Re: [Qemu-devel] [PATCH v2] qmp-shell: add persistent command history

[Nir Soffer]

On Fri, Mar 3, 2017 at 9:29 PM, John Snow <address@hidden> wrote:
>
>
> On 03/03/2017 02:26 PM, Nir Soffer wrote:
>> On Fri, Mar 3, 2017 at 8:54 PM, John Snow <address@hidden> wrote:
>>> Use the existing readline history function we are utilizing
>>> to provide persistent command history across instances of qmp-shell.
>>>
>>> This assists entering debug commands across sessions that may be
>>> interrupted by QEMU sessions terminating, where the qmp-shell has
>>> to be relaunched.
>>>
>>> Signed-off-by: John Snow <address@hidden>
>>> ---
>>>
>>> v2: Adjusted the errors to whine about non-ENOENT errors, but still
>>>     intercept all errors as non-fatal.
>>>     Save history atexit() to match bash standard behavior
>>>
>>>  scripts/qmp/qmp-shell | 19 +++++++++++++++++++
>>>  1 file changed, 19 insertions(+)
>>>
>>> diff --git a/scripts/qmp/qmp-shell b/scripts/qmp/qmp-shell
>>> index 0373b24..55a8285 100755
>>> --- a/scripts/qmp/qmp-shell
>>> +++ b/scripts/qmp/qmp-shell
>>> @@ -70,6 +70,9 @@ import json
>>>  import ast
>>>  import readline
>>>  import sys
>>> +import os
>>> +import errno
>>> +import atexit
>>>
>>>  class QMPCompleter(list):
>>>      def complete(self, text, state):
>>> @@ -109,6 +112,7 @@ class QMPShell(qmp.QEMUMonitorProtocol):
>>>          self._pretty = pretty
>>>          self._transmode = False
>>>          self._actions = list()
>>> +        self._histfile = os.path.join(os.path.expanduser('~'), 
>>> '.qmp_history')
>>>
>>>      def __get_address(self, arg):
>>>          """
>>> @@ -137,6 +141,21 @@ class QMPShell(qmp.QEMUMonitorProtocol):
>>>          # XXX: default delimiters conflict with some command names (eg. 
>>> query-),
>>>          # clearing everything as it doesn't seem to matter
>>>          readline.set_completer_delims('')
>>> +        try:
>>> +            readline.read_history_file(self._histfile)
>>> +        except Exception as e:
>>> +            if isinstance(e, IOError) and e.errno == errno.ENOENT:
>>> +                # File not found. No problem.
>>> +                pass
>>> +            else:
>>> +                print "Failed to read history '%s'; %s" % (self._histfile, 
>>> e)
>>
>> I would handle only IOError, since any other error means a bug in this code
>> or in the underlying readline library, and the best way to handle this is to
>> let it fail loudly.
>>
>
> Disagree. No reason to stop the shell from working because a QOL feature
> didn't initialize correctly.
>
> The warning will be enough to solicit reports and fixes if necessary.

I agree, the current solution is good tradeoff.

One thing missing, is a call to readline.set_history_length, without
it the history
will grow without limit, see:
https://docs.python.org/2/library/readline.html#readline.set_history_length

>
>>> +        atexit.register(self.__save_history)
>>> +
>>> +    def __save_history(self):
>>> +        try:
>>> +            readline.write_history_file(self._histfile)
>>> +        except Exception as e:
>>> +            print "Failed to save history file '%s'; %s" % 
>>> (self._histfile, e)
>>>
>>>      def __parse_value(self, val):
>>>          try:
>>
>> But I think this is good enough and useful as is.
>>
>> Reviewed-by: Nir Soffer <address@hidden>
>>