On Fri, Mar 18, 2022 at 04:51:10PM -0300, Daniel Henrique Barboza wrote: > > > On 3/18/22 00:43, David Gibson wrote: > > On Thu, Mar 17, 2022 at 04:29:14PM +0000, Dr. David Alan Gilbert wrote: > > > * Peter Maydell (peter.mayd...@linaro.org) wrote: > > > > On Thu, 17 Mar 2022 at 14:03, Daniel Henrique Barboza > > > > <danielhb...@gmail.com> wrote: > > > > > I've been looking into converting some vmstate_register() calls to > > > > > use dc->vmsd, > > > > > using as a base the docs in docs/devel/migration.rst. This doc > > > > > mentions that we > > > > > can either register the vmsd by using vmstate_register() or we can > > > > > use dc->vmsd > > > > > for qdev-based devices. > > > > > > > > > > When trying to convert this vmstate() call for the qdev alternative > > > > > (hw/ppc/spapr_drc.c, > > > > > drc_realize()) I found this: > > > > > > > > > > vmstate_register(VMSTATE_IF(drc), spapr_drc_index(drc), > > > > > &vmstate_spapr_drc, > > > > > drc); > > > > > > > > > > spapr_drc_index() is an unique identifier for these DRC devices and > > > > > it's being used > > > > > as instance_id. It is not clear to me how we can keep using this same > > > > > instance_id when > > > > > using the dc->vmsd alternative. By looking a bit into migration files > > > > > I understood > > > > > that if dc->vmsd is being used the instance_id is always > > > > > autogenerated. Is that correct? > > > > > > > > Not entirely. It is the intended common setup, but because changing > > > > the ID value breaks migration compatibility there is a mechanism > > > > for saying "my device is special and needs to set the instance ID > > > > to something else" -- qdev_set_legacy_instance_id(). > > > > > > Yes, this is normally only an issue for 'system' or memory mapped > > > devices; for things hung off a bus that has it's own device naming, > > > then each instance of a device has it's own device due to the bus name > > > so instance_id's aren't used. Where you've got a few of the > > > same device with the same name, and no bus for them to be named by, then > > > the instance_id is used to uniquify them. > > > Thanks for the info. qdev_set_legacy_instance_id() was the missing piece I was > looking for to continue with the dc->vmsd transition I'd like to do. > > > > > > Thanks for the information. I remember deciding at the time that just > > using vmsd wouldn't work for the DRCs because we needed this fixed > > index. At the time either qdev_set_legacy_instance_id() didn't exist, > > or I didn't know about it, hence the explicit vmstate_register() call > > so that an explicit instance id could be supplied. > > > > This is the commit that introduced DRC migration: > > > commit a50919dddf148b0a2008db4a0593dbe69e1059c0 > Author: Daniel Henrique Barboza <danie...@linux.vnet.ibm.com> > Date: Mon May 22 16:35:49 2017 -0300 > > hw/ppc: migrating the DRC state of hotplugged devices > > > I'd say you can cut yourself some slack this time. Blame that guy > instead.
Man, not that guy again! ;-) I think I must have done something similar with some other migration component. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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