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 <jc...@redhat.com> --- 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); +} -- 1.9.3