helper: Visit directory entries in order.

Previously in febootstrap-supermin-helper we would visit the
files in supermin.d in arbitrary (ie. readdir) order.  This has
caused a series of heisenbugs where some implicit dependency
between these files has not been honoured.  The latest one is
that '/etc/localtime' can be added to the appliance before '/etc'
has been created (and this operation fails).

Instead of continuing to chase these, this commit forces us to
visit the files in filename order by sorting them before visiting
them.

Note that in libguestfs, the current order is sufficient, because
the files are called:

base.img
daemon.img
hostfiles

1 files changed, 31 insertions, 9 deletions

diff --git a/helper/appliance.c b/helper/appliance.c
index 4cbebf4..e014b12 100644
--- a/helper/appliance.c
+++ b/helper/appliance.c
@@ -123,27 +123,28 @@ iterate_inputs (char **inputs, int nr_inputs, struct writer *writer)
   }
 }
 
+static int
+string_compare (const void *p1, const void *p2)
+{
+  return strcmp (* (char * const *) p1, * (char * const *) p2);
+}
+
 static void
 iterate_input_directory (const char *dirname, int dirfd, struct writer *writer)
 {
-  char path[PATH_MAX];
-  strcpy (path, dirname);
-  size_t len = strlen (dirname);
-  path[len++] = '/';
-
-  char *inputs[] = { path };
-
   DIR *dir = fdopendir (dirfd);
   if (dir == NULL)
     error (EXIT_FAILURE, errno, "fdopendir: %s", dirname);
 
+  char **entries = NULL;
+  size_t nr_entries = 0, nr_alloc = 0;
+
   struct dirent *d;
   while ((errno = 0, d = readdir (dir)) != NULL) {
     if (d->d_name[0] == '.') /* ignore ., .. and any hidden files. */
       continue;
 
-    strcpy (&path[len], d->d_name);
-    iterate_inputs (inputs, 1, writer);
+    add_string (&entries, &nr_entries, &nr_alloc, d->d_name);
   }
 
   if (errno != 0)
@@ -151,6 +152,27 @@ iterate_input_directory (const char *dirname, int dirfd, struct writer *writer)
 
   if (closedir (dir) == -1)
     error (EXIT_FAILURE, errno, "closedir: %s", dirname);
+
+  add_string (&entries, &nr_entries, &nr_alloc, NULL);
+
+  /* Visit directory entries in order.  In febootstrap <= 2.8 we
+   * didn't impose any order, but that led to some difficult
+   * heisenbugs.
+   */
+  sort (entries, string_compare);
+
+  char path[PATH_MAX];
+  strcpy (path, dirname);
+  size_t len = strlen (dirname);
+  path[len++] = '/';
+
+  char *inputs[] = { path };
+
+  size_t i;
+  for (i = 0; entries[i] != NULL; ++i) {
+    strcpy (&path[len], entries[i]);
+    iterate_inputs (inputs, 1, writer);
+  }
 }
 
 /* Copy kernel modules.