fsck: Implement a partial commit reason bitmask

After the corruption has been fixed with "ostree fsck -a --delete", a
second run of the "ostree fsck" command will print X partial commits
not verified and exit with a zero.

The zero exit code makes it hard to detect if a repair operation needs
to be run.  When ever fsck creates a partial commit it should add a
reason for the partial commit to the state file found in
state/<hash>.commitpartial.  This will allow a future execution of the
fsck to still return an error indicating that the repository is still
in the damaged state, awaiting repair.

Additional reason codes could be added in the future for why a partial
commit exists.

Text from: https://github.com/ostreedev/ostree/pull/1880
====
cgwalters commented:

To restate, the core issue is that it's valid to have partial commits
for reasons other than fsck pruned bad objects, and libostree doesn't
have a way to distinguish.

Another option perhaps is to write e.g. fsck-partial into the
statefile state/<hash>.commitpartial which would mean "partial, and
expected to exist but was pruned by fsck" and fsck would continue to
error out until the commit was re-pulled. Right now the partial stamp
file is empty, so it'd be fully compatible to write a rationale into
it.
====

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

Closes: #1910
Approved by: cgwalters

src/libostree/ostree-repo-commit.c

@@ -1873,6 +1873,57 @@ ensure_txn_refs (OstreeRepo *self)
                                                        g_free);
 }
 
+/**
+ * ostree_repo_mark_commit_partial_reason:
+ * @self: Repo
+ * @checksum: Commit SHA-256
+ * @is_partial: Whether or not this commit is partial
+ * @in_state: Reason bitmask for partial commit
+ * @error: Error
+ *
+ * Allows the setting of a reason code for a partial commit. Presently
+ * it only supports setting reason bitmask to
+ * OSTREE_REPO_COMMIT_STATE_FSCK_PARTIAL, or
+ * OSTREE_REPO_COMMIT_STATE_NORMAL.  This will allow successive ostree
+ * fsck operations to exit properly with an error code if the
+ * repository has been truncated as a result of fsck trying to repair
+ * it.
+ *
+ * Since: 2019.4
+ */
+gboolean
+ostree_repo_mark_commit_partial_reason (OstreeRepo     *self,
+                                        const char     *checksum,
+                                        gboolean        is_partial,
+                                        OstreeRepoCommitState in_state,
+                                        GError        **error)
+{
+  g_autofree char *commitpartial_path = _ostree_get_commitpartial_path (checksum);
+  if (is_partial)
+    {
+      glnx_autofd int fd = openat (self->repo_dir_fd, commitpartial_path,
+                                   O_EXCL | O_CREAT | O_WRONLY | O_CLOEXEC | O_NOCTTY, 0644);
+      if (fd == -1)
+        {
+          if (errno != EEXIST)
+            return glnx_throw_errno_prefix (error, "open(%s)", commitpartial_path);
+        }
+      else
+        {
+          if (in_state & OSTREE_REPO_COMMIT_STATE_FSCK_PARTIAL)
+            if (glnx_loop_write (fd, "f", 1) < 0)
+              return glnx_throw_errno_prefix (error, "write(%s)", commitpartial_path);
+        }
+    }
+  else
+    {
+      if (!ot_ensure_unlinked_at (self->repo_dir_fd, commitpartial_path, 0))
+        return FALSE;
+    }
+
+  return TRUE;
+}
+
 /**
  * ostree_repo_mark_commit_partial:
  * @self: Repo
@@ -1880,9 +1931,10 @@ ensure_txn_refs (OstreeRepo *self)
  * @is_partial: Whether or not this commit is partial
  * @error: Error
  *
- * Commits in "partial" state do not have all their child objects written. This
- * occurs in various situations, such as during a pull, but also if a "subpath"
- * pull is used, as well as "commit only" pulls.
+ * Commits in the "partial" state do not have all their child objects
+ * written.  This occurs in various situations, such as during a pull,
+ * but also if a "subpath" pull is used, as well as "commit only"
+ * pulls.
  *
  * This function is used by ostree_repo_pull_with_options(); you
  * should use this if you are implementing a different type of transport.
@@ -1895,24 +1947,9 @@ ostree_repo_mark_commit_partial (OstreeRepo     *self,
                                  gboolean        is_partial,
                                  GError        **error)
 {
-  g_autofree char *commitpartial_path = _ostree_get_commitpartial_path (checksum);
-  if (is_partial)
-    {
-      glnx_autofd int fd = openat (self->repo_dir_fd, commitpartial_path,
-                                   O_EXCL | O_CREAT | O_WRONLY | O_CLOEXEC | O_NOCTTY, 0644);
-      if (fd == -1)
-        {
-          if (errno != EEXIST)
-            return glnx_throw_errno_prefix (error, "open(%s)", commitpartial_path);
-        }
-    }
-  else
-    {
-      if (!ot_ensure_unlinked_at (self->repo_dir_fd, commitpartial_path, 0))
-        return FALSE;
-    }
-
-  return TRUE;
+  return ostree_repo_mark_commit_partial_reason (self, checksum, is_partial,
+                                                 OSTREE_REPO_COMMIT_STATE_NORMAL,
+                                                 error);
 }
 
 /**