On 09/01/2015 04:30 PM, Jeff Cody wrote: > 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(+)
Reviewed-by: Eric Blake <ebl...@redhat.com>
> +
> +static const char * const id_subsys_str[] = {
> + [ID_QDEV] = "qdev",
> + [ID_BLOCK] = "block",
> +};
We're inconsistent on whether there should be a space in '*const'
(compare commit a91e211 with b86f461, for example). But since qemu.git
has both spellings in various contexts, it's probably not worth changing
here.
> +
> + rnd = g_random_int_range(0, 99);
Thankfully, g_random_* is a PRNG that is not consuming system entropy
(auto-generated names should not be starving /dev/random).
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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