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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 07e4fead45 ("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: Omar Sandoval <osandov@fb.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Omar Sandoval 2017-01-31 14:53:17 -08:00 committed by Jens Axboe
parent 0dba1314d4
commit a7c5437b0b
2 changed files with 44 additions and 0 deletions
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36
fs/debugfs/inode.c
View File

@ -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;

8
include/linux/debugfs.h
View File

@ -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)