Jeff Cody <jc...@redhat.com> writes:
> 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.
Then that patch should add ID_QDEV.
>> 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).
Covered by your artistic license :)
>> > + ID_BLOCK,
>> > + ID_MAX /* last element, used as array size */
>> > +} IdSubSystems;
>> > +
>> > +char *id_generate(IdSubSystems id);
>> > bool id_wellformed(const char *id);
>> >
>> > /* path.c */
>> [...]
