Messages in this thread | | | Date | Mon, 18 Jan 2021 08:39:59 -0500 | From | Sasha Levin <> | Subject | Re: [PATCH] kbuild: give SUBLEVEL more room in KERNEL_VERSION |
| |
On Mon, Jan 18, 2021 at 10:24:33AM +0100, Greg KH wrote: >On Mon, Jan 18, 2021 at 10:21:16AM +0100, Greg KH wrote: >> On Sun, Jan 17, 2021 at 08:49:51PM -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. >> > >> > The downside here is that Linus will have 8 bits less to play with, but >> > given our current release cadence (~10 weeks), the number of Linus's >> > fingers & toes (20), and the current VERSION (5) we can calculate that >> > VERSION will overflow in just over 1,000 years, so I'm kicking this can >> > down the road. >> > >> > Cc: stable@kernel.org >> > Signed-off-by: Sasha Levin <sashal@kernel.org> >> > --- >> > Makefile | 4 ++-- >> > 1 file changed, 2 insertions(+), 2 deletions(-) >> > >> > diff --git a/Makefile b/Makefile >> > index 9e73f82e0d863..dc2bad7a440d8 100644 >> > --- a/Makefile >> > +++ b/Makefile >> > @@ -1252,8 +1252,8 @@ endef >> > >> > define filechk_version.h >> > echo \#define LINUX_VERSION_CODE $(shell \ >> > - expr $(VERSION) \* 65536 + 0$(PATCHLEVEL) \* 256 + 0$(SUBLEVEL)); \ >> > - echo '#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))' >> > + expr $(VERSION) \* 16777216 + 0$(PATCHLEVEL) \* 65536 + 0$(SUBLEVEL)); \ >> > + echo '#define KERNEL_VERSION(a,b,c) (((a) << 24) + ((b) << 16) + (c))' >> >> As much as I agree, this will break in-tree users of LINUX_VERSION_CODE >> that try to suck out the version/patchlevel number of the kernel release >> into their own fields. Things like USB host controller strings, v4l >> ioctl reports, scsi driver ioctls, and other places do fun bit-movements >> to try to unreverse this bit packing. >> >> So how about we just provide a "real" version/subversion/revision >> #define as well, and clean up all in-kernel users, so we can get this to >> work, and we can change it in the future more easily. > >Or, I can just stop doing stable releases at .255 and then abuse the >EXTRAVERSION field to put in sub-revision values. > >Or, we can just not worry about it as anyone using these really old >kernels, userspace will work just fine (the number going backwards for >these fields isn't going to break anything), it's only any crazy >out-of-tree code that will get confused if they are trying to do >different build options based on SUBLEVEL :)
I think it would also affect code that doesn't do things based on SBULEVEL. Consider something like:
if (LINUX_VERSION_CODE < KERNEL_VERSION(4,5,0))
Which will cause 4.4.256 to now change the result of that comparison.
-- Thanks, Sasha
| |