On 10/18/24 15:31, Daniel P. Berrangé wrote:
On Tue, Oct 15, 2024 at 03:17:18PM +0200, Paolo Bonzini wrote:
On top of this, the required version of bindgen is still too new
for Debian 12 and Ubuntu 22.04. This is fixed by the last four patches.
This is an RFC for two reasons. First, because it would be a valid
decision to delay enabling of Rust until at least some of these
features are available in all supported distros.
Lets say we maximise our back compatibility today, and have to
carry some sub-optimal code patterns.
1, 2, 3, 4 years down the lines, we can gradually eliminate
those undesired code patterns / workarounds, as older distros
naturally age-out of our matrix. After 4 years our entire
matrix will have cycled, so we're not needing to carry this
debt for very long (4 years is not long in the context of a
project like QEMU which has been going several decades)
I agree, for what it's worth.
Personally I tend towards quicker adoption of Rust, despite
the need for short term workarounds, as they'll disappear
again reasonably quickly.
Yes, especially since (as Kevin pointed out) most of the workarounds are
okay in terms of maintainability. If the worst is "if let", and it only
occurs in a dependency, we're in a good place overall.
Another possibility
could be to accept Rust 1.64.0 but require installing a newer bindgen
(0.66.x for example) on those two distros with an older release.
How difficult is it to get newer 'bindgen' installed on these
platforms ? The audience here is not so much distros trying to
package new QEMU, as that's ony relevant for new distro, but
rather it is end usrs/contributors building QEMU for themslves.
Very simple - "cargo install bindgen-cli", as already seen in the
fedora-rust-nightly container's Dockerfile (note: building QEMU does
_not_ need cargo). In fact we could in fact do it via libvirt-ci, and
it's quite possible that MacOS or some BSDs will need it.
Personally I'd be okay with allowing Debian 12 but not Ubuntu 22.04, for
various reasons:
- Ubuntu 22.04 has a new rustc and an old bindgen---so it's really just
laziness.
- any workarounds for Debian 12 would last shorter, and anyway
- Debian 12 has the really important feature (--allowlist-file), whereas
the lack of --generate-cstr is only annoying.
Can it be done automagically in the same way we "do the right thing"
with the 3rd party crates we depend on, or is bindgen special in
some way that makes it more inconvenient for users ?
bindgen is special in that it has a metric ton of indirect dependencies,
which we'd all have to write a meson.build for (by hand). :/
On the last point, see
https://lists.nongnu.org/archive/html/qemu-devel/2024-10/msg02688.html
with that series, it should be just a matter of adding '--enable-rust'
in a few key jobs.
Indeed, thanks.
Paolo
