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

[John Snow <jsnow@redhat.com>]

On 03/03/2017 02:26 PM, Nir Soffer wrote:
> On Fri, Mar 3, 2017 at 8:54 PM, John Snow <jsnow@redhat.com> 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 <jsnow@redhat.com>
>> ---
>>
>> 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.

>> +        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 <nirsof@gmail.com>
>