Re: [PATCH 3/3] kbuild: introduce KERNEL_VERSION2 and LINUX_VERSION_CODE2

[Greg KH]

On Fri, Feb 05, 2021 at 10:50:33PM -0500, Sasha Levin wrote:
> SUBLEVEL only has 8 bits of space, which means that we'll overflow it
> once it reaches 256.
> 
> Few of the stable branches will imminently overflow SUBLEVEL while
> there's no risk of overflowing VERSION.
> 
> Thus, give SUBLEVEL 8 more bits which will be stolen from VERSION, this
> should create a better balance between the different version numbers we
> use.
> 
> We can't however use the original KERNEL_VERSION and LINUX_VERSION_CODE
> as userspace has created ABI dependency on their structure, and we risk
> breaking this userspace by modifying the layout of the version integers.
> 
> Cc: stable@xxxxxxxxxx
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  Makefile                                       | 8 +++++++-
>  drivers/net/ethernet/mellanox/mlx5/core/main.c | 4 ++--
>  drivers/usb/core/hcd.c                         | 4 ++--
>  drivers/usb/gadget/udc/aspeed-vhub/hub.c       | 4 ++--
>  include/linux/usb/composite.h                  | 4 ++--
>  kernel/sys.c                                   | 2 +-
>  tools/perf/tests/bpf-script-example.c          | 2 +-
>  tools/perf/tests/bpf-script-test-kbuild.c      | 2 +-
>  tools/perf/tests/bpf-script-test-prologue.c    | 2 +-
>  9 files changed, 19 insertions(+), 13 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 157be50c691e5..2177c548e4c24 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1266,7 +1266,13 @@ define filechk_version.h
>  		expr $(VERSION) \* 65536 + 0$(PATCHLEVEL) \* 256 + $(SUBLEVEL)); \
>  	fi;                                                              \
>  	echo '#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) +  \
> -	((c) > 255 ? 255 : (c)))'
> +	((c) > 255 ? 255 : (c)))';                                       \
> +	echo \#define LINUX_VERSION_CODE2 $(shell                        \

Wait, no, who will use LINUX_VERSION_CODE2()?  Why export something like
this to userspace that no one is asking for?

> +	expr $(VERSION) \* 16777216 + 0$(PATCHLEVEL) \* 65536 + 0$(SUBLEVEL)); \
> +	echo \#define LINUX_VERSION_MAJOR $(VERSION);                    \
> +	echo \#define LINUX_VERSION_PATCHLEVEL $(PATCHLEVEL);            \
> +	echo \#define LINUX_VERSION_SUBLEVEL $(SUBLEVEL);                \

These are good to have, and clean up kernel code.

thanks,

greg k-h