Re: [Qemu-devel] [RFC v3] qemu: Add virtio pmem device

[Luiz Capitulino <lcapitulino-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Thu, 19 Jul 2018 13:16:35 +0100
Stefan Hajnoczi <stefanha-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:

> On Thu, Jul 19, 2018 at 01:48:13AM -0400, Pankaj Gupta wrote:
> >   
> > >   
> > > >  This patch adds virtio-pmem Qemu device.
> > > > 
> > > >  This device presents memory address range information to guest
> > > >  which is backed by file backend type. It acts like persistent
> > > >  memory device for KVM guest. Guest can perform read and persistent
> > > >  write operations on this memory range with the help of DAX capable
> > > >  filesystem.
> > > > 
> > > >  Persistent guest writes are assured with the help of virtio based
> > > >  flushing interface. When guest userspace space performs fsync on
> > > >  file fd on pmem device, a flush command is send to Qemu over VIRTIO
> > > >  and host side flush/sync is done on backing image file.
> > > > 
> > > > Changes from RFC v2:
> > > > - Use aio_worker() to avoid Qemu from hanging with blocking fsync
> > > >   call - Stefan
> > > > - Use virtio_st*_p() for endianess - Stefan
> > > > - Correct indentation in qapi/misc.json - Eric
> > > > 
> > > > Signed-off-by: Pankaj Gupta <pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> > > > ---
> > > >  hw/virtio/Makefile.objs                     |   3 +
> > > >  hw/virtio/virtio-pci.c                      |  44 +++++
> > > >  hw/virtio/virtio-pci.h                      |  14 ++
> > > >  hw/virtio/virtio-pmem.c                     | 241
> > > >  ++++++++++++++++++++++++++++
> > > >  include/hw/pci/pci.h                        |   1 +
> > > >  include/hw/virtio/virtio-pmem.h             |  42 +++++
> > > >  include/standard-headers/linux/virtio_ids.h |   1 +
> > > >  qapi/misc.json                              |  26 ++-
> > > >  8 files changed, 371 insertions(+), 1 deletion(-)
> > > >  create mode 100644 hw/virtio/virtio-pmem.c
> > > >  create mode 100644 include/hw/virtio/virtio-pmem.h
> > > > 
> > > > diff --git a/hw/virtio/Makefile.objs b/hw/virtio/Makefile.objs
> > > > index 1b2799cfd8..7f914d45d0 100644
> > > > --- a/hw/virtio/Makefile.objs
> > > > +++ b/hw/virtio/Makefile.objs
> > > > @@ -10,6 +10,9 @@ obj-$(CONFIG_VIRTIO_CRYPTO) += virtio-crypto.o
> > > >  obj-$(call land,$(CONFIG_VIRTIO_CRYPTO),$(CONFIG_VIRTIO_PCI)) +=
> > > >  virtio-crypto-pci.o
> > > >  
> > > >  obj-$(CONFIG_LINUX) += vhost.o vhost-backend.o vhost-user.o
> > > > +ifeq ($(CONFIG_MEM_HOTPLUG),y)
> > > > +obj-$(CONFIG_LINUX) += virtio-pmem.o
> > > > +endif
> > > >  obj-$(CONFIG_VHOST_VSOCK) += vhost-vsock.o
> > > >  endif
> > > >  
> > > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> > > > index 3a01fe90f0..93d3fc05c7 100644
> > > > --- a/hw/virtio/virtio-pci.c
> > > > +++ b/hw/virtio/virtio-pci.c
> > > > @@ -2521,6 +2521,49 @@ static const TypeInfo virtio_rng_pci_info = {
> > > >      .class_init    = virtio_rng_pci_class_init,
> > > >  };
> > > >  
> > > > +/* virtio-pmem-pci */
> > > > +
