Re: [dpdk-dev] [PATCH] usertools/dpdk-telemetry: print name of app when connected

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, Feb 16, 2021 at 10:40:36AM +0000, Burakov, Anatoly wrote:
> On 16-Feb-21 9:44 AM, Bruce Richardson wrote:
> > When the dpdk-telemetry client connects to a DPDK instance, we can use the
> > PID provided in the initial connection message to query from /proc the name
> > of the process we are connected to, and display that to the user. We use
> > the "cmdline" procfs entry for the query since that is available on both
> > Linux and FreeBSD (assuming procfs is mounted on the BSD instance).
> > 
> > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > ---
> >   usertools/dpdk-telemetry.py | 5 +++++
> >   1 file changed, 5 insertions(+)
> > 
> > diff --git a/usertools/dpdk-telemetry.py b/usertools/dpdk-telemetry.py
> > index 181859658f..82b91f346f 100755
> > --- a/usertools/dpdk-telemetry.py
> > +++ b/usertools/dpdk-telemetry.py
> > @@ -45,6 +45,11 @@ def handle_socket(path):
> >           return
> >       json_reply = read_socket(sock, 1024)
> >       output_buf_len = json_reply["max_output_len"]
> > +    pid = json_reply["pid"]
> > +    if os.path.exists('/proc/' + str(pid) + '/cmdline'):
> > +        with open('/proc/' + str(pid) + '/cmdline') as f:
> 
> First of all, this is better done using os.path.join:
> 
> path = os.path.join('/proc', str(pid), 'cmdline')
> if os.path.exists(path):
>     with open(path) as f:
>         ...

Ok, I forgot that os.path.join can take > 2 parameters.

> 
> More importantly this isn't terribly Pythonic as it's not over-using
> exceptions :) IMO a better way would be:
> 
> try:
>     with open(path) as f:
>         ...
> except IOError as e:
>     # ignore if doesn't exist
>     if e.errno != errno.ENOENT:
>         raise
> 

Yes, I was thinking that I just wanted any exceptions to be raised, but you
right that I should just ignore the not-found one and skip the printout.

> > +            argv0 = f.read(1024).split('\0')[0]
> > +            print("Connected to application: '" + os.path.basename(argv0) + "'")
> 
> Also, formatting is better than concatenation, e.g. at least:
> 
> bname = os.path.basename(argv0)
> print("Connected to application: '{}'".format(bname))
> 
And f-strings are best of all, but we need python 3.6 for those. :-) I
consider use of format vs concat a matter of taste, but I'll update as you
suggest.

Thanks for the review.

/Bruce

PS: Python 3.5 has had its final release late last year:
https://www.python.org/downloads/release/python-3510/
We should soon consider updating our minimum required version to Python
3.6, allowing us to use f-strings in our python code rather than
concatenation or explicit format calls.