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Re: [Qemu-block] [PATCH v2 1/2] util - add automated ID generation utili
From: |
Jeff Cody |
Subject: |
Re: [Qemu-block] [PATCH v2 1/2] util - add automated ID generation utility |
Date: |
Tue, 1 Sep 2015 20:08:21 -0400 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
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 <address@hidden>
> > ---
> > include/qemu-common.h | 8 ++++++++
> > util/id.c | 36 ++++++++++++++++++++++++++++++++++++
> > 2 files changed, 44 insertions(+)
>
> Reviewed-by: Eric Blake <address@hidden>
>
> > +
> > +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