blockdev: add PARENT_DEVICES

As `PARENT_DEVICES` is used multiple times, initialize once at the
begining and read them then, add this in `get_parent_devices()`
according to #923 (comment)

Author: HuijingHei

src/blockdev.rs

@@ -1,10 +1,17 @@
 use camino::Utf8Path;
 use std::path::Path;
+use std::sync::OnceLock;
 
 use anyhow::{bail, Context, Result};
 use bootc_blockdev::PartitionTable;
 use fn_error_context::context;
 
+/// Get parent devices and save
+pub fn get_parent_devices(devices: Option<Vec<String>>) -> &'static [String] {
+    static PARENT_DEVICES: OnceLock<Vec<String>> = OnceLock::new();
+    PARENT_DEVICES.get_or_init(|| devices.unwrap())
+}
+
 #[context("get parent devices from mount point boot")]
 pub fn get_devices<P: AsRef<Path>>(target_root: P) -> Result<Vec<String>> {
     let target_root = target_root.as_ref();

src/cli/bootupctl.rs

@@ -1,5 +1,5 @@
 use crate::bootupd;
-use anyhow::Result;
+use anyhow::{Context, Result};
 use clap::Parser;
 use log::LevelFilter;
 
@@ -129,13 +129,15 @@ impl CtlCommand {
     /// Runner for `update` verb.
     fn run_update() -> Result<()> {
         ensure_running_in_systemd()?;
-        bootupd::client_run_update()
+        let sysroot = prep_before_update()?;
+        bootupd::client_run_update(&sysroot)
     }
 
     /// Runner for `update` verb.
     fn run_adopt_and_update() -> Result<()> {
         ensure_running_in_systemd()?;
-        bootupd::client_run_adopt_and_update()
+        let sysroot = prep_before_update()?;
+        bootupd::client_run_adopt_and_update(&sysroot)
     }
 
     /// Runner for `validate` verb.
@@ -213,3 +215,14 @@ fn run_status_in_container(json_format: bool) -> Result<()> {
     }
     Ok(())
 }
+
+/// Initialize parent devices to prepare the update
+fn prep_before_update() -> Result<openat::Dir> {
+    let sysroot = openat::Dir::open("/").context("Opening root dir")?;
+    let devices = crate::blockdev::get_devices("/").context("get parent devices")?;
+    // initialize parent devices before update
+    crate::blockdev::get_parent_devices(Some(devices));
+    // check if we can get value
+    crate::blockdev::get_parent_devices(None);
+    Ok(sysroot)
+}