On Tue, Sep 01, 2015 at 04:55:16PM -0600, Eric Blake wrote: > 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. >
If this ends up needing another rev, I'll change it for you :) > > + > > + 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). > Yup. Thanks, Jeff