalloc(len + 1, GFP_ATOMIC);
> + if (buf)
> + ret = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, len + 1);
> +
> + spin_unlock_bh(&css_set_lock);
> + mutex_unlock(&cgroup_mutex);
> +
> + if (len <= 0)
> + return len;
> + if (!buf)
> + return -ENOMEM;
> + if (ret == len) {
> + seq_escape(sf, buf, " \t\n\\");
> + ret = 0;
> + } else if (ret >= 0)
> + ret = -EINVAL;
> + kfree(buf);
> + return ret;
> +}
> +
> static int cgroup_show_options(struct seq_file *seq,
> struct kernfs_root *kf_root)
> {
> @@ -5430,6 +5464,7 @@ static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
> .mkdir = cgroup_mkdir,
> .rmdir = cgroup_rmdir,
> .rename = cgroup_rename,
> + .show_path = cgroup_show_path,
> };
>
> static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
> --
> 2.7.4
>
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