src/fsverity: drop support for SHA-256

Just to prove that we can.  This is going to make the unit tests fail
but the examples still ought to work...

Author: allisonkarlitskaya

src/fsverity/hashvalue.rs

@@ -1,7 +1,7 @@
 use core::{fmt, hash::Hash};
 
 use hex::FromHexError;
-use sha2::{digest::FixedOutputReset, digest::Output, Digest, Sha256, Sha512};
+use sha2::{digest::FixedOutputReset, digest::Output, Digest, Sha512};
 use zerocopy::{FromBytes, Immutable, IntoBytes, KnownLayout, Unaligned};
 
 pub trait FsVerityHashValue
@@ -74,35 +74,12 @@ where
     }
 }
 
-impl fmt::Debug for Sha256HashValue {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "sha256:{}", self.to_hex())
-    }
-}
-
 impl fmt::Debug for Sha512HashValue {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "sha512:{}", self.to_hex())
     }
 }
 
-#[derive(Clone, Eq, FromBytes, Hash, Immutable, IntoBytes, KnownLayout, PartialEq, Unaligned)]
-#[repr(C)]
-pub struct Sha256HashValue([u8; 32]);
-
-impl From<Output<Sha256>> for Sha256HashValue {
-    fn from(value: Output<Sha256>) -> Self {
-        Self(value.into())
-    }
-}
-
-impl FsVerityHashValue for Sha256HashValue {
-    type Digest = Sha256;
-    const ALGORITHM: u8 = 1;
-    const EMPTY: Self = Self([0; 32]);
-    const ID: &str = "sha256";
-}
-
 #[derive(Clone, Eq, FromBytes, Hash, Immutable, IntoBytes, KnownLayout, PartialEq, Unaligned)]
 #[repr(C)]
 pub struct Sha512HashValue([u8; 64]);

src/fsverity/mod.rs

@@ -6,7 +6,7 @@ use std::{io::Error, os::fd::AsFd};
 
 use thiserror::Error;
 
-pub use hashvalue::{FsVerityHashValue, Sha256HashValue, Sha512HashValue};
+pub use hashvalue::{FsVerityHashValue, Sha512HashValue};
 
 /// Measuring fsverity failed.
 #[derive(Error, Debug)] // can't derive PartialEq because of std::io::Error