kernfs: combine ino/id lookup functions into kernfs_find_and_get_node_by_id()

kernfs_find_and_get_node_by_ino() looks the kernfs_node matching the
specified ino.  On top of that, kernfs_get_node_by_id() and
kernfs_fh_get_inode() implement full ID matching by testing the rest
of ID.

On surface, confusingly, the two are slightly different in that the
latter uses 0 gen as wildcard while the former doesn't - does it mean
that the latter can't uniquely identify inodes w/ 0 gen?  In practice,
this is a distinction without a difference because generation number
starts at 1.  There are no actual IDs with 0 gen, so it can always
safely used as wildcard.

Let's simplify the code by renaming kernfs_find_and_get_node_by_ino()
to kernfs_find_and_get_node_by_id(), moving all lookup logics into it,
and removing now unnecessary kernfs_get_node_by_id().

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/kernfs/dir.c

@@ -696,17 +696,22 @@ struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
 }
 
 /*
- * kernfs_find_and_get_node_by_ino - get kernfs_node from inode number
+ * kernfs_find_and_get_node_by_id - get kernfs_node from node id
  * @root: the kernfs root
- * @ino: inode number
+ * @id: the target node id
+ *
+ * @id's lower 32bits encode ino and upper gen.  If the gen portion is
+ * zero, all generations are matched.
  *
  * RETURNS:
  * NULL on failure. Return a kernfs node with reference counter incremented
  */
-struct kernfs_node *kernfs_find_and_get_node_by_ino(struct kernfs_root *root,
+struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root,
-						    unsigned int ino)
+						   u64 id)
 {
 	struct kernfs_node *kn;
+	ino_t ino = kernfs_id_ino(id);
+	u32 gen = kernfs_id_gen(id);
 
 	spin_lock(&kernfs_idr_lock);
 
@@ -714,6 +719,10 @@ struct kernfs_node *kernfs_find_and_get_node_by_ino(struct kernfs_root *root,
 	if (!kn)
 		goto err_unlock;
 
+	/* 0 matches all generations */
+	if (unlikely(gen && kernfs_gen(kn) != gen))
+		goto err_unlock;
+
 	/*
 	 * ACTIVATED is protected with kernfs_mutex but it was clear when
 	 * @kn was added to idr and we just wanna see it set.  No need to

fs/kernfs/kernfs-internal.h

@@ -109,8 +109,6 @@ struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
 				    const char *name, umode_t mode,
 				    kuid_t uid, kgid_t gid,
 				    unsigned flags);
-struct kernfs_node *kernfs_find_and_get_node_by_ino(struct kernfs_root *root,
-						    unsigned int ino);
 
 /*
  * file.c

fs/kernfs/mount.c

@@ -53,24 +53,6 @@ const struct super_operations kernfs_sops = {
 	.show_path	= kernfs_sop_show_path,
 };
 
-/*
- * Similar to kernfs_fh_get_inode, this one gets kernfs node from inode
- * number and generation
- */
-struct kernfs_node *kernfs_get_node_by_id(struct kernfs_root *root, u64 id)
-{
-	struct kernfs_node *kn;
-
-	kn = kernfs_find_and_get_node_by_ino(root, kernfs_id_ino(id));
-	if (!kn)
-		return NULL;
-	if (kernfs_gen(kn) != kernfs_id_gen(id)) {
-		kernfs_put(kn);
-		return NULL;
-	}
-	return kn;
-}
-
 static struct inode *kernfs_fh_get_inode(struct super_block *sb,
 		u64 ino, u32 generation)
 {
@@ -81,7 +63,8 @@ static struct inode *kernfs_fh_get_inode(struct super_block *sb,
 	if (ino == 0)
 		return ERR_PTR(-ESTALE);
 
-	kn = kernfs_find_and_get_node_by_ino(info->root, ino);
+	kn = kernfs_find_and_get_node_by_id(info->root,
+					    ino | ((u64)generation << 32));
 	if (!kn)
 		return ERR_PTR(-ESTALE);
 	inode = kernfs_get_inode(sb, kn);
@@ -89,11 +72,6 @@ static struct inode *kernfs_fh_get_inode(struct super_block *sb,
 	if (!inode)
 		return ERR_PTR(-ESTALE);
 
-	if (generation && inode->i_generation != generation) {
-		/* we didn't find the right inode.. */
-		iput(inode);
-		return ERR_PTR(-ESTALE);
-	}
 	return inode;
 }
 

include/linux/kernfs.h

@@ -393,7 +393,8 @@ void kernfs_kill_sb(struct super_block *sb);
 
 void kernfs_init(void);
 
-struct kernfs_node *kernfs_get_node_by_id(struct kernfs_root *root, u64 id);
+struct kernfs_node *kernfs_find_and_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)

kernel/cgroup/cgroup.c

@@ -5790,7 +5790,7 @@ void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen)
 {
 	struct kernfs_node *kn;
 
-	kn = kernfs_get_node_by_id(cgrp_dfl_root.kf_root, id);
+	kn = kernfs_find_and_get_node_by_id(cgrp_dfl_root.kf_root, id);
 	if (!kn)
 		return;
 	kernfs_path(kn, buf, buflen);