Re: [Qemu-devel] [QEMU PATCH v8 2/3] migration: migrate QTAILQ

[Dr. David Alan Gilbert]

* Jianjun Duan (address@hidden) wrote:
> 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. We created VMStateInfo vmstate_info_qtailq
> for QTAILQ. Similar VMStateInfo can be created for other data structures
> such as list.
> 
> 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 <address@hidden>
> ---
>  include/migration/vmstate.h | 20 ++++++++++++++
>  include/qemu/queue.h        | 46 +++++++++++++++++++++++++++++++
>  migration/trace-events      |  4 +++
>  migration/vmstate.c         | 67 
> +++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 137 insertions(+)
> 
> diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> index d0e37b5..318a6f1 100644
> --- a/include/migration/vmstate.h
> +++ b/include/migration/vmstate.h
> @@ -251,6 +251,7 @@ 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)
> @@ -662,6 +663,25 @@ extern const VMStateInfo vmstate_info_bitmap;
>      .offset       = offsetof(_state, _field),                        \
>  }
>  
> +/* For QTAILQ that need customized handling.
> + * Target QTAILQ needs be properly initialized.
> + * _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,                                \
> +    .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 342073f..e9378fa 100644
> --- a/include/qemu/queue.h
> +++ b/include/qemu/queue.h
> @@ -438,4 +438,50 @@ struct {                                                 
>                \
>  #define QTAILQ_PREV(elm, headname, field) \
>          (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
>  
> +#define RAW_FIELD(base, offset)                                              
>   \
> +        ((char *) (base) + offset)
> +
> +/*
> + * Offsets of layout of a tail queue head.
> + */
> +#define QTAILQ_FIRST_OFFSET 0
> +#define QTAILQ_LAST_OFFSET (sizeof(void *))

OK, you might want to add some asserts somewhere in a .c just to catch if
any of these offsets change.

