Remove snapshot unit type

Snapshots were never useful or used for anything. Many systemd
developers that I spoke to at systemd.conf2015, didn't even know they
existed, so it is fairly safe to assume that this type can be deleted
without harm.

The fundamental problem with snapshots is that the state of the system
is dynamic, devices come and go, users log in and out, timers fire...
and restoring all units to some state from the past would "undo"
those changes, which isn't really possible.

Tested by creating a snapshot, running the new binary, and checking
that the transition did not cause errors, and the snapshot is gone,
and snapshots cannot be created anymore.

New systemctl says:
Unknown operation snapshot.
Old systemctl says:
Failed to create snapshot: Support for snapshots has been removed.

IgnoreOnSnaphost settings are warned about and ignored:
Support for option IgnoreOnSnapshot= has been removed and it is ignored

http://lists.freedesktop.org/archives/systemd-devel/2015-November/034872.html

1 files changed, 0 insertions, 8 deletions

diff --git a/src/core/unit.h b/src/core/unit.h
index 6f775c5ce1..6455f201b4 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -203,9 +203,6 @@ struct Unit {
         /* Ignore this unit when isolating */
         bool ignore_on_isolate;
 
-        /* Ignore this unit when snapshotting */
-        bool ignore_on_snapshot;
-
         /* Did the last condition check succeed? */
         bool condition_result;
         bool assert_result;
@@ -248,7 +245,6 @@ typedef enum UnitSetPropertiesMode {
 #include "socket.h"
 #include "busname.h"
 #include "target.h"
-#include "snapshot.h"
 #include "device.h"
 #include "automount.h"
 #include "swap.h"
@@ -343,9 +339,6 @@ struct UnitVTable {
          * shall release its runtime resources */
         void (*release_resources)(Unit *u);
 
-        /* Return true when this unit is suitable for snapshotting */
-        bool (*check_snapshot)(Unit *u);
-
         /* Invoked on every child that died */
         void (*sigchld_event)(Unit *u, pid_t pid, int code, int status);
 
@@ -443,7 +436,6 @@ DEFINE_CAST(SERVICE, Service);
 DEFINE_CAST(SOCKET, Socket);
 DEFINE_CAST(BUSNAME, BusName);
 DEFINE_CAST(TARGET, Target);
-DEFINE_CAST(SNAPSHOT, Snapshot);
 DEFINE_CAST(DEVICE, Device);
 DEFINE_CAST(MOUNT, Mount);
 DEFINE_CAST(AUTOMOUNT, Automount);