Re: [PATCH] scripts: improve error from qemu-trace-stap on missing 'stap'

["Daniel P. Berrangé" <berrange@redhat.com>]

Hi Stefan,

Are you ok with queuing this patch ?

On Fri, Dec 06, 2024 at 11:45:24AM +0000, Daniel P. Berrangé wrote:
> If the 'stap' binary is missing in $PATH, a huge trace is thrown
> 
>   $ qemu-trace-stap list /usr/bin/qemu-system-x86_64
>   Traceback (most recent call last):
>   File "/usr/bin/qemu-trace-stap", line 169, in <module>
>   main()
>   File "/usr/bin/qemu-trace-stap", line 165, in main
>   args.func(args)
>   File "/usr/bin/qemu-trace-stap", line 83, in cmd_run
>   subprocess.call(stapargs)
>   File "/usr/lib64/python3.12/subprocess.py", line 389, in call
>   with Popen(*popenargs, **kwargs) as p:
>   ^^^^^^^^^^^^^^^^^^^^^^^^^^^
>   File "/usr/lib64/python3.12/subprocess.py", line 1026, in {}init{}
>   self._execute_child(args, executable, preexec_fn, close_fds,
>   File "/usr/lib64/python3.12/subprocess.py", line 1955, in _execute_child
>   raise child_exception_type(errno_num, err_msg, err_filename)
>   FileNotFoundError: [Errno 2] No such file or directory: 'stap'
> 
> With this change the user now gets
> 
>   $ qemu-trace-stap list /usr/bin/qemu-system-x86_64
>   Unable to find 'stap' in $PATH
> 
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
>  scripts/qemu-trace-stap | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/scripts/qemu-trace-stap b/scripts/qemu-trace-stap
> index eb6e951ff2..e983460ee7 100755
> --- a/scripts/qemu-trace-stap
> +++ b/scripts/qemu-trace-stap
> @@ -56,6 +56,7 @@ def tapset_dir(binary):
>  
>  
>  def cmd_run(args):
> +    stap = which("stap")
>      prefix = probe_prefix(args.binary)
>      tapsets = tapset_dir(args.binary)
>  
> @@ -76,7 +77,7 @@ def cmd_run(args):
>  
>      # We request an 8MB buffer, since the stap default 1MB buffer
>      # can be easily overflowed by frequently firing QEMU traces
> -    stapargs = ["stap", "-s", "8", "-I", tapsets ]
> +    stapargs = [stap, "-s", "8", "-I", tapsets ]
>      if args.pid is not None:
>          stapargs.extend(["-x", args.pid])
>      stapargs.extend(["-e", script])
> @@ -84,6 +85,7 @@ def cmd_run(args):
>  
>  
>  def cmd_list(args):
> +    stap = which("stap")
>      tapsets = tapset_dir(args.binary)
>  
>      if args.verbose:
> @@ -96,7 +98,7 @@ def cmd_list(args):
>  
>          if verbose:
>              print("Listing probes with name '%s'" % script)
> -        proc = subprocess.Popen(["stap", "-I", tapsets, "-l", script],
> +        proc = subprocess.Popen([stap, "-I", tapsets, "-l", script],
>                                  stdout=subprocess.PIPE,
>                                  universal_newlines=True)
>          out, err = proc.communicate()
> -- 
> 2.46.0
> 

With regards,
Daniel
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