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

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 16-Feb-21 11:02 AM, Bruce Richardson wrote:
> 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.

'raise' will raise the exception up the stack, so you'll still get your 
exceptions that way - you'll just skip the one that says the file 
doesn't exist. plus, it also has a benefit of avoiding TOCTOU race :)

> 
>>> +            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.
> 

I seem to have a lot of difficulty remembering syntax for f-strings :P

-- 
Thanks,
Anatoly