lib/bootloader: Write to PReP partition for ppc64le

Bootloader code currently writes required data to base/parent
device (eg /dev/sda). This logic does not work for ppc64le
architecture as bootloader configuration has to be written
to PRePboot partition(typically first partition of disk).

This patch adds code to identify PowerPC-PReP-boot partition
(for ppc64le architecture) using lsblk command and writes
bootloader data to it.

Signed-off-by: Sachin Sant <sachinp@linux.ibm.com>

Author: sacsant

lib/src/bootloader.rs

@@ -1,3 +1,5 @@
+use std::process::Command;
+use std::str;
 use anyhow::Result;
 use camino::Utf8Path;
 use fn_error_context::context;
@@ -13,14 +15,39 @@ pub(crate) fn install_via_bootupd(
     rootfs: &Utf8Path,
     configopts: &crate::install::InstallConfigOpts,
 ) -> Result<()> {
+    let device_str: &str;
+    let prepboot_dir;
     let verbose = std::env::var_os("BOOTC_BOOTLOADER_DEBUG").map(|_| "-vvvv");
     // bootc defaults to only targeting the platform boot method.
     let bootupd_opts = (!configopts.generic_image).then_some(["--update-firmware", "--auto"]);
+
+    if cfg!(target_arch = "powerpc64") {
+        // get PowerPC-PReP-boot device information
+        let result = Command::new("lsblk")
+            .args([
+                "--noheadings",
+                "--paths",
+                "--filter",
+                &(format!(r#"'PARTLABEL=="PowerPC-PReP-boot"'"#)),
+                "--output",
+                &(format!("NAME")),
+            ])
+            .arg(device)
+            .output()?;
+        if !result.status.success() {
+            println!("{}", String::from_utf8_lossy(&result.stderr));
+            anyhow::bail!("lsblkh failed with {}", result.status);
+        }
+        prepboot_dir = String::from_utf8(result.stdout)?;
+        device_str = prepboot_dir.trim();
+    } else {
+        device_str = device.as_str()
+    }
     let args = ["backend", "install", "--write-uuid"]
         .into_iter()
         .chain(verbose)
         .chain(bootupd_opts.iter().copied().flatten())
-        .chain(["--device", device.as_str(), rootfs.as_str()]);
+        .chain(["--device", device_str, rootfs.as_str()]);
     Task::new("Running bootupctl to install bootloader", "bootupctl")
         .args(args)
         .verbose()