Re: [Qemu-devel] [QEMU RFC PATCH v3 4/6] Migration: migrate QTAILQ

[Jianjun Duan <duanj@linux.vnet.ibm.com>]

On 05/31/2016 12:54 PM, Paolo Bonzini wrote:
> 
> 
> ----- Original Message -----
>> From: "Jianjun Duan" <duanj@linux.vnet.ibm.com>
>> To: qemu-devel@nongnu.org
>> Cc: qemu-ppc@nongnu.org, duanj@linux.vnet.ibm.com, dmitry@daynix.com, "peter maydell" <peter.maydell@linaro.org>,
>> kraxel@redhat.com, mst@redhat.com, david@gibson.dropbear.id.au, pbonzini@redhat.com, veroniabahaa@gmail.com,
>> quintela@redhat.com, "amit shah" <amit.shah@redhat.com>, mreitz@redhat.com, kwolf@redhat.com, rth@twiddle.net,
>> aurelien@aurel32.net, "leon alrae" <leon.alrae@imgtec.com>, blauwirbel@gmail.com, "mark cave-ayland"
>> <mark.cave-ayland@ilande.co.uk>, mdroth@linux.vnet.ibm.com
>> Sent: Tuesday, May 31, 2016 8:02:42 PM
>> Subject: [QEMU RFC PATCH v3 4/6] Migration: migrate QTAILQ
>>
>> Currently we cannot directly transfer a QTAILQ instance because of the
>> limitation in the migration code. Here we introduce an approach to
>> transfer such structures. In our approach such a structure is tagged
>> with VMS_CSTM. We then modified vmstate_save_state and vmstate_load_state
>> so that when VMS_CSTM is encountered, put and get from VMStateInfo are
>> called respectively. This approach will be used to transfer pending_events
>> and ccs_list in spapr state.
>>
>> We also create some macros in qemu/queue.h to access a QTAILQ using pointer
>> arithmetic. This ensures that we do not depend on the implementation
>> details about QTAILQ in the migration code.
>>
>> Signed-off-by: Jianjun Duan <duanj@linux.vnet.ibm.com>
>> ---
>>  include/migration/vmstate.h | 22 +++++++++++++
>>  include/qemu/queue.h        | 32 ++++++++++++++++++
>>  migration/vmstate.c         | 79
>>  +++++++++++++++++++++++++++++++++++++++++++++
>>  3 files changed, 133 insertions(+)
>>
>> diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
>> index 56a4171..da4ef7f 100644
>> --- a/include/migration/vmstate.h
>> +++ b/include/migration/vmstate.h
>> @@ -185,6 +185,8 @@ enum VMStateFlags {
>>       * to determine the number of entries in the array. Only valid in
>>       * combination with one of VMS_VARRAY*. */
>>      VMS_MULTIPLY_ELEMENTS = 0x4000,
>> +    /* For fields which need customized handling, such as QTAILQ in
>> queue.h*/
>> +    VMS_CSTM            = 0x8000,
> 
> Please call this VMS_LINKED.  It can be adapted to other data
> structures in qemu/queue.h if there is a need later on.
> 
>>  };
>>  
>>  struct VMStateField {
>> @@ -245,6 +247,7 @@ extern const VMStateInfo vmstate_info_timer;
>>  extern const VMStateInfo vmstate_info_buffer;
>>  extern const VMStateInfo vmstate_info_unused_buffer;
>>  extern const VMStateInfo vmstate_info_bitmap;
>> +extern const VMStateInfo vmstate_info_qtailq;
>>  
>>  #define type_check_2darray(t1,t2,n,m) ((t1(*)[n][m])0 - (t2*)0)
>>  #define type_check_array(t1,t2,n) ((t1(*)[n])0 - (t2*)0)
>> @@ -656,6 +659,25 @@ extern const VMStateInfo vmstate_info_bitmap;
>>      .offset       = offsetof(_state, _field),                        \
>>  }
>>  
>> +/* For QTAILQ that need customized handling
>> + * _type: type of QTAILQ element
>> + * _next: name of QTAILQ entry field in QTAILQ element
>> + * _vmsd: VMSD for QTAILQ element
>> + * size: size of QTAILQ element
>> + * start: offset of QTAILQ entry in QTAILQ element
>> + */
>> +#define VMSTATE_QTAILQ_V(_field, _state, _version, _vmsd, _type, _next)  \
>> +{                                                                        \
>> +    .name         = (stringify(_field)),                                 \
>> +    .version_id   = (_version),                                          \
>> +    .vmsd         = &(_vmsd),                                            \
>> +    .size         = sizeof(_type),                                       \
>> +    .info         = &vmstate_info_qtailq,                                \
>> +    .flags        = VMS_CSTM,                                            \
>> +    .offset       = offsetof(_state, _field),                            \
>> +    .start        = offsetof(_type, _next),                              \
>> +}
>> +
>>  /* _f : field name
>>     _f_n : num of elements field_name
>>     _n : num of elements
>> diff --git a/include/qemu/queue.h b/include/qemu/queue.h
>> index f781aa2..003e368 100644
>> --- a/include/qemu/queue.h
>> +++ b/include/qemu/queue.h
>> @@ -437,3 +437,35 @@ struct {
>> \
>>          (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
>>  
>>  #endif  /* !QEMU_SYS_QUEUE_H_ */
>> +
>> +/*
>> + * Offsets of layout of a tail queue head.
