On Fri, 2011-01-28 at 15:12 +0100, Petr Uzel wrote:
> Hi,
>
> RFC:
>
> Sometimes, when there are multiple processes generating time-based
> UUIDs in a loop (each of them using multiple threads), it can happen
> that the socket backlog in uuidd daemon is full and so the connection
> request is refused. uuid_generate_time() then fallbacks to unsafe way of
> generating UUID, which may cause duplicate time-based UUIDs to be
> generated.
Interesting catch. Could this not be resolved with a small pause
(nanosleep), avoiding the socket backlog? Not sure if it's best for a
library though.
>
> The problem with libuuid interface is that it is impossible to
> inform the caller of uuid_generate_time() that unsafe fallback has
> been used (the function returns void).
>
> This patch introduces new function,
>
> int uuid_generate_time_nf(uuid_t out) /* nf = "no fallback" */
>
> which, in case uuidd was needed, but for whatever reason could not be
> used, returns -1 and leaves content in @out undefined.
>
> Signed-off-by: Petr Uzel <petr.uzel@xxxxxxx>
> ---
> shlibs/uuid/src/gen_uuid.c | 40 +++++++++++++++++++++++++++++++++++-----
> shlibs/uuid/src/uuid.h | 1 +
> shlibs/uuid/src/uuid.sym | 10 +++++++++-
> 3 files changed, 45 insertions(+), 6 deletions(-)
>
> diff --git a/shlibs/uuid/src/gen_uuid.c b/shlibs/uuid/src/gen_uuid.c
> index a90bd8e..45af07f 100644
> --- a/shlibs/uuid/src/gen_uuid.c
> +++ b/shlibs/uuid/src/gen_uuid.c
> @@ -587,7 +587,17 @@ void uuid__generate_time(uuid_t out, int *num)
> uuid_pack(&uu, out);
> }
>
> -void uuid_generate_time(uuid_t out)
> +/*
> + * Generate time-based UUID and store it to @out
> + *
> + * If @fallback is nonzero and uuidd is needed, but could not be used,
> + * then do not use the usafe fallback.
> + *
> + * Returns 0 on success, -1 on failure (could not connect to uuidd and
> + * @fallback=0)
> + *
> + */
> +static int uuid_generate_time_generic(uuid_t out, int fallback)
> {
> #ifdef HAVE_TLS
> THREAD_LOCAL int num = 0;
> @@ -607,7 +617,7 @@ void uuid_generate_time(uuid_t out)
> last_time = time(0);
> uuid_unpack(out, &uu);
> num--;
> - return;
> + return 0;
> }
> num = 0;
> }
> @@ -620,14 +630,34 @@ void uuid_generate_time(uuid_t out)
> }
> num--;
> uuid_pack(&uu, out);
> - return;
> + return 0;
> }
> #else
> if (get_uuid_via_daemon(UUIDD_OP_TIME_UUID, out, 0) == 0)
> - return;
> + return 0;
> #endif
>
> - uuid__generate_time(out, 0);
> + if (fallback) {
> + uuid__generate_time(out, 0);
> + return 0;
> + }
> + else
> + /* fallback==0: disabled */
> + return -1;
> +}
> +
> +void uuid_generate_time(uuid_t out)
> +{
> + (void)uuid_generate_time_generic(out, 1);
> +}
> +
> +
> +/*
> + * Same as uuid_generate_time, but with unsafe fallback disabled.
> + */
> +int uuid_generate_time_nf(uuid_t out)
> +{
> + return uuid_generate_time_generic(out, 0);
> }
>
>
> diff --git a/shlibs/uuid/src/uuid.h b/shlibs/uuid/src/uuid.h
> index e329bf7..c7442ee 100644
> --- a/shlibs/uuid/src/uuid.h
> +++ b/shlibs/uuid/src/uuid.h
> @@ -79,6 +79,7 @@ void uuid_copy(uuid_t dst, const uuid_t src);
> void uuid_generate(uuid_t out);
> void uuid_generate_random(uuid_t out);
> void uuid_generate_time(uuid_t out);
> +int uuid_generate_time_nf(uuid_t out);
>
> /* isnull.c */
> int uuid_is_null(const uuid_t uu);
> diff --git a/shlibs/uuid/src/uuid.sym b/shlibs/uuid/src/uuid.sym
> index 05d9f39..719f133 100644
> --- a/shlibs/uuid/src/uuid.sym
> +++ b/shlibs/uuid/src/uuid.sym
> @@ -1,6 +1,6 @@
> /*
> * The symbol versioning ensures that a new application requiring symbol foo()
> - * can't run with old libblkid.so not providing foo() - the global SONAME
> + * can't run with old libuuid.so not providing foo() - the global SONAME
> * version info can't enforce this since we never change the SONAME.
> *
> * The original libuuid from e2fsprogs (<=1.41.5) does not to use
> @@ -31,3 +31,11 @@ global:
> local:
> *;
> };
> +
> +/*
> + * version(s) since util-linux 2.19
> + */
> +UUID_2.19 {
> +global:
> + uuid_generate_time_nf;
> +} UUID_1.0;
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