From: Omar Sandoval <osandov@xxxxxx>
We don't always have easy access to the dentry of a file or directory we
created in debugfs. Add a helper which allows us to get a dentry we
previously created.
The motivation for this change is a problem with blktrace and the blk-mq
debugfs entries introduced in 07e4fead45e6 ("blk-mq: create debugfs
directory tree"). Namely, in some cases, the directory that blktrace
needs to create may already exist, but in other cases, it may not. We
_could_ rely on a bunch of implied knowledge to decide whether to create
the directory or not, but it's much cleaner on our end to just look it
up.
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Omar Sandoval <osandov@xxxxxx>
---
fs/debugfs/inode.c | 36 ++++++++++++++++++++++++++++++++++++
include/linux/debugfs.h | 8 ++++++++
2 files changed, 44 insertions(+)
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index f17fcf89e18e..7fb1732a3630 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -248,6 +248,42 @@ static struct file_system_type debug_fs_type = {
};
MODULE_ALIAS_FS("debugfs");
+/**
+ * debugfs_lookup() - look up an existing debugfs file
+ * @name: a pointer to a string containing the name of the file to look up.
+ * @parent: a pointer to the parent dentry of the file.
+ *
+ * This function will return a pointer to a dentry if it succeeds. If the file
+ * doesn't exist or an error occurs, %NULL will be returned. The returned
+ * dentry must be passed to dput() when it is no longer needed.
+ *
+ * If debugfs is not enabled in the kernel, the value -%ENODEV will be
+ * returned.
+ */
+struct dentry *debugfs_lookup(const char *name, struct dentry *parent)
+{
+ struct dentry *dentry;
+
+ if (IS_ERR(parent))
+ return NULL;
+
+ if (!parent)
+ parent = debugfs_mount->mnt_root;
+
+ inode_lock(d_inode(parent));
+ dentry = lookup_one_len(name, parent, strlen(name));
+ inode_unlock(d_inode(parent));
+
+ if (IS_ERR(dentry))
+ return NULL;
+ if (!d_really_is_positive(dentry)) {
+ dput(dentry);
+ return NULL;
+ }
+ return dentry;
+}
+EXPORT_SYMBOL_GPL(debugfs_lookup);
+
static struct dentry *start_creating(const char *name, struct dentry *parent)
{
struct dentry *dentry;
diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index 014cc564d1c4..c0befcf41b58 100644
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -80,6 +80,8 @@ static const struct file_operations __fops = { \
#if defined(CONFIG_DEBUG_FS)
+struct dentry *debugfs_lookup(const char *name, struct dentry *parent);
+
struct dentry *debugfs_create_file(const char *name, umode_t mode,
struct dentry *parent, void *data,
const struct file_operations *fops);
@@ -181,6 +183,12 @@ ssize_t debugfs_write_file_bool(struct file *file, const char __user *user_buf,
* want to duplicate the design decision mistakes of procfs and devfs again.
*/
+static inline struct dentry *debugfs_lookup(const char *name,
+ struct dentry *parent)
+{
+ return ERR_PTR(-ENODEV);
+}
+
static inline struct dentry *debugfs_create_file(const char *name, umode_t mode,
struct dentry *parent, void *data,
const struct file_operations *fops)
--
2.11.0
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