On Tue, Oct 13, 2015 at 09:37:29AM +0200, Markus Armbruster wrote:
> Jeff Cody <jc...@redhat.com> writes:
>
> > Multiple sub-systems in QEMU may find it useful to generate IDs
> > for objects that a user may reference via QMP or HMP. This patch
> > presents a standardized way to do it, so that automatic ID generation
> > follows the same rules.
> >
> > This patch enforces the following rules when generating an ID:
> >
> > 1.) Guarantee no collisions with a user-specified ID
> > 2.) Identify the sub-system the ID belongs to
> > 3.) Guarantee of uniqueness
> > 4.) Spoiling predictability, to avoid creating an assumption
> > of object ordering and parsing (i.e., we don't want users to think
> > they can guess the next ID based on prior behavior).
> >
> > The scheme for this is as follows (no spaces):
> >
> > # subsys D RR
> > Reserved char --| | | |
> > Subsystem String ----| | |
> > Unique number (64-bit) --| |
> > Two-digit random number ---|
> >
> > For example, a generated node-name for the block sub-system may look
> > like this:
> >
> > #block076
> >
> > The caller of id_generate() is responsible for freeing the generated
> > node name string with g_free().
> >
> > Reviewed-by: John Snow <js...@redhat.com>
> > Reviewed-by: Eric Blake <ebl...@redhat.com>
> > Reviewed-by: Alberto Garcia <be...@igalia.com>
> > Signed-off-by: Jeff Cody <jc...@redhat.com>
> > ---
> > include/qemu-common.h | 8 ++++++++
> > util/id.c | 37 +++++++++++++++++++++++++++++++++++++
> > 2 files changed, 45 insertions(+)
> >
> > diff --git a/include/qemu-common.h b/include/qemu-common.h
> > index 0bd212b..2f74540 100644
> > --- a/include/qemu-common.h
> > +++ b/include/qemu-common.h
> > @@ -246,6 +246,14 @@ int64_t qemu_strtosz_suffix_unit(const char *nptr,
> > char **end,
> > #define STR_OR_NULL(str) ((str) ? (str) : "null")
> >
> > /* id.c */
> > +
> > +typedef enum IdSubSystems {
> > + ID_QDEV,
>
> ID_QDEV is not used in this series. Do you intend to use it in a
> followup-series? Can we reasonably expect that series will be accepted?
>
John Arbuckle has a patch on list that uses it. I haven't reviewed
it, however - but I guess it depends ultimately on whether qdev will
allow autogeneration for its IDs or not.
> You could sidestep these questions by making id_generate() take a string
> argument ;)
>
I'd rather avoid having each system specifying a string inline in
their code. It is cleaner to have the strings defined in a central
location, I think (not to mention, easier to reference).
> > + ID_BLOCK,
> > + ID_MAX /* last element, used as array size */
> > +} IdSubSystems;
> > +
> > +char *id_generate(IdSubSystems id);
> > bool id_wellformed(const char *id);
> >
> > /* path.c */
> [...]
