sev: silence warnings under snp-only feature build

Building with default-features=false, features=["openssl","snp"] (no
"sev" feature) triggers five warnings. Fix each at the source.

error.rs: "use openssl::error::ErrorStack" on cfg(all(openssl, sev)).

firmware/host/types/snp.rs: replace unreachable "_" arms in TcbVersion's
Encoder/Decoder.

launch/linux/snp.rs: tag legacy "pub struct Init" (KVM_SEV_INIT payload,
only consumed via the "sev" feature path) with #[allow(dead_code)] so
it compiles cleanly under snp-only.

Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>

Author: rouming

src/error.rs

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0
 
-#[cfg(feature = "openssl")]
+#[cfg(all(feature = "openssl", feature = "sev"))]
 use openssl::error::ErrorStack;
 use std::{
     array::TryFromSliceError,

src/firmware/host/types/snp.rs

@@ -527,7 +527,8 @@ impl Encoder<Generation> for TcbVersion {
         let buffer = match generation {
             Generation::Milan | Generation::Genoa => self.to_legacy_bytes(),
             Generation::Turin | Generation::Venice => self.to_turin_bytes(),
-            _ => {
+            #[cfg(feature = "sev")]
+            Generation::Naples | Generation::Rome => {
                 return Err(std::io::Error::new(
                     std::io::ErrorKind::Unsupported,
                     "Unsupported Processor Generation for TCB writing",
@@ -548,7 +549,8 @@ impl Decoder<Generation> for TcbVersion {
             Generation::Turin | Generation::Venice => {
                 Ok(TcbVersion::from_turin_bytes(&reader.read_bytes()?))
             }
-            _ => Err(std::io::Error::new(
+            #[cfg(feature = "sev")]
+            Generation::Naples | Generation::Rome => Err(std::io::Error::new(
                 std::io::ErrorKind::Unsupported,
                 "Unsupported Processor Generation for TCB parsing",
             )),

src/launch/linux/sev.rs

@@ -11,10 +11,12 @@ use std::{
 
 /// Initialize the SEV platform context.
 #[repr(C)]
+#[allow(dead_code)]
 pub struct Init;
 
 /// Initialize the SEV-ES platform context.
 #[repr(C)]
+#[allow(dead_code)]
 pub struct EsInit;
 
 #[derive(Clone, Copy)]

src/launch/linux/snp.rs

@@ -9,6 +9,7 @@ use std::marker::PhantomData;
 /// Initialize the SEV-SNP platform in KVM.
 #[derive(Default)]
 #[repr(C, packed)]
+#[allow(dead_code)]
 pub struct Init {
     /// Reserved space, must be always set to 0 when issuing the ioctl.
     flags: u64,

src/lib.rs

@@ -111,6 +111,7 @@ pub mod error;
 /// Module for Encoding and Decoding types.
 pub mod parser;
 
+#[cfg(feature = "sev")]
 use crate::parser::Decoder;
 
 #[cfg(all(feature = "sev", feature = "dangerous_hw_tests"))]

src/util/parser_helper/mod.rs

@@ -4,6 +4,8 @@ mod read_ext;
 
 mod write_ext;
 
+#[allow(unused_imports)]
 pub(crate) use read_ext::ReadExt;
 
+#[allow(unused_imports)]
 pub(crate) use write_ext::WriteExt;

src/util/parser_helper/read_ext.rs

@@ -3,6 +3,7 @@
 use crate::parser::Decoder;
 use std::io::Read;
 
+#[allow(dead_code)]
 pub trait ReadExt: Read {
     /// Convenience: read a value with unit params.
     fn read_bytes<T>(&mut self) -> Result<T, std::io::Error>

src/util/parser_helper/write_ext.rs

@@ -2,6 +2,7 @@
 use crate::parser::Encoder;
 use std::io::Write;
 
+#[allow(dead_code)]
 pub trait WriteExt: Write {
     /// Write a value using its Encoder implementation and the provided params
     fn write_bytes<T, P>(&mut self, value: T, params: P) -> Result<(), std::io::Error>