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

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Oct 13, 2023 at 02:26:03PM +0900, Akihiko Odaki 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.


This is fine - I would be ok to replace support with an error message
and failure. Not checking that a capability is supported however
isn't a good idea. And once we do - do we still gain anything by
not working around that?

> > 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.