checkout: Support a "pure addition" mode

I plan to use this for `rpm-ostree livefs`.
coreos/rpm-ostree#639

man/ostree-checkout.xml

@@ -89,6 +89,14 @@ Boston, MA 02111-1307, USA.
                 </para></listitem>
             </varlistentry>
 
+            <varlistentry>
+                <term><option>--union-add</option></term>
+
+                <listitem><para>
+                    Keep existing directories and files.
+                </para></listitem>
+            </varlistentry>
+
             <varlistentry>
                 <term><option>--allow-noent</option></term>
 

src/libostree/ostree-repo-checkout.c

@@ -201,8 +201,16 @@ checkout_file_from_input_at (OstreeRepo     *self,
       while (G_UNLIKELY (res == -1 && errno == EINTR));
       if (res == -1)
         {
-          glnx_set_error_from_errno (error);
-          goto out;
+          if (errno == EEXIST && options->overwrite_mode == OSTREE_REPO_CHECKOUT_OVERWRITE_ADD_FILES)
+            {
+              ret = TRUE;
+              goto out;
+            }
+          else
+            {
+              glnx_set_error_from_errno (error);
+              goto out;
+            }
         }
 
       if (options->mode != OSTREE_REPO_CHECKOUT_MODE_USER)
@@ -240,6 +248,11 @@ checkout_file_from_input_at (OstreeRepo     *self,
       while (G_UNLIKELY (fd == -1 && errno == EINTR));
       if (fd == -1)
         {
+          if (errno == EEXIST && options->overwrite_mode == OSTREE_REPO_CHECKOUT_OVERWRITE_ADD_FILES)
+            {
+              ret = TRUE;
+              goto out;
+            }
           glnx_set_error_from_errno (error);
           goto out;
         }
@@ -362,6 +375,12 @@ checkout_file_hardlink (OstreeRepo                          *self,
     {
       ret_was_supported = FALSE;
     }
+  else if (errno == EEXIST && options->overwrite_mode == OSTREE_REPO_CHECKOUT_OVERWRITE_ADD_FILES)
+    {
+      /* In this mode, we keep existing content.  Still need to mark the hardlink as supported.
+       */
+      ret_was_supported = TRUE;
+    }
   else if (errno == EEXIST && options->overwrite_mode == OSTREE_REPO_CHECKOUT_OVERWRITE_UNION_FILES)
     { 
       /* Idiocy, from man rename(2)
@@ -573,6 +592,7 @@ checkout_one_file_at (OstreeRepo                        *repo,
   /* Fall back to copy if we couldn't hardlink */
   if (need_copy)
     {
+      g_assert (!options->no_copy_fallback);
       if (!ostree_repo_load_file (repo, checksum, &input, NULL, &xattrs,
                                   cancellable, error))
         goto out;
@@ -655,7 +675,9 @@ checkout_tree_at (OstreeRepo                        *self,
   while (G_UNLIKELY (res == -1 && errno == EINTR));
   if (res == -1)
     {
-      if (errno == EEXIST && options->overwrite_mode == OSTREE_REPO_CHECKOUT_OVERWRITE_UNION_FILES)
+      if (errno == EEXIST &&
+          (options->overwrite_mode == OSTREE_REPO_CHECKOUT_OVERWRITE_UNION_FILES
+           || options->overwrite_mode == OSTREE_REPO_CHECKOUT_OVERWRITE_ADD_FILES))
         did_exist = TRUE;
       else
         {

src/libostree/ostree-repo.h

@@ -722,11 +722,13 @@ typedef enum {
 /**
  * OstreeRepoCheckoutOverwriteMode:
  * @OSTREE_REPO_CHECKOUT_OVERWRITE_NONE: No special options
- * @OSTREE_REPO_CHECKOUT_OVERWRITE_UNION_FILES: When layering checkouts, overwrite earlier files, but keep earlier directories
+ * @OSTREE_REPO_CHECKOUT_OVERWRITE_UNION_FILES: When layering checkouts, unlink() and replace existing files, but do not modify existing directories
+ * @OSTREE_REPO_CHECKOUT_OVERWRITE_ADD_FILES: Only add new files/directories
  */
 typedef enum {
   OSTREE_REPO_CHECKOUT_OVERWRITE_NONE = 0,
-  OSTREE_REPO_CHECKOUT_OVERWRITE_UNION_FILES = 1
+  OSTREE_REPO_CHECKOUT_OVERWRITE_UNION_FILES = 1,
+  OSTREE_REPO_CHECKOUT_OVERWRITE_ADD_FILES = 2, /* Since: 2017.3 */
 } OstreeRepoCheckoutOverwriteMode;
 
