Re: [Qemu-devel] Should we auto-generate IDs?

[Daniel P. Berrange]

On Thu, Aug 27, 2015 at 12:03:38PM -0400, Programmingkid wrote:
> 
> On Aug 27, 2015, at 11:55 AM, Daniel P. Berrange wrote:
> 
> > On Thu, Aug 27, 2015 at 11:22:58AM -0400, Programmingkid wrote:
> >> 
> >> On Aug 27, 2015, at 11:19 AM, Daniel P. Berrange wrote:
> >> 
> >>> On Thu, Aug 27, 2015 at 11:13:25AM -0400, Programmingkid wrote:
> >>>>> 
> >>>>>> What is wrong with having a predictable ID?
> >>>>>> 
> >>>>> 
> >>>>> As Daniel and Eric have noted, it could be nice to have a predictable
> >>>>> ID.  My concern with a predictable ID is that it creates, across
> >>>>> multiple sub-systems, an ABI that we will then need to make sure
> >>>>> always works.
> >>>>> 
> >>>>> For instance, I don't want management software or a user to rely on us
> >>>>> parsing devices, or image filenames / block driver states in a certain
> >>>>> order, and then anticipate the ID name.  I am concerned about creating
> >>>>> an interface that may inadvertently "break" later on, and imposing a
> >>>>> burden on QEMU that isn't reasonable.  Perhaps it is enough to just
> >>>>> rely on documentation for this, without enforcing it in the scheme.
> >>>> 
> >>>> If we do nothing, QEMU stays broken. The monitor command device_del
> >>>> and others that need an ID will not work still. Hopefully any changes we
> >>>> make to QEMU will be robust enough stand the test of time.
> >>> 
> >>> That is not correct. It is possible for us to fix object_del / device_del
> >>> to accept the QOM object path. It isn't pretty but it is a solution that
> >>> gives everything a stable unique path ID to use for deletion even if the
> >>> user forgets to give a pretty path-less ID.
> >> 
> >> This QOM path might be better than nothing. Hopefully someone will make 
> >> this
> >> patch and share it with us.
> > 
> > I sent a patch to support that, since it turned out to be pretty
> > trivial to implement. So that at least solves the immediate blocking
> > issue of deleting devices with an ID. The question of usability and
> > auto-generated IDs can continue in parallel....
> > 
> > Regards,
> > Daniel
> 
> I applied your patch, but saw this error message when I tried to 'make' QEMU:
> 
>   GEN   qmp-commands.txt
> line 344: syntax error: expected EQMP, found SQMP
> make: *** [qmp-commands.txt] Error 1
> make: *** Deleting file `qmp-commands.txt'
> 
> Know what it means?

It means I should have run 'make' again after adding the documentation
to detect the bug :-) I'll send another patch....

Regards,
Daniel
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