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Commit a7c5437b authored by Omar Sandoval's avatar Omar Sandoval Committed by Jens Axboe
Browse files

debugfs: add debugfs_lookup() 



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 07e4fead ("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.

Signed-off-by: default avatarOmar Sandoval <osandov@fb.com>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 0dba1314

fs/debugfs/inode.c

+36 −0
Original line number Diff line number Diff line
@@ -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;

include/linux/debugfs.h

+8 −0
Original line number Diff line number Diff line
@@ -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)