Re: [PATCH 0/3] HID: make raw output callback more flexible

Michael Poole
2010-02-03T01:25:37Z

Bastien Nocera writes:

> On Fri, 2010-01-29 at 19:46 -0500, Michael Poole wrote:
>> > [1]: Comments on the patch at
>> > http://thread.gmane.org/gmane.linux.bluez.kernel/4279 would be
>> > appreciated
>>
>> This patch does not work for me. Before, the first time after each
>> boot
>> that I tried to connect to an Apple Magic Mouse, it failed with -14
>> (EFAULT). With this patch, it fails with -22 (EINVAL) instead. The
>> -EFAULT *was* due to hidp_parse()'s copy_from_user(). I have not
>> looked
>> yet to see where the -EINVAL is coming from -- would that help? (Both
>> with and without your patch, the second attempt to connect works.)
>
> I don't get -EFAULT anymore (it was failing to copy the rd_data from
> user-space), but I do get -EINVALs now. I haven't investigated it
> though. My guess is that the hid parser fails.
>
> Could you compare the sizes of the data gathered in user-space?

The bug mysteriously disappeared when I tried to apply kgdb to the
problem. Your patch won't do the trick because the hidp_connadd_req
structure has also gone out of scope by the time the hid-(whatever)
probe function is called. The ioctl has returned to the user, but the
new hid-(whatever) module is not yet loaded.

That is, the sequence looks like this:

- Application triggers hidp_sock_ioctl(socket, HIDPCONNADD, &connadd).
- This starts the connection, and returns 0...
- ... but also indicates that some other module needs to be loaded.

- User-space loads the appropriate module does init_module()...
- which calls the module_init() function...
- which calls hid_register_driver()...
- which eventually attaches the new driver to the device...
- triggering the module's probe() function to call hid_parse()...
- hid_parse() fails because its hidp_connadd_req is gone.

Marcel, I think this is a case where the subsystem maintainer should
make the call on how to fix it. I can write and locally test a patch,
but I don't want to assume that (for example) the desired solution is to
keep a copy of the Report descriptor in the hidp_session. The USB HID
core sends a GET_DESCRIPTOR request for the Report descriptor, which
isn't practical here because that descriptor is only available through
SDP.

Michael Poole