Re: [PATCH v3 22/23] vhost-user-blk: add some useful trace-points

[Vladimir Sementsov-Ogievskiy]

On 04.11.25 00:28, Michael S. Tsirkin wrote:

On Wed, Oct 15, 2025 at 05:58:06PM +0300, Vladimir Sementsov-Ogievskiy wrote:

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@yandex-team.ru>
Reviewed-by: Daniil Tatianin <d-tatia...@yandex-team.ru>
Reviewed-by: Raphael Norwitz <raphael.s.norw...@gmail.com>
---
  hw/block/trace-events     | 10 ++++++++++
  hw/block/vhost-user-blk.c | 19 +++++++++++++++++++
  2 files changed, 29 insertions(+)

diff --git a/hw/block/trace-events b/hw/block/trace-events
index cc9a9f2460..dbaa5ca6cb 100644
--- a/hw/block/trace-events
+++ b/hw/block/trace-events
@@ -58,6 +58,16 @@ virtio_blk_handle_zone_mgmt(void *vdev, void *req, uint8_t 
op, int64_t sector, i
  virtio_blk_handle_zone_reset_all(void *vdev, void *req, int64_t sector, int64_t len) "vdev %p req %p 
sector 0x%" PRIx64 " cap 0x%" PRIx64 ""
  virtio_blk_handle_zone_append(void *vdev, void *req, int64_t sector) "vdev %p req %p, append 
sector 0x%" PRIx64 ""

+# vhost-user-blk.c

+vhost_user_blk_start_in(void *vdev) "vdev %p"
+vhost_user_blk_start_out(void *vdev) "vdev %p"
+vhost_user_blk_stop_in(void *vdev) "vdev %p"
+vhost_user_blk_stop_out(void *vdev) "vdev %p"
+vhost_user_blk_connect_in(void *vdev) "vdev %p"
+vhost_user_blk_connect_out(void *vdev) "vdev %p"
+vhost_user_blk_device_realize_in(void *vdev) "vdev %p"
+vhost_user_blk_device_realize_out(void *vdev) "vdev %p"
+
  # hd-geometry.c
  hd_geometry_lchs_guess(void *blk, int cyls, int heads, int secs) "blk %p LCHS %d 
%d %d"
  hd_geometry_guess(void *blk, uint32_t cyls, uint32_t heads, uint32_t secs, int trans) 
"blk %p CHS %u %u %u trans %d"
diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
index de7a810c93..a5daed4346 100644
--- a/hw/block/vhost-user-blk.c
+++ b/hw/block/vhost-user-blk.c
@@ -31,6 +31,7 @@
  #include "hw/virtio/virtio-access.h"
  #include "system/system.h"
  #include "system/runstate.h"
+#include "trace.h"

static const int user_feature_bits[] = {

      VIRTIO_BLK_F_SIZE_MAX,
@@ -137,6 +138,8 @@ static int vhost_user_blk_start(VirtIODevice *vdev, Error 
**errp)
      VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
      int i, ret;

+ trace_vhost_user_blk_start_in(vdev);

+
      if (!k->set_guest_notifiers) {
          error_setg(errp, "binding does not support guest notifiers");
          return -ENOSYS;
@@ -192,6 +195,8 @@ static int vhost_user_blk_start(VirtIODevice *vdev, Error 
**errp)
      }
      s->started_vu = true;

+ trace_vhost_user_blk_start_out(vdev);

+
      return ret;

err_guest_notifiers:

@@ -212,6 +217,8 @@ static int vhost_user_blk_stop(VirtIODevice *vdev)
      int ret;
      bool force_stop = false;

+ trace_vhost_user_blk_stop_in(vdev);

+
      if (!s->started_vu) {
          return 0;
      }
@@ -233,6 +240,9 @@ static int vhost_user_blk_stop(VirtIODevice *vdev)
      }

vhost_dev_disable_notifiers(&s->dev, vdev);

+
+    trace_vhost_user_blk_stop_out(vdev);
+
      return ret;
  }

@@ -340,6 +350,8 @@ static int vhost_user_blk_connect(DeviceState *dev, Error **errp)

      VHostUserBlk *s = VHOST_USER_BLK(vdev);
      int ret = 0;

+ trace_vhost_user_blk_connect_in(vdev);

+
      if (s->connected) {
          return 0;
      }
@@ -365,6 +377,8 @@ static int vhost_user_blk_connect(DeviceState *dev, Error 
**errp)
          ret = vhost_user_blk_start(vdev, errp);
      }

+ trace_vhost_user_blk_connect_out(vdev);

+
      return ret;
  }

@@ -455,6 +469,8 @@ static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)

      int retries;
      int i, ret;

+ trace_vhost_user_blk_device_realize_in(vdev);

+
      if (!s->chardev.chr) {
          error_setg(errp, "chardev is mandatory");
          return;
@@ -514,6 +530,9 @@ static void vhost_user_blk_device_realize(DeviceState *dev, 
Error **errp)
      qemu_chr_fe_set_handlers(&s->chardev,  NULL, NULL,
                               vhost_user_blk_event, NULL, (void *)dev,
                               NULL, true);
+
+    trace_vhost_user_blk_device_realize_out(vdev);
+
      return;

virtio_err:

Is it ok that on error there's an in trace but not an out trace?

I thought about it.

In my opinion, switching to use common "out: " and gotos instead of simple 
returns,
is too much pay for proper out trace-points.

So, it's a compromise: we have at least trace-point on success-out, and don't 
make
the code more complicated just for good trace points.

Probably, we can invent some smart macro, which will inject out tracepoint using
g_auto...

--
Best regards,
Vladimir