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

[Dave Airlie]

On 23 June 2016 at 23:25, Emil Velikov <emil.l.velikov at gmail.com> 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 page linked looks like a policy/guidelines one and I'm struggling
> to see any examples of how things were resolved for project X or Y :-\
>
>>
>> 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.
>
> A couple of humble requests a) can you get some very rough measurement
> how long all the hashing takes, b) please try to avoid adding extra
> external dependencies (not sure how many people will like that).
>

I think you should be taking that as a NAK for this approach.

If one of the reasons for not using the git_sha1 is we can't detect
patches from distros, and one distro is knowingly going to have to
patch the approach out, then the approach isn't really suitable.

I'm also not sure but does running make install on the same tree twice
re-generate this file? or did we take that into a/c?

Dave.