Currently in both Debian and Ubuntu we ship like close to 40 .deb packages
that have linux-libc-dev (for native/multiarch, cross, ports, mipses).
Each one of them is like 1.5MB, however they actually all have the same and
repeated content.
the bulk of headers are the same on all arches (and enforced via
multi-arch:same), asm-generic is also the same for all of them, and then
kernel-arch asm headers are unique - but only for given kernel arches (not
all of the debian arch names).
Currently there are only 13 kernel archs for unique asm-arch headers, but
in Debian we have multiple reuses of the same kernel archs with different
userspace abi properties (arm = armel armhf, mips = 12 mips archs, powerpc
= 4, x86 = 3, and so on).
It seems wasteful on disk, build-time, and derivative build time to package
all of these separately. Especially since there is a chain of src:linux
building native ones + linux-source as a .deb; which is then used by
cross-toolchain-base{,-ports,-mips} to unpack and rebuild linux headers
again, and publish. When in practice src:linux itself could build an
efficient libc-dev packages for all arches as an arch:all package and
Multi-Arch:foreign.
I have implemented example packaging of that as a standalone source package
https://ppa.launchpadcontent.net/xnox/nonvirt/ubuntu/pool/main/l/linux-uapi/
The linux-libc-dev is native & multiarch uapi headers for all arches. The
linux-libc-dev-alpha-cross is all debian arch crosses. It is implemented
using hardlinks to maintain all the same paths that are currently being
used by all the arch:any linux-libc-dev packages, and the
linux-libc-dev-*-cross packages. In total they provide equivalent
functionality as 40+ linux-libc-dev* current debs in either Debian or
Ubuntu.
Is this something that the debian kernel team could consider supporting /
building as either standalone source package, or out of src:linux directly?
as this would reduce 40+ .deb duplication in the mirror pools of the same
content; and will eliminate build-depends on linux-source (and thus
built-using) from src:cross-toolchain-base* and will actually ensure that
all kernel headers for native / multiarch / cross arches are updated
simultaneously, without need to wait for all arch:any builds to catch up
first. It also gives ability to trivially create freestanding toolchains to
any of the arches without actually building a full debian port for or
having a working kernel for a given port.
The obvious things missing from the packaging is to create all the
breaks/replaces/provides, and update cross-toolchain-base packages to
match. Also probably using symlinks rather than hard links, with
linux-libc-dev-cross likely depending on the native one.
Separately for Ubuntu, due to the number of kernel built, I would likely
want to upload source package that produces linux-libc-dev as a separate
source package such that linux-libc-dev is actually only updated when
needed, rather than on every kernel upload. As there is no need to rev
linux-libc-dev as often as kernel uploads are done. But I do hope to see if
this approach for linux-libc-dev can be coordinated to ensure compatible
cross-toolchain-base changes.
--
okurrr,
Dimitri
