Re: [Qemu-devel] [PATCH 03/10] s390x/css: add vmstate entities for css

[Halil Pasic <pasic@linux.vnet.ibm.com>]

On 05/19/2017 04:55 PM, Dr. David Alan Gilbert wrote:
> * Halil Pasic (pasic@linux.vnet.ibm.com) wrote:
>>
>>
>> On 05/15/2017 08:01 PM, Dr. David Alan Gilbert wrote:
>>> * Halil Pasic (pasic@linux.vnet.ibm.com) wrote:
>>>>
>>>>
>>>> On 05/08/2017 06:45 PM, Dr. David Alan Gilbert wrote:
>>>>> * Halil Pasic (pasic@linux.vnet.ibm.com) 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 <pasic@linux.vnet.ibm.com>
>>>>>> ---
>>>>>>  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.
> 
--------------------------------8<------------------------------------------

>From a0b6c725b114745c8434f683133995c4e33d936e Mon Sep 17 00:00:00 2001
From: Halil Pasic <pasic@linux.vnet.ibm.com>
Date: Tue, 9 May 2017 12:06:42 +0200
Subject: [PATCH 1/1] s390x/css: replace info with VMSTATE_WITH_TMP

Convert s VMSatateInfo based solution manipulating the migration stream
directly to VMSTATE_WITH_TMP witch keeps IO and transformation logic
separate.

Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
---
 hw/s390x/css.c         | 56 ++++++++++++++++++++++++++++++++------------------
 include/hw/s390x/css.h |  4 ++--
 2 files changed, 38 insertions(+), 22 deletions(-)

diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index 694365b395..71d1b95e3f 100644
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -224,41 +224,57 @@ const VMStateDescription vmstate_subch_dev = {
     }
 };
 
-static int css_get_ind_addr(QEMUFile *f, void *pv, size_t size,
-                            VMStateField *field)
-{
+typedef struct IndAddrPtrTmp {
+    IndAddr **parent;
+    uint64_t addr;
     int32_t len;
-    IndAddr **ind_addr = pv;
+} IndAddrPtrTmp;
 
-    len = qemu_get_be32(f);
-    if (len != 0) {
-        *ind_addr = get_indicator(qemu_get_be64(f), len);
+static int post_load_ind_addr(void *opaque, int version_id)
+{
+    IndAddrPtrTmp *ptmp = opaque;
+    IndAddr **ind_addr = ptmp->parent;
+
+    if (ptmp->len != 0) {
+        *ind_addr = get_indicator(ptmp->addr, ptmp->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)
+static void pre_save_ind_addr(void *opaque)
 {
-    IndAddr *ind_addr = *(IndAddr **) pv;
+    IndAddrPtrTmp *ptmp = opaque;
+    IndAddr *ind_addr = *(ptmp->parent);
 
     if (ind_addr != NULL) {
-        qemu_put_be32(f, ind_addr->len);
-        qemu_put_be64(f, ind_addr->addr);
+        ptmp->len = ind_addr->len;
+        ptmp->addr = ind_addr->addr;
     } else {
-        qemu_put_be32(f, 0);
-        qemu_put_be64(f, 0UL);
+        ptmp->len = 0;
+        ptmp->addr = 0L;
     }
-    return 0;
 }
 
-const VMStateInfo vmstate_info_ind_addr = {
-    .name = "s390_ind_addr",
-    .get = css_get_ind_addr,
-    .put = css_put_ind_addr
+const VMStateDescription vmstate_ind_addr_tmp = {
+    .name = "s390_ind_addr_tmp",
+    .pre_save = pre_save_ind_addr,
+    .post_load = post_load_ind_addr,
+
+    .fields = (VMStateField[]) {
+        VMSTATE_INT32(len, IndAddrPtrTmp),
+        VMSTATE_UINT64(addr, IndAddrPtrTmp),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+const VMStateDescription vmstate_ind_addr = {
+    .name = "s390_ind_addr_tmp",
+    .fields = (VMStateField[]) {
+        VMSTATE_WITH_TMP(IndAddr*, IndAddrPtrTmp, vmstate_ind_addr_tmp),
+        VMSTATE_END_OF_LIST()
+    }
 };
 
 typedef struct CssImage {
diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
index be5eb81ece..efe7cafef0 100644
--- a/include/hw/s390x/css.h
+++ b/include/hw/s390x/css.h
@@ -106,10 +106,10 @@ typedef struct IndAddr {
     QTAILQ_ENTRY(IndAddr) sibling;
 } IndAddr;
 
-extern const VMStateInfo vmstate_info_ind_addr;
+extern const VMStateDescription vmstate_ind_addr;
 
 #define VMSTATE_PTR_TO_IND_ADDR(_f, _s)                                   \
-    VMSTATE_SINGLE(_f, _s, 1 , vmstate_info_ind_addr, IndAddr*)
+    VMSTATE_STRUCT(_f, _s, 1, vmstate_ind_addr, IndAddr*)
 
 IndAddr *get_indicator(hwaddr ind_addr, int len);
 void release_indicator(AdapterInfo *adapter, IndAddr *indicator);
-- 
2.11.2