Re: [Qemu-devel] [PATCH v2 1/2] util - add automated ID generation utility

[Jeff Cody <jcody@redhat.com>]

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 <jcody@redhat.com>
> > ---
> >  include/qemu-common.h |  8 ++++++++
> >  util/id.c             | 36 ++++++++++++++++++++++++++++++++++++
> >  2 files changed, 44 insertions(+)
> 
> Reviewed-by: Eric Blake <eblake@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