Commit 8118f095 authored by Alexander Graf's avatar Alexander Graf Committed by Juan Quintela
Browse files

migration: Append JSON description of migration stream 



One of the annoyances of the current migration format is the fact that
it's not self-describing. In fact, it's not properly describing at all.
Some code randomly scattered throughout QEMU elaborates roughly how to
read and write a stream of bytes.

We discussed an idea during KVM Forum 2013 to add a JSON description of
the migration protocol itself to the migration stream. This patch
adds a section after the VM_END migration end marker that contains
description data on what the device sections of the stream are composed of.

This approach is backwards compatible with any QEMU version reading the
stream, because QEMU just stops reading after the VM_END marker and ignores
any data following it.

With an additional external program this allows us to decipher the
contents of any migration stream and hopefully make migration bugs easier
to track down.

Signed-off-by: default avatarAlexander Graf <agraf@suse.de>
Signed-off-by: default avatarAmit Shah <amit.shah@redhat.com>
Signed-off-by: default avatarJuan Quintela <quintela@redhat.com>
parent 97221400

hw/pci/pci.c

+1 −1
Original line number Diff line number Diff line
@@ -513,7 +513,7 @@ void pci_device_save(PCIDevice *s, QEMUFile *f) 
     * This makes us compatible with old devices

     * which never set or clear this bit. */

    s->config[PCI_STATUS] &= ~PCI_STATUS_INTERRUPT;

    vmstate_save_state(f, pci_get_vmstate(s), s);

    vmstate_save_state(f, pci_get_vmstate(s), s, NULL);

    /* Restore the interrupt status bit. */

    pci_update_irq_status(s);

}

hw/scsi/spapr_vscsi.c

+1 −1
Original line number Diff line number Diff line
@@ -630,7 +630,7 @@ static void vscsi_save_request(QEMUFile *f, SCSIRequest *sreq) 
    vscsi_req *req = sreq->hba_private;

    assert(req->active);



    vmstate_save_state(f, &vmstate_spapr_vscsi_req, req);

    vmstate_save_state(f, &vmstate_spapr_vscsi_req, req, NULL);



    DPRINTF("VSCSI: saving tag=%u, current desc#%d, offset=%x\n",

            req->qtag, req->cur_desc_num, req->cur_desc_offset);

hw/virtio/virtio.c

+1 −1
Original line number Diff line number Diff line
@@ -955,7 +955,7 @@ void virtio_save(VirtIODevice *vdev, QEMUFile *f) 
    }



    /* Subsections */

    vmstate_save_state(f, &vmstate_virtio, vdev);

    vmstate_save_state(f, &vmstate_virtio, vdev, NULL);

}



int virtio_set_features(VirtIODevice *vdev, uint32_t val)

include/migration/migration.h

+1 −0
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ 
#define QEMU_VM_SECTION_END          0x03

#define QEMU_VM_SECTION_FULL         0x04

#define QEMU_VM_SUBSECTION           0x05

#define QEMU_VM_VMDESCRIPTION        0x06



struct MigrationParams {

    bool blk;

include/migration/vmstate.h

+2 −1
Original line number Diff line number Diff line
@@ -29,6 +29,7 @@ 
#ifndef CONFIG_USER_ONLY

#include <migration/qemu-file.h>

#endif

#include <qjson.h>



typedef void SaveStateHandler(QEMUFile *f, void *opaque);

typedef int LoadStateHandler(QEMUFile *f, void *opaque, int version_id);
@@ -801,7 +802,7 @@ extern const VMStateInfo vmstate_info_bitmap; 
int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,

                       void *opaque, int version_id);

void vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,

                        void *opaque);

                        void *opaque, QJSON *vmdesc);



int vmstate_register_with_alias_id(DeviceState *dev, int instance_id,

                                   const VMStateDescription *vmsd,