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Message-Id: <1454057651-23959-6-git-send-email-serge.hallyn@ubuntu.com>
Date: Fri, 29 Jan 2016 02:54:08 -0600
From: serge.hallyn@...ntu.com
To: linux-kernel@...r.kernel.org
Cc: adityakali@...gle.com, tj@...nel.org, linux-api@...r.kernel.org,
containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
lxc-devel@...ts.linuxcontainers.org, akpm@...ux-foundation.org,
ebiederm@...ssion.com, gregkh@...uxfoundation.org,
lizefan@...wei.com, hannes@...xchg.org,
"Serge E. Hallyn" <serge.hallyn@...onical.com>
Subject: [PATCH 5/8] kernfs: define kernfs_node_dentry
From: Aditya Kali <adityakali@...gle.com>
Add a new kernfs api is added to lookup the dentry for a particular
kernfs path.
Signed-off-by: Aditya Kali <adityakali@...gle.com>
Signed-off-by: Serge E. Hallyn <serge.hallyn@...onical.com>
Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
Changelog:
20151116 - Don't allow user namespaces to bind new subsystems
20151118 - postpone the FS_USERNS_MOUNT flag until the
last patch, until we can convince ourselves it
is safe.
20151207 - Switch to walking up the kernfs path from kn root.
20151208 - Split out the kernfs change
- Style changes
- Switch from pr_crit to WARN_ON
- Reorder arguments to kernfs_obtain_root
- rename kernfs_obtain_root to kernfs_node_dentry
20160104 - kernfs_node_dentry: lock inode for lookup_one_len()
---
fs/kernfs/mount.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/kernfs.h | 2 ++
2 files changed, 71 insertions(+)
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index 8eaf417..074bb8b 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -14,6 +14,7 @@
#include <linux/magic.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
+#include <linux/namei.h>
#include "kernfs-internal.h"
@@ -62,6 +63,74 @@ struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
return NULL;
}
+/*
+ * find the next ancestor in the path down to @child, where @parent was the
+ * ancestor whose descendant we want to find.
+ *
+ * Say the path is /a/b/c/d. @child is d, @parent is NULL. We return the root
+ * node. If @parent is b, then we return the node for c.
+ * Passing in d as @parent is not ok.
+ */
+static struct kernfs_node *
+find_next_ancestor(struct kernfs_node *child, struct kernfs_node *parent)
+{
+ if (child == parent) {
+ pr_crit_once("BUG in find_next_ancestor: called with parent == child");
+ return NULL;
+ }
+
+ while (child->parent != parent) {
+ if (!child->parent)
+ return NULL;
+ child = child->parent;
+ }
+
+ return child;
+}
+
+/**
+ * kernfs_node_dentry - get a dentry for the given kernfs_node
+ * @kn: kernfs_node for which a dentry is needed
+ * @sb: the kernfs super_block
+ */
+struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
+ struct super_block *sb)
+{
+ struct dentry *dentry;
+ struct kernfs_node *knparent = NULL;
+
+ BUG_ON(sb->s_op != &kernfs_sops);
+
+ dentry = dget(sb->s_root);
+
+ /* Check if this is the root kernfs_node */
+ if (!kn->parent)
+ return dentry;
+
+ knparent = find_next_ancestor(kn, NULL);
+ if (WARN_ON(!knparent))
+ return ERR_PTR(-EINVAL);
+
+ do {
+ struct dentry *dtmp;
+ struct kernfs_node *kntmp;
+
+ if (kn == knparent)
+ return dentry;
+ kntmp = find_next_ancestor(kn, knparent);
+ if (WARN_ON(!kntmp))
+ return ERR_PTR(-EINVAL);
+ mutex_lock(&d_inode(dentry)->i_mutex);
+ dtmp = lookup_one_len(kntmp->name, dentry, strlen(kntmp->name));
+ mutex_unlock(&d_inode(dentry)->i_mutex);
+ dput(dentry);
+ if (IS_ERR(dtmp))
+ return dtmp;
+ knparent = kntmp;
+ dentry = dtmp;
+ } while (1);
+}
+
static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
{
struct kernfs_super_info *info = kernfs_info(sb);
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 716bfde..c06c442 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -284,6 +284,8 @@ struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry);
struct kernfs_root *kernfs_root_from_sb(struct super_block *sb);
struct inode *kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn);
+struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
+ struct super_block *sb);
struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
unsigned int flags, void *priv);
void kernfs_destroy_root(struct kernfs_root *root);
--
1.7.9.5
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