Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> writes:
> 28.11.2019 23:29, Markus Armbruster wrote:
>> Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> writes:
>>
>>> 28.11.2019 17:23, Markus Armbruster wrote:
>>>> Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> 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.
>>>>>
>>>>> But very few functions instead get Error **errp as IN-argument:
>>>>> it's assumed to be set (or, maybe, NULL), and callee should clean it,
>>>>> or add some information.
>>>>>
>>>>> In such cases, rename errp to errp_in.
>>>>
>>>> Missing: why is the rename useful?
>>>
>>> The main reason is to prepare for coccinelle part.
>>
>> It's not a prerequisite for applying the patches Coccinelle produces,
>> only a prerequisite for running Coccinelle.
>>
>>>> It's useful if it helps readers recognize unusual Error ** parameters,
>>>> and recognizing unusual Error ** parameters is actually a problem. I'm
>>>> not sure it is, but my familiarity with the Error interface may blind
>>>> me.
>>>>
>>>> How many functions have unusual Error **parameters? How are they used?
>>>> Any calls that could easily be mistaken as the usual case? See [*]
>>>> below.
[...]
>>>> [*] The information I asked for above is buried in these patches. I'll
>>>> try to dig it up as I go reviewing them.
>>>>
>>>> Second, it risks some of these "further patches" overtake this one, and
>>>> then its commit message will be misleading. Moreover, the other commits
>>>> will lack context.
[...]
>>>>> diff --git a/util/error.c b/util/error.c
>>>>> index d4532ce318..275586faa8 100644
>>>>> --- a/util/error.c
>>>>> +++ b/util/error.c
[...]
>>>>> @@ -271,11 +271,11 @@ void error_free(Error *err)
>>>>> }
>>>>> }
>>>>>
>>>>> -void error_free_or_abort(Error **errp)
>>>>> +void error_free_or_abort(Error **errp_in)
>>>>> {
>>>>> - assert(errp && *errp);
>>>>> - error_free(*errp);
>>>>> - *errp = NULL;
>>>>> + assert(errp_in && *errp_in);
>>>>> + error_free(*errp_in);
>>>>> + *errp_in = NULL;
>>
>> This one is actually in/out.
>>
>> To make the compiler check errp_in is truly an in-argument, we can
>> declare it as Error *const *errp_in.
>>
>> But we can save ourselves the trouble of renaming it; the const should
>> suffice to tell both human readers and Coccinelle that this is not your
>> common out-argument. I think I like this better than relying on a
>> naming convention. What about you?
>
> I think it's good idea... But what to do with error_free_or_abort, and other
> functions
> which get filled errp, and want to set it to NULL? Patch 21 adds three such
> functions..
>
> Maybe, add assert(errp) at start of such functions, and catch it by
> coccinelle (not sure
> that it is possible)?
I went through the git branch you provided.
These get rid of unusual Error ** parameters:
01e10667d1 hmp: drop Error pointer indirection in hmp_handle_error
606bfb7520 vnc: drop Error pointer indirection in vnc_client_io_error
Get rid of them by peeling off an indirection.
These try to make unusual Error ** parameters stand out:
51e73b3305 error: rename errp to errp_in where it is IN-argument
Four renames.
Three functions modify the error, name @errp_in is okay, my const
proposal works.
error_free_or_abort() clears *errp_in, name @errp_in is misleading,
const doesn't work.
f7bdfd42da qdev-monitor: well form error hint helpers
Two renames. Both functions modify the error, rename is okay, const
works.
9d4aac7299 nbd: well form nbd_iter_channel_error errp handler
One rename, from @local_err. nbd_iter_channel_error() clears *errp_in,
name @errp_in is misleading, const doesn't work.
fb1bd83c40 ppc: well form kvmppc_hint_smt_possible error hint helper
One rename. The function modify the error, rename is okay, const works.
e024e89b10 9pfs: well form error hint helpers
Two renames. Both functions modify the error, rename is okay, const
works.
These make usual Error ** parameters look, well, more usual:
c01649d999 hw/core/qdev: cleanup Error ** variables
a5f6424163 block/snapshot: rename Error ** parameter to more common errp
ae200ca21e hw/i386/amd_iommu: rename Error ** parameter to more common errp
561f73e681 qga: rename Error ** parameter to more common errp
12589a96cd monitor/qmp-cmds: rename Error ** parameter to more common errp
f608fc5999 hw/s390x: rename Error ** parameter to more common errp
747a90d044 hw/tpm: rename Error ** parameter to more common errp
3d19e66610 hw/usb: rename Error ** parameter to more common errp
07366648ef include/qom/object.h: rename Error ** parameter to more common
errp
These don't touch Error ** parameter declarations:
f6e4fffc16 hw/core/loader-fit: fix freeing errp in fit_load_fdt
b5bba880ae net/net: Clean up variable shadowing in net_client_init()
4a4462ce4c hw/sd: drop extra whitespace in sdhci_sysbus_realize() header
d52d44e822 backends/cryptodev: drop local_err from
cryptodev_backend_complete()
7e95d30766 hw/vfio/ap: drop local_err from vfio_ap_realize
Unusual Error ** parameters that can be made Error *const *errp should
not also need a rename, neither to avoid confusion about @errp's role,
nor to help Coccinelle.
Unusual Error ** parameters that can't be made Error *const *errp:
nbd_iter_channel_error(): parameter is called @local_err. Confusion
seems as unlikely without the rename as with it. Coccinelle should
not need the rename. No need to touch. I'm willing to accept your
assertion change.
error_free_or_abort(): parameter is called @errp. Confusion seems
as unlikely without the rename as with it. Coccinelle should not
need the rename. I'm willing to accept a rename to @local_err
regardless.
I pushed my fixups to git://repo.or.cz/qemu/armbru.git branch error-prep
for your convenience. The commit messages of the fixed up commits need
rephrasing, of course.
