On Fri, Feb 05, 2021 at 07:11:05PM +0100, Mauro Carvalho Chehab wrote: > Em Fri, 5 Feb 2021 12:31:05 -0500 > Tony Battersby <tonyb@xxxxxxxxxxxxxxx> escreveu: > > > On 2/4/21 6:00 AM, Jiri Slaby wrote: > > > Agreed. But currently, sublevel won't "wrap", it will "overflow" to > > > patchlevel. And that might be a problem. So we might need to update the > > > header generation using e.g. "sublevel & 0xff" (wrap around) or > > > "sublevel > 255 : 255 : sublevel" (be monotonic and get stuck at 255). > > > > > > In both LINUX_VERSION_CODE generation and KERNEL_VERSION proper. > > > > My preference would be to be monotonic and get stuck at 255 to avoid > > breaking out-of-tree modules. If needed, add another macro that > > increases the number of bits that can be used to check for sublevels > > > 255, while keeping the old macros for compatibility reasons. Since > > sublevels > 255 have never existed before, any such checks must be > > newly-added, so they can be required to use the new macros. > > > > I do not run the 4.4/4.9 kernels usually, but I do sometimes test a wide > > range of kernels from 3.18 (gasp!) up to the latest when bisecting, > > benchmarking, or debugging problems. And I use a number of out-of-tree > > modules that rely on the KERNEL_VERSION to make everything work. Some > > out-of-tree modules like an updated igb network driver might be needed > > to make it possible to test the old kernel on particular hardware. > > > > In the worst case, I can patch LINUX_VERSION_CODE and KERNEL_VERSION > > locally to make out-of-tree modules work. Or else just not test kernels > > with sublevel > 255. > > Overflowing LINUX_VERSION_CODE breaks media applications. Several media > APIs have an ioctl that returns the Kernel version: > > drivers/media/cec/core/cec-api.c: caps.version = LINUX_VERSION_CODE; > drivers/media/mc/mc-device.c: info->media_version = LINUX_VERSION_CODE; > drivers/media/v4l2-core/v4l2-ioctl.c: cap->version = LINUX_VERSION_CODE; > drivers/media/v4l2-core/v4l2-subdev.c: cap->version = LINUX_VERSION_CODE; This always struck me as odd, because why can't they just use the uname(2) syscall instead? > Those can be used by applications in order to enable some features that > are available only after certain Kernel versions. > > This is somewhat deprecated, in favor of the usage of some other > capability fields, but for instance, the v4l2-compliance userspace tool > have two such checks: > > utils/v4l2-compliance/v4l2-compliance.cpp > 640: fail_on_test((vcap.version >> 16) < 3); > 641: if (vcap.version >= 0x050900) // Present from 5.9.0 onwards > > As far as I remember, all such checks are against major.minor. So, > something like: > > sublevel = (sublevel > 0xff) ? 0xff : sublevel; > > inside KERNEL_VERSION macro should fix such regression at -stable. I think if we clamp KERNEL_VERSION at 255 we should be fine for anyone checking this type of thing. Sasha has posted patches to do this. thanks, greg k-h