 _OSTREE_PUBLIC

src/ostree/ot-builtin-checkout.c

@@ -36,6 +36,7 @@ static gboolean opt_allow_noent;
 static gboolean opt_disable_cache;
 static char *opt_subpath;
 static gboolean opt_union;
+static gboolean opt_union_add;
 static gboolean opt_whiteouts;
 static gboolean opt_from_stdin;
 static char *opt_from_file;
@@ -63,6 +64,7 @@ static GOptionEntry options[] = {
   { "disable-cache", 0, 0, G_OPTION_ARG_NONE, &opt_disable_cache, "Do not update or use the internal repository uncompressed object cache", NULL },
   { "subpath", 0, 0, G_OPTION_ARG_STRING, &opt_subpath, "Checkout sub-directory PATH", "PATH" },
   { "union", 0, 0, G_OPTION_ARG_NONE, &opt_union, "Keep existing directories, overwrite existing files", NULL },
+  { "union-add", 0, 0, G_OPTION_ARG_NONE, &opt_union_add, "Keep existing files/directories, only add new", NULL },
   { "whiteouts", 0, 0, G_OPTION_ARG_NONE, &opt_whiteouts, "Process 'whiteout' (Docker style) entries", NULL },
   { "allow-noent", 0, 0, G_OPTION_ARG_NONE, &opt_allow_noent, "Do nothing if specified path does not exist", NULL },
   { "from-stdin", 0, 0, G_OPTION_ARG_NONE, &opt_from_stdin, "Process many checkouts from standard input", NULL },
@@ -87,14 +89,23 @@ process_one_checkout (OstreeRepo           *repo,
    * `ostree_repo_checkout_at` until such time as we have a more
    * convenient infrastructure for testing C APIs with data.
    */
-  if (opt_disable_cache || opt_whiteouts || opt_require_hardlinks)
+  if (opt_disable_cache || opt_whiteouts || opt_require_hardlinks || opt_union_add)
     {
       OstreeRepoCheckoutAtOptions options = { 0, };
-      
+
       if (opt_user_mode)
         options.mode = OSTREE_REPO_CHECKOUT_MODE_USER;
-      if (opt_union)
+      /* Can't union these */
+      if (opt_union && opt_union_add)
+        {
+          g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                       "Cannot specify both --union and --union-add");
+          goto out;
+        }
+      else if (opt_union)
         options.overwrite_mode = OSTREE_REPO_CHECKOUT_OVERWRITE_UNION_FILES;
+      else if (opt_union_add)
+        options.overwrite_mode = OSTREE_REPO_CHECKOUT_OVERWRITE_ADD_FILES;
       if (opt_whiteouts)
         options.process_whiteouts = TRUE;
       if (subpath)

tests/basic-test.sh

@@ -19,7 +19,7 @@
 
 set -euo pipefail
 
-echo "1..62"
+echo "1..63"
 
 $CMD_PREFIX ostree --version > version.yaml
 python -c 'import yaml; yaml.safe_load(open("version.yaml"))'
@@ -279,6 +279,24 @@ cd checkout-test2-union
 assert_file_has_content ./yet/another/tree/green "leaf"
 echo "ok checkout union 1"
 
+cd ${test_tmpdir}
+$OSTREE commit -b test-union-add --tree=ref=test2
+$OSTREE checkout test-union-add checkout-test-union-add
+echo 'file for union add testing' > checkout-test-union-add/union-add-test
+echo 'another file for union add testing' > checkout-test-union-add/union-add-test2
+$OSTREE commit -b test-union-add --tree=dir=checkout-test-union-add
+rm checkout-test-union-add -rf
+# Check out previous
+$OSTREE checkout test-union-add^ checkout-test-union-add
+assert_not_has_file checkout-test-union-add/union-add-test
+assert_not_has_file checkout-test-union-add/union-add-test2
+# Now create a file we don't want overwritten
+echo 'existing file for union add' > checkout-test-union-add/union-add-test
+$OSTREE checkout --union-add test-union-add checkout-test-union-add
+assert_file_has_content checkout-test-union-add/union-add-test 'existing file for union add'
+assert_file_has_content checkout-test-union-add/union-add-test2 'another file for union add testing'
+echo "ok checkout union add"
+
 cd ${test_tmpdir}
 rm -rf shadow-repo
 mkdir shadow-repo