Re: [PATCH] common/tracing: use /sys/kernel/tracing at first

["Darrick J. Wong" <djwong@kernel.org>]

On Sat, May 11, 2024 at 12:46:41PM +0800, Zorro Lang wrote:
> On Fri, May 10, 2024 at 08:17:54AM -0700, Darrick J. Wong wrote:
> > On Fri, May 10, 2024 at 12:33:39PM +0800, Zorro Lang wrote:
> > > To avoid the dependence of debugfs, tracefs is mounted on another
> > > place -- /sys/kernel/tracing now. But for the compatibility, the
> > > /sys/kernel/debug/tracing is still there. So change _require_ftrace
> > > helper, try to use the new /sys/kernel/tracing path at first, or
> > > fallback to the old one if it's not supported.
> > > 
> > > xfs/499 uses ftrace, so call _require_ftrace in it.
> > > 
> > > Signed-off-by: Zorro Lang <zlang@kernel.org>
> > > ---
> > >  common/tracing | 13 +++++++++----
> > >  tests/xfs/499  |  6 +++---
> > >  2 files changed, 12 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/common/tracing b/common/tracing
> > > index b3051c27..8613d044 100644
> > > --- a/common/tracing
> > > +++ b/common/tracing
> > > @@ -4,11 +4,16 @@
> > >  #
> > >  # Routines for dealing with ftrace (or any other tracing).
> > >  
> > > -FTRACE_INSTANCES_DIR="/sys/kernel/debug/tracing/instances/"
> > > -
> > >  _require_ftrace() {
> > > -	test -d "$FTRACE_INSTANCES_DIR" || \
> > > -		_notrun "kernel does not support ftrace"
> > > +	if [ -d /sys/kernel/tracing/instances/ ];then
> > > +		FTRACE_ROOT="/sys/kernel/tracing"
> > > +		FTRACE_INSTANCES_DIR="/sys/kernel/tracing/instances"
> > 
> > To answer my own question, this new path has been in Debian since at
> > least 2021.
> 
> Oh, I thought the /sys/kernel/tracing was created in linux v4.1 :
>   cc31004a4aa7 ("tracefs: Add directory /sys/kernel/tracing")
> 
> But might be used in different distro widely later.

That creates an empty /sys/kernel/tracing directory, but userspace still
has to mount something to it, hence
/lib/systemd/system/sys-kernel-tracing.mount.

--D

> > 
> > > +	elif [ -d /sys/kernel/debug/tracing/instances/ ];then
> > > +		FTRACE_ROOT="/sys/kernel/debug/tracing"
> > > +		FTRACE_INSTANCES_DIR="/sys/kernel/debug/tracing/instances"
> > > +	else
> > > +		_notrun "The ftrace is not supported, or tracefs is not mounted"
> > > +	fi
> > >  }
> > >  
> > >  _ftrace_cleanup() {
> > > diff --git a/tests/xfs/499 b/tests/xfs/499
> > > index 9672f95d..883415dc 100755
> > > --- a/tests/xfs/499
> > > +++ b/tests/xfs/499
> > > @@ -14,18 +14,18 @@ _begin_fstest auto quick
> > >  _register_cleanup "_cleanup" BUS
> > >  
> > >  # Import common functions.
> > > +. ./common/tracing
> > 
> > You could probably get rid of the "Import common functions" comment.
> 
> Sure, will change that when I merge it.
> 
> > 
> > This looks good!
> > Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> 
> Thanks,
> Zorro
> 
> > 
> > --D
> > 
> > >  
> > >  # real QA test starts here
> > >  _supported_fs xfs
> > > +_require_ftrace
> > >  _require_command "$CC_PROG" "cc"
> > >  
> > >  cprog=$tmp.ftrace.c
> > >  oprog=$tmp.ftrace
> > >  sedprog=$tmp.ftrace.sed
> > >  
> > > -ftrace_dir=$DEBUGFS_MNT/tracing/events/xfs
> > > -
> > > -test -d $ftrace_dir || _notrun "ftrace not enabled"
> > > +ftrace_dir=$FTRACE_ROOT/events/xfs
> > >  
> > >  # The second argument to __print_symbolic is stringified in the tracepoint's
> > >  # fmt file, so we look for "{ NUM, STRING }" and try to separate each of them
> > > -- 
> > > 2.44.0
> > > 
> > > 
> > 
>