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

From: Markus Armbruster
Subject: Re: [Qemu-devel] [PATCH v2] usb: assign unique serial numbers to hid devices
Date: Wed, 19 Sep 2018 15:13:38 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)

Gerd Hoffmann <address@hidden> writes:

>   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.

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