Introduce "xen-save-devices-state"

- add an "is_ram" flag to SaveStateEntry;

- register_savevm_live sets is_ram for live_savevm devices;

- introduce a "xen-save-devices-state" QAPI command that can be used to save
the state of all devices, but not the RAM or the block devices of the
VM.

Changes in v8:

- rename save-devices-state to xen-save-devices-state.

Changes in v7:

- rename save_devices to save-devices-state.

Changes in v6:

- remove the is_ram parameter from register_savevm_live and sets is_ram
if the device is a live_savevm device;

- introduce save_devices as a QAPI command, write a better description
for it;

- fix CODING_STYLE;

- introduce a new doc to explain the save format used by save_devices.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Acked-by: Luiz Capitulino <lcapitulino@redhat.com>

docs/xen-save-devices-state.txt

@@ -0,0 +1,34 @@
+= Save Devices =
+
+QEMU has code to load/save the state of the guest that it is running.
+These are two complementary operations.  Saving the state just does
+that, saves the state for each device that the guest is running.
+
+These operations are normally used with migration (see migration.txt),
+however it is also possible to save the state of all devices to file,
+without saving the RAM or the block devices of the VM.
+
+This operation is called "xen-save-devices-state" (see
+QMP/qmp-commands.txt)
+
+
+The binary format used in the file is the following:
+
+
+-------------------------------------------
+
+32 bit big endian: QEMU_VM_FILE_MAGIC
+32 bit big endian: QEMU_VM_FILE_VERSION
+
+for_each_device
+{
+    8 bit:              QEMU_VM_SECTION_FULL
+    32 bit big endian:  section_id
+    8 bit:              idstr (ID string) length
+    string:             idstr (ID string)
+    32 bit big endian:  instance_id
+    32 bit big endian:  version_id
+    buffer:             device specific data
+}
+
+8 bit: QEMU_VM_EOF

qapi-schema.json

@@ -1593,3 +1593,22 @@
 { 'command': 'qom-list-types',
   'data': { '*implements': 'str', '*abstract': 'bool' },
   'returns': [ 'ObjectTypeInfo' ] }
+
+##
+# @xen-save-devices-state:
+#
+# Save the state of all devices to file. The RAM and the block devices
+# of the VM are not saved by this command.
+#
+# @filename: the file to save the state of the devices to as binary
+# data. See xen-save-devices-state.txt for a description of the binary
+# format.
+#
+# Returns: Nothing on success
+#          If @filename cannot be opened, OpenFileFailed
+#          If an I/O error occurs while writing the file, IOError
+#
+# Since: 1.1
+##
+{ 'command': 'xen-save-devices-state', 'data': {'filename': 'str'} }
+

qmp-commands.hx

@@ -441,6 +441,33 @@ Example:
 Note: inject-nmi is only supported for x86 guest currently, it will
       returns "Unsupported" error for non-x86 guest.
 
+EQMP
+
+    {
+        .name       = "xen-save-devices-state",
+        .args_type  = "filename:F",
+    .mhandler.cmd_new = qmp_marshal_input_xen_save_devices_state,
+    },
+
+SQMP
+xen-save-devices-state
+-------
+
+Save the state of all devices to file. The RAM and the block devices
+of the VM are not saved by this command.
+
+Arguments:
+
+- "filename": the file to save the state of the devices to as binary
+data. See xen-save-devices-state.txt for a description of the binary
+format.
+
+Example:
+
+-> { "execute": "xen-save-devices-state",
+     "arguments": { "filename": "/tmp/save" } }
+<- { "return": {} }
+
 EQMP
 
     {

savevm.c

@@ -84,6 +84,7 @@
 #include "qemu-timer.h"
 #include "cpus.h"
 #include "memory.h"
+#include "qmp-commands.h"
 
 #define SELF_ANNOUNCE_ROUNDS 5
 
@@ -1177,6 +1178,7 @@ typedef struct SaveStateEntry {
     void *opaque;
     CompatEntry *compat;
     int no_migrate;
+    int is_ram;
 } SaveStateEntry;
 
 
@@ -1241,6 +1243,10 @@ int register_savevm_live(DeviceState *dev,
     se->opaque = opaque;
     se->vmsd = NULL;
     se->no_migrate = 0;
+    /* if this is a live_savem then set is_ram */
+    if (save_live_state != NULL) {
+        se->is_ram = 1;
+    }
 
     if (dev && dev->parent_bus && dev->parent_bus->info->get_dev_path) {
         char *id = dev->parent_bus->info->get_dev_path(dev);
@@ -1728,6 +1734,45 @@ out:
     return ret;
 }
 
+static int qemu_save_device_state(QEMUFile *f)
+{
+    SaveStateEntry *se;
+
+    qemu_put_be32(f, QEMU_VM_FILE_MAGIC);
+    qemu_put_be32(f, QEMU_VM_FILE_VERSION);
+
+    cpu_synchronize_all_states();
+
+    QTAILQ_FOREACH(se, &savevm_handlers, entry) {
+        int len;
+
+        if (se->is_ram) {
+            continue;
+        }
+        if (se->save_state == NULL && se->vmsd == NULL) {
+            continue;
+        }
+
+        /* Section type */
+        qemu_put_byte(f, QEMU_VM_SECTION_FULL);
+        qemu_put_be32(f, se->section_id);
+
+        /* ID string */
+        len = strlen(se->idstr);
+        qemu_put_byte(f, len);
+        qemu_put_buffer(f, (uint8_t *)se->idstr, len);
+
+        qemu_put_be32(f, se->instance_id);
+        qemu_put_be32(f, se->version_id);
+
+        vmstate_save(f, se);
+    }
+
+    qemu_put_byte(f, QEMU_VM_EOF);
+
+    return qemu_file_get_error(f);
+}
+
 static SaveStateEntry *find_se(const char *idstr, int instance_id)
 {
     SaveStateEntry *se;
@@ -2109,6 +2154,32 @@ void do_savevm(Monitor *mon, const QDict *qdict)
         vm_start();
 }
 
+void qmp_xen_save_devices_state(const char *filename, Error **errp)
+{
+    QEMUFile *f;
+    int saved_vm_running;
+    int ret;
+
+    saved_vm_running = runstate_is_running();
+    vm_stop(RUN_STATE_SAVE_VM);
+
+    f = qemu_fopen(filename, "wb");
+    if (!f) {
+        error_set(errp, QERR_OPEN_FILE_FAILED, filename);
+        goto the_end;
+    }
+    ret = qemu_save_device_state(f);
+    qemu_fclose(f);
+    if (ret < 0) {
+        error_set(errp, QERR_IO_ERROR);
+    }
+
+ the_end:
+    if (saved_vm_running)
+        vm_start();
+    return;
+}
+
 int load_vmstate(const char *name)
 {
     BlockDriverState *bs, *bs_vm_state;