On 09/01/2015 11:23 AM, Jeff Cody wrote: > Multiple sub-systems in QEMU may find it useful to generated 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 predictibility, 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 --| | | | > Subsytem String -----| | |
s/Subsytem/Subsystem/ > Unique number (64-bit) --| | > Two-digit random number ---| > > For example, a generated node-name for the block sub-system may take the > look like this: s/take the// > > #block076 > > The caller of id_generate() is responsible for freeing the generated > node name string with g_free(). > > Signed-off-by: Jeff Cody <[email protected]> > --- > include/qemu-common.h | 8 ++++++++ > util/id.c | 35 +++++++++++++++++++++++++++++++++++ > 2 files changed, 43 insertions(+) > > +char *id_generate(IdSubSystems id) > +{ > + const char *id_subsys_str[] = { s/id_/const id_/ > + [ID_QDEV] = "qdev", > + [ID_BLOCK] = "block", > + }; Do we want some sort of compile-time assertion that we have entries for all id values?... > + > + static uint64_t id_counters[ID_MAX]; > + uint32_t rnd; > + > + assert(id < ID_MAX); ...maybe in the form of assert(id_subsys_str[id]) > + > + rnd = g_random_int_range(0, 99); > + > + return g_strdup_printf("%c%s%" PRIu64 "%" PRId32, ID_SPECIAL_CHAR, > + id_subsys_str[id], > + id_counters[id]++, > + rnd); > +} > Looks reasonable to me. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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