> > > > +static void virtio_pmem_pci_realize(VirtIOPCIProxy *vpci_dev, Error
> > > > **errp)
> > > > +{
> > > > +    VirtIOPMEMPCI *vpmem = VIRTIO_PMEM_PCI(vpci_dev);
> > > > +    DeviceState *vdev = DEVICE(&vpmem->vdev);
> > > > +
> > > > +    qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
> > > > +    object_property_set_bool(OBJECT(vdev), true, "realized", errp);
> > > > +}
> > > > +
> > > > +static void virtio_pmem_pci_class_init(ObjectClass *klass, void *data)
> > > > +{
> > > > +    DeviceClass *dc = DEVICE_CLASS(klass);
> > > > +    VirtioPCIClass *k = VIRTIO_PCI_CLASS(klass);
> > > > +    PCIDeviceClass *pcidev_k = PCI_DEVICE_CLASS(klass);
> > > > +    k->realize = virtio_pmem_pci_realize;
> > > > +    set_bit(DEVICE_CATEGORY_MISC, dc->categories);
> > > > +    pcidev_k->vendor_id = PCI_VENDOR_ID_REDHAT_QUMRANET;
> > > > +    pcidev_k->device_id = PCI_DEVICE_ID_VIRTIO_PMEM;
> > > > +    pcidev_k->revision = VIRTIO_PCI_ABI_VERSION;
> > > > +    pcidev_k->class_id = PCI_CLASS_OTHERS;
> > > > +}
> > > > +
> > > > +static void virtio_pmem_pci_instance_init(Object *obj)
> > > > +{
> > > > +    VirtIOPMEMPCI *dev = VIRTIO_PMEM_PCI(obj);
> > > > +
> > > > +    virtio_instance_init_common(obj, &dev->vdev, sizeof(dev->vdev),
> > > > +                                TYPE_VIRTIO_PMEM);
> > > > +    object_property_add_alias(obj, "memdev", OBJECT(&dev->vdev), "memdev",
> > > > +                              &error_abort);
> > > > +}
> > > > +
> > > > +static const TypeInfo virtio_pmem_pci_info = {
> > > > +    .name          = TYPE_VIRTIO_PMEM_PCI,
> > > > +    .parent        = TYPE_VIRTIO_PCI,
> > > > +    .instance_size = sizeof(VirtIOPMEMPCI),
> > > > +    .instance_init = virtio_pmem_pci_instance_init,
> > > > +    .class_init    = virtio_pmem_pci_class_init,
> > > > +};
> > > > +
> > > > +
> > > >  /* virtio-input-pci */
> > > >  
> > > >  static Property virtio_input_pci_properties[] = {
> > > > @@ -2714,6 +2757,7 @@ static void virtio_pci_register_types(void)
> > > >      type_register_static(&virtio_balloon_pci_info);
> > > >      type_register_static(&virtio_serial_pci_info);
> > > >      type_register_static(&virtio_net_pci_info);
> > > > +    type_register_static(&virtio_pmem_pci_info);
> > > >  #ifdef CONFIG_VHOST_SCSI
> > > >      type_register_static(&vhost_scsi_pci_info);
> > > >  #endif
> > > > diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
> > > > index 813082b0d7..fe74fcad3f 100644
> > > > --- a/hw/virtio/virtio-pci.h
> > > > +++ b/hw/virtio/virtio-pci.h
> > > > @@ -19,6 +19,7 @@
> > > >  #include "hw/virtio/virtio-blk.h"
> > > >  #include "hw/virtio/virtio-net.h"
> > > >  #include "hw/virtio/virtio-rng.h"
> > > > +#include "hw/virtio/virtio-pmem.h"
> > > >  #include "hw/virtio/virtio-serial.h"
> > > >  #include "hw/virtio/virtio-scsi.h"
> > > >  #include "hw/virtio/virtio-balloon.h"
> > > > @@ -57,6 +58,7 @@ typedef struct VirtIOInputHostPCI VirtIOInputHostPCI;
> > > >  typedef struct VirtIOGPUPCI VirtIOGPUPCI;
> > > >  typedef struct VHostVSockPCI VHostVSockPCI;
