rust: Fix all cargo clippy findings

- Remove useless type conversion in uvdevice.rs
- Replace useless comparison in hostname.rs
- Replace unnecessary unwrap patterns in pvapconfig
- Use sort_by_key instead of sort_by in pvimg example

Command line used to get the findings:

  $ clippy --all-features -- --cap-lints=warn
  warning: useless conversion to the same type: `u64`
    --> pv_core/src/uvdevice.rs:56:28
     |
  56 |         rc = ioctl(raw_fd, cmd.try_into().unwrap(), cb.as_ptr_mut());
     |                            ^^^^^^^^^^^^^^
     |
     = help: consider removing `.try_into()`
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_conversion
     = note: `#[warn(clippy::useless_conversion)]` on by default

  warning: this comparison involving the minimum or maximum element for this type contains a case that is always true or always false
    --> utils/src/hostname.rs:60:13
     |
  60 |     assert!(isize::try_from(buf_len).unwrap() <= isize::MAX);
     |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     |
     = help: because `isize::MAX` is the maximum value for this type, this comparison is always true
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#absurd_extreme_comparisons
     = note: `#[warn(clippy::absurd_extreme_comparisons)]` on by default

  warning: `utils` (lib) generated 1 warning
      Checking pvebc v0.12.0 (/home/mhartmay/git/s390-tools/rust/pvebc)
  warning: consider using `sort_unstable_by_key`
     --> pvapconfig/src/ap.rs:177:9
      |
  177 |         self.0.sort_unstable_by(|a, b| b.gen.cmp(&a.gen));
      |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      |
      = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_sort_by
      = note: `#[warn(clippy::unnecessary_sort_by)]` on by default
  help: try
      |
  177 -         self.0.sort_unstable_by(|a, b| b.gen.cmp(&a.gen));
  177 +         self.0.sort_unstable_by_key(|b| std::cmp::Reverse(b.gen));

  warning: called `unwrap_err` on `r` after checking its variant with `is_err`
    --> pvapconfig/src/main.rs:55:29
     |
  54 |         if $r.is_err() {
     |         -------------- help: try: `if let Err(<item>) = r`
  55 |             eprintln!("{}", $r.unwrap_err());
     |                             ^^^^^^^^^^^^^^^
  ...
  87 |     on_error_print_and_exit!(r);
     |     --------------------------- in this macro invocation
     |
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_unwrap
     = note: this warning originates in the macro `on_error_print_and_exit` (in Nightly builds, run with -Z macro-backtrace for more info)

  warning: this `repeat().take()` can be written more concisely
    --> pvimg/src/se_img_comps/bootloader/ipl.rs:95:21
     |
  95 |           let comps = iter::repeat(ipl_pb0_pv_comp::default())
     |  _____________________^
  96 | |             .take(num_comp)
     | |___________________________^ help: consider using `repeat_n()` instead: `std::iter::repeat_n(ipl_pb0_pv_comp::default(), num_comp)`
     |
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_repeat_n
     = note: `#[warn(clippy::manual_repeat_n)]` on by default

  warning: this `repeat().take()` can be written more concisely
     --> pvimg/src/se_img_comps/bootloader/ipl.rs:113:21
      |
  113 |         let comps = iter::repeat(comp).take(num_comp).collect();
      |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `repeat_n()` instead: `std::iter::repeat_n(comp, num_comp)`
      |
      = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_repeat_n

Reviewed-by: Timo Keller <tkeller@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Marc Hartmayer <marc@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

rust/pv_core/src/uvdevice.rs

@@ -53,7 +53,7 @@ fn ioctl_raw(raw_fd: RawFd, cmd: u64, cb: &mut IoctlCb) -> Result<()> {
     // SAFETY: the passed pointer points to a valid memory region that
     // contains the expected C-struct. The struct outlives this function.
     unsafe {
-        rc = ioctl(raw_fd, cmd.try_into().unwrap(), cb.as_ptr_mut());
+        rc = ioctl(raw_fd, cmd, cb.as_ptr_mut());
     }
 
     // NOTE io::Error handles all errnos ioctl uses

rust/pvapconfig/src/ap.rs

@@ -174,7 +174,7 @@ impl ApqnList {
     /// Sort this Apqnlist by card generation:
     /// newest generation first, older generations last.
     pub fn sort_by_gen(&mut self) {
-        self.0.sort_unstable_by(|a, b| b.gen.cmp(&a.gen));
+        self.0.sort_unstable_by_key(|b| std::cmp::Reverse(b.gen));
     }
 
     /// Check MK restriction

rust/pvapconfig/src/main.rs

@@ -51,8 +51,8 @@ macro_rules! println_and_exit_failure {
 /// returns with exit failure.
 macro_rules! on_error_print_and_exit {
     ($r:expr) => {
-        if $r.is_err() {
-            eprintln!("{}", $r.unwrap_err());
+        if let Err(e) = $r {
+            eprintln!("{}", e);
             return ExitCode::FAILURE;
         }
     };

rust/pvimg/examples/create-sehdr/main.rs

@@ -176,7 +176,7 @@ fn main() -> anyhow::Result<()> {
     let mut secure_comp_builer = SecuredComponentBuilder::new_v1(false)?;
 
     // Sort components by address in ascending order
-    args.components.sort_by(|a, b| a.addr.cmp(&b.addr));
+    args.components.sort_by_key(|a| a.addr);
     for component_arg in args.components {
         info!("## Preparing {}", component_arg);
         let mut comp = Comp {

rust/pvimg/src/se_img_comps/bootloader/ipl.rs

@@ -92,9 +92,7 @@ use std::iter;
 
 impl ipl_parameter_block {
     pub fn size(num_comp: usize) -> Result<usize> {
-        let comps = iter::repeat(ipl_pb0_pv_comp::default())
-            .take(num_comp)
-            .collect();
+        let comps = std::iter::repeat_n(ipl_pb0_pv_comp::default(), num_comp).collect();
         let ipib = Self {
             pv: ipl_pb0_pv {
                 components: comps,
@@ -110,7 +108,7 @@ impl ipl_parameter_block {
 impl ipl_pb0_pv {
     pub fn size(num_comp: usize) -> Result<usize> {
         let comp = ipl_pb0_pv_comp::default();
-        let comps = iter::repeat(comp).take(num_comp).collect();
+        let comps = std::iter::repeat_n(comp, num_comp).collect();
         let ipl = Self {
             components: comps,
             ..Default::default()

rust/utils/src/hostname.rs

@@ -57,7 +57,7 @@ pub fn gethostname() -> io::Result<String> {
         }
     }
 
-    assert!(isize::try_from(buf_len).unwrap() <= isize::MAX);
+    assert!(buf_len <= isize::MAX as usize);
 
     // SAFETY: We made sure that `buf` is:
     // 1. NUL-terminated