Re: [PATCH v3 01/11] tap: Remove tap_probe_vnet_hdr_len()

[Jason Wang]

On Fri, Oct 13, 2023 at 1:26 PM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>
> On 2023/10/13 14:00, Jason Wang wrote:
> > On Fri, Oct 13, 2023 at 12:14 PM Akihiko Odaki <akihiko.odaki@daynix.com> 
> > wrote:
> >>
> >> On 2023/10/13 10:38, Jason Wang wrote:
> >>> On Wed, Oct 11, 2023 at 11:40 PM Akihiko Odaki <akihiko.odaki@daynix.com> 
> >>> wrote:
> >>>>
> >>>> It was necessary since an Linux older than 2.6.35 may implement the
> >>>> virtio-net header but may not allow to change its length. Remove it
> >>>> since such an old Linux is no longer supported.
> >>>
> >>> Where can I see this agreement?
> >>
> >> docs/about/build-platforms.rst says:
> >>   > The project aims to support the most recent major version at all times
> >>   > for up to five years after its initial release. Support for the
> >>   > previous major version will be dropped 2 years after the new major
> >>   > version is released or when the vendor itself drops support, whichever
> >>   > comes first. In this context, third-party efforts to extend the
> >>   > lifetime of a distro are not considered, even when they are endorsed
> >>   > by the vendor (eg. Debian LTS); the same is true of repositories that
> >>   > contain packages backported from later releases (e.g. Debian
> >>   > backports). Within each major release, only the most recent minor
> >>   > release is considered.
> >>   >
> >>   > For the purposes of identifying supported software versions available
> >>   > on Linux, the project will look at CentOS, Debian, Fedora, openSUSE,
> >>   > RHEL, SLES and Ubuntu LTS. Other distros will be assumed to ship
> >>   > similar software versions.
> >
> > Well it also says:
> >
> > """
> > If a platform is not listed here, it does not imply that QEMU won't
> > work. If an unlisted platform has comparable software versions to a
> > listed platform, there is every expectation that it will work.
> > """
> >
> > A lot of downstream have customized build scripts.
>
> Still Linux versions older than 2.6.35 do not look like "comparable
> software versions to a listed platform" in my opinion.

Linux provides ABI compatibility so I don't know why, unless there is
a strong dependency on a specific new syscall introduced after 2.6.35.

>
> > And is something similar to such removal that has been done for other
> > subsystems?
>
> With commit c42e77a90d ("qemu/osdep: Remove fallback for
> MAP_FIXED_NOREPLACE"), I remove the support for glibc older than 2.28.
> Linux 2.6.35 is even older.
>

Ok, this explains things a little bit. Btw, we also have soliars
support for TAP, time to drop that as well?

Thanks