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Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css |
Date: |
Fri, 19 May 2017 15:55:03 +0100 |
User-agent: |
Mutt/1.8.2 (2017-04-18) |
* Halil Pasic (address@hidden) wrote:
>
>
> On 05/15/2017 08:01 PM, Dr. David Alan Gilbert wrote:
> > * Halil Pasic (address@hidden) wrote:
> >>
> >>
> >> On 05/08/2017 06:45 PM, Dr. David Alan Gilbert wrote:
> >>> * Halil Pasic (address@hidden) wrote:
> >>>> As a preparation for switching to a vmstate based migration let us
> >>>> introduce vmstate entities (e.g. VMStateDescription) for the css entities
> >>>> to be migrated. Alongside some comments explaining or indicating the not
> >>>> migration of certain members are introduced too.
> >>>>
> >>>> No changes in behavior, we just added some dead code -- which should
> >>>> rise to life soon.
> >>>>
> >>>> Signed-off-by: Halil Pasic <address@hidden>
> >>>> ---
> >>>> hw/s390x/css.c | 276
> >>>> +++++++++++++++++++++++++++++++++++++++++++++++++
> >>>> include/hw/s390x/css.h | 10 +-
> >>>> 2 files changed, 285 insertions(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/hw/s390x/css.c b/hw/s390x/css.c
> >>>> index c03bb20..2bda7d0 100644
> >>>> --- a/hw/s390x/css.c
> >>>> +++ b/hw/s390x/css.c
> >>>> @@ -20,29 +20,231 @@
> >>>> #include "hw/s390x/css.h"
> >>>> #include "trace.h"
> >>>> #include "hw/s390x/s390_flic.h"
> >>>> +#include "hw/s390x/s390-virtio-ccw.h"
> >>>>
> >>
> >> [..]
> >>
> >>>> +static int css_get_ind_addr(QEMUFile *f, void *pv, size_t size,
> >>>> + VMStateField *field)
> >>>> +{
> >>>> + int32_t len;
> >>>> + IndAddr **ind_addr = pv;
> >>>> +
> >>>> + len = qemu_get_be32(f);
> >>>> + if (len != 0) {
> >>>> + *ind_addr = get_indicator(qemu_get_be64(f), len);
> >>>> + } else {
> >>>> + qemu_get_be64(f);
> >>>> + *ind_addr = NULL;
> >>>> + }
> >>>> + return 0;
> >>>> +}
> >>>> +
> >>>> +static int css_put_ind_addr(QEMUFile *f, void *pv, size_t size,
> >>>> + VMStateField *field, QJSON *vmdesc)
> >>>> +{
> >>>> + IndAddr *ind_addr = *(IndAddr **) pv;
> >>>> +
> >>>> + if (ind_addr != NULL) {
> >>>> + qemu_put_be32(f, ind_addr->len);
> >>>> + qemu_put_be64(f, ind_addr->addr);
> >>>> + } else {
> >>>> + qemu_put_be32(f, 0);
> >>>> + qemu_put_be64(f, 0UL);
> >>>> + }
> >>>> + return 0;
> >>>> +}
> >>>> +
> >>>> +const VMStateInfo vmstate_info_ind_addr = {
> >>>> + .name = "s390_ind_addr",
> >>>> + .get = css_get_ind_addr,
> >>>> + .put = css_put_ind_addr
> >>>> +};
> >>>
> >>> You should be able to avoid this .get/.put by using VMSTATE_WITH_TMP,
> >>> declare a temporary struct something like:
> >>> struct tmp_ind_addr {
> >>> IndAddr *parent;
> >>> uint32_t len;
> >>> uint64_t addr;
> >>> }
> >>>
> >>> and then your .get/.put routines turn into pre_save/post_load
> >>> routines to just setup the len/addr.
> >>>
> >>
> >> I don't think this is going to work -- unfortunately! You can see below,
> >> how this IndAddr* migration stuff is supposed to be used:
> >> the client code just uses the VMSTATE_PTR_TO_IND_ADDR macro as a
> >> field when describing state which needs and IndAddr* migrated.
