Re: [PATCH bpf-next 1/2] bpf: Add kfunc bpf_get_dentry_xattr() to read xattr from dentry

[Al Viro <viro@zeniv.linux.org.uk>]

On Thu, Jul 25, 2024 at 04:47:05PM -0700, Song Liu wrote:

> +__bpf_kfunc struct dentry *bpf_file_dentry(const struct file *file)
> +{
> +	/* file_dentry() does not hold reference to the dentry. We add a
> +	 * dget() here so that we can add KF_ACQUIRE flag to
> +	 * bpf_file_dentry().
> +	 */
> +	return dget(file_dentry(file));
> +}
> +
> +__bpf_kfunc struct dentry *bpf_dget_parent(struct dentry *dentry)
> +{
> +	return dget_parent(dentry);
> +}
> +
> +__bpf_kfunc void bpf_dput(struct dentry *dentry)
> +{
> +	return dput(dentry);
> +}

	If you keep a file reference, why bother grabbing dentry one?
If not, you have a very bad trouble if that opened file is the only
thing that keeps the filesystem busy.

	It's almost certainly a wrong interface; please, explain what
exactly are you trying to do here.