Re: [Qemu-devel] [PATCH v3 10/29] vhost+postcopy: Register shared ufd with postcopy

[Dr. David Alan Gilbert]

* Peter Xu (address@hidden) wrote:
> On Fri, Feb 16, 2018 at 01:16:06PM +0000, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <address@hidden>
> > 
> > Register the UFD that comes in as the response to the 'advise' method
> > with the postcopy code.
> > 
> > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> > ---
> >  hw/virtio/vhost-user.c   | 21 ++++++++++++++++++++-
> >  migration/postcopy-ram.h |  2 +-
> >  2 files changed, 21 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> > index 4f59993baa..dd4eb50668 100644
> > --- a/hw/virtio/vhost-user.c
> > +++ b/hw/virtio/vhost-user.c
> > @@ -24,6 +24,7 @@
> >  #include <sys/socket.h>
> >  #include <sys/un.h>
> >  #include <linux/vhost.h>
> > +#include <linux/userfaultfd.h>
> 
> Why this line?

Actually, we don't need this until a few patches later in
'Resolve client address' where we pick apart the message
received from the kernel.  I've moved it there.

> >  
> >  #define VHOST_MEMORY_MAX_NREGIONS    8
> >  #define VHOST_USER_F_PROTOCOL_FEATURES 30
> > @@ -155,6 +156,7 @@ struct vhost_user {
> >      CharBackend *chr;
> >      int slave_fd;
> >      NotifierWithReturn postcopy_notifier;
> > +    struct PostCopyFD  postcopy_fd;
> >  };
> >  
> >  static bool ioeventfd_enabled(void)
> > @@ -780,6 +782,17 @@ out:
> >      return ret;
> >  }
> >  
> > +/*
> > + * Called back from the postcopy fault thread when a fault is received on 
> > our
> > + * ufd.
> > + * TODO: This is Linux specific
> > + */
> > +static int vhost_user_postcopy_fault_handler(struct PostCopyFD *pcfd,
> > +                                             void *ufd)
> > +{
> > +    return 0;
> > +}
> > +
> >  /*
> >   * Called at the start of an inbound postcopy on reception of the
> >   * 'advise' command.
> > @@ -819,8 +832,14 @@ static int vhost_user_postcopy_advise(struct vhost_dev 
> > *dev, Error **errp)
> >          error_setg(errp, "%s: Failed to get ufd", __func__);
> >          return -1;
> >      }
> > +    fcntl(ufd, F_SETFL, O_NONBLOCK);
> 
> Only curious: would it work even without this line?

Probably; it's used in a poll() anyway, so it should be fine.

> >  
> > -    /* TODO: register ufd with userfault thread */
> > +    /* register ufd with userfault thread */
> > +    u->postcopy_fd.fd = ufd;
> > +    u->postcopy_fd.data = dev;
> > +    u->postcopy_fd.handler = vhost_user_postcopy_fault_handler;
> > +    u->postcopy_fd.idstr = "vhost-user"; /* Need to find unique name */
> > +    postcopy_register_shared_ufd(&u->postcopy_fd);
> >      return 0;
> >  }
> >  
> > diff --git a/migration/postcopy-ram.h b/migration/postcopy-ram.h
> > index 4bda5aa509..23efbdf346 100644
> > --- a/migration/postcopy-ram.h
> > +++ b/migration/postcopy-ram.h
> > @@ -153,7 +153,7 @@ struct PostCopyFD {
> >      /* Handler to be called whenever we get a poll event */
> >      pcfdhandler handler;
> >      /* A string to use in error messages */
> > -    char *idstr;
> > +    const char *idstr;
> 
> Move to previous patch?

Done.

Dave

> >  };
> >  
> >  /* Register a userfaultfd owned by an external process for
> > -- 
> > 2.14.3
> > 
> 
> -- 
> Peter Xu
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK