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Re: [Qemu-devel] [PATCH v2] usb: assign unique serial numbers to hid dev
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v2] usb: assign unique serial numbers to hid devices |
Date: |
Fri, 14 Sep 2018 15:46:15 +0100 |
User-agent: |
Mutt/1.10.1 (2018-07-13) |
* Gerd Hoffmann (address@hidden) 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 / address@hidden / Manchester, UK