fstab-generator: read both credentials in initrd

This makes the behavior consistent with the way we already do for
fstab and command line options.
In initrd, entries read from fstab.extra are mounted under /sysroot.

Author: yuwata

src/fstab-generator/fstab-generator.c

@@ -1309,14 +1309,16 @@ static int add_mounts_from_cmdline(void) {
         return ret;
 }
 
-static int add_mounts_from_creds(void) {
+static int add_mounts_from_creds(bool prefix_sysroot) {
         _cleanup_free_ void *b = NULL;
         struct mntent *me;
         int r, ret = 0;
         size_t bs;
 
+        assert(in_initrd() || !prefix_sysroot);
+
         r = read_credential_with_decryption(
-                        in_initrd() ? "fstab.extra.initrd" : "fstab.extra",
+                        in_initrd() && !prefix_sysroot ? "fstab.extra.initrd" : "fstab.extra",
                         &b, &bs);
         if (r <= 0)
                 return r;
@@ -1334,7 +1336,7 @@ static int add_mounts_from_creds(void) {
                                 me->mnt_type,
                                 me->mnt_opts,
                                 me->mnt_passno,
-                                /* prefix_sysroot = */ false,
+                                /* prefix_sysroot = */ prefix_sysroot,
                                 /* use_swap_enabled = */ true);
                 if (r < 0 && ret >= 0)
                         ret = r;
@@ -1575,10 +1577,16 @@ static int run_generator(void) {
         if (r < 0 && ret >= 0)
                 ret = r;
 
-        r = add_mounts_from_creds();
+        r = add_mounts_from_creds(/* prefix_sysroot = */ false);
         if (r < 0 && ret >= 0)
                 ret = r;
 
+        if (in_initrd()) {
+                r = add_mounts_from_creds(/* prefix_sysroot = */ true);
+                if (r < 0 && ret >= 0)
+                        ret = r;
+        }
+
         return ret;
 }