On Mon, Nov 16, 2015 at 05:14:37PM +0100, Thibaut Collet wrote:
> Fixes: 2b8819c6eee5 ("vhost-user: modify SET_LOG_BASE to pass mmap size and
> offset")
>
> For compatibility with old vhost backend content of the SET_LOG_BASE message
> can not be modified.
Hmm that's true. Interesting. But this only happens on migration,
right? And if VHOST_USER_PROTOCOL_F_LOG_SHMFD is not set
then we block migration. So how come the old message
is ever sent?
> The SET_LOG_BASE message payload is modified only if the
> VHOST_USER_PROTOCOL_F_LOG_SHMFD protocol feature has been negociated.
>
> The documentation has been updated accordingly with remarks from Marc André
> Lureau.
>
> Signed-off-by: Thibaut Collet <thibaut.col...@6wind.com>
> ---
> docs/specs/vhost-user.txt | 16 ++++++++++++++--
> hw/virtio/vhost-user.c | 12 +++++++++---
> 2 files changed, 23 insertions(+), 5 deletions(-)
>
> diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
> index 26dde2e..da4bf9c 100644
> --- a/docs/specs/vhost-user.txt
> +++ b/docs/specs/vhost-user.txt
> @@ -87,6 +87,14 @@ Depending on the request type, payload can be:
> User address: a 64-bit user address
> mmap offset: 64-bit offset where region starts in the mapped memory
>
> + * vhost user log description
> + -----------------
> + | size | offset |
> + -----------------
> +
> + size: a 64-bit size
> + Offset: a 64-bit offset where log starts in the mapped memory
> +
> In QEMU the vhost-user message is implemented with the following struct:
>
> typedef struct VhostUserMsg {
> @@ -280,14 +288,18 @@ Message types
>
> Id: 6
> Equivalent ioctl: VHOST_SET_LOG_BASE
> - Master payload: u64
> + Master payload: - u64 if slave has not the
> VHOST_USER_PROTOCOL_F_LOG_SHMFD
> + protocol feature
> + - vhost user log if slave has the
> + VHOST_USER_PROTOCOL_F_LOG_SHMFD protocol feature
> Slave payload: N/A
>
> Sets logging shared memory space.
> When slave has VHOST_USER_PROTOCOL_F_LOG_SHMFD protocol
> feature, the log memory fd is provided in the ancillary data of
> VHOST_USER_SET_LOG_BASE message, the size and offset of shared
> - memory area provided in the message.
> + memory area provided in the message and the message reply is an
> + empty message (size of 0).
>
>
> * VHOST_USER_SET_LOG_FD
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index c443602..dcdfd40 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -206,11 +206,17 @@ static int vhost_user_set_log_base(struct vhost_dev
> *dev, uint64_t base,
> VhostUserMsg msg = {
> .request = VHOST_USER_SET_LOG_BASE,
> .flags = VHOST_USER_VERSION,
> - .payload.log.mmap_size = log->size,
> - .payload.log.mmap_offset = 0,
> - .size = sizeof(msg.payload.log),
> };
>
> + if (shmfd) {
> + msg.payload.log.mmap_size = log->size;
> + msg.payload.log.mmap_offset = 0;
> + msg.size = sizeof(msg.payload.log);
> + } else {
> + msg.payload.u64 = base;
> + msg.size = sizeof(msg.payload.u64);
> + }
> +
> if (shmfd && log->fd != -1) {
> fds[fd_num++] = log->fd;
> }
> --
> 2.1.4
