linux-kernel - [PATCH 01/12] kernfs: add function to find kernfs

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Date:   Mon, 12 Nov 2018 10:56:21 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Jens Axboe <axboe@...nel.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Angelo Ruocco <angeloruocco90@...il.com>,
        Dennis Zhou <dennis@...nel.org>,
        Josef Bacik <josef@...icpanda.com>,
        Liu Bo <bo.liu@...ux.alibaba.com>,
        Bart Van Assche <bvanassche@....org>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        ulf.hansson@...aro.org, linus.walleij@...aro.org,
        broonie@...nel.org, bfq-iosched@...glegroups.com,
        oleksandr@...alenko.name, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Paolo Valente <paolo.valente@...aro.org>
Subject: [PATCH 01/12] kernfs: add function to find kernfs_node without increasing ref counter

From: Angelo Ruocco <angeloruocco90@...il.com>

The kernfs pseudo file system doesn't export any function to only find
a node by name, without also getting a reference on it.
But in some cases it is useful to just locate a kernfs node, while
using it or not depends on some other condition.

This commit adds a function to just look for a node, without getting
a reference on it.

Signed-off-by: Angelo Ruocco <angeloruocco90@...il.com>
Signed-off-by: Paolo Valente <paolo.valente@...aro.org>
---
 fs/kernfs/dir.c        | 13 +++++++++++++
 include/linux/kernfs.h |  7 +++++++
 2 files changed, 20 insertions(+)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 4ca0b5c18192..0003c665869d 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -892,6 +892,19 @@ static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
 	return parent;
 }
 
+struct kernfs_node *kernfs_find(struct kernfs_node *parent,
+				const unsigned char *name)
+{
+	struct kernfs_node *kn;
+
+	mutex_lock(&kernfs_mutex);
+	kn = kernfs_find_ns(parent, name, NULL);
+	mutex_unlock(&kernfs_mutex);
+
+	return kn;
+}
+EXPORT_SYMBOL_GPL(kernfs_find);
+
 /**
  * kernfs_find_and_get_ns - find and get kernfs_node with the given name
  * @parent: kernfs_node to search under
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 5b36b1287a5a..26e69d285964 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -309,6 +309,8 @@ 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_find(struct kernfs_node *parent,
+				const unsigned char *name);
 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);
@@ -391,6 +393,11 @@ 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_find(struct kernfs_node *parent, const char *name)
+{ return NULL; }
+
 static inline struct kernfs_node *
 kernfs_walk_and_get_ns(struct kernfs_node *parent, const char *path,
 		       const void *ns)
-- 
2.16.1