On Tue, 25 Aug 2015 13:54:23 +0600 Alexander Kuleshov <kuleshovmail@xxxxxxxxx> wrote:
> The debugfs_create_dir() function may fail and return error. If the
> root directory not created, we can't create anything inside it. This
> patch adds check for this case.
>
> ...
>
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -117,15 +117,21 @@ static const struct file_operations bdi_debug_stats_fops = {
>
> static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
> {
> - bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
> - bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
> - bdi, &bdi_debug_stats_fops);
> + if (bdi_debug_root) {
> + bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
> + if (bdi->debug_dir)
> + bdi->debug_stats = debugfs_create_file("stats", 0444,
> + bdi->debug_dir, bdi,
> + &bdi_debug_stats_fops);
> + }
If debugfs_create_dir() fails, debugfs_create_file() will go ahead and
attempt to create the debugfs file in the debugfs root directory:
: static struct dentry *start_creating(const char *name, struct dentry *parent)
: {
: ...
: /* If the parent is not specified, we create it in the root.
: * We need the root dentry to do this, which is in the super
: * block. A pointer to that is in the struct vfsmount that we
: * have around.
: */
: if (!parent)
: parent = debugfs_mount->mnt_root;
I'm not sure that this is very useful behaviour, and putting the files
in the wrong place is a very obscure way of informing the user that
debugfs_create_dir() failed :(
I don't think it's worth making little changes such as this - handling
debugfs failures needs a deeper rethink.
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