sysroot: Add an API to lock

If a system administrator happens to type `ostree admin upgrade`
multiple times, currently that will lead to a potentially corrupted
system.

I originally attempted to do locking *internally* in `libostree`, but
that didn't work out because currently a number of the commands
perform multi-step operations that all need to be serialized.  All of
the current code in `ostree admin deploy` is an example.

Therefore, allow callers to perform locking, as most of the higher
level logic is presently implemented there.

At some point, we can revisit having internal locking, but it will be
difficult.  A more likely approach would be similar to Java's approach
with concurrency on iterators - a "fail fast" method.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/ostree/ot-admin-builtin-deploy.c b/src/ostree/ot-admin-builtin-deploy.c
index 091a7eac..1872894b 100644
--- a/src/ostree/ot-admin-builtin-deploy.c
+++ b/src/ostree/ot-admin-builtin-deploy.c
@@ -79,6 +79,9 @@ ot_admin_builtin_deploy (int argc, char **argv, GCancellable *cancellable, GErro
 
   refspec = argv[1];
 
+  if (!ostree_sysroot_lock (sysroot, error))
+    goto out;
+
   if (!ostree_sysroot_load (sysroot, cancellable, error))
     goto out;
 
@@ -172,6 +175,8 @@ ot_admin_builtin_deploy (int argc, char **argv, GCancellable *cancellable, GErro
 
   ret = TRUE;
  out:
+  if (sysroot)
+    ostree_sysroot_unlock (sysroot);
   if (origin)
     g_key_file_unref (origin);
   if (context)