Add a notion of "physical" sysroot, use for remote writing

Using `${sysroot}` to mean the physical storage root: We don't want to write to
`${sysroot}/etc/ostree/remotes.d`, since nothing will read it, and really
`${sysroot}` should just have `/ostree` (ideally). Today the Anaconda rpmostree
code ends up writing there. Fix this by adding a notion of "physical" sysroot.
We determine whether the path is physical by checking for `/sysroot`, which
exists in deployment roots (and there shouldn't be a `${sysroot}/sysroot`).

In order to unit test this, I added a `--sysroot` argument to `remote add`.
However, doing this better would require reworking the command line parsing for
the `remote` argument to support specifying `--repo` or `--sysroot`, and I
didn't quite want to do that yet in this patch.

Closes: https://github.com/ostreedev/ostree/issues/892

Closes: #896
Approved by: jlebon

src/libostree/ostree-repo.c

@@ -32,6 +32,7 @@
 #include <glnx-console.h>
 
 #include "ostree-core-private.h"
+#include "ostree-sysroot-private.h"
 #include "ostree-remote-private.h"
 #include "ostree-repo-private.h"
 #include "ostree-repo-file.h"
@@ -447,6 +448,7 @@ ostree_repo_finalize (GObject *object)
   if (self->uncompressed_objects_dir_fd != -1)
     (void) close (self->uncompressed_objects_dir_fd);
   g_clear_object (&self->sysroot_dir);
+  g_weak_ref_clear (&self->sysroot);
   g_free (self->remotes_config_dir);
 
   if (self->loose_object_devino_hash)
@@ -525,10 +527,6 @@ ostree_repo_constructed (GObject *object)
 
   g_assert (self->repodir != NULL);
 
-  /* Ensure the "sysroot-path" property is set. */
-  if (self->sysroot_dir == NULL)
-    self->sysroot_dir = g_object_ref (_ostree_get_default_sysroot_path ());
-
   G_OBJECT_CLASS (ostree_repo_parent_class)->constructed (object);
 }
 
@@ -706,8 +704,6 @@ ostree_repo_new_default (void)
 gboolean
 ostree_repo_is_system (OstreeRepo   *repo)
 {
-  g_autoptr(GFile) default_repo_path = NULL;
-
   g_return_val_if_fail (OSTREE_IS_REPO (repo), FALSE);
 
   /* If we were created via ostree_sysroot_get_repo(), we know the answer is yes
@@ -716,8 +712,11 @@ ostree_repo_is_system (OstreeRepo   *repo)
   if (repo->is_system)
     return TRUE;
 
-  default_repo_path = get_default_repo_path (repo->sysroot_dir);
+  /* No sysroot_dir set?  Not a system repo then. */
+  if (!repo->sysroot_dir)
+    return FALSE;
 
+  g_autoptr(GFile) default_repo_path = get_default_repo_path (repo->sysroot_dir);
   return g_file_equal (repo->repodir, default_repo_path);
 }
 
@@ -894,23 +893,25 @@ impl_repo_remote_add (OstreeRepo     *self,
 
   remote = ostree_remote_new (name);
 
-  /* The OstreeRepo maintains its own internal system root path,
-   * so we need to not only check if a "sysroot" argument was given
-   * but also whether it's actually different from OstreeRepo's.
-   *
-   * XXX Having API regret about the "sysroot" argument now.
+  /* If a sysroot was provided, use it. Otherwise, see if this repo has a ref to
+   * a sysroot (and it's physical).
    */
-  gboolean different_sysroot = FALSE;
-  if (sysroot != NULL)
-    different_sysroot = !g_file_equal (sysroot, self->sysroot_dir);
+  g_autoptr(OstreeSysroot) sysroot_ref = NULL;
+  if (sysroot == NULL)
+    {
+      sysroot_ref = (OstreeSysroot*)g_weak_ref_get (&self->sysroot);
+      /* Only write to /etc/ostree/remotes.d if we are pointed at a deployment */
+      if (sysroot_ref != NULL && !sysroot_ref->is_physical)
+        sysroot = ostree_sysroot_get_path (sysroot_ref);
+    }
+  /* For backwards compat, also fall back to the sysroot-path variable */
+  if (sysroot == NULL && sysroot_ref == NULL)
+    sysroot = self->sysroot_dir;
 
-  if (different_sysroot || ostree_repo_is_system (self))
+  if (sysroot != NULL)
     {
       g_autoptr(GError) local_error = NULL;
 
-      if (sysroot == NULL)
-        sysroot = self->sysroot_dir;
-
       g_autoptr(GFile) etc_ostree_remotes_d = g_file_resolve_relative_path (sysroot, SYSCONF_REMOTES);
       if (!g_file_make_directory_with_parents (etc_ostree_remotes_d,
                                                cancellable, &local_error))