[Buildroot] [PATCH] package/qemu: add option to enable tracing (default no)

[Buildroot] [PATCH] package/qemu: add option to enable tracing (default no)

[unixmania]

From: Carlos Santos <unixmania@gmail.com>

Tracing is a development feature for debugging, profiling, and observing
QEMU execution. It does not make sense to enable it by default, so add a
config to enable the "log" tracing backend (the default one). Options to
select other backends may be added in the future.

Also pull a patch already reviewed upstream to install the trace events
file only if necessary:

    https://patchwork.kernel.org/project/qemu-devel/patch/20230408010410.281263-1-casantos@redhat.com/

Signed-off-by: Carlos Santos <unixmania@gmail.com>
---
 ...-trace-events-file-only-if-necessary.patch | 29 +++++++++++++++++++
 package/qemu/Config.in                        |  9 ++++++
 package/qemu/qemu.mk                          |  6 ++++
 3 files changed, 44 insertions(+)
 create mode 100644 package/qemu/0004-tracing-install-trace-events-file-only-if-necessary.patch

diff --git a/package/qemu/0004-tracing-install-trace-events-file-only-if-necessary.patch b/package/qemu/0004-tracing-install-trace-events-file-only-if-necessary.patch
new file mode 100644
index 0000000000..0db9a6b647
--- /dev/null
+++ b/package/qemu/0004-tracing-install-trace-events-file-only-if-necessary.patch
@@ -0,0 +1,29 @@
+From 5c43da1e4983cc3c209b325a5228b6149e0a0ccf Mon Sep 17 00:00:00 2001
+From: Carlos Santos <casantos@redhat.com>
+Date: Fri, 24 Mar 2023 21:40:22 -0300
+Subject: [PATCH] tracing: install trace events file only if necessary
+
+It is not useful when configuring with --enable-trace-backends=nop.
+
+Signed-off-by: Carlos Santos <casantos@redhat.com>
+Signed-off-by: Carlos Santos <unixmania@gmail.com>
+---
+ trace/meson.build | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/trace/meson.build b/trace/meson.build
+index 8e80be895c..30b1d942eb 100644
+--- a/trace/meson.build
++++ b/trace/meson.build
+@@ -64,7 +64,7 @@ trace_events_all = custom_target('trace-events-all',
+                                  input: trace_events_files,
+                                  command: [ 'cat', '@INPUT@' ],
+                                  capture: true,
+-                                 install: true,
++                                 install: get_option('trace_backends') != [ 'nop' ],
+                                  install_dir: qemu_datadir)
+ 
+ if 'ust' in get_option('trace_backends')
+-- 
+2.31.1
+
diff --git a/package/qemu/Config.in b/package/qemu/Config.in
index 6fb34a0dae..8d53ced300 100644
--- a/package/qemu/Config.in
+++ b/package/qemu/Config.in
@@ -106,6 +106,15 @@ config BR2_PACKAGE_QEMU_FDT
 	  Say 'y' here to have QEMU capable of constructing Device
 	  Trees, and passing them to the VMs.
 
+config BR2_PACKAGE_QEMU_TRACING
+	bool "Enable tracing"
+	help
+	  Say 'y' to enable the "log" tracing infrastructure in QEMU,
+	  used for debugging, profiling, and observing execution. For
+	  detailed documentation, see
+
+	  https://www.qemu.org/docs/master/devel/tracing.html
+
 endif # BR2_PACKAGE_QEMU_SYSTEM
 
 comment "systems emulation needs a toolchain w/ dynamic library"
diff --git a/package/qemu/qemu.mk b/package/qemu/qemu.mk
index c530896fa8..a020dd5226 100644
--- a/package/qemu/qemu.mk
+++ b/package/qemu/qemu.mk
@@ -159,6 +159,12 @@ else
 QEMU_OPTS += --disable-fdt
 endif
 
+ifeq ($(BR2_PACKAGE_QEMU_TRACING),y)
+QEMU_OPTS += --enable-trace-backends=log
+else
+QEMU_OPTS += --enable-trace-backends=nop
+endif
+
 ifeq ($(BR2_PACKAGE_QEMU_TOOLS),y)
 QEMU_OPTS += --enable-tools
 else
-- 
2.39.3

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Re: [Buildroot] [PATCH] package/qemu: add option to enable tracing (default no)

[Thomas Petazzoni via buildroot]

Hello Carlos,

On Wed, 12 Jul 2023 19:01:19 -0300
unixmania@gmail.com wrote:

> From: Carlos Santos <unixmania@gmail.com>
> 
> Tracing is a development feature for debugging, profiling, and observing
> QEMU execution. It does not make sense to enable it by default, so add a
> config to enable the "log" tracing backend (the default one). Options to
> select other backends may be added in the future.
> 
> Also pull a patch already reviewed upstream to install the trace events
> file only if necessary:
> 
>     https://patchwork.kernel.org/project/qemu-devel/patch/20230408010410.281263-1-casantos@redhat.com/
> 
> Signed-off-by: Carlos Santos <unixmania@gmail.com>
> ---
>  ...-trace-events-file-only-if-necessary.patch | 29 +++++++++++++++++++
>  package/qemu/Config.in                        |  9 ++++++
>  package/qemu/qemu.mk                          |  6 ++++
>  3 files changed, 44 insertions(+)
>  create mode 100644 package/qemu/0004-tracing-install-trace-events-file-only-if-necessary.patch

Applied to next after adding an "Upstream:" tag inside the patch, which
we now require (you get a "make check-package" warning if you don't
have this tag).

Thanks a lot!

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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