kernfs: convert kernfs_node->id from union kernfs_node_id to u64

kernfs_node->id is currently a union kernfs_node_id which represents
either a 32bit (ino, gen) pair or u64 value.  I can't see much value
in the usage of the union - all that's needed is a 64bit ID which the
current code is already limited to.  Using a union makes the code
unnecessarily complicated and prevents using 64bit ino without adding
practical benefits.

This patch drops union kernfs_node_id and makes kernfs_node->id a u64.
ino is stored in the lower 32bits and gen upper.  Accessors -
kernfs[_id]_ino() and kernfs[_id]_gen() - are added to retrieve the
ino and gen.  This simplifies ID handling less cumbersome and will
allow using 64bit inos on supported archs.

This patch doesn't make any functional changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Alexei Starovoitov <ast@kernel.org>

3 files changed, 37 insertions, 29 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index f6b048902d6c..815fff49d555 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -616,7 +616,7 @@ static inline bool cgroup_is_populated(struct cgroup *cgrp)
 /* returns ino associated with a cgroup */
 static inline ino_t cgroup_ino(struct cgroup *cgrp)
 {
-	return cgrp->kn->id.ino;
+	return kernfs_ino(cgrp->kn);
 }
 
 /* cft/css accessors for cftype->write() operation */
@@ -687,13 +687,12 @@ static inline void cgroup_kthread_ready(void)
 	current->no_cgroup_migration = 0;
 }
 
-static inline union kernfs_node_id *cgroup_get_kernfs_id(struct cgroup *cgrp)
+static inline u64 cgroup_get_kernfs_id(struct cgroup *cgrp)
 {
-	return &cgrp->kn->id;
+	return cgrp->kn->id;
 }
 
-void cgroup_path_from_kernfs_id(const union kernfs_node_id *id,
-					char *buf, size_t buflen);
+void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen);
 #else /* !CONFIG_CGROUPS */
 
 struct cgroup_subsys_state;
@@ -718,9 +717,9 @@ 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 union kernfs_node_id *cgroup_get_kernfs_id(struct cgroup *cgrp)
+static inline union u64 cgroup_get_kernfs_id(struct cgroup *cgrp)
 {
-	return NULL;
+	return 0;
 }
 
 static inline struct cgroup *cgroup_parent(struct cgroup *cgrp)
@@ -739,8 +738,8 @@ static inline bool task_under_cgroup_hierarchy(struct task_struct *task,
 	return true;
 }
 
-static inline void cgroup_path_from_kernfs_id(const union kernfs_node_id *id,
-	char *buf, size_t buflen) {}
+static inline void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen)
+{}
 #endif /* !CONFIG_CGROUPS */
 
 #ifdef CONFIG_CGROUPS
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index f797ccc650e7..b2fc5c8ef6d9 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -104,21 +104,6 @@ struct kernfs_elem_attr {
 	struct kernfs_node	*notify_next;	/* for kernfs_notify() */
 };
 
-/* represent a kernfs node */
-union kernfs_node_id {
-	struct {
-		/*
-		 * blktrace will export this struct as a simplified 'struct
-		 * fid' (which is a big data struction), so userspace can use
-		 * it to find kernfs node. The layout must match the first two
-		 * fields of 'struct fid' exactly.
-		 */
-		u32		ino;
-		u32		generation;
-	};
-	u64			id;
-};
-
 /*
  * kernfs_node - the building block of kernfs hierarchy.  Each and every
  * kernfs node is represented by single kernfs_node.  Most fields are
@@ -155,7 +140,12 @@ struct kernfs_node {
 
 	void			*priv;
 
-	union kernfs_node_id	id;
+	/*
+	 * 64bit unique ID.  Lower 32bits carry the inode number and lower
+	 * generation.
+	 */
+	u64			id;
+
 	unsigned short		flags;
 	umode_t			mode;
 	struct kernfs_iattrs	*iattr;
@@ -292,6 +282,26 @@ static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
 	return kn->flags & KERNFS_TYPE_MASK;
 }
 
+static inline ino_t kernfs_id_ino(u64 id)
+{
+	return (u32)id;
+}
+
+static inline u32 kernfs_id_gen(u64 id)
+{
+	return id >> 32;
+}
+
+static inline ino_t kernfs_ino(struct kernfs_node *kn)
+{
+	return kernfs_id_ino(kn->id);
+}
+
+static inline ino_t kernfs_gen(struct kernfs_node *kn)
+{
+	return kernfs_id_gen(kn->id);
+}
+
 /**
  * kernfs_enable_ns - enable namespace under a directory
  * @kn: directory of interest, should be empty
@@ -383,8 +393,7 @@ void kernfs_kill_sb(struct super_block *sb);
 
 void kernfs_init(void);
 
-struct kernfs_node *kernfs_get_node_by_id(struct kernfs_root *root,
-	const union kernfs_node_id *id);
+struct kernfs_node *kernfs_get_node_by_id(struct kernfs_root *root, u64 id);
 #else	/* CONFIG_KERNFS */
 
 static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 95e50677476b..b4f0ffe1817e 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -152,7 +152,7 @@ DEFINE_EVENT(writeback_dirty_inode_template, writeback_dirty_inode,
 
 static inline ino_t __trace_wb_assign_cgroup(struct bdi_writeback *wb)
 {
-	return wb->memcg_css->cgroup->kn->id.ino;
+	return cgroup_ino(wb->memcg_css->cgroup);
 }
 
 static inline ino_t __trace_wbc_assign_cgroup(struct writeback_control *wbc)
@@ -260,7 +260,7 @@ TRACE_EVENT(track_foreign_dirty,
 		__entry->ino		= inode ? inode->i_ino : 0;
 		__entry->memcg_id	= wb->memcg_css->id;
 		__entry->cgroup_ino	= __trace_wb_assign_cgroup(wb);
-		__entry->page_cgroup_ino = page->mem_cgroup->css.cgroup->kn->id.ino;
+		__entry->page_cgroup_ino = cgroup_ino(page->mem_cgroup->css.cgroup);
 	),
 
 	TP_printk("bdi %s[%llu]: ino=%lu memcg_id=%u cgroup_ino=%lu page_cgroup_ino=%lu",