Re: [PATCH] usb: f_mass_storage: test whether thread is running before starting another

[Andrzej Pietrasiewicz]

Hi MichaÅ,

W dniu 07.04.2016 o 18:40, Michal Nazarewicz pisze:
> > On Thu, 7 Apr 2016, Michal Nazarewicz wrote:
> > > This makes me suspect itâs not possible to link a function instance to
> > > the same configuration twice, but now that I think about it, Iâm not
> > > quite sure what would happen if one did:
> > >
> > > 	ln -s functions/mass_storage.0 configs/c.1/foo
> > > 	ln -s functions/mass_storage.0 configs/c.1/bar
>
> On Thu, Apr 07 2016, Alan Stern wrote:
> > Do you think it would be worthwhile to check for this possibility in
> > the driver and report an error?
>
> I think this should be (if it isnât already) blocked on configfs side.
> I cannot see a legitimate use of such configuration and I wouldnât be
> surprised if other function drivers broke as well.

Sorry about late response.

The function responsible for verifying if a symlink can be made is
in drivers/usb/gadget/configfs.c: config_usb_cfg_link()

There is a comment from the author:

	/*
	 * Make sure this function is from within our _this_ gadget and not
	 * from another gadget or a random directory.
	 * Also a function instance can only be linked once.
	 */

This is the code fragment of interest:

	list_for_each_entry(f, &cfg->func_list, list) {
		if (f->fi == fi) {
			ret = -EEXIST;
			goto out;
		}
	}


AP