machined: add new OpenRootDirectory() call to Machine objects

This new call returns a file descriptor for the root directory of a container.
This file descriptor may then be used to access the rest of the container's
file system, via openat() and similar calls. Since the file descriptor returned
is for the file system namespace inside of the container it may be used to
access all files of the container exactly the way the container itself would
see them. This is particularly useful for containers run directly from
loopback media, for example via systemd-nspawn's --image= switch. It also
provides access to directories such as /run of a container that are normally
not accessible to the outside of a container.

This replaces PR #2870.

Fixes: #2870

1 files changed, 21 insertions, 0 deletions

diff --git a/src/machine/machined-dbus.c b/src/machine/machined-dbus.c
index c9639c3cf2..31efa3695b 100644
--- a/src/machine/machined-dbus.c
+++ b/src/machine/machined-dbus.c
@@ -706,6 +706,26 @@ static int method_copy_machine(sd_bus_message *message, void *userdata, sd_bus_e
         return bus_machine_method_copy(message, machine, error);
 }
 
+static int method_open_machine_root_directory(sd_bus_message *message, void *userdata, sd_bus_error *error) {
+        Manager *m = userdata;
+        Machine *machine;
+        const char *name;
+        int r;
+
+        assert(message);
+        assert(m);
+
+        r = sd_bus_message_read(message, "s", &name);
+        if (r < 0)
+                return r;
+
+        machine = hashmap_get(m->machines, name);
+        if (!machine)
+                return sd_bus_error_setf(error, BUS_ERROR_NO_SUCH_MACHINE, "No machine '%s' known", name);
+
+        return bus_machine_method_open_root_directory(message, machine, error);
+}
+
 static int method_remove_image(sd_bus_message *message, void *userdata, sd_bus_error *error) {
         _cleanup_(image_unrefp) Image* i = NULL;
         const char *name;
@@ -1225,6 +1245,7 @@ const sd_bus_vtable manager_vtable[] = {
         SD_BUS_METHOD("BindMountMachine", "sssbb", NULL, method_bind_mount_machine, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("CopyFromMachine", "sss", NULL, method_copy_machine, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("CopyToMachine", "sss", NULL, method_copy_machine, SD_BUS_VTABLE_UNPRIVILEGED),
+        SD_BUS_METHOD("OpenMachineRootDirectory", "s", "h", method_open_machine_root_directory, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("RemoveImage", "s", NULL, method_remove_image, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("RenameImage", "ss", NULL, method_rename_image, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("CloneImage", "ssb", NULL, method_clone_image, SD_BUS_VTABLE_UNPRIVILEGED),