rust/pv: Refactor pv crate

Big refactoring patch of the pv crate. The main reason behind this
refactoring is to simplify testing and maintaining the pv crate while
keeping OpenSSL/libcurl dependencies optional. Using crate features
increases the number of targets that have to be tested. This refactoring
eliminates the use of features by splitting the functionality of pv into
a use OpenSSL and no-use-OpenSSL crate.

Split off some code from the pv crate into a pv_core crate. pv requires
pv_core and reexports all symbols. pv_base contains all code from former
pv that does not use OpenSSL or libcurl functionalities. The refactored
pv crate contains functionalities to generate requests and validate host
key documents. All features from pv are dropped as they are not needed
anymore and to streamline the codebase for easier use and testing. While
at it fix some documentation issues.

Users (pvsecret & pvapconfig) have next to no code change, besides the
different import of the crate.

Acked-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

rust/utils/src/lib.rs

@@ -27,3 +27,36 @@ macro_rules! release_string {
     env!("S390_TOOLS_RELEASE", "env 'S390_TOOLS_RELEASE' must be set for release builds. Trigger build using the s390-tools build system or export the variable yourself")
     }};
 }
+
+/// Asserts a constant expression evaluates to `true`.
+///
+/// If the expression is not evaluated to `true` the compilation will fail.
+#[macro_export]
+macro_rules! static_assert {
+    ($condition:expr) => {
+        const _: () = core::assert!($condition);
+    };
+}
+
+/// Asserts that a type has a specific size.
+///
+/// Useful to validate structs that are passed to C code.
+/// If the size has not the expected value the compilation will fail.
+///
+/// # Example
+/// ```rust
+/// # use utils::assert_size;
+/// # fn main() {}
+/// #[repr(C)]
+/// struct c_struct {
+///     v: u64,
+/// }
+/// assert_size!(c_struct, 8);
+/// // assert_size!(c_struct, 7);//won't compile
+/// ```
+#[macro_export]
+macro_rules! assert_size {
+    ($t:ty, $sz:expr ) => {
+        $crate::static_assert!(::std::mem::size_of::<$t>() == $sz);
+    };
+}