Re: [Qemu-block] [Qemu-devel] [PATCH v3 1/4] util - add automated ID generation utility

[Markus Armbruster]

Jeff Cody <address@hidden> writes:

> 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().
>
> Reviewed-by: John Snow <address@hidden>
> Reviewed-by: Eric Blake <address@hidden>
> Reviewed-by: Alberto Garcia <address@hidden>
> Signed-off-by: Jeff Cody <address@hidden>
> ---
>  include/qemu-common.h |  8 ++++++++
>  util/id.c             | 37 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 45 insertions(+)
>
> diff --git a/include/qemu-common.h b/include/qemu-common.h
> index 0bd212b..2f74540 100644
> --- a/include/qemu-common.h
> +++ b/include/qemu-common.h
> @@ -246,6 +246,14 @@ int64_t qemu_strtosz_suffix_unit(const char *nptr, char 
> **end,
>  #define STR_OR_NULL(str) ((str) ? (str) : "null")
>  
>  /* id.c */
> +
> +typedef enum IdSubSystems {
> +    ID_QDEV,

ID_QDEV is not used in this series.  Do you intend to use it in a
followup-series?  Can we reasonably expect that series will be accepted?

You could sidestep these questions by making id_generate() take a string
argument ;)

> +    ID_BLOCK,
> +    ID_MAX      /* last element, used as array size */
> +} IdSubSystems;
> +
> +char *id_generate(IdSubSystems id);
>  bool id_wellformed(const char *id);
>  
>  /* path.c */
[...]