This is just so to have the skeleton for a discussion on how to implement "blob" properly. I am hoping @jfree may have a good idea.

I feel like the scattered nature of debugfs material makes it incredibly difficult to work with.
Perhaps something along the lines of this would work:

static int
debugfs_blob_get(void *data, uint64_t *value)
{
	struct debugfs_blob_wrapper *blob = data;
	memcpy(value, blob->data, blob->size);
	return (0);
}

static int
debugfs_blob_set(void *data, uint64_t value)
{
	struct debugfs_blob_wrapper *blob = data;
	blob->size = sizeof(value);
	memcpy(blob->data, &value, blob->size);
	return (0);
}

I think the blob's fops should be defined manually rather than using DEFINE_DEBUGFS_ATTRIBUTE.
This will allow us to malloc the blob->data member in an open fop and free data in the release fop.
The problem is, this malloc would only account for a single sized blob. We would need to add bounds
checking in the blob's get and set functions to ensure safety.

Alternatively, we could dynamically malloc in debugfs_blob_set, but I do not know how to reliably free that.

I am not sure what the origin authors intended for the implementation. Let me know what you think.

I just took a quick glance, but everything looks good :)
Take a look at my inline comment, though.

Anyone care to further review / accept this?