From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57008) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1clAIk-0008Fw-TB for qemu-devel@nongnu.org; Tue, 07 Mar 2017 03:17:00 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1clAIh-0004Le-Jv for qemu-devel@nongnu.org; Tue, 07 Mar 2017 03:16:58 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48402) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1clAIh-0004LZ-BX for qemu-devel@nongnu.org; Tue, 07 Mar 2017 03:16:55 -0500 From: Markus Armbruster References: <20170303185427.32681-1-jsnow@redhat.com> <5303cac4-a8d8-bf89-b525-3b0fb1b19127@redhat.com> <871sua4y3u.fsf@dusky.pond.sub.org> <3fbdfabf-82b4-d774-d5f4-2c50a6d740dc@redhat.com> Date: Tue, 07 Mar 2017 09:16:52 +0100 In-Reply-To: <3fbdfabf-82b4-d774-d5f4-2c50a6d740dc@redhat.com> (John Snow's message of "Mon, 6 Mar 2017 12:56:45 -0500") Message-ID: <87efy9ijrf.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH v2] qmp-shell: add persistent command history List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: John Snow Cc: Nir Soffer , qemu-devel@nongnu.org John Snow writes: > On 03/06/2017 03:18 AM, Markus Armbruster wrote: >> Nir Soffer writes: >> >>> On Fri, Mar 3, 2017 at 9:29 PM, John Snow wrote: >>>> >>>> >>>> On 03/03/2017 02:26 PM, Nir Soffer wrote: >>>>> On Fri, Mar 3, 2017 at 8:54 PM, John Snow 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 >>>>>> --- >>>>>> >>>>>> 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') >> >> I selfishly object to this filename, because I'm using it with >> >> $ socat UNIX:/work/armbru/images/test-qmp READLINE,history=$HOME/.qmp_history,prompt='QMP> ' >> >> Just kidding. But seriously, shouldn't this be named after the >> *application* (qmp-shell) rather than the protocol (qmp)? >> > > Seeing as the history itself is the qmp-shell syntax, you are correct. > > (Hey, it would be interesting to store the generated QMP into the > qmp_history, though...!) Hah! Saving it would be easy enough, but reloading it... okay, call it a "backup" and declare victory when saving works. >>>>>> >>>>>> 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. >> >> For what it's worth, bash seems to silently ignore a history file it >> can't read. Tested by running "HISTFILE=xxx bash", then chmod 0 xxx, da >> capo. >> > > Right, done by example. > >>> 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 >> >> Should this be addressed for 2.9? >> > > You can add a limit if you want to; I don't have suggestions for which > completely arbitrary limit makes sense, so I left it blank intentionally. For what it's worth, bash defaults HISTSIZE to 500. GNU Readline lets users configure it in ~/.inputrc. Conditional configuration is possible, i.e. something like $if Qmp-shell set history-size 5000 $endif should work, provided qmp-shell sets rl_readline_name as it should. >>>>>> + 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 >>>>>