> + * Raw access of elements of a tail queue
> + */
> +#define QTAILQ_RAW_FIRST(head)                                               
>   \
> +        (*((void **) (RAW_FIELD(head,  QTAILQ_FIRST_OFFSET))))
> +#define QTAILQ_RAW_LAST(head)                                                
>   \
> +        (*((void ***) (RAW_FIELD(head,  QTAILQ_LAST_OFFSET))))
> +
> +/*
> + * Offsets of layout of a tail queue element.
> + */
> +#define QTAILQ_NEXT_OFFSET 0
> +#define QTAILQ_PREV_OFFSET (sizeof(void *))
> +
> +/*
> + * Raw access of elements of a tail entry
> + */
> +#define QTAILQ_RAW_NEXT(elm, entry)                                          
>   \
> +        (*((void **) (RAW_FIELD(elm, entry + QTAILQ_NEXT_OFFSET))))
> +#define QTAILQ_RAW_PREV(elm, entry)                                          
>   \
> +        (*((void ***) (RAW_FIELD(elm, entry + QTAILQ_PREV_OFFSET))))
> +/*
> + * Tail queue tranversal using pointer arithmetic.
> + */
> +#define QTAILQ_RAW_FOREACH(elm, head, entry)                                 
>   \
> +        for ((elm) = QTAILQ_RAW_FIRST(head);                                 
>   \
> +             (elm);                                                          
>   \
> +             (elm) = QTAILQ_RAW_NEXT(elm, entry))
> +/*
> + * Tail queue insertion using pointer arithmetic.
> + */
> +#define QTAILQ_RAW_INSERT_TAIL(head, elm, entry) do {                        
>   \
> +        QTAILQ_RAW_NEXT(elm, entry) = NULL;                                  
>   \
> +        QTAILQ_RAW_PREV(elm, entry) = QTAILQ_RAW_LAST(head);                 
>   \
> +        *QTAILQ_RAW_LAST(head) = (elm);                                      
>   \
> +        QTAILQ_RAW_LAST(head) = &QTAILQ_RAW_NEXT(elm, entry);                
>   \
> +} while (/*CONSTCOND*/0)
> +
>  #endif /* QEMU_SYS_QUEUE_H */
> diff --git a/migration/trace-events b/migration/trace-events
> index dfee75a..9a6ec59 100644
> --- a/migration/trace-events
> +++ b/migration/trace-events
> @@ -52,6 +52,10 @@ vmstate_n_elems(const char *name, int n_elems) "%s: %d"
>  vmstate_subsection_load(const char *parent) "%s"
>  vmstate_subsection_load_bad(const char *parent,  const char *sub, const char 
> *sub2) "%s: %s/%s"
>  vmstate_subsection_load_good(const char *parent) "%s"
> +get_qtailq(const char *name, int version_id) "%s v%d"
> +get_qtailq_end(const char *name, const char *reason, int val) "%s %s/%d"
> +put_qtailq(const char *name, int version_id) "%s v%d"
> +put_qtailq_end(const char *name, const char *reason) "%s %s"
>  
>  # migration/qemu-file.c
>  qemu_file_fclose(void) ""
> diff --git a/migration/vmstate.c b/migration/vmstate.c
> index d188afa..fcf808e 100644
> --- a/migration/vmstate.c
> +++ b/migration/vmstate.c
> @@ -5,6 +5,7 @@
>  #include "migration/vmstate.h"
>  #include "qemu/bitops.h"
>  #include "qemu/error-report.h"
> +#include "qemu/queue.h"
>  #include "trace.h"
>  #include "migration/qjson.h"
>  
> @@ -948,3 +949,69 @@ const VMStateInfo vmstate_info_bitmap = {
>      .get = get_bitmap,
>      .put = put_bitmap,
>  };
> +
> +/* get for QTAILQ
> + * meta data about the QTAILQ is encoded in a VMStateField structure
> + */
> +static int get_qtailq(QEMUFile *f, void *pv, size_t unused_size,
> +                      VMStateField *field)
> +{
> +    int ret = 0;
> +    const VMStateDescription *vmsd = field->vmsd;
> +    /* size of a QTAILQ element */
> +    size_t size = field->size;
> +    /* offset of the QTAILQ entry in a QTAILQ element */
> +    size_t entry_offset = field->start;
> +    int version_id = field->version_id;
> +    void *elm;
> +
> +    trace_get_qtailq(vmsd->name, version_id);
> +    if (version_id > vmsd->version_id) {
> +        error_report("%s %s",  vmsd->name, "too new");
> +        trace_get_qtailq_end(vmsd->name, "too new", -EINVAL);
> +
> +        return -EINVAL;
> +    }
> +    if (version_id < vmsd->minimum_version_id) {
> +        error_report("%s %s",  vmsd->name, "too old");
> +        trace_get_qtailq_end(vmsd->name, "too old", -EINVAL);
> +        return -EINVAL;
> +    }
> +
> +    while (qemu_get_byte(f)) {
> +        elm =  g_malloc(size);
> +        ret = vmstate_load_state(f, vmsd, elm, version_id);
> +        if (ret) {
> +            return ret;

You could just make that a break since you're returning ret
(that's otherwise all 0).  Still, not important, but could
be tidied if you need to regenerate the patch.
(and you could remove the 2nd space after elm =).

> +        }
> +        QTAILQ_RAW_INSERT_TAIL(pv, elm, entry_offset);
> +    }
> +
> +    trace_get_qtailq_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)
> +{
> +    const VMStateDescription *vmsd = field->vmsd;
> +    /* offset of the QTAILQ entry in a QTAILQ element*/
> +    size_t entry_offset = field->start;
> +    void *elm;
> +
> +    trace_put_qtailq(vmsd->name, vmsd->version_id);
> +
> +    QTAILQ_RAW_FOREACH(elm, pv, entry_offset) {
> +        qemu_put_byte(f, true);
> +        vmstate_save_state(f, vmsd, elm, vmdesc);
> +    }
> +    qemu_put_byte(f, false);
> +
> +    trace_put_qtailq_end(vmsd->name, "end");
> +}
> +const VMStateInfo vmstate_info_qtailq = {
> +    .name = "qtailq",
> +    .get  = get_qtailq,
> +    .put  = put_qtailq,
> +};

Reviewed-by: Dr. David Alan Gilbert <address@hidden>

> -- 
> 1.9.1
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK