Thread sysroot through adopt+update flow

More prep for #108
Similar to the previous PR for updates.

src/bootupd.rs

@@ -142,14 +142,14 @@ pub(crate) fn adopt_and_update(name: &str) -> Result<ContentMetadata> {
     } else {
         anyhow::bail!("Component {} has no available update", name);
     };
+    let mut state_guard = SavedState::acquire_write_lock(openat::Dir::open("/")?)
+        .context("Failed to acquire write lock")?;
+
     let inst = component
-        .adopt_update(&update)
+        .adopt_update(&state_guard.sysroot, &update)
         .context("Failed adopt and update")?;
     state.installed.insert(component.name().into(), inst);
 
-    let sysroot = openat::Dir::open("/")?;
-    let mut state_guard =
-        SavedState::acquire_write_lock(sysroot).context("Failed to acquire write lock")?;
     state_guard.update_state(&state)?;
     Ok(update)
 }

src/component.rs

@@ -30,7 +30,11 @@ pub(crate) trait Component {
     fn query_adopt(&self) -> Result<Option<Adoptable>>;
 
     /// Given an adoptable system and an update, perform the update.
-    fn adopt_update(&self, update: &ContentMetadata) -> Result<InstalledContent>;
+    fn adopt_update(
+        &self,
+        sysroot: &openat::Dir,
+        update: &ContentMetadata,
+    ) -> Result<InstalledContent>;
 
     /// Implementation of `bootupd install` for a given component.  This should
     /// gather data (or run binaries) from the source root, and install them

src/efi.rs

@@ -74,7 +74,11 @@ impl Component for EFI {
     }
 
     /// Given an adoptable system and an update, perform the update.
-    fn adopt_update(&self, updatemeta: &ContentMetadata) -> Result<InstalledContent> {
+    fn adopt_update(
+        &self,
+        sysroot: &openat::Dir,
+        updatemeta: &ContentMetadata,
+    ) -> Result<InstalledContent> {
         let meta = if let Some(meta) = self.query_adopt()? {
             meta
         } else {
@@ -83,8 +87,9 @@ impl Component for EFI {
 
         let esp = self.open_esp()?;
         validate_esp(&esp)?;
-        let updated =
-            openat::Dir::open(&component_updatedir("/", self)).context("opening update dir")?;
+        let updated = sysroot
+            .sub_dir(&component_updatedirname(self))
+            .context("opening update dir")?;
         let updatef = filetree::FileTree::new_from_dir(&updated).context("reading update dir")?;
         // For adoption, we should only touch files that we know about.
         let diff = updatef.relative_diff_to(&esp)?;