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:
parent
0dba1314d4
commit
a7c5437b0b
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@ -248,6 +248,42 @@ static struct file_system_type debug_fs_type = {
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};
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MODULE_ALIAS_FS("debugfs");
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/**
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* debugfs_lookup() - look up an existing debugfs file
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* @name: a pointer to a string containing the name of the file to look up.
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* @parent: a pointer to the parent dentry of the file.
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*
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* This function will return a pointer to a dentry if it succeeds. If the file
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* doesn't exist or an error occurs, %NULL will be returned. The returned
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* dentry must be passed to dput() when it is no longer needed.
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*
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* If debugfs is not enabled in the kernel, the value -%ENODEV will be
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* returned.
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*/
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struct dentry *debugfs_lookup(const char *name, struct dentry *parent)
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{
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struct dentry *dentry;
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if (IS_ERR(parent))
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return NULL;
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if (!parent)
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parent = debugfs_mount->mnt_root;
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inode_lock(d_inode(parent));
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dentry = lookup_one_len(name, parent, strlen(name));
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inode_unlock(d_inode(parent));
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if (IS_ERR(dentry))
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return NULL;
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if (!d_really_is_positive(dentry)) {
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dput(dentry);
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return NULL;
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}
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return dentry;
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}
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EXPORT_SYMBOL_GPL(debugfs_lookup);
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static struct dentry *start_creating(const char *name, struct dentry *parent)
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{
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struct dentry *dentry;
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@ -80,6 +80,8 @@ static const struct file_operations __fops = { \
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#if defined(CONFIG_DEBUG_FS)
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struct dentry *debugfs_lookup(const char *name, struct dentry *parent);
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struct dentry *debugfs_create_file(const char *name, umode_t mode,
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struct dentry *parent, void *data,
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const struct file_operations *fops);
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@ -181,6 +183,12 @@ ssize_t debugfs_write_file_bool(struct file *file, const char __user *user_buf,
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* want to duplicate the design decision mistakes of procfs and devfs again.
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*/
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static inline struct dentry *debugfs_lookup(const char *name,
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struct dentry *parent)
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{
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return ERR_PTR(-ENODEV);
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}
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static inline struct dentry *debugfs_create_file(const char *name, umode_t mode,
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struct dentry *parent, void *data,
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const struct file_operations *fops)
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