Originally, when the Rust upstream `alloc` standard library crate was
vendored in commit 057b8d257107 ("rust: adapt `alloc` crate to the
kernel"), a `README.md` file was added to explain the provenance and
licensing of the source files.

Thus do the same for the `zerocopy` crate.

Cc: Joshua Liebow-Feeser <joshlf@google.com>
Cc: Jack Wrenn <jswrenn@google.com>
Link: https://patch.msgid.link/20260608141439.182634-12-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

The kernel builds `core` with the `no_fp_fmt_parse` `--cfg`, which means
we do not have support for formatting floating point primitives. However,
`zerocopy` expects those implementations to exist:

    error[E0277]: `f32` doesn't implement `core::fmt::Display`
       --> rust/zerocopy/src/byteorder.rs:172:29
        |
    172 |                   $trait::fmt(&self.get(), f)
        |                   ----------- ^^^^^^^^^^^ the trait `core::fmt::Display` is not implemented for `f32`
        |                   |
        |                   required by a bound introduced by this call
    ...
    907 | / define_type!(
    908 | |     An,
    909 | |     "A 32-bit floating point number",
    910 | |     F32,
    ...   |
    922 | |     []
    923 | | );
        | |_- in this macro invocation
        |
        = help: the following other types implement trait `core::fmt::Display`:
                  i128
                  i16
                  i32
                  i64
                  i8
                  isize
                  u128
                  u16
                and 4 others
        = note: this error originates in the macro `impl_fmt_trait` which comes from the expansion of the macro `define_type` (in Nightly builds, run with -Z macro-backtrace for more info)

Thus work around it by skipping those implementations in `zerocopy`.

Ideally, `zerocopy` would have the equivalent of `no_fp_fmt_parse`;
and, indeed, upstream just added it [1] after I filed an issue [2]
about it as requested. We can try it in a future update of our
vendored copy.

Cc: Joshua Liebow-Feeser <joshlf@google.com>
Cc: Jack Wrenn <jswrenn@google.com>
Link: https://github.com/google/zerocopy/pull/3429 [1]
Link: https://github.com/google/zerocopy/issues/3426 [2]
Link: https://patch.msgid.link/20260608141439.182634-11-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Originally, when the Rust upstream `alloc` standard library crate was
vendored, the SPDX License Identifiers were added to every file so that
the license on those was clear. The same happened with the vendoring of
`proc_macro2`, `quote` and `syn`. Please see:

  commit 057b8d257107 ("rust: adapt `alloc` crate to the kernel")
  commit 69942c0a8965 ("rust: syn: add SPDX License Identifiers")
  commit ddfa1b279d08 ("rust: quote: add SPDX License Identifiers")
  commit a9acfceb9614 ("rust: proc-macro2: add SPDX License Identifiers")

Thus do the same for the `zerocopy` crate.

This makes `scripts/spdxcheck.py` pass: use parentheses like commit
06e9bfc1e57d ("ionic: make spdxcheck.py happy") did since we have two
`OR` operators in the expression (three licenses).

SPDX identifiers are not added to the `benches` files because they are
included in rendered documentation. Nevertheless, the `README.md` to be
added by a later commit mentions the license.

Finally, as requested, I filed an issue [1] with upstream about it.

Cc: Joshua Liebow-Feeser <joshlf@google.com>
Cc: Jack Wrenn <jswrenn@google.com>
Link: https://github.com/google/zerocopy/issues/3428 [1]
Link: https://patch.msgid.link/20260608141439.182634-10-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

This is a subset of the Rust `zerocopy` crate, version v0.8.50 (released
2026-05-31), licensed under "BSD-2-Clause OR Apache-2.0 OR MIT", from:

    https://github.com/google/zerocopy/tree/v0.8.50

The files are copied as-is, with no modifications whatsoever (not even
adding the SPDX identifiers).

The `benches` folder is added (i.e. not just `src` like in other cases)
since the files there are included in the rendered documentation,
as well as the `rustdoc` CSS style file that is needed to make those
visually more understandable.

For copyright details, please see:

    https://github.com/google/zerocopy/blob/v0.8.50/README.md?plain=1
    https://github.com/google/zerocopy/blob/v0.8.50/LICENSE-BSD
    https://github.com/google/zerocopy/blob/v0.8.50/LICENSE-APACHE
    https://github.com/google/zerocopy/blob/v0.8.50/LICENSE-MIT

The next two patches modify these files as needed for use within the
kernel. This patch split allows reviewers to double-check the import
and to clearly see the differences introduced.

The following script may be used to verify the contents:

    for path in $(cd rust/zerocopy/ && find . -type f); do
        curl --silent --show-error --location \
            https://github.com/google/zerocopy/raw/v0.8.50/$path \
            | diff --unified rust/zerocopy/$path - && echo $path: OK
    done

Cc: Joshua Liebow-Feeser <joshlf@google.com>
Cc: Jack Wrenn <jswrenn@google.com>
Link: https://patch.msgid.link/20260608141439.182634-9-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>