>> + */
>> +#define QTAILQ_FIRST_OFFSET 0
>> +#define QTAILQ_LAST_OFFSET (sizeof(void *))
>> +
>> +/*
>> + * Offsets of layout of a tail queue element.
>> + */
>> +#define QTAILQ_NEXT_OFFSET 0
>> +#define QTAILQ_PREV_OFFSET (sizeof(void *))
>> +
>> +/*
>> + * Tail queue tranversal using pointer arithmetic.
>> + */
>> +#define QTAILQ_RAW_FOREACH(elm, head, entry)
>> \
>> +        for ((elm) = *((void **) ((char *) (head) + QTAILQ_FIRST_OFFSET));
>> \
>> +             (elm);
>> \
>> +             (elm) =
>> \
>> +                 *((void **) ((char *) (elm) + (entry) +
>> QTAILQ_NEXT_OFFSET)))
>> +/*
>> + * Tail queue insertion using pointer arithmetic.
>> + */
>> +#define QTAILQ_RAW_INSERT_TAIL(head, elm, entry) do {
>> \
>> +        *((void **) ((char *) (elm) + (entry) + QTAILQ_NEXT_OFFSET)) = NULL;
>> \
>> +        *((void **) ((char *) (elm) + (entry) + QTAILQ_PREV_OFFSET)) =
>> \
>> +            *((void **) ((char *) (head) +QTAILQ_LAST_OFFSET));
>> \
>> +        **((void ***)((char *) (head) +QTAILQ_LAST_OFFSET)) = (elm);
>> \
>> +        *((void **) ((char *) (head) + QTAILQ_LAST_OFFSET)) =
>> \
>> +            (void *) ((char *) (elm) + (entry) + QTAILQ_NEXT_OFFSET);
>> \
>> +} while (/*CONSTCOND*/0)
>> diff --git a/migration/vmstate.c b/migration/vmstate.c
>> index 644ba1f..ff56650 100644
>> --- a/migration/vmstate.c
>> +++ b/migration/vmstate.c
>> @@ -5,7 +5,9 @@
>>  #include "migration/vmstate.h"
>>  #include "qemu/bitops.h"
>>  #include "qemu/error-report.h"
>> +#include "qemu/queue.h"
>>  #include "trace.h"
>> +#include "migration/qjson.h"
>>  
>>  static void vmstate_subsection_save(QEMUFile *f, const VMStateDescription
>>  *vmsd,
>>                                      void *opaque, QJSON *vmdesc);
>> @@ -120,6 +122,8 @@ int vmstate_load_state(QEMUFile *f, const
>> VMStateDescription *vmsd,
>>                  if (field->flags & VMS_STRUCT) {
>>                      ret = vmstate_load_state(f, field->vmsd, addr,
>>                                               field->vmsd->version_id);
>> +                } else if (field->flags & VMS_CSTM) {
>> +                    ret = field->info->get(f, addr, size, field);
>>                  } else {
>>                      ret = field->info->get(f, addr, size, NULL);
>>  
>> @@ -192,6 +196,8 @@ static const char *vmfield_get_type_name(VMStateField
>> *field)
>>  
>>      if (field->flags & VMS_STRUCT) {
>>          type = "struct";
>> +    } else if (field->flags & VMS_CSTM) {
>> +        type = "customized";
>>      } else if (field->info->name) {
>>          type = field->info->name;
>>      }
>> @@ -326,6 +332,8 @@ void vmstate_save_state(QEMUFile *f, const
>> VMStateDescription *vmsd,
>>                  }
>>                  if (field->flags & VMS_STRUCT) {
>>                      vmstate_save_state(f, field->vmsd, addr, vmdesc_loop);
>> +                } else if  (field->flags & VMS_CSTM) {
