From a0f1913637e6cd711aa721233b75eb2ec84d017b Mon Sep 17 00:00:00 2001 From: Jeff Cody Date: Mon, 12 Oct 2015 19:36:49 -0400 Subject: util - add automated ID generation utility 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 Reviewed-by: Eric Blake Reviewed-by: Alberto Garcia Signed-off-by: Jeff Cody Signed-off-by: Kevin Wolf --- util/id.c | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) (limited to 'util') diff --git a/util/id.c b/util/id.c index 09b22fb..bcc64d8 100644 --- a/util/id.c +++ b/util/id.c @@ -26,3 +26,40 @@ 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 PREFIX SUBSYSTEM NUMBER + * where: + * + * - PREFIX is the reserved character '#' + * - SUBSYSTEM identifies the subsystem creating the ID + * - NUMBER is a decimal number unique within SUBSYSTEM. + * + * Example: "#block146" + * + * Note that these IDs do not satisfy id_wellformed(). + * + * 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, 100); + + return g_strdup_printf("%c%s%" PRIu64 "%02" PRId32, ID_SPECIAL_CHAR, + id_subsys_str[id], + id_counters[id]++, + rnd); +} -- cgit v1.1