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

[Eric Engestrom]

On Wed, Jun 22, 2016 at 01:04:41PM +0100, 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`" > $@
> +
> +anv_timestamp.h: anv_timestamp.h.tmp
> +	@echo "Updating anv_timestamp.h"
> +	@if ! cmp -s anv_timestamp.h.tmp anv_timestamp.h; then \
> +		mv anv_timestamp.h.tmp anv_timestamp.h ;\
> +	else \
> +		rm anv_timestamp.h.tmp ;\
> +	fi

For the else branch to be taken, the target would have to be generated
twice within the same second, and I don't see why we would want to avoid
modifying anv_timestamp.h's timestamp in this case, since that would be
the only thing that would be changed, and said timestamp would be within
the same second anyway.
I suggest to drop the `if` and unconditionally do the move.

Since this wouldn't change the behaviour anyway, with or without my
suggestion this patch is:
Reviewed-by: Eric Engestrom <eric.engestrom at imgtec.com>

> +
> +BUILT_SOURCES = $(VULKAN_GENERATED_FILES) anv_timestamp.h
>  CLEANFILES = $(BUILT_SOURCES) dev_icd.json
>  EXTRA_DIST = \
>  	$(top_srcdir)/include/vulkan/vk_icd.h \
> diff --git a/src/intel/vulkan/anv_device.c b/src/intel/vulkan/anv_device.c
> index 97300c3..e395b1c 100644
> --- a/src/intel/vulkan/anv_device.c
> +++ b/src/intel/vulkan/anv_device.c
> @@ -28,7 +28,7 @@
>  #include <fcntl.h>
>  
>  #include "anv_private.h"
> -#include "git_sha1.h"
> +#include "anv_timestamp.h"
>  #include "util/strtod.h"
>  #include "util/debug.h"
>  
> @@ -426,7 +426,7 @@ void
>  anv_device_get_cache_uuid(void *uuid)
>  {
>     memset(uuid, 0, VK_UUID_SIZE);
> -   snprintf(uuid, VK_UUID_SIZE, "anv-%s", MESA_GIT_SHA1 + 4);
> +   snprintf(uuid, VK_UUID_SIZE, "anv-%s", ANV_TIMESTAMP);
>  }
>  
>  void anv_GetPhysicalDeviceProperties(
> -- 
> 2.8.2