Re: [PATCH v4 01/31] errp: rename errp to errp_in where it is IN-argument

[Vladimir Sementsov-Ogievskiy]

08.10.2019 15:05, Markus Armbruster wrote:
> Vladimir Sementsov-Ogievskiy <address@hidden> writes:
> 
>> 08.10.2019 12:08, Markus Armbruster wrote:
>>> Vladimir Sementsov-Ogievskiy <address@hidden> writes:
>>>
>>>> Error **errp is almost always OUT-argument: it's assumed to be NULL, or
>>>> pointer to NULL-initialized pointer, or pointer to error_abort or
>>>> error_fatal, for callee to report error.
>>>
>>> Yes.
>>>
>>>> But very few functions instead get Error **errp as IN-argument:
>>>> it's assumed to be set, and callee should clean it.
>>>
>>> What do you mean by "callee should clean"?  Let's see below.
>>>
>>>> In such cases, rename errp to errp_in.
>>>
>>> I acknowledge that errp arguments that don't have the usual meaning can
>>> be confusing.
>>>
>>> Naming can help, comments can help, but perhaps we can tweak the code to
>>> avoid the problem instead.  Let's see:
>>>
>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>>>> Reviewed-by: Eric Blake <address@hidden>
> [...]
>>> We can avoid the confusing Error **errp in all three cases by peeling
>>> off an indirection.  What do you think?
>>>
>>
>> I like the idea, thanks! I think, I'll try to make a patch.
>>
>> But you are right, unfortunately there more cases, at least, pointed by
>> Greg
>>
>> error_append_socket_sockfd_hint and
>> error_append_security_model_hint
>>
>> Which don't free error..
> 
> Neither do error_append_hint() and error_prepend().
> 
> For anything named error_append_FOO_hint() or error_prepend_FOO(),
> confusion seems unlikely.
> 
>>                           But if they append hint, they should always be 
>> called
>> on wrapped errp, accordingly to the problem about fatal_error, so they may
>> be converted to Error *err too.. Hmm, I should think about the script to find
>> such functions.
> 
> I figure I better read more of your series before I comment on this
> thought.
> 

Me trying to find more such functions:

script:
# cat ../up-fix-error_append_hint/find.py
#!/usr/bin/env python
import re
import sys

ret_type = r'^[^{};#]+( |\*|\*\*)'
name = r'(?P<name>\w+)'
args = r'\([^{};#]*Error \*\*errp[^{};#]*\)'
body_before_errp = r'((?<!errp)[^}]|(?<!^)})*'

caller = '(if ?|assert|' \
           'error_(v?prepend|get_pretty|append_hint|free|free_or_abort)|' \
           '(warn|error)_reportf?_err)'

# Match 'caller(errp', 'caller(*errp', 'errp ?'
access_errp = '(' + caller + r'\(\*?errp|errp \?)'

r = re.compile(ret_type + name + args + '\s*^\{' + body_before_errp + 
access_errp, re.M)

with open(sys.argv[1]) as f:
     text = f.read()

for m in r.finditer(text):
     print(m.groupdict()['name'])


search:
# git ls-files | grep '\.\(h\|c\)$' | while read f; do 
../up-fix-error_append_hint/find.py $f; done
vmdk_co_create_opts_cb
error_append_security_model_hint
error_append_socket_sockfd_hint
qemu_file_get_error_obj
hmp_handle_error
qbus_list_bus
qbus_list_dev
kvmppc_hint_smt_possible
vnc_client_io_error
error_handle_fatal
error_setv
error_prepend
error_setg_win32_internal
error_free_or_abort

vmdk_co_create_opts_cb and qemu_file_get_error_obj are false positives I think


-- 
Best regards,
Vladimir