[Qemu-devel] [PATCH 3/3] savevm: prevent snapshot overwriting and generate a default name

[Miguel Di Ciurcio Filho <miguel.filho@gmail.com>]

This patch address two issues.

1) When savevm is run using an previously saved snapshot id or name, it will
delete the original and create a new one, using the same id and name and not
prompting the user of what just happened.

This behaviour is not good, IMHO.

We add a '-f' parameter to savevm, to really force that to happen, in case the
user really wants to.

New behavior:
(qemu) savevm snap1
An snapshot named 'snap1' already exists

(qemu) savevm -f snap1

We do better error reporting in case '-f' is used too than before.

2) When savevm is run without a name or id, the name stays blank.

This is a first step to hide the internal id, because I don't see a reason to
expose this kind of internals to the user.

The new behavior is when savevm is run without parameters a name will be
created automaticaly, so the snapshot is accessible to the user without needing
the id when loadvm is run.

(qemu) savevm
(qemu) info snapshots
ID        TAG                 VM SIZE                DATE       VM CLOCK
1         vm-20100728134640      978K 2010-07-28 13:46:40   00:00:08.603

We use a name with the format 'vm-YYYYMMDDHHMMSS'.

TODO: I have no clue on how to create a timestamp string when using Windows.

Signed-off-by: Miguel Di Ciurcio Filho <miguel.filho@gmail.com>
---
 qemu-monitor.hx |    9 ++++---
 savevm.c        |   59 ++++++++++++++++++++++++++++++++----------------------
 2 files changed, 40 insertions(+), 28 deletions(-)

diff --git a/qemu-monitor.hx b/qemu-monitor.hx
index 9c27b31..94e8178 100644
--- a/qemu-monitor.hx
+++ b/qemu-monitor.hx
@@ -275,14 +275,15 @@ ETEXI
 
     {
         .name       = "savevm",
-        .args_type  = "name:s?",
-        .params     = "[tag|id]",
-        .help       = "save a VM snapshot. If no tag or id are provided, a new snapshot is created",
+        .args_type  = "force:-f,name:s?",
+        .params     = "[-f] [name]",
+        .help       = "save a VM snapshot. If no name is provided, a new one will be generated"
+		      "\n\t\t\t -f to overwrite an snapshot if it already exists",
         .mhandler.cmd = do_savevm,
     },
 
 STEXI
-@item savevm [@var{tag}|@var{id}]
+@item savevm [-f] [@var{tag}]
 @findex savevm
 Create a snapshot of the whole virtual machine. If @var{tag} is
 provided, it is used as human readable identifier. If there is already
diff --git a/savevm.c b/savevm.c
index fb38e8a..ae6f29f 100644
--- a/savevm.c
+++ b/savevm.c
@@ -1785,7 +1785,7 @@ static int del_existing_snapshots(Monitor *mon, const char *name)
 
 void do_savevm(Monitor *mon, const QDict *qdict)
 {
-    BlockDriverState *bs, *bs1;
+    BlockDriverState *bs_vm_state, *bs;
     QEMUSnapshotInfo sn1, *sn = &sn1, old_sn1, *old_sn = &old_sn1;
     int ret;
     QEMUFile *f;
@@ -1796,7 +1796,9 @@ void do_savevm(Monitor *mon, const QDict *qdict)
 #else
     struct timeval tv;
 #endif
+    struct tm tm;
     const char *name = qdict_get_try_str(qdict, "name");
+    int force = qdict_get_try_bool(qdict, "force", 0);
 
     /* Verify if there is a device that doesn't support snapshots and is writable */
     bs = NULL;
@@ -1813,8 +1815,8 @@ void do_savevm(Monitor *mon, const QDict *qdict)
         }
     }
 
-    bs = bdrv_snapshots();
-    if (!bs) {
+    bs_vm_state = bdrv_snapshots();
+    if (!bs_vm_state) {
         monitor_printf(mon, "No block device can accept snapshots\n");
         return;
     }
@@ -1825,15 +1827,6 @@ void do_savevm(Monitor *mon, const QDict *qdict)
     vm_stop(0);
 
     memset(sn, 0, sizeof(*sn));
-    if (name) {
-        ret = bdrv_snapshot_find(bs, old_sn, name);
-        if (ret >= 0) {
-            pstrcpy(sn->name, sizeof(sn->name), old_sn->name);
-            pstrcpy(sn->id_str, sizeof(sn->id_str), old_sn->id_str);
-        } else {
-            pstrcpy(sn->name, sizeof(sn->name), name);
-        }
-    }
 
     /* fill auxiliary fields */
 #ifdef _WIN32
@@ -1847,13 +1840,31 @@ void do_savevm(Monitor *mon, const QDict *qdict)
 #endif
     sn->vm_clock_nsec = qemu_get_clock(vm_clock);
 
-    /* Delete old snapshots of the same name */
-    if (name && del_existing_snapshots(mon, name) < 0) {
-        goto the_end;
+    if (name) {
+        ret = bdrv_snapshot_find(bs_vm_state, old_sn, name);
+        if (ret == 0) {
+            if (force) {
+                ret = del_existing_snapshots(mon, name);
+                if (ret < 0) {
+                    monitor_printf(mon, "Error deleting snapshot '%s', error: %d\n",
+                        name, ret);
+                    goto the_end;
+                }
+            } else {
+                monitor_printf(mon, "An snapshot named '%s' already exists\n", name);
+                goto the_end;
+            }
+        }
+
+        pstrcpy(sn->name, sizeof(sn->name), name);
+    } else {
+        /* TODO: handle Windows */
+        localtime_r(&tv.tv_sec, &tm);
+        strftime(sn->name, sizeof(sn->name), "vm-%Y%m%d%H%M%S", &tm);
     }
 
     /* save the VM state */
-    f = qemu_fopen_bdrv(bs, 1);
+    f = qemu_fopen_bdrv(bs_vm_state, 1);
     if (!f) {
         monitor_printf(mon, "Could not open VM state file\n");
         goto the_end;
@@ -1867,23 +1878,23 @@ void do_savevm(Monitor *mon, const QDict *qdict)
     }
 
     /* create the snapshots */
-
-    bs1 = NULL;
-    while ((bs1 = bdrv_next(bs1))) {
-        if (bdrv_can_snapshot(bs1)) {
+    bs = NULL;
+    while ((bs = bdrv_next(bs))) {
+        if (bdrv_can_snapshot(bs)) {
             /* Write VM state size only to the image that contains the state */
-            sn->vm_state_size = (bs == bs1 ? vm_state_size : 0);
-            ret = bdrv_snapshot_create(bs1, sn);
+            sn->vm_state_size = (bs_vm_state == bs ? vm_state_size : 0);
+            ret = bdrv_snapshot_create(bs, sn);
             if (ret < 0) {
                 monitor_printf(mon, "Error while creating snapshot on '%s'\n",
-                               bdrv_get_device_name(bs1));
+                               bdrv_get_device_name(bs));
             }
         }
     }
 
  the_end:
-    if (saved_vm_running)
+    if (saved_vm_running) {
         vm_start();
+    }
 }
 
 int load_vmstate(const char *name)
-- 
1.7.1