Re: [Qemu-devel] [PATCH v4 11/22] vhost-user: send log shm fd along with log_base

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Sep 21, 2015 at 10:05:22AM -0400, Marc-André Lureau wrote:
> 
> 
> ----- Original Message -----
> > On Sat, Sep 19, 2015 at 12:12:02PM +0200, marcandre.lureau@redhat.com wrote:
> > > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > 
> > > Send the shm for the dirty pages logging if the backend supports
> > > VHOST_USER_PROTOCOL_F_LOG_SHMFD.
> > > 
> > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > ---
> > >  hw/virtio/vhost-backend.c         |  3 ++-
> > >  hw/virtio/vhost-user.c            | 17 ++++++++++++++---
> > >  hw/virtio/vhost.c                 |  5 +++--
> > >  include/hw/virtio/vhost-backend.h |  4 +++-
> > >  4 files changed, 22 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
> > > index bf2d1d4..3f2d6ea 100644
> > > --- a/hw/virtio/vhost-backend.c
> > > +++ b/hw/virtio/vhost-backend.c
> > > @@ -66,7 +66,8 @@ static int vhost_scsi_get_abi_version(struct vhost_dev
> > > *dev, int *version)
> > >      return vhost_kernel_call(dev, VHOST_SCSI_GET_ABI_VERSION, version);
> > >  }
> > >  
> > > -static int vhost_set_log_base(struct vhost_dev *dev, uint64_t base)
> > > +static int vhost_set_log_base(struct vhost_dev *dev, uint64_t base,
> > > +                              struct vhost_log *log)
> > >  {
> > >      return vhost_kernel_call(dev, VHOST_SET_LOG_BASE, &base);
> > >  }
> > > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> > > index d3334f5..3cb5559 100644
> > > --- a/hw/virtio/vhost-user.c
> > > +++ b/hw/virtio/vhost-user.c
> > > @@ -26,7 +26,9 @@
> > >  #define VHOST_MEMORY_MAX_NREGIONS    8
> > >  
> > >  #define VHOST_USER_F_PROTOCOL_FEATURES 30
> > > -#define VHOST_USER_PROTOCOL_FEATURE_MASK 0x0ULL
> > > +
> > > +#define VHOST_USER_PROTOCOL_FEATURE_MASK 0x1ULL
> > > +#define VHOST_USER_PROTOCOL_F_LOG_SHMFD 0
> > >  
> > >  typedef enum VhostUserRequest {
> > >      VHOST_USER_NONE = 0,
> > > @@ -182,8 +184,11 @@ static int vhost_scsi_get_abi_version(struct vhost_dev
> > > *dev, int *version)
> > >      return -1;
> > >  }
> > >  
> > > -static int vhost_set_log_base(struct vhost_dev *dev, uint64_t base)
> > > +static int vhost_set_log_base(struct vhost_dev *dev, uint64_t base,
> > > +                              struct vhost_log *log)
> > >  {
> > > +    int fds[VHOST_MEMORY_MAX_NREGIONS];
> > > +    size_t fd_num = 0;
> > >      VhostUserMsg msg = {
> > >          .request = VHOST_USER_SET_LOG_BASE,
> > >          .flags = VHOST_USER_VERSION,
> > > @@ -191,7 +196,13 @@ static int vhost_set_log_base(struct vhost_dev *dev,
> > > uint64_t base)
> > >          .size = sizeof(m.u64),
> > >      };
> > >  
> > > -    vhost_user_write(dev, &msg, NULL, 0);
> > > +    if (virtio_has_feature(dev->protocol_features,
> > > +                           VHOST_USER_PROTOCOL_F_LOG_SHMFD) &&
> > > +        log->fd != -1) {
> > > +        fds[fd_num++] = log->fd;
> > > +    }
> > > +
> > > +    vhost_user_write(dev, &msg, fds, fd_num);
> > >  
> > >      return 0;
> > >  }
> > 
> > Doesn't this one have to get a response?
> > Otherwise the other side might still be using the old
> > buffer after we've updated this one.
> 
> That make sense, though I wonder about all other SET commands in the protocol then. Isn't there other commands that may change the fd or memory region over time?

I suspect most commands need to get a response but I think it's
best to fix this separately.

> > Probably need a protocol feature, but I guess we can reuse
> > VHOST_USER_PROTOCOL_F_LOG_SHMFD - IIUC logging doesn't
> > work without this anyway ...
> 
> ok
> 
> > 
> > 
> > > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> > > index 83ef164..0fa7b69 100644
> > > --- a/hw/virtio/vhost.c
> > > +++ b/hw/virtio/vhost.c
> > > @@ -359,7 +359,7 @@ static inline void vhost_dev_log_resize(struct
> > > vhost_dev* dev, uint64_t size)
> > >  
> > >      /* inform backend of log switching, this must be done before
> > >         releasing the current log, to ensure no logging is lost */
> > > -    r = dev->vhost_ops->vhost_set_log_base(dev, log_base);
> > > +    r = dev->vhost_ops->vhost_set_log_base(dev, log_base, log);
> > >      assert(r >= 0);
> > >      vhost_log_put(dev, true);
> > >      dev->log = log;
> > > @@ -1167,7 +1167,8 @@ int vhost_dev_start(struct vhost_dev *hdev,
> > > VirtIODevice *vdev)
> > >          hdev->log = vhost_log_get(hdev->log_size, share);
> > >          log_base = (uintptr_t)hdev->log->log;
> > >          r = hdev->vhost_ops->vhost_set_log_base(hdev,
> > > -                                                hdev->log_size ? log_base
> > > : 0);
> > > +                                                hdev->log_size ? log_base
> > > : 0,
> > > +                                                hdev->log);
> > >          if (r < 0) {
> > >              r = -errno;
> > >              goto fail_log;
> > > diff --git a/include/hw/virtio/vhost-backend.h
> > > b/include/hw/virtio/vhost-backend.h
> > > index 42cfb87..a87f0b3 100644
> > > --- a/include/hw/virtio/vhost-backend.h
> > > +++ b/include/hw/virtio/vhost-backend.h
> > > @@ -20,6 +20,7 @@ typedef enum VhostBackendType {
> > >  
> > >  struct vhost_dev;
> > >  struct vhost_memory;
> > > +struct vhost_log;
> > >  struct vhost_vring_file;
> > >  struct vhost_vring_state;
> > >  struct vhost_vring_addr;
> > > @@ -36,7 +37,8 @@ typedef int (*vhost_scsi_clear_endpoint_op)(struct
> > > vhost_dev *dev,
> > >                                              struct vhost_scsi_target
> > >                                              *target);
> > >  typedef int (*vhost_scsi_get_abi_version_op)(struct vhost_dev *dev,
> > >                                               int *version);
> > > -typedef int (*vhost_set_log_base_op)(struct vhost_dev *dev, uint64_t
> > > base);
> > > +typedef int (*vhost_set_log_base_op)(struct vhost_dev *dev, uint64_t base,
> > > +                                     struct vhost_log *log);
> > >  typedef int (*vhost_set_mem_table_op)(struct vhost_dev *dev,
> > >                                        struct vhost_memory *mem);
> > >  typedef int (*vhost_set_vring_addr_op)(struct vhost_dev *dev,
> > > --
> > > 2.4.3
> >