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[PATCH 2/5] kernfs: implement kernfs_walk_and_get()

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  [PATCH 2/5] kernfs: implement kernfs_walk_and_get() Tejun Heo <tj@kernel.org> - 2015-11-17 20:50 +0100
    Re: [PATCH 2/5] kernfs: implement kernfs_walk_and_get() David Miller <davem@davemloft.net> - 2015-11-17 22:30 +0100
      Re: [PATCH 2/5] kernfs: implement kernfs_walk_and_get() Tejun Heo <tj@kernel.org> - 2015-11-17 22:30 +0100
      Re: [PATCH 2/5] kernfs: implement kernfs_walk_and_get() Jan Engelhardt <jengelh@inai.de> - 2015-11-17 23:50 +0100

#1271620 — [PATCH 2/5] kernfs: implement kernfs_walk_and_get()

Implement kernfs_walk_and_get() which is similar to
kernfs_find_and_get() but can walk a path instead of just a name.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/kernfs/dir.c        | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/kernfs.h | 12 ++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 91e0045..95dc415 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -694,6 +694,31 @@ static struct kernfs_node *kernfs_find_ns(struct kernfs_node *parent,
 	return NULL;
 }
 
+static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
+					  const unsigned char *path,
+					  const void *ns)
+{
+	static char path_buf[PATH_MAX];	/* protected by kernfs_mutex */
+	int len = strlen(path);
+	char *p, *name;
+
+	lockdep_assert_held(&kernfs_mutex);
+
+	if (len >= PATH_MAX)
+		return NULL;
+
+	memcpy(path_buf, path, len + 1);
+	p = path_buf;
+
+	while ((name = strsep(&p, "/")) && parent) {
+		if (*name == '\0')
+			continue;
+		parent = kernfs_find_ns(parent, name, ns);
+	}
+
+	return parent;
+}
+
 /**
  * kernfs_find_and_get_ns - find and get kernfs_node with the given name
  * @parent: kernfs_node to search under
@@ -719,6 +744,29 @@ struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
 EXPORT_SYMBOL_GPL(kernfs_find_and_get_ns);
 
 /**
+ * kernfs_walk_and_get_ns - find and get kernfs_node with the given path
+ * @parent: kernfs_node to search under
+ * @path: path to look for
+ * @ns: the namespace tag to use
+ *
+ * Look for kernfs_node with path @path under @parent and get a reference
+ * if found.  This function may sleep and returns pointer to the found
+ * kernfs_node on success, %NULL on failure.
+ */
+struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
+					   const char *path, const void *ns)
+{
+	struct kernfs_node *kn;
+
+	mutex_lock(&kernfs_mutex);
+	kn = kernfs_walk_ns(parent, path, ns);
+	kernfs_get(kn);
+	mutex_unlock(&kernfs_mutex);
+
+	return kn;
+}
+
+/**
  * kernfs_create_root - create a new kernfs hierarchy
  * @scops: optional syscall operations for the hierarchy
  * @flags: KERNFS_ROOT_* flags
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 5d4e9c4..af51df3 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -274,6 +274,8 @@ void pr_cont_kernfs_path(struct kernfs_node *kn);
 struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn);
 struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
 					   const char *name, const void *ns);
+struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
+					   const char *path, const void *ns);
 void kernfs_get(struct kernfs_node *kn);
 void kernfs_put(struct kernfs_node *kn);
 
@@ -350,6 +352,10 @@ static inline struct kernfs_node *
 kernfs_find_and_get_ns(struct kernfs_node *parent, const char *name,
 		       const void *ns)
 { return NULL; }
+static inline struct kernfs_node *
+kernfs_walk_and_get_ns(struct kernfs_node *parent, const char *path,
+		       const void *ns)
+{ return NULL; }
 
 static inline void kernfs_get(struct kernfs_node *kn) { }
 static inline void kernfs_put(struct kernfs_node *kn) { }
@@ -431,6 +437,12 @@ kernfs_find_and_get(struct kernfs_node *kn, const char *name)
 }
 
 static inline struct kernfs_node *
+kernfs_walk_and_get(struct kernfs_node *kn, const char *path)
+{
+	return kernfs_walk_and_get_ns(kn, path, NULL);
+}
+
+static inline struct kernfs_node *
 kernfs_create_dir(struct kernfs_node *parent, const char *name, umode_t mode,
 		  void *priv)
 {
-- 
2.5.0

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#1271668

From: Tejun Heo <tj@kernel.org>
Date: Tue, 17 Nov 2015 14:40:37 -0500

> +	static char path_buf[PATH_MAX];	/* protected by kernfs_mutex */
> +	int len = strlen(path);
 ...
> +	if (len >= PATH_MAX)
> +		return NULL;
> +
> +	memcpy(path_buf, path, len + 1);

	static char path_buf[PATH_MAX];	/* protected by kernfs_mutex */
	int len = strlcpy(path_buf, path, PATH_MAX);
 ...
	if (len >= PATH_MAX)
		return NULL;
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#1271675

On Tue, Nov 17, 2015 at 04:20:40PM -0500, David Miller wrote:
> From: Tejun Heo <tj@kernel.org>
> Date: Tue, 17 Nov 2015 14:40:37 -0500
> 
> > +	static char path_buf[PATH_MAX];	/* protected by kernfs_mutex */
> > +	int len = strlen(path);
>  ...
> > +	if (len >= PATH_MAX)
> > +		return NULL;
> > +
> > +	memcpy(path_buf, path, len + 1);
> 
> 	static char path_buf[PATH_MAX];	/* protected by kernfs_mutex */
> 	int len = strlcpy(path_buf, path, PATH_MAX);
>  ...
> 	if (len >= PATH_MAX)
> 		return NULL;

That's a lot better.  Will update.

Thanks.

-- 
tejun
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#1271713

On Tuesday 2015-11-17 22:20, David Miller wrote:
>> +	static char path_buf[PATH_MAX];	/* protected by kernfs_mutex */
>> +	int len = strlen(path);
> ...
>> +	if (len >= PATH_MAX)
>> +		return NULL;
>> +
>> +	memcpy(path_buf, path, len + 1);
>
>	static char path_buf[PATH_MAX];	/* protected by kernfs_mutex */
>	int len = strlcpy(path_buf, path, PATH_MAX);
> ...
>	if (len >= PATH_MAX)
>		return NULL;

	if (len < 0 || len >= PATH_MAX)

strlcpy returns a size_t, which, when coerced into an int, could lead to
negative numbers. In that sense, "size_t len" probably seems like an even
better bet yet.
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