From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43212) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZWr22-00033w-1A for qemu-devel@nongnu.org; Tue, 01 Sep 2015 15:15:50 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZWr21-0005Pp-2B for qemu-devel@nongnu.org; Tue, 01 Sep 2015 15:15:45 -0400 Date: Tue, 1 Sep 2015 15:15:35 -0400 From: Jeff Cody Message-ID: <20150901191535.GF2669@localhost.localdomain> References: <17356f309b182f0df47567aeed40ab0e3cfc99d3.1441127976.git.jcody@redhat.com> <55E5F493.9060402@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55E5F493.9060402@redhat.com> Subject: Re: [Qemu-devel] [RFC PATCH 1/2] util - add automated ID generation utility List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake Cc: kwolf@redhat.com, qemu-block@nongnu.org, qemu-devel@nongnu.org, armbru@redhat.com, programmingkidx@gmail.com, jsnow@redhat.com On Tue, Sep 01, 2015 at 12:55:15PM -0600, Eric Blake wrote: > 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 > > --- > > 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_/ > Good point. > > + [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]) > Yes, I think we do. If one is missing, that is certainly a mistake, and we run the risk of collisions as well. > > > + > > + 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. > Thanks -Jeff