upgrade: Check imgref digest before pulling image

Previously, `rpm-ostree upgrade` was re-pulling a container image
each time, and thorwing it away if it realizes that the commit is
the same as the currently booted deployment, much later on.
Be smarter about this by checking the image reference digest, and
don't bother pulling the container image if the digest is the same.

rust/src/lib.rs

@@ -128,9 +128,22 @@ pub mod ffi {
         fn cliwrap_destdir() -> String;
     }
 
+    /// `ContainerImport` is currently identical to ostree-rs-ext's `Import` struct, because
+    /// cxx.rs currently requires types used as extern Rust types to be defined by the same crate
+    /// that contains the bridge using them, so we redefine an `ContainerImport` struct here.
+    pub(crate) struct ContainerImport {
+        pub ostree_commit: String,
+        pub image_digest: String,
+    }
+
     // sysroot_upgrade.rs
     extern "Rust" {
-        fn import_container(sysroot: Pin<&mut OstreeSysroot>, imgref: String) -> Result<String>;
+        fn import_container(
+            sysroot: Pin<&mut OstreeSysroot>,
+            imgref: String,
+        ) -> Result<Box<ContainerImport>>;
+
+        fn fetch_digest(imgref: String) -> Result<String>;
     }
 
     // core.rs

rust/src/sysroot_upgrade.rs

@@ -6,19 +6,31 @@ use crate::cxxrsutil::*;
 use anyhow::{Context, Result};
 use std::convert::TryInto;
 use std::pin::Pin;
+use crate::ffi::ContainerImport;
 
 /// Import ostree commit in container image using ostree-rs-ext's API.
-pub fn import_container(
+pub(crate) fn import_container(
     mut sysroot: Pin<&mut crate::FFIOstreeSysroot>,
     imgref: String,
-) -> CxxResult<String> {
+) -> CxxResult<Box<ContainerImport>> {
     // TODO: take a GCancellable and monitor it, and drop the import task (which is how async cancellation works in Rust).
     let sysroot = &sysroot.gobj_wrap();
     let repo = &sysroot.get_repo(gio::NONE_CANCELLABLE)?;
     let imgref = imgref.as_str().try_into()?;
-    let commit = build_runtime()?
+    let imported = build_runtime()?
         .block_on(async { ostree_ext::container::import(&repo, &imgref, None).await })?;
-    Ok(commit.ostree_commit)
+    Ok(Box::new(ContainerImport {
+        ostree_commit: imported.ostree_commit,
+        image_digest: imported.image_digest,
+    }))
+}
+
+/// Fetch the image digest for `imgref` using ostree-rs-ext's API.
+pub(crate) fn fetch_digest(imgref: String) -> CxxResult<String> {
+    let imgref = imgref.as_str().try_into()?;
+    let digest = build_runtime()?
+        .block_on(async { ostree_ext::container::fetch_manifest_info(&imgref).await })?;
+    Ok(digest.manifest_digest)
 }
 
 fn build_runtime() -> Result<tokio::runtime::Runtime> {

src/daemon/rpmostree-sysroot-upgrader.cxx

@@ -426,9 +426,24 @@ rpmostree_sysroot_upgrader_pull_base (RpmOstreeSysrootUpgrader  *self,
         if (override_commit)
           return glnx_throw (error, "Specifying commit overrides for container-image-reference type refspecs is not supported");
 
-        auto commit = rpmostreecxx::import_container(*self->sysroot, std::string(refspec));
+        /* Check to see if the digest that `refspec` points to is the same before pulling a new container image. */
+        const char *cur_digest = rpmostree_origin_get_container_image_reference_digest (self->origin);
+        if (cur_digest)
+          {
+            auto new_digest = rpmostreecxx::fetch_digest(std::string(refspec));
+            if (strcmp (new_digest.c_str(), cur_digest) == 0)
+              {
+                /* No new digest. */
+                *out_changed = FALSE;
+                return TRUE;
+              }
+          }
+
+        auto import = rpmostreecxx::import_container(*self->sysroot, std::string(refspec));
 
