Re: [Qemu-devel] [PATCH v3 13/28] vhost-user: check vhost_user_{read, write}() return value

["Marc-André Lureau" <mlureau@redhat.com>]

Hi

----- Original Message -----
> On Wed, Jul 06, 2016 at 08:47:06PM +0200, marcandre.lureau@redhat.com wrote:
> > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > 
> > More error checking to break code flow and report appropriate errors.
> > 
> > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> 
> So this will cause asserts here:
> 
>     /* 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, log);
>     assert(r >= 0);

That's why there is a previous patch "vhost: do not assert() on vhost_ops failure". Although there is still some abort() on migration. This is a corner case that isn't yet solved. I think it would make sense for the backend to state that it is disconnected, and for vhost to ingore migration ops failure in this case.

> which is the opposite of what we want.
> 
> For vhost_net ioctl failure is a fatal error bit for
> vhost user this means backend exited and will not change
> memory so it's benign.
> 
> the right thing to do is to return 0 status to caller on most errors.
> 
> If that is necessary for debugging, add a printout for now.

Yes, I am adding a VHOST_OPS_DEBUG as you proposed

> 
> > ---
> >  hw/virtio/vhost-user.c | 50
> >  ++++++++++++++++++++++++++++++++++----------------
> >  1 file changed, 34 insertions(+), 16 deletions(-)
> > 
> > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> > index 5dae496..819481d 100644
> > --- a/hw/virtio/vhost-user.c
> > +++ b/hw/virtio/vhost-user.c
> > @@ -214,12 +214,14 @@ static int vhost_user_set_log_base(struct vhost_dev
> > *dev, uint64_t base,
> >          fds[fd_num++] = log->fd;
> >      }
> >  
> > -    vhost_user_write(dev, &msg, fds, fd_num);
> > +    if (vhost_user_write(dev, &msg, fds, fd_num) < 0) {
> > +        return -1;
> > +    }
> >  
> >      if (shmfd) {
> >          msg.size = 0;
> >          if (vhost_user_read(dev, &msg) < 0) {
> > -            return 0;
> > +            return -1;
> >          }
> >  
> >          if (msg.request != VHOST_USER_SET_LOG_BASE) {
> > @@ -275,7 +277,9 @@ static int vhost_user_set_mem_table(struct vhost_dev
> > *dev,
> >      msg.size += sizeof(msg.payload.memory.padding);
> >      msg.size += fd_num * sizeof(VhostUserMemoryRegion);
> >  
> > -    vhost_user_write(dev, &msg, fds, fd_num);
> > +    if (vhost_user_write(dev, &msg, fds, fd_num) < 0) {
> > +        return -1;
> > +    }
> >  
> >      return 0;
> >  }
> > @@ -290,7 +294,9 @@ static int vhost_user_set_vring_addr(struct vhost_dev
> > *dev,
> >          .size = sizeof(msg.payload.addr),
> >      };
> >  
> > -    vhost_user_write(dev, &msg, NULL, 0);
> > +    if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
> > +        return -1;
> > +    }
> >  
> >      return 0;
> >  }
> > @@ -313,7 +319,9 @@ static int vhost_set_vring(struct vhost_dev *dev,
> >          .size = sizeof(msg.payload.state),
> >      };
> >  
> > -    vhost_user_write(dev, &msg, NULL, 0);
> > +    if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
> > +        return -1;
> > +    }
> >  
> >      return 0;
> >  }
> > @@ -360,10 +368,12 @@ static int vhost_user_get_vring_base(struct vhost_dev
> > *dev,
> >          .size = sizeof(msg.payload.state),
> >      };
> >  
> > -    vhost_user_write(dev, &msg, NULL, 0);
> > +    if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
> > +        return -1;
> > +    }
> >  
> >      if (vhost_user_read(dev, &msg) < 0) {
> > -        return 0;
> > +        return -1;
> >      }
> >  
> >      if (msg.request != VHOST_USER_GET_VRING_BASE) {
> > @@ -401,7 +411,9 @@ static int vhost_set_vring_file(struct vhost_dev *dev,
> >          msg.payload.u64 |= VHOST_USER_VRING_NOFD_MASK;
> >      }
> >  
> > -    vhost_user_write(dev, &msg, fds, fd_num);
> > +    if (vhost_user_write(dev, &msg, fds, fd_num) < 0) {
> > +        return -1;
> > +    }
> >  
> >      return 0;
> >  }
> > @@ -427,7 +439,9 @@ static int vhost_user_set_u64(struct vhost_dev *dev,
> > int request, uint64_t u64)
> >          .size = sizeof(msg.payload.u64),
> >      };
> >  
> > -    vhost_user_write(dev, &msg, NULL, 0);
> > +    if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
> > +        return -1;
> > +    }
> >  
> >      return 0;
> >  }
> > @@ -455,10 +469,12 @@ static int vhost_user_get_u64(struct vhost_dev *dev,
> > int request, uint64_t *u64)
> >          return 0;
> >      }
> >  
> > -    vhost_user_write(dev, &msg, NULL, 0);
> > +    if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
> > +        return -1;
> > +    }
> >  
> >      if (vhost_user_read(dev, &msg) < 0) {
> > -        return 0;
> > +        return -1;
> >      }
> >  
> >      if (msg.request != request) {
> > @@ -489,7 +505,9 @@ static int vhost_user_set_owner(struct vhost_dev *dev)
> >          .flags = VHOST_USER_VERSION,
> >      };
> >  
> > -    vhost_user_write(dev, &msg, NULL, 0);
> > +    if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
> > +        return -1;
> > +    }
> >  
> >      return 0;
> >  }
> > @@ -501,7 +519,9 @@ static int vhost_user_reset_device(struct vhost_dev
> > *dev)
> >          .flags = VHOST_USER_VERSION,
> >      };
> >  
> > -    vhost_user_write(dev, &msg, NULL, 0);
> > +    if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
> > +        return -1;
> > +    }
> >  
> >      return 0;
> >  }
> > @@ -588,7 +608,6 @@ static bool vhost_user_requires_shm_log(struct
> > vhost_dev *dev)
> >  static int vhost_user_migration_done(struct vhost_dev *dev, char*
> >  mac_addr)
> >  {
> >      VhostUserMsg msg = { 0 };
> > -    int err;
> >  
> >      assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);
> >  
> > @@ -605,8 +624,7 @@ static int vhost_user_migration_done(struct vhost_dev
> > *dev, char* mac_addr)
> >          memcpy((char *)&msg.payload.u64, mac_addr, 6);
> >          msg.size = sizeof(msg.payload.u64);
> >  
> > -        err = vhost_user_write(dev, &msg, NULL, 0);
> > -        return err;
> > +        return vhost_user_write(dev, &msg, NULL, 0);
> >      }
> >      return -1;
> >  }
> > --
> > 2.9.0
>