Re: [Qemu-devel] [PATCH v2] usb: assign unique serial numbers to hid devices

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Gerd Hoffmann (kraxel@redhat.com) wrote:
>   Hi,
> 
> > OK, so now I've found the bit about the magic 42; commit 7b074a22 of
> > yours; recommended checking for 42 for knowing we had autosuspend;
> > what's actually in the current fedora hid rules is serial!=1 - I wonder
> > what others have.
> 
> Whatever upstream systemd/udev has I guess ...
> 
> A bit of history ...
> 
>  * First there was nothing.
>  * Then I added a rule to udev checking for serial == 42
>    (this is in rhel-6).
>  * Then systemd + udev merged.
>  * Then I changed the rule to check for serial != 1 instead, so we can
>    use any serial but "1" which is the one the old broken devices had
>    (this is in rhel-7).  March 2014 in upstream systemd.
>  * Then all usb power management rules where dropped from systemd (June
>    2015).  Which I figured today, after wondering that the rules are
>    gone in fedora 28.
> 
> So, three years ago the serial number check was dropped upstream, yet I
> hav't seen a single report about autosuspend issues (or cpu usage for
> usb emulation going up, which is the typical symtom).
> 
> So I figured I can stop worring that changing the serial number will
> break things and just do it.
> 
> And even if it turns out autosuspend is still an issue:  I think
> meanwhile we can really stop worrying about guests running in old qemu
> versions with broken usb suspend (fixed in 0.13 !).  If needed we can
> enable autosuspend unconditionally in guests.

OK, so what about the other question - which serial number do we end up
with after this patch; do we get the 89126/28754/68284 or do we get the
path based one from your change that calls usb_desc_create_serial?

Dave

> cheers,
>   Gerd
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK