Re: [Qemu-devel] [PATCH 4/4] 9pfs: add a size parameter to init_iov_from_pdu

[Greg Kurz <groug@kaod.org>]

On Mon, 21 Nov 2016 13:39:32 -0800
Stefano Stabellini <sstabellini@kernel.org> wrote:

> Not all 9pfs transports share memory between request and response. For
> those who don't, it is necessary to know how much memory is required in
> the response.
> 
> Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
> ---

IIUC the transport used in Xen requires you pass the size when sending a
P9_RREAD message back to the guest, i.e. only in the case when is_write is
false, correct ?

If so, for better clarity, what about having two distinct init_in_iov_from_pdu
and init_out_iov_from_pdu ops, with an explicit comment in the virtio-9p
implementation of init_in_iov_from_pdu so that someone isn't tempted to drop
the apparently unused size argument ? Would this be ok for you on the Xen
side ?

Cheers.

--
Greg

>  hw/9pfs/9p.c               | 2 +-
>  hw/9pfs/9p.h               | 2 +-
>  hw/9pfs/virtio-9p-device.c | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index b6ec042..b82212b 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -1652,7 +1652,7 @@ static void v9fs_init_qiov_from_pdu(QEMUIOVector *qiov, V9fsPDU *pdu,
>      struct iovec *iov;
>      unsigned int niov;
>  
> -    pdu->s->transport->init_iov_from_pdu(pdu, &iov, &niov, is_write);
> +    pdu->s->transport->init_iov_from_pdu(pdu, &iov, &niov, is_write, skip + size);
>  
>      qemu_iovec_init_external(&elem, iov, niov);
>      qemu_iovec_init(qiov, niov);
> diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
> index ab398d0..c830188 100644
> --- a/hw/9pfs/9p.h
> +++ b/hw/9pfs/9p.h
> @@ -348,7 +348,7 @@ struct V9fsTransport {
>      ssize_t     (*pdu_vmarshal)(V9fsPDU *pdu, size_t offset, const char *fmt, va_list ap);
>      ssize_t     (*pdu_vunmarshal)(V9fsPDU *pdu, size_t offset, const char *fmt, va_list ap);
>      void        (*init_iov_from_pdu)(V9fsPDU *pdu, struct iovec **piov,
> -                              unsigned int *pniov, bool is_write);
> +                              unsigned int *pniov, bool is_write, size_t size);
>      void        (*push_and_notify)(V9fsPDU *pdu);
>  };
>  
> diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
> index e1a37a4..e2b27e8 100644
> --- a/hw/9pfs/virtio-9p-device.c
> +++ b/hw/9pfs/virtio-9p-device.c
> @@ -172,7 +172,7 @@ static ssize_t virtio_pdu_vunmarshal(V9fsPDU *pdu, size_t offset,
>  }
>  
>  static void virtio_init_iov_from_pdu(V9fsPDU *pdu, struct iovec **piov,
> -                              unsigned int *pniov, bool is_write)
> +                              unsigned int *pniov, bool is_write, size_t size)
>  {
>      V9fsState *s = pdu->s;
>      V9fsVirtioState *v = container_of(s, V9fsVirtioState, state);