docs: clarify package_mode_copy_to_boot; better statvfs errors. Use anyhow context for statvfs failures instead of raw_os_error.

AI-assisted: implementation reviewed by Claude. Some suggestions was added.

Author: yasminvalim

src/component.rs

@@ -86,7 +86,7 @@ pub(crate) trait Component {
     /// Locating efi vendor dir
     fn get_efi_vendor(&self, sysroot: &Path) -> Result<Option<String>>;
 
-    /// Copy from /usr/lib/efi to boot/ESP (package mode)
+    /// Merge `/usr/lib/efi` onto the ESP for package-mode systems (EFI components only).
     fn package_mode_copy_to_boot(&self, root: &Path) -> Result<()>;
 }
 

src/efi.rs

@@ -854,7 +854,7 @@ impl Component for Efi {
         }
     }
 
-    /// Package mode copy: Simple copy from /usr/lib/efi to boot/ESP.
+    /// Package mode: merge `/usr/lib/efi` onto the ESP (write alongside, then atomic rename).
     fn package_mode_copy_to_boot(&self, root: &Path) -> Result<()> {
         self.package_mode_copy_to_boot_impl(root)
     }

src/util.rs

@@ -63,8 +63,7 @@ pub(crate) fn available_space_bytes(dir: &openat::Dir) -> Result<u64> {
 
 pub(crate) fn ensure_writable_mount<P: AsRef<Path>>(p: P) -> Result<()> {
     let p = p.as_ref();
-    let stat =
-        rustix::fs::statvfs(p).map_err(|e| std::io::Error::from_raw_os_error(e.raw_os_error()))?;
+    let stat = rustix::fs::statvfs(p).with_context(|| format!("statvfs {:?}", p))?;
     if !stat.f_flag.contains(rustix::fs::StatVfsMountFlags::RDONLY) {
         return Ok(());
     }