sysroot: Support boot counting for boot entries

Add support for boot counting for bootloader entries [1].
The boot counting data is stored in the name of the boot loader entry.
A boot loader entry file name may contain a plus (+) followed by a number.
This may optionally be followed by a minus (-) followed by a second number.
The dot (.) and file name suffix (conf or efi) must immediately follow.

All "pending" entries (in the middle of boot counting) are automatically
removed during creation of new boot entries for new deployments.

Testing:
$ ostree admin deploy 91fc19319be9e79d07159303dff125f40f10e5c25614630dcbed23d95e36f907
Copying /etc changes: 2 modified, 3 removed, 4 added
bootfs is sufficient for calculated new size: 0 bytes
Transaction complete; bootconfig swap: yes; bootversion: boot.0.1, deployment count change: 1

$ ls /boot/loader/entries
ostree-1+3.conf  ostree-2+3.conf

[1] https://uapi-group.org/specifications/specs/boot_loader_specification/#boot-counting
Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>

src/libostree/ostree-sysroot-deploy.c

@@ -62,6 +62,8 @@
   SD_ID128_MAKE (e8, 64, 6c, d6, 3d, ff, 46, 25, b7, 79, 09, a8, e7, a4, 09, 94)
 #endif
 
+#define BOOT_COUNT_MAX_RETRIES 3
+
 /* How much additional space we require available on top of what we accounted
  * during the early prune fallocate space check. This accounts for anything not
  * captured directly by `get_kernel_layout_size()` like writing new BLS entries.
@@ -1776,12 +1778,12 @@ parse_os_release (const char *contents, const char *split)
   return ret;
 }
 
-/* Generate the filename we will use in /boot/loader/entries for this deployment.
+/* Generate the entry name we will use in /boot/loader/entries for this deployment.
  * The provided n_deployments should be the total number of target deployments (which
  * might be different from the cached value in the sysroot).
  */
 static char *
-bootloader_entry_filename (OstreeSysroot *sysroot, guint n_deployments,
+bootloader_entry_name (OstreeSysroot *sysroot, guint n_deployments,
                            OstreeDeployment *deployment)
 {
   guint index = n_deployments - ostree_deployment_get_index (deployment);
@@ -1792,12 +1794,50 @@ bootloader_entry_filename (OstreeSysroot *sysroot, guint n_deployments,
   if (use_old_naming)
     {
       const char *stateroot = ostree_deployment_get_osname (deployment);
-      return g_strdup_printf ("ostree-%d-%s.conf", index, stateroot);
+      return g_strdup_printf ("ostree-%d-%s", index, stateroot);
     }
   else
     {
-      return g_strdup_printf ("ostree-%d.conf", index);
+      return g_strdup_printf ("ostree-%d", index);
+    }
+}
+
+/* Drop all temporary entries in /boot/loader/entries for this deployment,
+ * which were created during automatic boot assesment
+ * https://systemd.io/AUTOMATIC_BOOT_ASSESSMENT/
+ */
+static gboolean
+bootloader_remove_tmp_entries (int dfd, const char *entry_name, GCancellable *cancellable,
+                               GError **error)
+{
+  g_auto(GLnxDirFdIterator) dfd_iter = { 0, };
+  g_autofree char *entry_name_init = g_strdup_printf ("%s+%d", entry_name, BOOT_COUNT_MAX_RETRIES);
+
+  if (!glnx_dirfd_iterator_init_at (dfd, ".", FALSE, &dfd_iter, error))
+    return FALSE;
+
+  while (TRUE)
+    {
+      struct dirent *dent = NULL;
+
+      if (!glnx_dirfd_iterator_next_dent_ensure_dtype (&dfd_iter, &dent, cancellable, error))
+        return FALSE;
+      if (dent == NULL)
+        break;
+
+      /* Don't remove default boot entry (with +3 suffix) */
+      if (g_str_has_prefix (dent->d_name, entry_name_init))
+        continue;
+
+      if (g_str_has_prefix (dent->d_name, entry_name))
+        {
+          if (!glnx_shutil_rm_rf_at (dfd_iter.fd, dent->d_name, cancellable, error))
+            return FALSE;
+        }
+
     }
+
+    return TRUE;
 }
 
 /* Given @deployment, prepare it to be booted; basically copying its
@@ -1834,7 +1874,7 @@ install_deployment_kernel (OstreeSysroot *sysroot, int new_bootversion,
   const char *bootcsum = ostree_deployment_get_bootcsum (deployment);
   g_autofree char *bootcsumdir = g_strdup_printf ("ostree/%s-%s", osname, bootcsum);
   g_autofree char *bootconfdir = g_strdup_printf ("loader.%d/entries", new_bootversion);
-  g_autofree char *bootconf_name = bootloader_entry_filename (sysroot, n_deployments, deployment);
+  g_autofree char *bootconf_name = bootloader_entry_name (sysroot, n_deployments, deployment);
 
   if (!glnx_shutil_mkdir_p_at (sysroot->boot_fd, bootcsumdir, 0775, cancellable, error))
     return FALSE;
@@ -2146,8 +2186,13 @@ install_deployment_kernel (OstreeSysroot *sysroot, int new_bootversion,
   if (!glnx_opendirat (sysroot->boot_fd, bootconfdir, TRUE, &bootconf_dfd, error))
     return FALSE;
 
+  g_autofree char *bootconf_filename = g_strdup_printf ("%s+%d.conf", bootconf_name, BOOT_COUNT_MAX_RETRIES);
+
+  if (!bootloader_remove_tmp_entries(bootconf_dfd, bootconf_name, cancellable, error))
+    return FALSE;
+
   if (!ostree_bootconfig_parser_write_at (ostree_deployment_get_bootconfig (deployment),
-                                          bootconf_dfd, bootconf_name, cancellable, error))
+                                          bootconf_dfd, bootconf_filename, cancellable, error))
     return FALSE;
 
   return TRUE;
@@ -4176,14 +4221,19 @@ ostree_sysroot_deployment_set_kargs_in_place (OstreeSysroot *self, OstreeDeploym
       ostree_bootconfig_parser_set (new_bootconfig, "options", kargs_str);
 
       g_autofree char *bootconf_name
-          = bootloader_entry_filename (self, self->deployments->len, deployment);
+          = bootloader_entry_name (self, self->deployments->len, deployment);
 
       g_autofree char *bootconfdir = g_strdup_printf ("loader.%d/entries", self->bootversion);
       glnx_autofd int bootconf_dfd = -1;
       if (!glnx_opendirat (self->boot_fd, bootconfdir, TRUE, &bootconf_dfd, error))
         return FALSE;
 
-      if (!ostree_bootconfig_parser_write_at (new_bootconfig, bootconf_dfd, bootconf_name,
+      g_autofree char *bootconf_filename = g_strdup_printf ("%s+%d.conf", bootconf_name, BOOT_COUNT_MAX_RETRIES);
+
+      if (!bootloader_remove_tmp_entries(bootconf_dfd, bootconf_name, cancellable, error))
+        return FALSE;
+
+      if (!ostree_bootconfig_parser_write_at (new_bootconfig, bootconf_dfd, bootconf_filename,
                                               cancellable, error))
         return FALSE;
     }