After a deeper research, we realized that only the uuidd provides the
guarantee of uniqueness of UUIDs across different CPUs and different UIDs.
Without it, there is a probability that two different processes on two
different CPUs with a different UID will call uuid_generate_time_safe()
in the same time and generate duplicated UUIDs.
There is a LIBUUID_CLOCK_FILE that should prevent it. But this approach
can work properly for a single UID only. And creating it world-writable
file would cause more problems that it will fix.
That is why I propose that uuid_generate_time_safe() should always
return -1 in case that it cannot interact with uuidd.
To realize this, uuid_generate_time_generic() should return -1 instead
of __uuid_generate_time() return code.
It should not break uuidd, as it calls __uuid_generate_time() directly.
In the last month, we had a discussion about one clock file per UID and
one for uuidd as a solution of LIBUUID_CLOCK_FILE being handled in a
first-UID-wins manner. It could improve the situation, but only for
UUIDs generated by the same UID.
Both changes are partially mutually exclusive: If
uuid_generate_time_safe() will always return -1, there will be no chance
to inform the program, that the alternative synchronization was used.
(This information could still be useful.) That it why I propose a small
change of API:
Add a new return code of uuid_generate_time_safe().
== RETURN VALUE
The newly created UUID is returned in the memory location pointed to by
_out_. *uuid_generate_time_safe*() returns zero if the UUID has been
generated in a safe manner, 1 if the UUID has been generated in a manner
that is safe for a single UID, -1 otherwise.
--
Best Regards / S pozdravem,
Stanislav Brabec
software developer
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SUSE LINUX, s. r. o. e-mail: [email protected]
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Stanislav Brabec wrote:
> After a deeper research, we realized that only the uuidd provides the
> guarantee of uniqueness of UUIDs across different CPUs and different UIDs.
Sorry, bad list.
--
Best Regards / S pozdravem,
Stanislav Brabec
software developer
---------------------------------------------------------------------
SUSE LINUX, s. r. o. e-mail: [email protected]
Křižíkova 148/34 (Corso IIa) tel: +420 284 084 060
186 00 Praha 8-Karlín fax: +420 284 084 001
Czech Republic http://www.suse.cz/
PGP: 830B 40D5 9E05 35D8 5E27 6FA3 717C 209F A04F CD76