[PATCH] tracing: deprecate "ust" tracing backend

[PATCH] tracing: deprecate "ust" tracing backend

[Paolo Bonzini]

The "ust" backend is complex (tracetool contains two output formats just
for that backend).  It is not clear if if it has any users, and LTTng
anyway can use the uprobe tracepoints provided by the "dtrace" backend,
therefore deprecate "ust".

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 docs/about/deprecated.rst | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
index aa300bbd507..57250f9d47f 100644
--- a/docs/about/deprecated.rst
+++ b/docs/about/deprecated.rst
@@ -533,3 +533,12 @@ command documentation for details on the ``fdset`` usage.
 
 The ``zero-blocks`` capability was part of the block migration which
 doesn't exist anymore since it was removed in QEMU v9.1.
+
+Host features
+-------------
+
+``ust`` tracing backend
+-----------------------
+
+LTTng can use uprobe tracepoints, therefore it is recommended to use
+the ``dtrace`` backend instead.
-- 
2.51.0

Re: [PATCH] tracing: deprecate "ust" tracing backend

[Daniel P. Berrangé]

On Fri, Sep 19, 2025 at 12:10:21PM +0200, Paolo Bonzini wrote:
> The "ust" backend is complex (tracetool contains two output formats just
> for that backend).  It is not clear if if it has any users, and LTTng
> anyway can use the uprobe tracepoints provided by the "dtrace" backend,
> therefore deprecate "ust".
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  docs/about/deprecated.rst | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
> index aa300bbd507..57250f9d47f 100644
> --- a/docs/about/deprecated.rst
> +++ b/docs/about/deprecated.rst
> @@ -533,3 +533,12 @@ command documentation for details on the ``fdset`` usage.
>  
>  The ``zero-blocks`` capability was part of the block migration which
>  doesn't exist anymore since it was removed in QEMU v9.1.
> +
> +Host features
> +-------------
> +
> +``ust`` tracing backend
> +-----------------------
> +
> +LTTng can use uprobe tracepoints, therefore it is recommended to use
> +the ``dtrace`` backend instead.

meson.build should call

   warning('ust trace backend is deprecated, use dtrace backend for uprobe support')


if the user requests ust at build time.

With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|