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  • Re: Rust for Linux and host-only libraries

    From =?ISO-8859-1?Q?Fabian_Gr=FCnbichler@21:1/5 to Miguel Ojeda on Fri Apr 19 20:40:01 2024
    On April 19, 2024 7:09:15 PM GMT+02:00, Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> wrote:
    Hi Ximin, Sylvestre, Fabian, all,

    In Rust for Linux, we are considering using host-only/userspace Rust >libraries (e.g. `syn`), and we were asked to check whether it would be >possible to just pick them from the distribution (since, in principle,
    they don't require kernel-specific changes).

    What is the policy in Debian for those? I was told about
    `debcargo-conf` by Zixing Liu, and indeed I can see e.g. `syn` there
    in `librust-syn-dev`, which places the sources at >`/usr/share/cargo/registry/`, which is great for what we need. Is that >correct? This would be useful for kernel developers that do not trust >third-party repositories (not even Rust's/crates.io/the upstream
    repository).

    Yes, all crates packaged by the Rust team (and most packaged for consumption by other packages/as build-deps by people outside of the team) ship their (patched for distro use) sources in a subdir there. The patches (except for wholesale exclusions of
    bundled C code and similar things, which is done via orig tarball repacking) are also shipped there, so the delta is easily reviewable. The whole directory structure can be used as (partial) drop-in for crates.io by configuring cargo accordingly (in
    Debian packaging this is done by a cargo wrapper shipped in /usr/share/cargo/bin/cargo, but that one is probably not suitable as-is for kernel stuff - it or rather its output might serve as an example for the needed cargo config runes though ;))

    By the way, is there a way to query where the sources are (i.e. that
    path) in a "standard" way (e.g. like `pkg-config`)? Or, at least, can
    we assume it should be stable? (e.g. for automated detection and/or >instructions we may want to provide).

    Not really - other than that directory being in the format the cargo expects for registry replacement, which is the same structure as `cargo vendor` creates. There is no index or .pc equivalent - the Cargo.toml file inside each crate has all the info and
    more in a standardized fashion after all :)

    I don't except this to change anytime soon (basically - only if stable dynamic linking becomes feasible and we stop shipping the sources in binary packages altogether ;) or if cargo itself completely revamps how it supports vendoring). If we know people/
    projects outside of Debian packaging are using this, adding a comment in the tooling that currently decides those paths (and their contents/structure) so that we know we should discuss or at least give a heads up about any planned fundamental changes
    should be easy to do :)

    Don't hesitate to reach out if you have further questions or go ahead with using the packaged crate sources!

    While there is considerable overlap w.r.t. subscribers, there is a second Debian rust list for discussions (debian-rust@lists.debian.org) - this one here gets all the automated notifications for all team maintained packages, so is rather high volume and
    things can get overlooked sometimes.

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  • From =?ISO-8859-1?Q?Fabian_Gr=FCnbichler@21:1/5 to Miguel Ojeda on Fri Apr 19 23:00:01 2024
    On April 19, 2024 8:44:12 PM GMT+02:00, Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> wrote:
    On Fri, Apr 19, 2024 at 8:13 PM Fabian Grünbichler ><debian@fabian.gruenbichler.email> wrote:

    Yes, all crates packaged by the Rust team (and most packaged for consumption by other packages/as build-deps by people outside of the team) ship their (patched for distro use) sources in a subdir there. The patches (except for wholesale exclusions of
    bundled C code and similar things, which is done via orig tarball repacking) are also shipped there, so the delta is easily reviewable. The whole directory structure can be used as (partial) drop-in for crates.io by configuring cargo accordingly (in
    Debian packaging this is done by a cargo wrapper shipped in /usr/share/cargo/bin/cargo, but that one is probably not suitable as-is for kernel stuff - it or rather its output might serve as an example for the needed cargo config runes though ;))

    Thanks for the quick reply!

    I see -- in principle, we only need the sources, i.e. we would not
    compile the crates using Cargo. Are the patches applied to the sources >already, or are they applied by that cargo wrapper you mention at
    build time? (Well, assuming users should use the patched versions).

    No, the patches are already applied in the source files shipped by librust-xxx-dev, if there are any. The cargo wrapper takes care of other things, like instructing cargo to use the packaged sources and setting rustflags and similar options. You should
    be able to use the same sources with manual rustc invocations without cargo or our wrapper just fine :)

    There's a bit of peculiarity around the versioning - the librust-.. packages provide all the semver prefixes of their version as well, so you can express "I want crate X in a semver compatible version of at least 2.3" via a versioned dependency (by
    depending on librust-x-2-dev with a version of at least 2.3), but also the more restricted variants (e.g., X in some 2.3.n version, or a specific 2.3.4 version, by depending on librust-2.3-dev resp. librust-2.3.4-dev). Normally, the actual package
    providing all of those is librust-X-dev, except when we need to package more than one version of X, then there might be a librust-X-dev in version A (providing all the semver prefixes of A), and another package librust-X-B-dev, where B is the shortest
    semver-breaking prefix of a semver incompatible version older than A (providing all semver prefixes of that version). A might be 2.3.4 and B 1 (with B's full version being 1.2.0, for example). Most of that won't be relevant for you - except that you want
    to depend on e.g. librust-syn-1-dev if you want syn 1.x, even if the actual "real" package is called librust-syn-dev, as the latter might also contain syn 0.x or 2.x in other distros/releases. Hope this was not too confusing ;)

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