package mode: use write-alongside + atomic rename and check ESP space

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Author: yasminvalim

src/efi.rs

@@ -248,35 +248,67 @@ impl Efi {
         clear_efi_target(&product_name)?;
         create_efi_boot_entry(device, esp_part_num.trim(), &loader, &product_name)
     }
+    /// Copy EFI components to ESP using the same "write alongside + atomic rename" pattern
+    /// as bootable container updates, so the system stays bootable if any step fails.
     fn copy_efi_components_to_esp(
         &self,
         sysroot_dir: &openat::Dir,
         esp_dir: &openat::Dir,
-        esp_path: &Path,
+        _esp_path: &Path,
         efi_components: &[EFIComponent],
     ) -> Result<()> {
-        let dest_str = esp_path
+        // Build a merged source tree in a temp dir (same layout as desired ESP/EFI)
+        let temp_dir = tempfile::tempdir().context("Creating temp dir for EFI merge")?;
+        let temp_efi_path = temp_dir.path().join("EFI");
+        std::fs::create_dir_all(&temp_efi_path)
+            .with_context(|| format!("Creating {}", temp_efi_path.display()))?;
+        let temp_efi_str = temp_efi_path
             .to_str()
-            .with_context(|| format!("Invalid UTF-8: {}", esp_path.display()))?;
+            .context("Temp EFI path is not valid UTF-8")?;
 
         for efi_comp in efi_components {
             log::info!(
-                "Copying EFI component {} version {} to ESP at {}",
+                "Merging EFI component {} version {} into update tree",
                 efi_comp.name,
-                efi_comp.version,
-                esp_path.display()
+                efi_comp.version
             );
+            // Copy contents of component's EFI dir (e.g. fedora/) into temp_efi_path so merged
+            // layout is EFI/fedora/..., not EFI/EFI/fedora/...
+            let src_efi_contents = format!("{}/.", efi_comp.path);
+            filetree::copy_dir_with_args(sysroot_dir, src_efi_contents.as_str(), temp_efi_str, OPTIONS)
+                .with_context(|| format!("Copying {} to merge dir", efi_comp.path))?;
+        }
 
-            filetree::copy_dir_with_args(sysroot_dir, efi_comp.path.as_str(), dest_str, OPTIONS)
-                .with_context(|| {
-                    format!(
-                        "Failed to copy {} from {} to {}",
-                        efi_comp.name, efi_comp.path, dest_str
-                    )
-                })?;
+        // Ensure ESP/EFI exists (e.g. first install)
+        esp_dir.ensure_dir_all(std::path::Path::new("EFI"), 0o755)?;
+        let esp_efi_dir = esp_dir.sub_dir("EFI").context("Opening ESP EFI dir")?;
+
+        let source_dir =
+            openat::Dir::open(&temp_efi_path).context("Opening merged EFI source dir")?;
+        let source_filetree =
+            filetree::FileTree::new_from_dir(&source_dir).context("Building source filetree")?;
+        let current_filetree =
+            filetree::FileTree::new_from_dir(&esp_efi_dir).context("Building current filetree")?;
+        let diff = current_filetree
+            .diff(&source_filetree)
+            .context("Computing EFI diff")?;
+
+        // Check available space before writing to prevent partial updates when the partition is full
+        let required_bytes = current_filetree.total_size() + source_filetree.total_size();
+        let available_bytes = util::available_space_bytes(&esp_efi_dir)?;
+        if available_bytes < required_bytes {
+            anyhow::bail!(
+                "ESP has insufficient free space for update: need {} MiB, have {} MiB",
+                required_bytes / (1024 * 1024),
+                available_bytes / (1024 * 1024)
+            );
         }
 
-        // Sync the whole ESP filesystem 
+        // Same logic as bootable container: write to .btmp.* then atomic rename
+        filetree::apply_diff(&source_dir, &esp_efi_dir, &diff, None)
+            .context("Applying EFI update (write alongside + atomic rename)")?;
+
+        // Sync the whole ESP filesystem
         fsfreeze_thaw_cycle(esp_dir.open_file(".")?)?;
 
         Ok(())

src/filetree.rs

@@ -202,6 +202,16 @@ impl FileTree {
         Ok(Self { children })
     }
 
+    /// Total size in bytes of all files in the tree (for space checks).
+    #[cfg(any(
+        target_arch = "x86_64",
+        target_arch = "aarch64",
+        target_arch = "riscv64"
+    ))]
+    pub(crate) fn total_size(&self) -> u64 {
+        self.children.values().map(|m| m.size).sum()
+    }
+
     /// Determine the changes *from* self to the updated tree
     #[cfg(any(
         target_arch = "x86_64",

src/util.rs

@@ -1,9 +1,11 @@
 use std::collections::HashSet;
+use std::os::unix::io::AsRawFd;
 use std::path::Path;
 use std::process::Command;
 
 use anyhow::{bail, Context, Result};
 use openat_ext::OpenatDirExt;
+use rustix::fd::BorrowedFd;
 
 /// Parse an environment variable as UTF-8
 #[allow(dead_code)]
@@ -51,9 +53,18 @@ pub(crate) fn filenames(dir: &openat::Dir) -> Result<HashSet<String>> {
     Ok(ret)
 }
 
+/// Return the available space in bytes on the filesystem containing the given directory.
+/// Uses f_bavail * f_frsize from fstatvfs to avoid partial updates when the partition is full.
+pub(crate) fn available_space_bytes(dir: &openat::Dir) -> Result<u64> {
+    let fd = unsafe { BorrowedFd::borrow_raw(dir.as_raw_fd()) };
+    let st = rustix::fs::fstatvfs(fd)?;
+    Ok((st.f_bavail as u64) * (st.f_frsize as u64))
+}
+
 pub(crate) fn ensure_writable_mount<P: AsRef<Path>>(p: P) -> Result<()> {
     let p = p.as_ref();
-    let stat = rustix::fs::statvfs(p)?;
+    let stat = rustix::fs::statvfs(p)
+        .map_err(|e| std::io::Error::from_raw_os_error(e.raw_os_error()))?;
     if !stat.f_flag.contains(rustix::fs::StatVfsMountFlags::RDONLY) {
         return Ok(());
     }
@@ -121,3 +132,4 @@ impl Drop for SignalTerminationGuard {
         signal_hook_registry::unregister(self.0);
     }
 }
+