Re: [PATCH v2 1/2] vhost: dirty log should be per backend type

[Si-Wei Liu <si-wei.liu@oracle.com>]

Hi Michael,

I'm taking off for 2+ weeks, but please feel free to provide comment and 
feedback while I'm off. I'll be checking emails still, and am about to 
address any opens as soon as I am back.

Thanks,
-Siwei

On 2/14/2024 3:50 AM, Si-Wei Liu wrote:
> There could be a mix of both vhost-user and vhost-kernel clients
> in the same QEMU process, where separate vhost loggers for the
> specific vhost type have to be used. Make the vhost logger per
> backend type, and have them properly reference counted.
>
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
> ---
>   hw/virtio/vhost.c | 49 +++++++++++++++++++++++++++++++++++++------------
>   1 file changed, 37 insertions(+), 12 deletions(-)
>
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 2c9ac79..ef6d9b5 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -43,8 +43,8 @@
>       do { } while (0)
>   #endif
>   
> -static struct vhost_log *vhost_log;
> -static struct vhost_log *vhost_log_shm;
> +static struct vhost_log *vhost_log[VHOST_BACKEND_TYPE_MAX];
> +static struct vhost_log *vhost_log_shm[VHOST_BACKEND_TYPE_MAX];
>   
>   /* Memslots used by backends that support private memslots (without an fd). */
>   static unsigned int used_memslots;
> @@ -287,6 +287,8 @@ static int vhost_set_backend_type(struct vhost_dev *dev,
>           r = -1;
>       }
>   
> +    assert(dev->vhost_ops->backend_type == backend_type || r < 0);
> +
>       return r;
>   }
>   
> @@ -319,16 +321,23 @@ static struct vhost_log *vhost_log_alloc(uint64_t size, bool share)
>       return log;
>   }
>   
> -static struct vhost_log *vhost_log_get(uint64_t size, bool share)
> +static struct vhost_log *vhost_log_get(VhostBackendType backend_type,
> +                                       uint64_t size, bool share)
>   {
> -    struct vhost_log *log = share ? vhost_log_shm : vhost_log;
> +    struct vhost_log *log;
> +
> +    if (backend_type == VHOST_BACKEND_TYPE_NONE ||
> +        backend_type >= VHOST_BACKEND_TYPE_MAX)
> +        return NULL;
> +
> +    log = share ? vhost_log_shm[backend_type] : vhost_log[backend_type];
>   
>       if (!log || log->size != size) {
>           log = vhost_log_alloc(size, share);
>           if (share) {
> -            vhost_log_shm = log;
> +            vhost_log_shm[backend_type] = log;
>           } else {
> -            vhost_log = log;
> +            vhost_log[backend_type] = log;
>           }
>       } else {
>           ++log->refcnt;
> @@ -340,11 +349,20 @@ static struct vhost_log *vhost_log_get(uint64_t size, bool share)
>   static void vhost_log_put(struct vhost_dev *dev, bool sync)
>   {
>       struct vhost_log *log = dev->log;
> +    VhostBackendType backend_type;
>   
>       if (!log) {
>           return;
>       }
>   
> +    assert(dev->vhost_ops);
> +    backend_type = dev->vhost_ops->backend_type;
> +
> +    if (backend_type == VHOST_BACKEND_TYPE_NONE ||
> +        backend_type >= VHOST_BACKEND_TYPE_MAX) {
> +        return;
> +    }
> +
>       --log->refcnt;
>       if (log->refcnt == 0) {
>           /* Sync only the range covered by the old log */
> @@ -352,13 +370,13 @@ static void vhost_log_put(struct vhost_dev *dev, bool sync)
>               vhost_log_sync_range(dev, 0, dev->log_size * VHOST_LOG_CHUNK - 1);
>           }
>   
> -        if (vhost_log == log) {
> +        if (vhost_log[backend_type] == log) {
>               g_free(log->log);
> -            vhost_log = NULL;
> -        } else if (vhost_log_shm == log) {
> +            vhost_log[backend_type] = NULL;
> +        } else if (vhost_log_shm[backend_type] == log) {
>               qemu_memfd_free(log->log, log->size * sizeof(*(log->log)),
>                               log->fd);
> -            vhost_log_shm = NULL;
> +            vhost_log_shm[backend_type] = NULL;
>           }
>   
>           g_free(log);
> @@ -376,7 +394,8 @@ static bool vhost_dev_log_is_shared(struct vhost_dev *dev)
>   
>   static inline void vhost_dev_log_resize(struct vhost_dev *dev, uint64_t size)
>   {
> -    struct vhost_log *log = vhost_log_get(size, vhost_dev_log_is_shared(dev));
> +    struct vhost_log *log = vhost_log_get(dev->vhost_ops->backend_type,
> +                                          size, vhost_dev_log_is_shared(dev));
>       uint64_t log_base = (uintptr_t)log->log;
>       int r;
>   
> @@ -2037,8 +2056,14 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings)
>           uint64_t log_base;
>   
>           hdev->log_size = vhost_get_log_size(hdev);
> -        hdev->log = vhost_log_get(hdev->log_size,
> +        hdev->log = vhost_log_get(hdev->vhost_ops->backend_type,
> +                                  hdev->log_size,
>                                     vhost_dev_log_is_shared(hdev));
> +        if (!hdev->log) {
> +            VHOST_OPS_DEBUG(r, "vhost_log_get failed");
> +            goto fail_vq;
> +        }
> +
>           log_base = (uintptr_t)hdev->log->log;
>           r = hdev->vhost_ops->vhost_set_log_base(hdev,
>                                                   hdev->log_size ? log_base : 0,