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Re: [Qemu-devel] [PATCH v2 2/4] scripts: qmp-shell: Expand support for Q


From: John Snow
Subject: Re: [Qemu-devel] [PATCH v2 2/4] scripts: qmp-shell: Expand support for QMP expressions
Date: Wed, 22 Apr 2015 13:33:24 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0



On 04/22/2015 01:18 PM, Eric Blake wrote:
On 04/22/2015 10:21 AM, John Snow wrote:
This includes support for [] expressions, single-quotes in
QMP expressions (which is not strictly a part of JSON), and
the ability to use "True" or "False" literals instead of
JSON's lowercased 'true' and 'false' literals.

qmp-shell currently allows you to describe values as
JSON expressions:
key={"key":{"key2":"val"}}

But it does not currently support arrays, which are needed
for serializing and deserializing transactions:
key=[{"type":"drive-backup","data":{...}}]

qmp-shell also only currently accepts doubly quoted strings
as-per JSON spec, but QMP allows single quotes.

Lastly, python allows you to utilize "True" or "False" as
boolean literals, but JSON expects "true" or "false". Expand
qmp-shell to allow the user to type either, converting to the
correct type.

Well, when easy to do.  See below for more discussion...


As a consequence of the above, the key=val parsing is also improved
to give better error messages if a key=val token is not provided.

CAVEAT: The parser is still extremely rudimentary and does not
expect to find spaces in {} nor [] expressions. This patch does
not improve this functionality.

If someone cares about this, they can fix it later.  As I said in the v1
review, qmp-shell is mostly for debugging and testsuites, and we can
live with the caveats for now.


Signed-off-by: John Snow <address@hidden>
---
  scripts/qmp/qmp-shell | 44 ++++++++++++++++++++++++++++----------------
  1 file changed, 28 insertions(+), 16 deletions(-)

As far as I can tell, this makes qmp-shell strictly more useful, so I
have no qualms giving:

Reviewed-by: Eric Blake <address@hidden>


diff --git a/scripts/qmp/qmp-shell b/scripts/qmp/qmp-shell
index a9632ec..4cdcb6c 100755
--- a/scripts/qmp/qmp-shell
+++ b/scripts/qmp/qmp-shell
@@ -88,23 +88,35 @@ class QMPShell(qmp.QEMUMonitorProtocol):
          # clearing everything as it doesn't seem to matter
          readline.set_completer_delims('')

+    def __parse_value(self, val):
+        try:
+            return int(val)
+        except ValueError:
+            pass
+
+        if val.lower() == 'true':
+            return True
+        if val.lower() == 'false':
+            return False

...as promised earlier,

This allows param=tRuE (neither JSON nor Python), but that's a minor
price to pay to get both param=true (param=JSON style) and param=True
(param=Python style) to work.  Meanwhile...

+        if val.startswith(('{', '[')):
+            try:
+                return json.loads(val)

This statement accepts param=JSON style, as in:
  param={ "foo":true }
but it rejects (as invalid JSON):
  param={ 'foo':true }
  param={ "foo":True }
  param={ 'foo':True }

+            except ValueError:
+                pass
+            try:
+                return ast.literal_eval(val)

And this statement accepts param=Python style, as in:
  param={ "foo":True }
  param={ 'foo':True }
but it rejects (as invalid Python):
  param={ "foo":true }
  param={ 'foo':true }

Of those four combinations, QMP accepts:
  param={ "foo":true }
  param={ 'foo':true }
while rejecting:
  param={ "foo":True }
  param={ 'foo':True }

So among the four combinations of single/double quoting vs upper/lower
casing of boolean literals, qmp-shell now accepts three variants, but we
have a case that QMP accepts but qmp-shell rejects (single quotes mixed
with lower-case true).

Not the end of the world (again, if someone wants all four cases to work
in qmp-shell and/or QMP proper, they can provide a patch later to
further enhance things).  But maybe worth expanding that CAVEAT in the
commit message to acknowledge the issues.

At any rate, doesn't affect my R-b given above.


Yes, unfortunately the object literals still must comply with some sort of standard, neither of which is truly QMP: They must either be Python or JSON.

key=val pairs can/will accept true/TRUE/tRuE etc as well, which I think is probably acceptable since that falls within the realm of "qmp-shell syntax" which doesn't necessarily have to maintain similarities to JSON/QMP/etc. I could probably go back and adjust it to just lowercase the first letter, but this is probably only ever going to be a typo (which we can unambiguously resolve) and the generated QMP (if -v is present) will of course appear correctly formatted.

GIQO: Garbage in, QMP out? :)

I will author an additional patch as an add-on a bit later that documents all the quirks to help improve the usability of this little tool.

Probably I'll also update the QMP banner to display a quick help message.

Thank you,
--John



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