Re: [Qemu-devel] [PATCH] migration: Correctly handle subsections with no 'needed' function

[Juan Quintela <quintela@redhat.com>]

Peter Maydell <peter.maydell@linaro.org> wrote:
> Currently the vmstate subsection handling code treats a subsection
> with no 'needed' function pointer as if it were the subsection
> list terminator, so the subsection is never transferred and nor
> is any subsection following it in the list.
>
> Handle NULL 'needed' function pointers in subsections in the same
> way that we do for top level VMStateDescription structures:
> treat the subsection as always being needed.
>
> This doesn't change behaviour for the current set of devices
> in the tree, because all subsections declare a 'needed' function.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> NB: last para in the commit message is only true once the
> "Arm migration fixes for 3.0" patchset has been committed.
> We could optionally drop some of the "use a dummy needed fn"
> changes once this is in...
>
> I thought I'd sent this out a few days back, but apparently not,
> since it's not on-list...
>
>  migration/vmstate.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/migration/vmstate.c b/migration/vmstate.c
> index 6b9079bb51e..0bc240a3175 100644
> --- a/migration/vmstate.c
> +++ b/migration/vmstate.c
> @@ -418,7 +418,7 @@ int vmstate_save_state_v(QEMUFile *f, const VMStateDescription *vmsd,
>  static const VMStateDescription *
>  vmstate_get_subsection(const VMStateDescription **sub, char *idstr)
>  {
> -    while (sub && *sub && (*sub)->needed) {
> +    while (sub && *sub) {
>          if (strcmp(idstr, (*sub)->name) == 0) {
>              return *sub;
>          }

Ack to this one.  Code supposed that needed was alwasy !=0.  We don't
really care on the reception side.  Good spotted.

> @@ -486,8 +486,8 @@ static int vmstate_subsection_save(QEMUFile *f, const VMStateDescription *vmsd,
>      int ret = 0;
>  
>      trace_vmstate_subsection_save_top(vmsd->name);
> -    while (sub && *sub && (*sub)->needed) {
> -        if ((*sub)->needed(opaque)) {
> +    while (sub && *sub) {
> +        if (vmstate_save_needed(*sub, opaque)) {
>              const VMStateDescription *vmsdsub = *sub;
>              uint8_t len;


I am not so sure about this one.  Why are we having a subsection without
a ->needed function?  I don't know why that it is useful for.  if we
don't have a needed function, then it is just better to just add that
"subsection" to the normal section, increase the version number and live
with that, no?

Later, Juan.