On Oct 13, 2015, at 11:26 AM, Markus Armbruster wrote: > 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).
I can see the benefit of using a string. The id_generate() function could use va_args like printf() uses to allow almost any kind of string argument. An empty string argument could mean to default to ID_MAX. But I also think using an enumeration is good enough, so either way is good.