Repository: Handle non-existing directories in garbage collection

For example, if there has been no streams created, we don't want to
fail with some random ENOENT.

Signed-off-by: Alexander Larsson <alexl@redhat.com>

Author: alexlarsson

crates/composefs/src/repository.rs

@@ -25,7 +25,7 @@ use crate::{
     },
     mount::mount_composefs_at,
     splitstream::{DigestMap, SplitStreamReader, SplitStreamWriter},
-    util::{proc_self_fd, replace_symlinkat, Sha256Digest},
+    util::{filter_errno, proc_self_fd, replace_symlinkat, Sha256Digest},
 };
 
 /// Call openat() on the named subdirectory of "dirfd", possibly creating it first.
@@ -491,15 +491,31 @@ impl<ObjectID: FsVerityHashValue> Repository<ObjectID> {
     fn gc_category(&self, category: &str) -> Result<HashSet<ObjectID>> {
         let mut objects = HashSet::new();
 
-        let category_fd = self.openat(category, OFlags::RDONLY | OFlags::DIRECTORY)?;
+        let category_fd = match filter_errno(
+            self.openat(category, OFlags::RDONLY | OFlags::DIRECTORY),
+            Errno::NOENT,
+        )
+        .context("Opening {category} dir in repository")?
+        {
+            Some(fd) => fd,
+            None => {
+                return Ok(objects);
+            }
+        };
 
-        let refs = openat(
-            &category_fd,
-            "refs",
-            OFlags::RDONLY | OFlags::DIRECTORY,
-            Mode::empty(),
-        )?;
-        Self::walk_symlinkdir(refs, &mut objects)?;
+        if let Some(refs) = filter_errno(
+            openat(
+                &category_fd,
+                "refs",
+                OFlags::RDONLY | OFlags::DIRECTORY,
+                Mode::empty(),
+            ),
+            Errno::NOENT,
+        )
+        .context("Opening {category}/refs dir in repository")?
+        {
+            Self::walk_symlinkdir(refs, &mut objects)?;
+        }
 
         for item in Dir::read_from(&category_fd)? {
             let entry = item?;

crates/composefs/src/util.rs

@@ -140,6 +140,17 @@ pub fn replace_symlinkat(
     Err(Errno::EXIST)
 }
 
+pub fn filter_errno<T>(
+    result: rustix::io::Result<T>,
+    ignored: Errno,
+) -> rustix::io::Result<Option<T>> {
+    match result {
+        Ok(result) => Ok(Some(result)),
+        Err(err) if err == ignored => Ok(None),
+        Err(err) => Err(err),
+    }
+}
+
 #[cfg(test)]
 mod test {
     use similar_asserts::assert_eq;