Re: [dpdk-dev] [04/12] vhost: introduce postcopy's advise message

[Bruce Richardson <bruce.richardson@intel.com>]

On Fri, Sep 28, 2018 at 01:40:25PM +0300, Ilya Maximets wrote:
> On 27.09.2018 11:28, Ilya Maximets wrote:
> > On 26.09.2018 10:26, Maxime Coquelin wrote:
> >> This patch opens a userfaultfd and sends it back to Qemu's
> >> VHOST_USER_POSTCOPY_ADVISE request.
> >>
> >> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> >> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> >> ---
> >>  lib/librte_vhost/vhost.h      |  2 ++
> >>  lib/librte_vhost/vhost_user.c | 37 +++++++++++++++++++++++++++++++++++
> >>  lib/librte_vhost/vhost_user.h |  3 ++-
> >>  3 files changed, 41 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> >> index 25ffd7614..21722d8a8 100644
> >> --- a/lib/librte_vhost/vhost.h
> >> +++ b/lib/librte_vhost/vhost.h
> >> @@ -363,6 +363,8 @@ struct virtio_net {
> >>  	int			slave_req_fd;
> >>  	rte_spinlock_t		slave_req_lock;
> >>  
> >> +	int			postcopy_ufd;
> >> +
> >>  	/*
> >>  	 * Device id to identify a specific backend device.
> >>  	 * It's set to -1 for the default software implementation.
> >> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
> >> index a9b429598..bdfe2cac0 100644
> >> --- a/lib/librte_vhost/vhost_user.c
> >> +++ b/lib/librte_vhost/vhost_user.c
> >> @@ -24,9 +24,13 @@
> >>  #include <stdlib.h>
> >>  #include <string.h>
> >>  #include <unistd.h>
> >> +#include <fcntl.h>
> >> +#include <linux/userfaultfd.h>
> > 
> > Maybe we need compile time check for this header existence?
> > Otherwise, this will bump minimal kernel version for default linux build
> > to something like 4.3.
> 
> We'll need a config option here (disabled by default) and guard all
> the postcopy related code.
> Meson build will be able to detect the header file and enable
> the config if possible. Like this:
> 
> lib/librte_vhost/meson.build:
> if cc.has_header('linux/userfaultfd.h')
>        dpdk_conf.set10('RTE_LIBRTE_VHOST_POSTCOPY', true)

Are you sure you want 'set10' rather than 'set'. Set is probably easier
because it ensures no define on false, while set10 has a define of 0. This
has caught me out before.

FYI, you can also avoid the if by putting the condition into the define:

	dpdk_conf.set('RTE_LIBRTE_VHOST_POSTCOPY', cc.has_header('...'))

/Bruce