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

[Akihiko Odaki]

On 2023/10/16 14:25, Jason Wang wrote:
> 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.

This patch drops a pre-check for ioctl introduced with 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?

Do you mean Solaris? Honestly I don't know. I don't think anyone dares 
to use QEMU on Solaris (or to use Solaris at all), but apparently Oracle 
has not abandoned it yet.