linux-kernel - RE: [virtio-dev] Re: [PATCH v6 kernel 2/5] virtio-balloon: define new feature bit and head struct

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Message-ID: <F2CBF3009FA73547804AE4C663CAB28E3C3576D9@shsmsx102.ccr.corp.intel.com>
Date:   Thu, 19 Jan 2017 01:30:57 +0000
From:   "Li, Liang Z" <liang.z.li@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "virtio-dev@...ts.oasis-open.org" <virtio-dev@...ts.oasis-open.org>,
        "qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "amit.shah@...hat.com" <amit.shah@...hat.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "cornelia.huck@...ibm.com" <cornelia.huck@...ibm.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "david@...hat.com" <david@...hat.com>,
        "aarcange@...hat.com" <aarcange@...hat.com>,
        "dgilbert@...hat.com" <dgilbert@...hat.com>,
        "quintela@...hat.com" <quintela@...hat.com>
Subject: RE: [virtio-dev] Re: [PATCH v6 kernel 2/5] virtio-balloon: define
 new feature bit and head struct

> > > > > > Signed-off-by: Liang Li <liang.z.li@...el.com>
> > > > > > Cc: Michael S. Tsirkin <mst@...hat.com>
> > > > > > Cc: Paolo Bonzini <pbonzini@...hat.com>
> > > > > > Cc: Cornelia Huck <cornelia.huck@...ibm.com>
> > > > > > Cc: Amit Shah <amit.shah@...hat.com>
> > > > > > Cc: Dave Hansen <dave.hansen@...el.com>
> > > > > > Cc: Andrea Arcangeli <aarcange@...hat.com>
> > > > > > Cc: David Hildenbrand <david@...hat.com>
> > > > > > ---
> > > > > >  include/uapi/linux/virtio_balloon.h | 12 ++++++++++++
> > > > > >  1 file changed, 12 insertions(+)
> > > > > >
> > > > > > diff --git a/include/uapi/linux/virtio_balloon.h
> > > > > > b/include/uapi/linux/virtio_balloon.h
> > > > > > index 343d7dd..2f850bf 100644
> > > > > > --- a/include/uapi/linux/virtio_balloon.h
> > > > > > +++ b/include/uapi/linux/virtio_balloon.h
> > > > > > @@ -34,10 +34,14 @@
> > > > > >  #define VIRTIO_BALLOON_F_MUST_TELL_HOST	0 /* Tell
> before
> > > > > reclaiming pages */
> > > > > >  #define VIRTIO_BALLOON_F_STATS_VQ	1 /* Memory Stats
> virtqueue
> > > > > */
> > > > > >  #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM	2 /* Deflate
> > > balloon
> > > > > on OOM */
> > > > > > +#define VIRTIO_BALLOON_F_PAGE_RANGE	3 /* Send page info
> > > > > with ranges */
> > > > > >
> > > > > >  /* Size of a PFN in the balloon interface. */  #define
> > > > > > VIRTIO_BALLOON_PFN_SHIFT 12
> > > > > >
> > > > > > +/* Bits width for the length of the pfn range */
> > > > >
> > > > > What does this mean? Couldn't figure it out.
> > > > >
> > > > > > +#define VIRTIO_BALLOON_NR_PFN_BITS 12
> > > > > > +
> > > > > >  struct virtio_balloon_config {
> > > > > >  	/* Number of pages host wants Guest to give up. */
> > > > > >  	__u32 num_pages;
> > > > > > @@ -82,4 +86,12 @@ struct virtio_balloon_stat {
> > > > > >  	__virtio64 val;
> > > > > >  } __attribute__((packed));
> > > > > >
> > > > > > +/* Response header structure */ struct
> > > > > > +virtio_balloon_resp_hdr {
> > > > > > +	__le64 cmd : 8; /* Distinguish different requests type */
> > > > > > +	__le64 flag: 8; /* Mark status for a specific request type */
> > > > > > +	__le64 id : 16; /* Distinguish requests of a specific type */
> > > > > > +	__le64 data_len: 32; /* Length of the following data, in
> > > > > > +bytes */
> > > > >
> > > > > This use of __le64 makes no sense.  Just use u8/le16/le32 pls.
> > > > >
> > > >
> > > > Got it, will change in the next version.
> > > >
> > > > And could help take a look at other parts? as well as the QEMU part.
> > > >
> > > > Thanks!
> > > > Liang
> > >
> > > Yes but first I would like to understand how come no fields in this
> > > new structure come up if I search for them in the following patch. I
> > > don't see why
> >
> > It's not true, all of the field will be referenced in the following
> > patches except the 'reserved' filed.
> 
> But none of these are used in the following patch 3.

Yes. Only 'data_len' is used in patch 3, and for expansibility maybe at least 'cmd' is needed to. I should set it in patch 3 to some default value even
it's not currently useful. 'flag' and 'id' are for patch 4. I just want to reuse the 'struct virtio_balloon_resp_hdr' and make the code simpler.

Thanks!
Liang