[PATCH 07/10] kernfs: combine ino/id lookup functions into kernfs_find_and_get_node_by_id()

Tejun Heo
2019-11-05T00:00:24Z

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>
---
fs/kernfs/dir.c | 17 +++++++++++++----
fs/kernfs/kernfs-internal.h | 2 --
fs/kernfs/mount.c | 26 ++------------------------
include/linux/kernfs.h | 3 ++-
kernel/cgroup/cgroup.c | 2 +-
5 files changed, 18 insertions(+), 32 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index c67afb591e5b..5dcf19d4adbc 100644
--- a/fs/kernfs/dir.c
+++ b/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,
- unsigned int ino)
+struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root,
+ 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
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 02ce570a9a3c..2f3c51d55261 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/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
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index f05d5d6f926d..8aed2cccd002 100644
--- a/fs/kernfs/mount.c
+++ b/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;
}

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index b2fc5c8ef6d9..38267cc9420c 100644
--- a/include/linux/kernfs.h
+++ b/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)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index c6bd1a5a1977..b5dcbee5aa6c 100644
--- a/kernel/cgroup/cgroup.c
+++ b/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);
--
2.17.1