Merge pull request #161 from snapcore/core-or-ubuntu-core

Prefer the "core" snap is one is available.

spread-tests/main/core-is-preferred/task.yaml

@@ -0,0 +1,10 @@
+summary: The snap named 'core' is preferred to the snap 'ubuntu-core'
+prepare: |
+    snap install --devmode snapd-hacker-toolbelt
+    snap install core
+execute: |
+    snapd-hacker-toolbelt.busybox cat /meta/snap.yaml | grep -q -F 'name: core'
+restore: |
+    snap remove snapd-hacker-toolbelt
+    # XXX: the core snap cannot be removed, we should use a trick to remove it
+    # in some other way but this can wait.

src/mount-support.c

@@ -48,6 +48,32 @@
  **/
 #define SC_VOID_DIR "/var/lib/snapd/void"
 
+/**
+ * Get the path to the mounted core snap on the host distribution.
+ *
+ * The core snap may be named just "core" (preferred) or "ubuntu-core"
+ * (legacy).  The mount point dependes on build-time configuration and may
+ * differ from distribution to distribution.
+ **/
+static const char *sc_get_outer_core_mount_point()
+{
+	const char *core_path = SNAP_MOUNT_DIR "/core/current/";
+	const char *ubuntu_core_path = SNAP_MOUNT_DIR "/ubuntu-core/current/";
+	static const char *result = NULL;
+	if (result == NULL) {
+		if (access(core_path, F_OK) == 0) {
+			// Use the "core" snap if available.
+			result = core_path;
+		} else if (access(ubuntu_core_path, F_OK) == 0) {
+			// If not try to fall back to the "ubuntu-core" snap.
+			result = ubuntu_core_path;
+		} else {
+			die("cannot locate the core snap");
+		}
+	}
+	return result;
+}
+
 static void setup_private_mount(const char *security_tag)
 {
 	uid_t uid = getuid();
@@ -254,7 +280,7 @@ static void setup_snappy_os_mounts()
 		die("cannot create temporary directory for the root file system");
 	}
 	// Bind mount the OS snap into the rootfs directory.
-	const char *core_snap_dir = SNAP_MOUNT_DIR "/ubuntu-core/current";
+	const char *core_snap_dir = sc_get_outer_core_mount_point();
 	debug("bind mounting core snap: %s -> %s", core_snap_dir, rootfs_dir);
 	if (mount(core_snap_dir, rootfs_dir, NULL, MS_BIND, NULL) != 0) {
 		die("cannot bind mount core snap: %s to %s", core_snap_dir,

src/quirks.c

@@ -31,6 +31,32 @@
 // XXX: for smaller patch, this should be in utils.h later
 #include "user-support.h"
 
+/**
+ * Get the path to the mounted core snap in the execution environment.
+ *
+ * The core snap may be named just "core" (preferred) or "ubuntu-core"
+ * (legacy).  The mount point does not depend on build-time configuration and
+ * does not differ from distribution to distribution.
+ **/
+static const char *sc_get_inner_core_mount_point()
+{
+	const char *core_path = "/snap/core/current/";
+	const char *ubuntu_core_path = "/snap/ubuntu-core/current/";
+	static const char *result = NULL;
+	if (result == NULL) {
+		if (access(core_path, F_OK) == 0) {
+			// Use the "core" snap if available.
+			result = core_path;
+		} else if (access(ubuntu_core_path, F_OK) == 0) {
+			// If not try to fall back to the "ubuntu-core" snap.
+			result = ubuntu_core_path;
+		} else {
+			die("cannot locate the core snap");
+		}
+	}
+	return result;
+}
+
 /**
  * Mount a tmpfs at a given directory.
  *
@@ -155,8 +181,10 @@ void sc_setup_quirks()
 		die("cannot move /var/lib/snapd to %s", snapd_tmp);
 	}
 	// now let's make /var/lib the vanilla /var/lib from the core snap
-	sc_quirk_create_writable_mimic("/var/lib",
-				       "/snap/ubuntu-core/current/var/lib",
+	char buf[PATH_MAX];
+	must_snprintf(buf, sizeof buf, "%s/var/lib",
+		      sc_get_inner_core_mount_point());
+	sc_quirk_create_writable_mimic("/var/lib", buf,
 				       MS_RDONLY | MS_REC | MS_SLAVE | MS_NODEV
 				       | MS_NOSUID);
 	// now let's move /var/lib/snapd (that was originally there) back

src/snap-confine.apparmor.in

@@ -107,7 +107,7 @@
 
     # mount calls to setup the pivot_root based chroot with the core snap as
     # the root filesystem.
-    mount options=(rw bind) @SNAP_MOUNT_DIR@/ubuntu-core/*/ -> /tmp/snap.rootfs_*/,
+    mount options=(rw bind) @SNAP_MOUNT_DIR@/{,ubuntu-}core/*/ -> /tmp/snap.rootfs_*/,
 
     mount options=(rw rbind) /dev/ -> /tmp/snap.rootfs_*/dev/,
     mount options=(rw rbind) /etc/ -> /tmp/snap.rootfs_*/etc/,
@@ -125,7 +125,7 @@
     mount options=(rw rbind) {/usr,}/lib/modules/ -> /tmp/snap.rootfs_*/lib/modules/,
     mount options=(rw rbind) /var/log/ -> /tmp/snap.rootfs_*/var/log/,
     mount options=(rw rbind) /usr/src/ -> /tmp/snap.rootfs_*/usr/src/,
-    mount options=(rw bind) @SNAP_MOUNT_DIR@/ubuntu-core/*/etc/alternatives/ -> /tmp/snap.rootfs_*/etc/alternatives/,
+    mount options=(rw bind) @SNAP_MOUNT_DIR@/{,ubuntu-}core/*/etc/alternatives/ -> /tmp/snap.rootfs_*/etc/alternatives/,
 
     # Allow to mkdir /var/lib/snapd/hostfs
     /var/lib/snapd/hostfs/ rw,
@@ -189,7 +189,7 @@
     /tmp/snapd.quirks_*/ rw,
     mount options=(move) /var/lib/snapd/ -> /tmp/snapd.quirks_*/,
     mount fstype=tmpfs options=(rw nodev nosuid) none -> /var/lib/,
-    mount options=(ro rbind) /snap/ubuntu-core/*/var/lib/** -> /var/lib/**,
+    mount options=(ro rbind) /snap/{,ubuntu-}core/*/var/lib/** -> /var/lib/**,
     umount /var/lib/snapd/,
     mount options=(move) /tmp/snapd.quirks_*/ -> /var/lib/snapd/,