Add "transient" unlock

I was thinking a bit more recently about the "live" changes
stuff https://github.com/coreos/rpm-ostree/issues/639
(particularly since https://github.com/coreos/rpm-ostree/pull/2060 )
and I realized reading the last debates in that issue that
there's really a much simpler solution; do exactly the same
thing we do for `ostree admin unlock`, except mount it read-only
by default.

Then, anything that wants to modify it does the same thing
libostree does for `/sysroot` and `/boot` as of recently; create
a new mount namespace and do the modifications there.

The advantages of this are numerous.  First, we already have
all of the code, it's basically just plumbing through a new
entry in the state enumeration and passing `MS_RDONLY` into
the `mount()` system call.

"live" changes here also naturally don't persist, unlike what
we are currently doing in rpm-ostree.

1 files changed, 17 insertions, 1 deletions

diff --git a/src/ostree/ot-admin-builtin-unlock.c b/src/ostree/ot-admin-builtin-unlock.c
index cd466183..6c265f54 100644
--- a/src/ostree/ot-admin-builtin-unlock.c
+++ b/src/ostree/ot-admin-builtin-unlock.c
@@ -31,9 +31,11 @@
 #include <err.h>
 
 static gboolean opt_hotfix;
+static gboolean opt_transient;
 
 static GOptionEntry options[] = {
   { "hotfix", 0, 0, G_OPTION_ARG_NONE, &opt_hotfix, "Retain changes across reboots", NULL },
+  { "transient", 0, 0, G_OPTION_ARG_NONE, &opt_transient, "Mount overlayfs read-only by default", NULL },
   { NULL }
 };
 
@@ -67,7 +69,17 @@ ot_admin_builtin_unlock (int argc, char **argv, OstreeCommandInvocation *invocat
       goto out;
     }
 
-  target_state = opt_hotfix ? OSTREE_DEPLOYMENT_UNLOCKED_HOTFIX : OSTREE_DEPLOYMENT_UNLOCKED_DEVELOPMENT;
+  if (opt_hotfix && opt_transient)
+    {
+      glnx_throw (error, "Cannot specify both --hotfix and --transient");
+      goto out;
+    }
+  else if (opt_hotfix)
+    target_state = OSTREE_DEPLOYMENT_UNLOCKED_HOTFIX;
+  else if (opt_transient)
+    target_state = OSTREE_DEPLOYMENT_UNLOCKED_TRANSIENT;
+  else
+    target_state = OSTREE_DEPLOYMENT_UNLOCKED_DEVELOPMENT;
 
   if (!ostree_sysroot_deployment_unlock (sysroot, booted_deployment,
                                          target_state, cancellable, error))
@@ -87,6 +99,10 @@ ot_admin_builtin_unlock (int argc, char **argv, OstreeCommandInvocation *invocat
       g_print ("Development mode enabled.  A writable overlayfs is now mounted on /usr.\n"
                "All changes there will be discarded on reboot.\n");
       break;
+    case OSTREE_DEPLOYMENT_UNLOCKED_TRANSIENT:
+      g_print ("A writable overlayfs is prepared for /usr, but is mounted read-only by default.\n"
+               "All changes there will be discarded on reboot.\n");
+      break;
     }
 
   ret = TRUE;