[fshost] Verify open success during migration recursive copy.

Without verifying this we can race in the tests because the file or
directory may not actually be created by the time we verify it. More
than that, src may be empty which means that we never interact with
the dst copy again and never verify that it was successfully created
before destroying the old filesystem.

Bug: 405230091
Change-Id: I9bb1324f04285bb65f449c76afe43cbc87f635b2
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1234224
Commit-Queue: Martin Lindsay <[email protected]>
Reviewed-by: Aaron Drew <[email protected]>

Author: Martin Lindsay

src/storage/fshost/src/copier.rs

@@ -23,11 +23,15 @@ pub fn recursive_copy<'a>(
                     fio::PERM_READABLE,
                 )
                 .context("open src dir")?;
-                let dst = fuchsia_fs::directory::open_directory_async(
+                // Verifying the OnOpen event when creating the destination directory, otherwise we
+                // never confirm that this directory was successfully created if the source
+                // directory turns out to be empty.
+                let dst = fuchsia_fs::directory::open_directory(
                     dst,
                     entry.name.as_str(),
                     fio::Flags::FLAG_MAYBE_CREATE | fio::PERM_WRITABLE,
                 )
+                .await
                 .context("open dst dir")?;
                 recursive_copy(&src, &dst)
                     .await
@@ -39,11 +43,15 @@ pub fn recursive_copy<'a>(
                     fio::PERM_READABLE,
                 )
                 .context("open src file")?;
-                let dst = fuchsia_fs::directory::open_file_async(
+                // Verifying the OnOpen event when creating the destination file, otherwise we never
+                // confirm that this file was successfully created if the source file turns out to
+                // be empty.
+                let dst = fuchsia_fs::directory::open_file(
                     dst,
                     entry.name.as_str(),
                     fio::Flags::FLAG_MAYBE_CREATE | fio::PERM_WRITABLE,
                 )
+                .await
                 .context("open dst file")?;
                 loop {
                     let bytes = src