> > > >  typedef struct VirtIOCryptoPCI VirtIOCryptoPCI;
> > > > +typedef struct VirtIOPMEMPCI VirtIOPMEMPCI;
> > > >  
> > > >  /* virtio-pci-bus */
> > > >  
> > > > @@ -274,6 +276,18 @@ struct VirtIOBlkPCI {
> > > >      VirtIOBlock vdev;
> > > >  };
> > > >  
> > > > +/*
> > > > + * virtio-pmem-pci: This extends VirtioPCIProxy.
> > > > + */
> > > > +#define TYPE_VIRTIO_PMEM_PCI "virtio-pmem-pci"
> > > > +#define VIRTIO_PMEM_PCI(obj) \
> > > > +        OBJECT_CHECK(VirtIOPMEMPCI, (obj), TYPE_VIRTIO_PMEM_PCI)
> > > > +
> > > > +struct VirtIOPMEMPCI {
> > > > +    VirtIOPCIProxy parent_obj;
> > > > +    VirtIOPMEM vdev;
> > > > +};
> > > > +
> > > >  /*
> > > >   * virtio-balloon-pci: This extends VirtioPCIProxy.
> > > >   */
> > > > diff --git a/hw/virtio/virtio-pmem.c b/hw/virtio/virtio-pmem.c
> > > > new file mode 100644
> > > > index 0000000000..08c96d7e80
> > > > --- /dev/null
> > > > +++ b/hw/virtio/virtio-pmem.c
> > > > @@ -0,0 +1,241 @@
> > > > +/*
> > > > + * Virtio pmem device
> > > > + *
> > > > + * Copyright (C) 2018 Red Hat, Inc.
> > > > + * Copyright (C) 2018 Pankaj Gupta <pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> > > > + *
> > > > + * This work is licensed under the terms of the GNU GPL, version 2.
> > > > + * See the COPYING file in the top-level directory.
> > > > + *
> > > > + */
> > > > +
> > > > +#include "qemu/osdep.h"
> > > > +#include "qapi/error.h"
> > > > +#include "qemu-common.h"
> > > > +#include "qemu/error-report.h"
> > > > +#include "hw/virtio/virtio-access.h"
> > > > +#include "hw/virtio/virtio-pmem.h"
> > > > +#include "hw/mem/memory-device.h"
> > > > +#include "block/aio.h"
> > > > +#include "block/thread-pool.h"
> > > > +
> > > > +typedef struct VirtIOPMEMresp {
> > > > +    int ret;
> > > > +} VirtIOPMEMResp;
> > > > +
> > > > +typedef struct VirtIODeviceRequest {
> > > > +    VirtQueueElement elem;
> > > > +    int fd;
> > > > +    VirtIOPMEM *pmem;
> > > > +    VirtIOPMEMResp resp;
> > > > +} VirtIODeviceRequest;
> > > > +
> > > > +static int worker_cb(void *opaque)
> > > > +{
> > > > +    VirtIODeviceRequest *req = opaque;
> > > > +    int err = 0;
> > > > +
> > > > +    /* flush raw backing image */
> > > > +    err = fsync(req->fd);
> > > > +    if (err != 0) {
> > > > +        err = errno;
> > > > +    }
> > > > +    req->resp.ret = err;  
> > > 
> > > Host question: are you returning the guest errno code to the host?  
> > 
> > No. I am returning error code from the host in-case of host fsync
> > failure, otherwise returning zero.  
> 
> I think that's what Luiz meant.  errno constants are not portable
> between operating systems and architectures.  Therefore they cannot be
> used in external interfaces in software that expects to communicate with
> other systems.

Oh, thanks. Only saw this email now.

> It will be necessary to define specific constants for virtio-pmem
> instead of passing errno from the host to guest.

Yes, defining your own constants work. But I think the only fsync()
error that will make sense for the guest is EIO. The other errors
only make sense for the host.