[06/11] cgroup: export fhandle info for a cgroup

Commit Message

Shaohua Li June 2, 2017, 9:53 p.m. UTC

From: Shaohua Li <[e-mail]>

Add an API to export cgroup fhandle info. We don't export a full 'struct
file_handle', there are unrequired info. Sepcifically, cgroup is always
a directory, so we don't need a 'FILEID_INO32_GEN_PARENT' type fhandle,
we only need export the inode number and generation number just like
what generic_fh_to_parent does. And we can avoid the overhead of getting
an inode too, since kernfs_node has all the info required.

Signed-off-by: Shaohua Li <[e-mail]>
---
 fs/kernfs/mount.c           | 11 +++++++++++
 include/linux/cgroup-defs.h |  2 ++
 include/linux/cgroup.h      |  8 ++++++++
 include/linux/kernfs.h      |  8 ++++++++
 kernel/cgroup/cgroup.c      |  3 +++
 5 files changed, 32 insertions(+)

Comments

Tejun Heo June 12, 2017, 6:44 p.m. UTC | #1

On Fri, Jun 02, 2017 at 02:53:59PM -0700, Shaohua Li wrote:
> From: Shaohua Li <[e-mail]>
> 
> Add an API to export cgroup fhandle info. We don't export a full 'struct
> file_handle', there are unrequired info. Sepcifically, cgroup is always
> a directory, so we don't need a 'FILEID_INO32_GEN_PARENT' type fhandle,
> we only need export the inode number and generation number just like
> what generic_fh_to_parent does. And we can avoid the overhead of getting
> an inode too, since kernfs_node has all the info required.

Can't we just make it an integral (optional) part of kernfs?  So that
cgroup just needs to indicate that it wants to expose fhandles when
creating its kernfs instance?

Thanks.

Patch

diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index 11c5aba..d24d816 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -65,6 +65,17 @@  const struct super_operations kernfs_sops = {
 	.show_path	= kernfs_sop_show_path,
 };
 
+/*
+ * A special version of export_encode_fh(). This will avoid to get inode and
+ * then do the fhandle encoding. This function must match with export_encode_fh
+ * and the kernfs node should be a directory.
+ */
+void kernfs_encode_node_id(struct kernfs_node *kn, struct kernfs_node_id *id)
+{
+	id->ino = kn->ino;
+	id->gen = kn->generation;
+}
+
 static struct inode *kernfs_fh_get_inode(struct super_block *sb,
 		u64 ino, u32 generation)
 {
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 2174594..8b6d9e2 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -308,6 +308,8 @@  struct cgroup {
 	/* used to store eBPF programs */
 	struct cgroup_bpf bpf;
 
+	struct kernfs_node_id node_id;
+
 	/* ids of the ancestors at each level including self */
 	int ancestor_ids[];
 };
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index ed2573e..c30dda8 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -589,6 +589,10 @@  static inline void cgroup_kthread_ready(void)
 	current->no_cgroup_migration = 0;
 }
 
+static inline struct kernfs_node_id *cgroup_get_node_id(struct cgroup *cgrp)
+{
+	return &cgrp->node_id;
+}
 #else /* !CONFIG_CGROUPS */
 
 struct cgroup_subsys_state;
@@ -611,6 +615,10 @@  static inline int cgroup_init_early(void) { return 0; }
 static inline int cgroup_init(void) { return 0; }
 static inline void cgroup_init_kthreadd(void) {}
 static inline void cgroup_kthread_ready(void) {}
+static inline struct kernfs_node_id *cgroup_get_node_id(struct cgroup *cgrp)
+{
+	return NULL;
+}
 
 static inline bool task_under_cgroup_hierarchy(struct task_struct *task,
 					       struct cgroup *ancestor)
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 15c805f..932d89f 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -247,6 +247,12 @@  struct kernfs_ops {
 #endif
 };
 
+/* match with 'struct fid' */
+struct kernfs_node_id {
+	u32 ino;
+	u32 gen;
+};
+
 #ifdef CONFIG_KERNFS
 
 static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
@@ -339,6 +345,8 @@  struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns);
 
 void kernfs_init(void);
 
+void kernfs_encode_node_id(struct kernfs_node *kn, struct kernfs_node_id *id);
+
 #else	/* CONFIG_KERNFS */
 
 static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 206d8df..489672d 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1692,6 +1692,7 @@  int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask, int ref_flags)
 		goto exit_root_id;
 	}
 	root_cgrp->kn = root->kf_root->kn;
+	kernfs_encode_node_id(root_cgrp->kn, &root_cgrp->node_id);
 
 	ret = css_populate_dir(&root_cgrp->self);
 	if (ret)
@@ -4209,6 +4210,8 @@  int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
 	/* let's create and online css's */
 	kernfs_activate(kn);
 
+	kernfs_encode_node_id(kn, &cgrp->node_id);
+
 	ret = 0;
 	goto out_unlock;