On 10/05/2016 09:56 AM, Dr. David Alan Gilbert wrote:
> * Jianjun Duan (du...@linux.vnet.ibm.com) 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. In our approach such a structure is tagged
>> with VMS_LINKED. We then modified vmstate_save_state and vmstate_load_state
>> so that when VMS_LINKED is encountered, put and get from VMStateInfo are
>> called respectively. 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.
>
> I think we're going to need a way to have a more flexible
> loops; and thus my choice here wouldn't be to use the .get/.put together
> with the VMSD; but I think we'll end up needing a new
> data structure, maybe a VMStateLoop *loop in VMStateField.
>
> So would it be easier if you added that new member, then you wouldn't have to
> modify every get() and put() function that already exists in the previous
> patch.
>
> Specifically, your format of QTAILQ is perfectly reasonable - a
> byte before each entry which is 1 to indicate there's an entry or 0
> to indicate termination, but there are lots of other variants, e.g.
>
> a) put_scsi_requests uses that byte to hold a flag, so it's 0,1,2
> 0 still means terminate but 1 or 2 set a flag in the structure.
I quickly take a look of put_scsi_requests. It is transferring a QTAILQ of
SCSIRequest. However it goes into the structure inside to dump the
elements out.
If using my approach, I would have a VMSD for SCSIRequest. The
additional byte used to indicate the end of the queue would lie outside
the SCSCIRequest data block, so there would be no confusion.
> b) slirp_state_load also uses a null byte termination but not off a QTAILQ
> (although I think it could be flipped for one) (it uses '42' for the
> non-0 value, but looks like it could become 1)
> c) virtio_blk also rolls it's own linked list but again with the 0/1 byte
>
> Now how would I modify your QTAILQ load/store to do (a) without copying the
> whole
> thing?
>
> Dave
>
>>
>> Signed-off-by: Jianjun Duan <du...@linux.vnet.ibm.com>
>> ---
>> include/migration/vmstate.h | 26 ++++++++++++++++++
>> include/qemu/queue.h | 32 ++++++++++++++++++++++
>> migration/trace-events | 4 +++
>> migration/vmstate.c | 66
>> +++++++++++++++++++++++++++++++++++++++++++++
>> 4 files changed, 128 insertions(+)
>>
>> diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
>> index 459dd4a..e60c994 100644
>> --- a/include/migration/vmstate.h
>> +++ b/include/migration/vmstate.h
>> @@ -186,6 +186,12 @@ 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.
>> + * When this flag is set in VMStateField, info->get/put will
>> + * be used in vmstate_load/save_state instead of recursive call.
>> + * User should implement set info to handle the concerned data
>> structure.
>> + */
>> + VMS_LINKED = 0x8000,
>> };
>>
>> struct VMStateField {
>> @@ -246,6 +252,7 @@ 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)
>> @@ -657,6 +664,25 @@ 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_LINKED, \
>> + .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..12c3f80 100644
>> --- a/include/qemu/queue.h
>> +++ b/include/qemu/queue.h
>> @@ -438,4 +438,36 @@ struct {
>> \
>> #define QTAILQ_PREV(elm, headname, field) \
>> (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
>>
>> +/*
>> + * 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)
>> +
>> #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 66802cb..192db8a 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);
>> @@ -121,6 +123,8 @@ 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_LINKED) {
>> + ret = field->info->get(f, addr, size, field);
>> } else {
>> ret = field->info->get(f, addr, size, NULL);
>>
>> @@ -193,6 +197,8 @@ static const char *vmfield_get_type_name(VMStateField
>> *field)
>>
>> if (field->flags & VMS_STRUCT) {
>> type = "struct";
>> + } else if (field->flags & VMS_LINKED) {
>> + type = "linked";
>> } else if (field->info->name) {
>> type = field->info->name;
>> }
>> @@ -327,6 +333,8 @@ 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_LINKED) {
>> + field->info->put(f, addr, size, field, vmdesc_loop);
>> } else {
>> field->info->put(f, addr, size, NULL, NULL);
>> }
>> @@ -939,3 +947,61 @@ 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)
>> +{
>> + 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_get_qtailq(vmsd->name, version_id);
>> + if (version_id > vmsd->version_id) {
>> + trace_get_qtailq_end(vmsd->name, "too new", -EINVAL);
>
> Can you make those error_report's please - if it fails we want to
> see why in the log.
>
> Dave
>
>> + return -EINVAL;
>> + }
>> + if (version_id < vmsd->minimum_version_id) {
>> + 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;
>> + }
>> + QTAILQ_RAW_INSERT_TAIL(pv, elm, entry);
>> + }
>> +
>> + 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;
>> + size_t entry = field->start;
>> + void *elm;
>> +
>> + trace_put_qtailq(vmsd->name, vmsd->version_id);
>> +
>> + QTAILQ_RAW_FOREACH(elm, pv, entry) {
>> + 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,
>> +};
>> --
>> 1.9.1
>>
> --
> Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
>
Thanks,
Jianjun
