[RFC] fs: add userspace critical mounts event support

[Luis R. Rodriguez]

On Tue, Oct 4, 2016 at 5:12 PM, Linus Torvalds
<torvalds at linux-foundation.org> wrote:
> On Tue, Oct 4, 2016 at 5:00 PM, Luis R. Rodriguez <mcgrof at kernel.org> wrote:
>>
>> I am not sure how/why a firmware loading daemon would be a better
>> idea now. What Marc describes that Josh proposed with signals for
>> userspcae seems more aligned with what we likely need
>
> Quite frankly, I doubt you want a signal.
>
> You will want to have some way to specify where the firmware files
> are. Right now we have "fw_path[]" which is hardcoded except for the
> first entry that can be set as a module parameter. But you'd probably
> want to expand on that, which implies some /sys or /proc interface.
>
> And once you do that, wouldn't it make more sense to just make the
> "update the firmware path /proc/sys/kernel/fw_path file" make things
> re-search for firmware?

We can, but re-searching for firmware assumes we cache pending
firmware, we currently don't, we just either process sync or async
firmware requests.

> In other words, the interface has to be something *sensible*. Not some
> idiotic ad-hoc "send a signal" (of which that stupid original patch
> was just a very odd example).

Note that the races are beyond firmware, so all
kernel_read_file_from_path() users, as such re-using such old /sys/
interafeces for firmware will not suffice to cover all ground now for
the same race for other possible users.

 Luis