>> +                    field->info->put(f, addr, size, field, vmdesc_loop);
>>                  } else {
>>                      field->info->put(f, addr, size, NULL, NULL);
>>                  }
>> @@ -938,3 +946,74 @@ const VMStateInfo vmstate_info_bitmap = {
>>      .get = get_bitmap,
>>      .put = put_bitmap,
>>  };
>> +
>> +/*get for QTAILQ */
>> +static int get_qtailq(QEMUFile *f, void *pv, size_t unused_size,
>> +                      VMStateField *field)
>> +{
>> +    bool link;
>> +    int ret = 0;
>> +    const VMStateDescription *vmsd = field->vmsd;
>> +    size_t size = field->size;
>> +    size_t entry = field->start;
>> +    int version_id = field->version_id;
>> +    void *elm;
>> +
>> +    trace_vmstate_load_state(vmsd->name, version_id);
>> +    if (version_id > vmsd->version_id) {
>> +        trace_vmstate_load_state_end(vmsd->name, "too new", -EINVAL);
>> +        return -EINVAL;
>> +    }
>> +    if (version_id < vmsd->minimum_version_id) {
>> +        trace_vmstate_load_state_end(vmsd->name, "too old", -EINVAL);
>> +        return -EINVAL;
>> +    }
>> +
>> +    while (true) {
>> +        vmstate_info_bool.get(f, &link, sizeof(bool), NULL);
> 
> You can use qemu_get_byte here, and likewise qemu_put_byte below in
> put_qtailq.

qemu_get/put is indeed better choice.
> 
>> +        if (!link) {
>> +            break;
>> +        }
>> +
>> +        elm =  g_malloc(size);
>> +        ret = vmstate_load_state(f, vmsd, elm, version_id);
>> +        if (ret) {
>> +            return ret;
>> +        }
>> +        QTAILQ_RAW_INSERT_TAIL(pv, elm, entry);
>> +    }
>> +
>> +    trace_vmstate_load_state_end(vmsd->name, "end", ret);
>> +    return ret;
>> +}
>> +
>> +/* put for QTAILQ */
>> +static void put_qtailq(QEMUFile *f, void *pv, size_t unused_size,
>> +                       VMStateField *field, QJSON *vmdesc)
>> +{
>> +    bool link = true;
>> +    const VMStateDescription *vmsd = field->vmsd;
>> +    size_t entry = field->start;
>> +    void *elm;
>> +
>> +    if (vmdesc) {
>> +        json_prop_str(vmdesc, "vmsd_name", vmsd->name);
>> +        json_prop_int(vmdesc, "version", vmsd->version_id);
>> +        json_start_array(vmdesc, "fields");
> 
> You need to store the fields exactly once here, even if there are
> 0 or >1 elements.
> 
Do you mean the json entries? I think it is already doing that.
> Otherwise looks great now!
> 
> Paolo
> 
>> +    }
>> +
>> +    QTAILQ_RAW_FOREACH(elm, pv, entry) {
>> +        vmstate_info_bool.put(f, &link, sizeof(bool), NULL, NULL);
>> +        vmstate_save_state(f, vmsd, elm, vmdesc);
>> +    }
>> +    link = false;
>> +    vmstate_info_bool.put(f, &link, sizeof(bool), NULL, NULL);
>> +    if (vmdesc) {
>> +        json_end_array(vmdesc);
>> +    }
>> +}
>> +const VMStateInfo vmstate_info_qtailq = {
>> +    .name = "qtailq",
>> +    .get  = get_qtailq,
>> +    .put  = put_qtailq,
>> +};
>> --
>> 1.9.1
>>
>>
> 

Thanks,
Jianjun