From patchwork Tue Sep 1 22:30:15 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jeff Cody X-Patchwork-Id: 513086 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 9BD7C14018C for ; Wed, 2 Sep 2015 08:31:12 +1000 (AEST) Received: from localhost ([::1]:59082 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZWu58-0004Xz-ET for incoming@patchwork.ozlabs.org; Tue, 01 Sep 2015 18:31:10 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49034) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZWu4P-0003mp-Cs for qemu-devel@nongnu.org; Tue, 01 Sep 2015 18:30:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZWu4O-00034P-Cj for qemu-devel@nongnu.org; Tue, 01 Sep 2015 18:30:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51539) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZWu4L-00033q-Cq; Tue, 01 Sep 2015 18:30:21 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (Postfix) with ESMTPS id 21CA2A3039; Tue, 1 Sep 2015 22:30:21 +0000 (UTC) Received: from localhost (ovpn-112-61.phx2.redhat.com [10.3.112.61]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id t81MUJY2014629 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA256 bits=256 verify=NO); Tue, 1 Sep 2015 18:30:20 -0400 From: Jeff Cody To: qemu-devel@nongnu.org Date: Tue, 1 Sep 2015 18:30:15 -0400 Message-Id: <45295c490f1d7c2c2209a19fba8c656967d03d5b.1441140367.git.jcody@redhat.com> In-Reply-To: References: In-Reply-To: References: X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 209.132.183.28 Cc: kwolf@redhat.com, qemu-block@nongnu.org, jsnow@redhat.com, armbru@redhat.com, programmingkidx@gmail.com Subject: [Qemu-devel] [PATCH v2 1/2] util - add automated ID generation utility X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org 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(). Signed-off-by: Jeff Cody Reviewed-by: Eric Blake Reviewed-by: John Snow Reviewed-by: Alberto Garcia --- include/qemu-common.h | 8 ++++++++ util/id.c | 36 ++++++++++++++++++++++++++++++++++++ 2 files changed, 44 insertions(+) diff --git a/include/qemu-common.h b/include/qemu-common.h index bbaffd1..f6b0105 100644 --- a/include/qemu-common.h +++ b/include/qemu-common.h @@ -237,6 +237,14 @@ int64_t strtosz_suffix_unit(const char *nptr, char **end, #define STR_OR_NULL(str) ((str) ? (str) : "null") /* id.c */ + +typedef enum IdSubSystems { + ID_QDEV, + ID_BLOCK, + ID_MAX /* last element, used as array size */ +} IdSubSystems; + +char *id_generate(IdSubSystems); bool id_wellformed(const char *id); /* path.c */ diff --git a/util/id.c b/util/id.c index 09b22fb..9457f2d 100644 --- a/util/id.c +++ b/util/id.c @@ -26,3 +26,39 @@ bool id_wellformed(const char *id) } return true; } + +#define ID_SPECIAL_CHAR '#' + +static const char * const id_subsys_str[] = { + [ID_QDEV] = "qdev", + [ID_BLOCK] = "block", +}; + +/* Generates an ID of the form: + * + * "#block146", + * + * where: + * - "#" is always the reserved character '#' + * - "block" refers to the subsystem identifed via IdSubSystems + * and id_subsys_str[] + * - "1" is a unique number (up to a uint64_t) for the subsystem + * - "46" is a zero-padded two digit pseudo-random number + * + * The caller is responsible for freeing the returned string with g_free() + */ +char *id_generate(IdSubSystems id) +{ + static uint64_t id_counters[ID_MAX]; + uint32_t rnd; + + assert(id < ID_MAX); + assert(id_subsys_str[id]); + + rnd = g_random_int_range(0, 99); + + return g_strdup_printf("%c%s%" PRIu64 "%02" PRId32, ID_SPECIAL_CHAR, + id_subsys_str[id], + id_counters[id]++, + rnd); +}