> >>
> >> The problem is, we do not know in what state will this field
> >> be embedded, the pre_save/post_load called by put_tmp/get_tmp
> >> is however copying the pointer to this state into the parent.
> >> So instead of having a pointer to IndAddr* in those functions
> >> and updating it accordingly, I would have to find the IndAddr*
> >> in some arbitrary state (in our case VirtioCcwDevice) first,
> >> and I lack information for that.
> >>
> >> If it's hard to follow I can give you the patch I was debugging
> >> to come to this conclusion. (By the way I ended up with 10
> >> lines of code more than in this version, and although I think
> >> it looks nicer, it's simpler only if one knows how WITH_TMP
> >> works. My plan was to ask you which version do you like more
> >> and go with that before I realized it ain't gonna work.)
> >>
> >
> > Yes, I see - I've got some similar other cases; the challenge
> > is it's a custom allocator - 'get_indicator' - and it's used
> > as fields in a few places. Hmm.
> >
> >
>
> The problem can be worked around by wrapping the WITH_TMP into a another
> vmsd and using VMSTATE_STRUCT for describing the field in question. It's
> quite some boilerplate (+16 lines). Should I post the patch here?
Yes please.
> We could also consider making WITH_TMP act as a normal field.
> Working on the whole state looks like a bit like a corner case:
> we have some stuff adjacent in the migration stream, and we have
> to map it on multiple fields (and vice-versa). Getting the whole
> state with a pointer to a certain field could work via container_of.
You do need to know which field you're working on to be able to safely
use container_of, so I'm not sure how it would work for you in this
case.
The other thought I'd had was that perhaps we could change the temporary
structure in VMSTATE_WITH_TMP to:
struct foo {
struct whatever **parent;
so now you could write to *parent in cases like these.
> Btw, I would rather call it get_indicator a factory method or even a
> constructor than an allocator, but I think we understand each-other
> anyway.
Yes; I'm not too worried about the actual name as long as it's short
and obvious.
I'd thought of 'allocator' since in most cases it's used where the
load-time code allocates memory for the object being loaded.
A constructor is normally something I think of as happening after
allocation; and a factory, hmm maybe. However, if it does the right
thing I wouldn't object to any of those names.
Dave
P.S. I'm out for about a week.
> Regards,
> Halil
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- [Qemu-devel] [PATCH 00/10] migration: s390x css migration, Halil Pasic, 2017/05/05
- [Qemu-devel] [PATCH 02/10] s390x: add css_migration_enabled to machine class, Halil Pasic, 2017/05/05
- [Qemu-devel] [PATCH 04/10] s390x/css: add vmstate macro for CcwDevice, Halil Pasic, 2017/05/05
- [Qemu-devel] [PATCH 01/10] s390x: add helper get_machine_class, Halil Pasic, 2017/05/05
- [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css, Halil Pasic, 2017/05/05
- Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css, Dr. David Alan Gilbert, 2017/05/08
- Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css, Halil Pasic, 2017/05/09
- Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css, Dr. David Alan Gilbert, 2017/05/15
- Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css, Halil Pasic, 2017/05/18
- Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css,
Dr. David Alan Gilbert <=
- Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css, Halil Pasic, 2017/05/19
- Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css, Halil Pasic, 2017/05/19
- Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css, Dr. David Alan Gilbert, 2017/05/19
- Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css, Halil Pasic, 2017/05/19
- Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css, Dr. David Alan Gilbert, 2017/05/19
- Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css, Halil Pasic, 2017/05/19
- Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css, Halil Pasic, 2017/05/09
[Qemu-devel] [PATCH 05/10] virtio-ccw: add vmstate entities for VirtioCcwDevice, Halil Pasic, 2017/05/05
[Qemu-devel] [PATCH 06/10] virtio-ccw: use vmstate way for config migration, Halil Pasic, 2017/05/05