install: pull grubconfigs from the source root

When doing install with the `--src-root` argument, make sure grub static
configs are copied from the source root rather than the running root.

See bootc-dev/bootc#1559

Author: jbtrystram

src/bios.rs

@@ -190,7 +190,7 @@ impl Component for Bios {
                 .context("Failed to backup GRUB config")?;
         }
 
-        crate::grubconfigs::install(&destdir, None, true)?;
+        crate::grubconfigs::install(&destdir, None, None, true)?;
 
         // Remove the real config if it is symlink and will not
         // if /boot/grub2/grub.cfg is file

src/bootupd.rs

@@ -116,7 +116,12 @@ pub(crate) fn install(
                 target_arch = "powerpc64",
                 target_arch = "riscv64"
             ))]
-            crate::grubconfigs::install(sysroot, installed_efi_vendor.as_deref(), uuid)?;
+            crate::grubconfigs::install(
+                sysroot,
+                Some(&source_root),
+                installed_efi_vendor.as_deref(),
+                uuid,
+            )?;
             // On other architectures, assume that there's nothing to do.
         }
         None => {}

src/efi.rs

@@ -273,7 +273,7 @@ impl Component for Efi {
                 .context("Failed to backup GRUB config")?;
         }
 
-        grubconfigs::install(&sysroot, Some(&vendor), true)?;
+        grubconfigs::install(&sysroot, None, Some(&vendor), true)?;
         // Synchronize the filesystem containing /boot/efi/EFI/{vendor} to disk.
         fsfreeze_thaw_cycle(efidir.open_file(".")?)?;
 

src/grubconfigs.rs

@@ -1,4 +1,5 @@
 use std::fmt::Write;
+use std::io::Read;
 use std::os::unix::io::AsRawFd;
 use std::path::{Path, PathBuf};
 
@@ -25,6 +26,7 @@ const GRUBCONFIG_FILE_MODE: u32 = 0o600;
 #[context("Installing static GRUB configs")]
 pub(crate) fn install(
     target_root: &openat::Dir,
+    src_root: Option<&openat::Dir>,
     installed_efi_vendor: Option<&str>,
     write_uuid: bool,
 ) -> Result<()> {
@@ -40,12 +42,23 @@ pub(crate) fn install(
         bootdir.create_dir(GRUB2DIR, 0o700)?;
     }
 
+    let configdir = if let Some(src_root) = src_root {
+        // strip the leading `/` to make the path relative to the given
+        // source root
+        src_root.sub_dir(Path::new(CONFIGDIR).strip_prefix("/")?)?
+    } else {
+        openat::Dir::open(Path::new(CONFIGDIR))?
+    };
+
     let mut config = String::from("# Generated by bootupd / do not edit\n\n");
 
-    let pre = std::fs::read_to_string(Path::new(CONFIGDIR).join("grub-static-pre.cfg"))?;
+    let mut pre = String::new();
+    configdir
+        .open_file("grub-static-pre.cfg")?
+        .read_to_string(&mut pre)?;
     config.push_str(pre.as_str());
 
-    let dropindir = openat::Dir::open(&Path::new(CONFIGDIR).join(DROPINDIR))?;
+    let dropindir = configdir.sub_dir(Path::new(DROPINDIR))?;
     // Sort the files for reproducibility
     let mut entries = dropindir
         .list_dir(".")?
@@ -62,7 +75,9 @@ pub(crate) fn install(
             continue;
         }
         writeln!(config, "\n### BEGIN {name} ###")?;
-        let dropin = std::fs::read_to_string(Path::new(CONFIGDIR).join(DROPINDIR).join(name))?;
+        let mut dropin = String::new();
+        dropindir.open_file(name)?.read_to_string(&mut dropin)?;
+
         config.push_str(dropin.as_str());
         writeln!(config, "### END {name} ###")?;
         println!("Added {name}");
@@ -103,8 +118,8 @@ pub(crate) fn install(
             .sub_dir_optional("boot/efi/EFI")
             .context("Opening /boot/efi/EFI")?;
         if let Some(efidir) = dest_efidir {
-            efidir
-                .copy_file(&Path::new(CONFIGDIR).join("grub-static-efi.cfg"), target)
+            configdir
+                .copy_file_at("grub-static-efi.cfg", &efidir, target)
                 .context("Copying static EFI")?;
             println!("Installed: {target:?}");
             if let Some(uuid_path) = uuid_path {
@@ -155,7 +170,7 @@ mod tests {
         std::fs::create_dir_all(tdp.join("boot/grub2"))?;
         std::fs::create_dir_all(tdp.join("boot/efi/EFI/BOOT"))?;
         std::fs::create_dir_all(tdp.join("boot/efi/EFI/fedora"))?;
-        install(&td, Some("fedora"), false).unwrap();
+        install(&td, None, Some("fedora"), false).unwrap();
 
         assert!(td.exists("boot/grub2/grub.cfg")?);
         assert!(td.exists("boot/efi/EFI/fedora/grub.cfg")?);