On 3/17/2024 8:20 PM, Jason Wang wrote:
On Sat, Mar 16, 2024 at 2:33 AM Si-Wei Liu <si-wei....@oracle.com> wrote:
On 3/14/2024 8:50 PM, Jason Wang wrote:
On Fri, Mar 15, 2024 at 5:39 AM Si-Wei Liu <si-wei....@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.
It's better to describe what's the advantage of doing this.
Yes, I can add that to the log. Although it's a niche use case, it was
actually a long standing limitation / bug that vhost-user and
vhost-kernel loggers can't co-exist per QEMU process, but today it's
just silent failure that may be ended up with. This bug fix removes that
implicit limitation in the code.
Ok.
Suggested-by: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: Si-Wei Liu <si-wei....@oracle.com>
---
v3->v4:
- remove checking NULL return value from vhost_log_get
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 | 45 +++++++++++++++++++++++++++++++++------------
1 file changed, 33 insertions(+), 12 deletions(-)
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 2c9ac79..612f4db 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);
+ }
+
Under which condition could we hit this?
Just in case some other function inadvertently corrupted this earlier,
we have to capture discrepancy in the first place... On the other hand,
it will be helpful for other vhost backend writers to diagnose day-one
bug in the code. I feel just code comment here will not be
sufficient/helpful.
See below.
It seems not good to assert a local logic.
It seems to me quite a few local asserts are in the same file already,
vhost_save_backend_state,
For example it has assert for
assert(!dev->started);
which is not the logic of the function itself but require
vhost_dev_start() not to be called before.
But it looks like this patch you assert the code just a few lines
above the assert itself?
Yes, that was the intent - for e.g. xxx_ops may contain corrupted
xxx_ops.backend_type already before coming to this
vhost_set_backend_type() function. And we may capture this corrupted
state by asserting the expected xxx_ops.backend_type (to be consistent
with the backend_type passed in), which needs be done in the first place
when this discrepancy is detected. In practice I think there should be
no harm to add this assert, but this will add warranted guarantee to the
current code.
Regards,
-Siwei
dev->vhost_ops = &xxx_ops;
...
assert(dev->vhost_ops->backend_type == backend_type)
?
Thanks
vhost_load_backend_state,
vhost_virtqueue_mask, vhost_config_mask, just to name a few. Why local
assert a problem?
Thanks,
-Siwei
Thanks
