Re: [PATCH v3 1/2] vhost: dirty log should be per backend type

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

On 3/14/2024 8:25 AM, Eugenio Perez Martin wrote:
> On Thu, Mar 14, 2024 at 9:38 AM Si-Wei Liu <si-wei.liu@oracle.com> 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>
>> ---
>> v2->v3:
>>    - remove non-effective assertion that never be reached
>>    - do not return NULL from vhost_log_get()
>>    - add neccessary assertions to vhost_log_get()
>>
>> ---
>>   hw/virtio/vhost.c | 50 ++++++++++++++++++++++++++++++++++++++------------
>>   1 file changed, 38 insertions(+), 12 deletions(-)
>>
>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
>> index 2c9ac79..efe2f74 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 +287,10 @@ static int vhost_set_backend_type(struct vhost_dev *dev,
>>           r = -1;
>>       }
>>
>> +    if (r == 0) {
>> +        assert(dev->vhost_ops->backend_type == backend_type);
>> +    }
>> +
>>       return r;
>>   }
>>
>> @@ -319,16 +323,22 @@ 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;
>> +
>> +    assert(backend_type > VHOST_BACKEND_TYPE_NONE);
>> +    assert(backend_type < VHOST_BACKEND_TYPE_MAX);
>> +
>> +    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 +350,20 @@ 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 +371,13 @@ 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 +395,8 @@ 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 +2057,14 @@ 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) {
> I thought vhost_log_get couldn't return NULL :).
Sure, missed that. Will post a revised v4.

-Siwei
>
> Other than that,
>
> Acked-by: Eugenio Pérez <eperezma@redhat.com>
>
>> +            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,
>> --
>> 1.8.3.1
>>