compose: Always put workdir on same filesystem as pkgcache

This ensures that we always get hardlinks when checking out of the
pkgcache. This works right now because we indirectly require the target
bare-user repo and the pkgcache to be on the same filesystem by setting
`no_copy_fallback` in the core (I say "indirectly" because that setting
only enforces the workdir to be on the same filesystem as the pkgcache
repo, but since the workdir is currently placed inside the bare-user
repo...).

However, I'd like to change the requirement of a bare-user repo so that
one can commit into a repo on a different file system or a repo of a
different type (e.g. archive repo). This is prep for that.

Closes: #1657
Approved by: cgwalters

src/app/rpmostree-compose-builtin-tree.c

@@ -264,16 +264,10 @@ install_packages (RpmOstreeTreeComposeContext  *self,
 #undef TMP_SELINUX_ROOTFS
   }
 
-  /* For unified core, we have a pkgcache repo. This may be auto-created under
+  /* For unified core, we have a pkgcache repo. This is auto-created under the cachedir. */
-   * the workdir, or live explicitly in the dir for --cache.
-   */
   if (opt_unified_core)
     {
-      self->pkgcache_repo = ostree_repo_create_at (self->cachedir_dfd, "pkgcache-repo",
+      g_assert (self->pkgcache_repo);
-                                                   OSTREE_REPO_MODE_BARE_USER, NULL,
-                                                   cancellable, error);
-      if (!self->pkgcache_repo)
-        return FALSE;
 
       if (!opt_cachedir)
         {
@@ -529,53 +523,83 @@ rpm_ostree_compose_context_new (const char    *treefile_pathstr,
 
   if (opt_unified_core)
     {
+      /* Unified mode works very differently. We ignore --workdir because we want to be sure
+       * that we're going to get hardlinks. The only way to be sure of this is to place the
+       * workdir underneath the pkgcache repo. */
+
       if (opt_workdir)
         g_printerr ("note: --workdir is ignored for --ex-unified-core\n");
 
-      /* For unified core, our workdir must be underneath the repo tmp/
+      /* We also really want a bare-user repo. We hard require that for now, but down the
-       * in order to use hardlinks.  We also really want a bare-user repo.
+       * line we may automatically do a pull-local from the bare-user repo to the archive.
-       * We hard require that for now, but down the line we may automatically
-       * do a pull-local from the bare-user repo to the archive.
        */
       if (ostree_repo_get_mode (self->repo) != OSTREE_REPO_MODE_BARE_USER)
         return glnx_throw (error, "--ex-unified-core requires a bare-user repository");
-      if (!glnx_mkdtempat (ostree_repo_get_dfd (self->repo), "tmp/rpm-ostree-compose.XXXXXX", 0700,
-                           &self->workdir_tmp, error))
-        return FALSE;
-      /* Note special handling of this aliasing in _finalize() */
-      self->workdir_dfd = self->workdir_tmp.fd;
 
-    }
+      if (opt_cachedir)
-  else if (!opt_workdir)
+        {
-    {
+          if (!glnx_opendirat (AT_FDCWD, opt_cachedir, TRUE, &self->cachedir_dfd, error))
-      if (!glnx_mkdtempat (AT_FDCWD, "/var/tmp/rpm-ostree.XXXXXX", 0700, &self->workdir_tmp, error))
+            return glnx_prefix_error (error, "Opening cachedir");
+
+          /* Put workdir beneath cachedir, which is where the pkgcache repo also is */
+          if (!glnx_mkdtempat (self->cachedir_dfd, "rpm-ostree-compose.XXXXXX", 0700,
+                               &self->workdir_tmp, error))
+            return FALSE;
+        }
+      else
+        {
+          /* Put cachedir under the target repo: makes things more efficient if it's
+           * bare-user, and otherwise just restricts IO to within the same fs. If for
+           * whatever reason users don't want to run the compose there (e.g. weird
+           * filesystems that aren't fully POSIX compliant), they can just use --cachedir.
+           */
+          if (!glnx_mkdtempat (ostree_repo_get_dfd (self->repo),
+                               "tmp/rpm-ostree-compose.XXXXXX", 0700,
+                               &self->workdir_tmp, error))
+            return FALSE;
+
+          self->cachedir_dfd = self->workdir_tmp.fd;
+        }
+
+      self->pkgcache_repo = ostree_repo_create_at (self->cachedir_dfd, "pkgcache-repo",
+                                                   OSTREE_REPO_MODE_BARE_USER, NULL,
+                                                   cancellable, error);
+      if (!self->pkgcache_repo)
         return FALSE;
+
       /* Note special handling of this aliasing in _finalize() */
       self->workdir_dfd = self->workdir_tmp.fd;
     }
   else
     {
-      if (!glnx_opendirat (AT_FDCWD, opt_workdir, FALSE, &self->workdir_dfd, error))
+      if (!opt_workdir)
-        return FALSE;
+        {
+          if (!glnx_mkdtempat (AT_FDCWD, "/var/tmp/rpm-ostree.XXXXXX", 0700, &self->workdir_tmp, error))
+            return FALSE;
+          /* Note special handling of this aliasing in _finalize() */
+          self->workdir_dfd = self->workdir_tmp.fd;
+        }
+      else
+        {
+          if (!glnx_opendirat (AT_FDCWD, opt_workdir, FALSE, &self->workdir_dfd, error))
+            return FALSE;
+        }
+
+      if (opt_cachedir)
+        {
+          if (!glnx_opendirat (AT_FDCWD, opt_cachedir, TRUE, &self->cachedir_dfd, error))
+            return glnx_prefix_error (error, "Opening cachedir");
+        }
+      else
+        {
+          self->cachedir_dfd = fcntl (self->workdir_dfd, F_DUPFD_CLOEXEC, 3);
+          if (self->cachedir_dfd < 0)
+            return glnx_throw_errno_prefix (error, "fcntl");
+        }
     }
 
   self->treefile_path = g_file_new_for_path (treefile_pathstr);
 
-  if (opt_cachedir)
-    {
-      if (!glnx_opendirat (AT_FDCWD, opt_cachedir, TRUE, &self->cachedir_dfd, error))
-        {
-          g_prefix_error (error, "Opening cachedir '%s': ", opt_cachedir);
-          return FALSE;
-        }
-    }
-  else
-    {
-      self->cachedir_dfd = fcntl (self->workdir_dfd, F_DUPFD_CLOEXEC, 3);
-      if (self->cachedir_dfd < 0)
-        return glnx_throw_errno_prefix (error, "fcntl");
-    }
-
   self->metadata = rpmostree_composeutil_read_json_metadata (opt_metadata_json, error);
   if (!self->metadata)
     return FALSE;