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Re: [Qemu-devel] [RFC PATCH 1/2] util - add automated ID generation util
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [RFC PATCH 1/2] util - add automated ID generation utility |
Date: |
Tue, 1 Sep 2015 12:55:15 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 |
On 09/01/2015 11:23 AM, Jeff Cody wrote:
> Multiple sub-systems in QEMU may find it useful to generated 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 predictibility, 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 --| | | |
> Subsytem String -----| | |
s/Subsytem/Subsystem/
> Unique number (64-bit) --| |
> Two-digit random number ---|
>
> For example, a generated node-name for the block sub-system may take the
> look like this:
s/take the//
>
> #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 | 35 +++++++++++++++++++++++++++++++++++
> 2 files changed, 43 insertions(+)
>
> +char *id_generate(IdSubSystems id)
> +{
> + const char *id_subsys_str[] = {
s/id_/const id_/
> + [ID_QDEV] = "qdev",
> + [ID_BLOCK] = "block",
> + };
Do we want some sort of compile-time assertion that we have entries for
all id values?...
> +
> + static uint64_t id_counters[ID_MAX];
> + uint32_t rnd;
> +
> + assert(id < ID_MAX);
...maybe in the form of assert(id_subsys_str[id])
> +
> + rnd = g_random_int_range(0, 99);
> +
> + return g_strdup_printf("%c%s%" PRIu64 "%" PRId32, ID_SPECIAL_CHAR,
> + id_subsys_str[id],
> + id_counters[id]++,
> + rnd);
> +}
>
Looks reasonable to me.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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