[Mesa-dev] [PATCH 2/4] anv: use cache uuid based on the build timestamp.

[Emil Velikov]

On 24 June 2016 at 03:32, Michel Dänzer <michel at daenzer.net> wrote:
> On 23.06.2016 22:25, Emil Velikov wrote:
>> On 23 June 2016 at 03:49, Michel Dänzer <michel at daenzer.net> wrote:
>>> On 22.06.2016 21:04, Emil Velikov wrote:
>>>> From: Emil Velikov <emil.velikov at collabora.com>
>>>>
>>>> Do not rely on the git sha1:
>>>>  - its current truncated form makes it less unique
>>>>  - it does not attribute for local (Vulkand or otherwise) changes
>>>>
>>>> Use a timestamp produced at the time of build. It's perfectly unique,
>>>> unless someone explicitly thinkers with their system clock. Even then
>>>> chances of producing the exact same one are very small, if not zero.
>>>>
>>>> Cc: Jason Ekstrand <jason at jlekstrand.net>
>>>> Cc: mesa-stable at lists.freedesktop.org
>>>> Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
>>>> ---
>>>> Current approach uses seconds since Epoch, but if people prefer we
>>>> can use nano seconds, combination of the two and/or other.
>>>> ---
>>>>  src/intel/vulkan/.gitignore   |  2 ++
>>>>  src/intel/vulkan/Makefile.am  | 15 ++++++++++++++-
>>>>  src/intel/vulkan/anv_device.c |  4 ++--
>>>>  3 files changed, 18 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/src/intel/vulkan/.gitignore b/src/intel/vulkan/.gitignore
>>>> index a496146..7ef6a48 100644
>>>> --- a/src/intel/vulkan/.gitignore
>>>> +++ b/src/intel/vulkan/.gitignore
>>>> @@ -2,3 +2,5 @@
>>>>  /anv_entrypoints.c
>>>>  /anv_entrypoints.h
>>>>  /dev_icd.json
>>>> +/anv_timestamp.h.tmp
>>>> +/anv_timestamp.h
>>>> diff --git a/src/intel/vulkan/Makefile.am b/src/intel/vulkan/Makefile.am
>>>> index 4d9ff90..8332ae5 100644
>>>> --- a/src/intel/vulkan/Makefile.am
>>>> +++ b/src/intel/vulkan/Makefile.am
>>>> @@ -131,7 +131,20 @@ anv_entrypoints.c : anv_entrypoints_gen.py $(vulkan_include_HEADERS)
>>>>       $(AM_V_GEN) cat $(vulkan_include_HEADERS) |\
>>>>       $(PYTHON2) $(srcdir)/anv_entrypoints_gen.py code > $@
>>>>
>>>> -BUILT_SOURCES = $(VULKAN_GENERATED_FILES)
>>>> +
>>>> +.PHONY: anv_timestamp.h.tmp
>>>> +anv_timestamp.h.tmp:
>>>> +     $(AM_V_GEN) echo "#define ANV_TIMESTAMP `date +%s`" > $@
>>>
>>> This conflicts with efforts to make builds reproducible, see e.g.
>>> https://wiki.debian.org/ReproducibleBuilds . One technique used by such
>>> efforts is to replace any timestamps with all 0s.
>>>
>> Thanks to letting me know before things got swapped with 0s. Is there
>> a way to contact/check how other projects have handled/resolved this ?
>
> The wiki page above has a link to
> https://wiki.debian.org/ReproducibleBuilds/Contribute which lists
> several ways to get in touch with people working on this.
>
Sweet, thanks.

>
>>> Would it be possible to generate a hash over all source files listed in
>>> any Makefile.sources, or something like that?
>>>
>> If you want to pursue that task please do.
>
> I'm not going to work on this, I merely suggested a possible alternative.
>
JFYI Pekka did mention the exact same alternative, and the above
mentioned 'limitations' came to play. Would be great if we didn't have
to care for either one, but I suspect that there's at least dozen of
people who do.

I'll check with the people leading the initiative for other ways,
meanwhile do you feel strongly against the patch ?

Thanks
Emil