-        new_base_rev = strdup (commit.c_str());
+        g_autofree char *image_digest = strdup (import->image_digest.c_str());
+        rpmostree_origin_set_container_image_reference_digest (self->origin, image_digest);
+        new_base_rev = strdup (import->ostree_commit.c_str());
         break;
       }
     case RPMOSTREE_REFSPEC_TYPE_CHECKSUM:

src/libpriv/rpmostree-origin.cxx

@@ -39,6 +39,9 @@ struct RpmOstreeOrigin {
   RpmOstreeRefspecType refspec_type;
   char *cached_refspec;
 
+  /* Container image digest, if tracking a container image reference */
+  char *cached_digest;
+
   /* Version data that goes along with the refspec */
   char *cached_override_commit;
 
@@ -154,6 +157,10 @@ rpmostree_origin_parse_keyfile (GKeyFile         *origin,
     {
       ret->refspec_type = RPMOSTREE_REFSPEC_TYPE_CONTAINER;
       ret->cached_refspec = util::move_nullify (imgref);
+
+      g_autofree char *digest = g_key_file_get_string (ret->kf, "origin", "container-image-reference-digest", NULL);
+      if (digest)
+        ret->cached_digest = util::move_nullify (digest);
     }
   else
     {
@@ -213,6 +220,12 @@ rpmostree_origin_remove_transient_state (RpmOstreeOrigin *origin)
   rpmostree_origin_set_override_commit (origin, NULL, NULL);
 }
 
+const char *
+rpmostree_origin_get_container_image_reference_digest (RpmOstreeOrigin *origin)
+{
+  return origin->cached_digest;
+}
+
 const char *
 rpmostree_origin_get_refspec (RpmOstreeOrigin *origin)
 {
@@ -460,6 +473,23 @@ rpmostree_origin_set_regenerate_initramfs (RpmOstreeOrigin *origin,
     g_key_file_get_string_list (origin->kf, "rpmostree", "initramfs-args", NULL, NULL);
 }
 
+void
+rpmostree_origin_set_container_image_reference_digest (RpmOstreeOrigin *origin,
+                                                       const char      *digest)
+{
+  if (digest != NULL)
+    {
+      g_key_file_set_string (origin->kf, "origin", "container-image-reference-digest", digest);
+    }
+  else
+    {
+      g_key_file_remove_key (origin->kf, "origin", "container-image-reference-digest", NULL);
+    }
+
+  g_free (origin->cached_digest);
+  origin->cached_digest = g_strdup (digest);
+}
+
 void
 rpmostree_origin_set_override_commit (RpmOstreeOrigin *origin,
                                       const char      *checksum,
@@ -538,6 +568,7 @@ rpmostree_origin_set_rebase_custom (RpmOstreeOrigin *origin,
       {
         /* Remove `TYPE_CONTAINER`-related keys */
         g_key_file_remove_key (origin->kf, "origin", RPMOSTREE_REFSPEC_CONTAINER_ORIGIN_KEY, NULL);
+        g_key_file_remove_key (origin->kf, "origin", "container-image-reference-digest", NULL);
 
         const char *refspec_key =
           g_key_file_has_key (origin->kf, "origin", RPMOSTREE_REFSPEC_OSTREE_BASE_ORIGIN_KEY, NULL) ?

src/libpriv/rpmostree-origin.h

@@ -57,6 +57,9 @@ rpmostree_origin_dup (RpmOstreeOrigin *origin);
 void
 rpmostree_origin_remove_transient_state (RpmOstreeOrigin *origin);
 
+const char *
+rpmostree_origin_get_container_image_reference_digest (RpmOstreeOrigin *origin);
+
 const char *
 rpmostree_origin_get_refspec (RpmOstreeOrigin *origin);
 
@@ -131,6 +134,10 @@ rpmostree_origin_set_regenerate_initramfs (RpmOstreeOrigin *origin,
                                            gboolean regenerate,
                                            char **args);
 
+void
+rpmostree_origin_set_container_image_reference_digest (RpmOstreeOrigin *origin,
+                                                       const char      *digest);
+
 void
 rpmostree_origin_set_override_commit (RpmOstreeOrigin *origin,
                                       const char      *checksum,