Re: [Qemu-block] [PATCH] nvme: add Get/Set Feature Timestamp support

[Klaus Birkelund]

Hi Kenneth,

On Thu, May 16, 2019 at 05:24:47PM -0600, Heitke, Kenneth wrote:
> Hi Klaus, thank you for you review. I have one comment inline
> 
> On 5/14/2019 12:02 AM, Klaus Birkelund wrote:
> > On Fri, Apr 05, 2019 at 03:41:17PM -0600, Kenneth Heitke wrote:
> > > Signed-off-by: Kenneth Heitke <address@hidden>
> > > ---
> > >   hw/block/nvme.c       | 120 +++++++++++++++++++++++++++++++++++++++++-
> > >   hw/block/nvme.h       |   3 ++
> > >   hw/block/trace-events |   2 +
> > >   include/block/nvme.h  |   2 +
> > >   4 files changed, 125 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> > > index 7caf92532a..e775e89299 100644
> > > --- a/hw/block/nvme.c
> > > +++ b/hw/block/nvme.c
> > > @@ -219,6 +219,30 @@ static uint16_t nvme_map_prp(QEMUSGList *qsg, 
> > > QEMUIOVector *iov, uint64_t prp1,
> > >       return NVME_INVALID_FIELD | NVME_DNR;
> > >   }
> > > +static uint16_t nvme_dma_write_prp(NvmeCtrl *n, uint8_t *ptr, uint32_t 
> > > len,
> > > +                                   uint64_t prp1, uint64_t prp2)
> > > +{
> > > +    QEMUSGList qsg;
> > > +    QEMUIOVector iov;
> > > +    uint16_t status = NVME_SUCCESS;
> > > +
> > > +    if (nvme_map_prp(&qsg, &iov, prp1, prp2, len, n)) {
> > > +        return NVME_INVALID_FIELD | NVME_DNR;
> > > +    }
> > > +    if (qsg.nsg > 0) {
> > > +        if (dma_buf_write(ptr, len, &qsg)) {
> > > +            status = NVME_INVALID_FIELD | NVME_DNR;
> > > +        }
> > > +        qemu_sglist_destroy(&qsg);
> > > +    } else {
> > > +        if (qemu_iovec_from_buf(&iov, 0, ptr, len) != len) {
> > 
> > This should be `qemu_iovec_to_buf`.
> > 
> 
> This function is transferring data from the "host" to the device so I
> believe I am using the correct function.
> 

Exactly, but this means that you need to populate `ptr` with data
described by the prps, hence dma_buf_*write* and qemu_iovec_*to*_buf. In
this case `ptr` is set to the address of the uint64_t timestamp, and
that is what we need to write to.