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trace: update docs with meson build information

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The documentation still refers to the makefile and the old sub-directory
layout. Meson works differently: tracetool output is placed into the
builddir with mangled filenames like <builddir>/trace/trace-accel_kvm.h
for the accel/kvm/ trace.h definition.

This meson setup also requires a manually-created accel/kvm/trace.h file
that #includes the <builddir>/trace/trace-accel_kvm.h file. Document
this!

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20210112165859.225534-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2021-01-12 16:58:59 +00:00
parent 3faf22ef44
commit 0dfb3ca73c
1 changed files with 34 additions and 23 deletions
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57
docs/devel/tracing.rst
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@ -39,40 +39,51 @@ Trace events
Sub-directory setup
-------------------
Each directory in the source tree can declare a set of static trace events
in a local "trace-events" file. All directories which contain "trace-events"
files must be listed in the "trace-events-subdirs" make variable in the top
level Makefile.objs. During build, the "trace-events" file in each listed
subdirectory will be processed by the "tracetool" script to generate code for
the trace events.
Each directory in the source tree can declare a set of trace events in a local
"trace-events" file. All directories which contain "trace-events" files must be
listed in the "trace_events_subdirs" variable in the top level meson.build
file. During build, the "trace-events" file in each listed subdirectory will be
processed by the "tracetool" script to generate code for the trace events.
The individual "trace-events" files are merged into a "trace-events-all" file,
which is also installed into "/usr/share/qemu" with the name "trace-events".
This merged file is to be used by the "simpletrace.py" script to later analyse
traces in the simpletrace data format.
In the sub-directory the following files will be automatically generated
The following files are automatically generated in <builddir>/trace/ during the
build:
- trace.c - the trace event state declarations
- trace.h - the trace event enums and probe functions
- trace-dtrace.h - DTrace event probe specification
- trace-dtrace.dtrace - DTrace event probe helper declaration
- trace-dtrace.o - binary DTrace provider (generated by dtrace)
- trace-ust.h - UST event probe helper declarations
- trace-<subdir>.c - the trace event state declarations
- trace-<subdir>.h - the trace event enums and probe functions
- trace-dtrace-<subdir>.h - DTrace event probe specification
- trace-dtrace-<subdir>.dtrace - DTrace event probe helper declaration
- trace-dtrace-<subdir>.o - binary DTrace provider (generated by dtrace)
- trace-ust-<subdir>.h - UST event probe helper declarations
Source files in the sub-directory should #include the local 'trace.h' file,
without any sub-directory path prefix. eg io/channel-buffer.c would do::
Here <subdir> is the sub-directory path with '/' replaced by '_'. For example,
"accel/kvm" becomes "accel_kvm" and the final filename for "trace-<subdir>.c"
becomes "trace-accel_kvm.c".
Source files in the source tree do not directly include generated files in
"<builddir>/trace/". Instead they #include the local "trace.h" file, without
any sub-directory path prefix. eg io/channel-buffer.c would do::
#include "trace.h"
To access the 'io/trace.h' file. While it is possible to include a trace.h
file from outside a source file's own sub-directory, this is discouraged in
general. It is strongly preferred that all events be declared directly in
the sub-directory that uses them. The only exception is where there are some
shared trace events defined in the top level directory trace-events file.
The top level directory generates trace files with a filename prefix of
"trace/trace-root" instead of just "trace". This is to avoid ambiguity between
a trace.h in the current directory, vs the top level directory.
The "io/trace.h" file must be created manually with an #include of the
corresponding "trace/trace-<subdir>.h" file that will be generated in the
builddir::
$ echo '#include "trace/trace-io.h"' >io/trace.h
While it is possible to include a trace.h file from outside a source file's own
sub-directory, this is discouraged in general. It is strongly preferred that
all events be declared directly in the sub-directory that uses them. The only
exception is where there are some shared trace events defined in the top level
directory trace-events file. The top level directory generates trace files
with a filename prefix of "trace/trace-root" instead of just "trace". This is
to avoid ambiguity between a trace.h in the current directory, vs the top level
directory.
Using trace events
------------------