| Message ID | 1453219845-30939-19-git-send-email-eblake@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Eric Blake <eblake@redhat.com> writes: > No backend was setting an error when ending the visit of a list > or implicit struct. That's a lie: qmp_input_end_list() does. But it shouldn't, as you explain below. Rephrase the commit message? > Make the callers a bit easier to follow by > making this a part of the contract, and removing the errp > argument - callers can then unconditionally end an object as > part of cleanup without having to think about whether a second > error is dominated by a first, because there is no second error. > > The only addition of &error_abort in this patch, in the function > qmp_input_end_list(), will never trigger unless a programming > bug creates a push(struct)/pop(list) or push(list)/pop(struct) > mismatch. > > A later patch will then tackle the larger task of splitting > visit_end_struct(), which can indeed set an error (and that > cleanup will also have the side-effect of removing the use of > error_abort added here). > > Signed-off-by: Eric Blake <eblake@redhat.com> > Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> Patch looks good. I like the simplification.
On 01/20/2016 12:03 PM, Markus Armbruster wrote: > Eric Blake <eblake@redhat.com> writes: > >> No backend was setting an error when ending the visit of a list >> or implicit struct. > > That's a lie: qmp_input_end_list() does. But it shouldn't, as you > explain below. Rephrase the commit message? I'm not sure why you call it a lie - qmp_input_end_list() will not set an error unless it is mistakenly paired with a push(struct), which none of our code base does. Or put another way, although qmp_input_pop() [called by qmp_input_end_list()] has a signature that can set an error, closer inspection shows that it will only do so when invoked to close out a struct, and not when closing out a list. But that's a blatant programmer mismatch, which none of our code base does, so no well-formed use of visitors can cause qmp_input_end_list() to set an error. > >> Make the callers a bit easier to follow by >> making this a part of the contract, and removing the errp >> argument - callers can then unconditionally end an object as >> part of cleanup without having to think about whether a second >> error is dominated by a first, because there is no second error. >> >> The only addition of &error_abort in this patch, in the function >> qmp_input_end_list(), will never trigger unless a programming >> bug creates a push(struct)/pop(list) or push(list)/pop(struct) >> mismatch. I'm open to wording suggestions. Maybe replace all of the above with: None of the existing .end_implicit_struct() implementations use errp. And of the existing .end_list() implementations, only qmp_input_end_list() even uses errp, but closer inspection shows that it will never be modified (errp is only passed to qmp_input_pop(), which will only set an error if the corresponding push was a struct rather than a list). We can turn that internal usage into an &error_abort, to protect against programmer mistakes of push(struct)/pop(list) or push(list)/pop(struct) mismatch. With that done, we can then make all public uses of visit_end_implicit_struct() and visit_end_list() easier to follow by removing the errp argument and making error-free operation part of the contract. Callers can then unconditionally end an object as part of cleanup without having to think about whether a second error is dominated by a first, because there is no possibility of a second error. >> >> A later patch will then tackle the larger task of splitting >> visit_end_struct(), which can indeed set an error (and that >> cleanup will also have the side-effect of removing the use of >> error_abort added here). >> >> Signed-off-by: Eric Blake <eblake@redhat.com> >> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> > > Patch looks good. I like the simplification. Would help to split this into two patches, one switching from qmp_input_pop(errp) into qmp_input_pop(&error_abort), and the other then removing unused errp argument?
Eric Blake <eblake@redhat.com> writes: > On 01/20/2016 12:03 PM, Markus Armbruster wrote: >> Eric Blake <eblake@redhat.com> writes: >> >>> No backend was setting an error when ending the visit of a list >>> or implicit struct. >> >> That's a lie: qmp_input_end_list() does. But it shouldn't, as you >> explain below. Rephrase the commit message? > > I'm not sure why you call it a lie - qmp_input_end_list() will not set > an error unless it is mistakenly paired with a push(struct), which none > of our code base does. Or put another way, although qmp_input_pop() > [called by qmp_input_end_list()] has a signature that can set an error, > closer inspection shows that it will only do so when invoked to close > out a struct, and not when closing out a list. But that's a blatant > programmer mismatch, which none of our code base does, so no well-formed > use of visitors can cause qmp_input_end_list() to set an error. Okay, it's not a lie if you consider the whole program. It looks like a lie locally. >>> Make the callers a bit easier to follow by >>> making this a part of the contract, and removing the errp >>> argument - callers can then unconditionally end an object as >>> part of cleanup without having to think about whether a second >>> error is dominated by a first, because there is no second error. >>> >>> The only addition of &error_abort in this patch, in the function >>> qmp_input_end_list(), will never trigger unless a programming >>> bug creates a push(struct)/pop(list) or push(list)/pop(struct) >>> mismatch. > > I'm open to wording suggestions. > > Maybe replace all of the above with: > > None of the existing .end_implicit_struct() implementations use errp. > And of the existing .end_list() implementations, only > qmp_input_end_list() even uses errp, but closer inspection shows that it > will never be modified (errp is only passed to qmp_input_pop(), which > will only set an error if the corresponding push was a struct rather > than a list). We can turn that internal usage into an &error_abort, to > protect against programmer mistakes of push(struct)/pop(list) or > push(list)/pop(struct) mismatch. > > With that done, we can then make all public uses of > visit_end_implicit_struct() and visit_end_list() easier to follow by > removing the errp argument and making error-free operation part of the > contract. Callers can then unconditionally end an object as part of > cleanup without having to think about whether a second error is > dominated by a first, because there is no possibility of a second error. Works for me. >>> A later patch will then tackle the larger task of splitting >>> visit_end_struct(), which can indeed set an error (and that >>> cleanup will also have the side-effect of removing the use of >>> error_abort added here). >>> >>> Signed-off-by: Eric Blake <eblake@redhat.com> >>> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> >> >> Patch looks good. I like the simplification. > > Would help to split this into two patches, one switching from > qmp_input_pop(errp) into qmp_input_pop(&error_abort), and the other then > removing unused errp argument? If it results in more readable commit messages.
diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c index 78d71e2..ffc2cd9 100644 --- a/hw/ppc/spapr_drc.c +++ b/hw/ppc/spapr_drc.c @@ -314,11 +314,7 @@ static void prop_get_fdt(Object *obj, Visitor *v, const char *name, return; } } - visit_end_list(v, &err); - if (err) { - error_propagate(errp, err); - return; - } + visit_end_list(v); break; } default: diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h index 6abfda7..7f512cf 100644 --- a/include/qapi/visitor-impl.h +++ b/include/qapi/visitor-impl.h @@ -24,11 +24,13 @@ struct Visitor void (*start_implicit_struct)(Visitor *v, void **obj, size_t size, Error **errp); - void (*end_implicit_struct)(Visitor *v, Error **errp); + /* May be NULL */ + void (*end_implicit_struct)(Visitor *v); void (*start_list)(Visitor *v, const char *name, Error **errp); GenericList *(*next_list)(Visitor *v, GenericList **list, Error **errp); - void (*end_list)(Visitor *v, Error **errp); + /* Must be set */ + void (*end_list)(Visitor *v); void (*type_enum)(Visitor *v, const char *name, int *obj, const char *const strings[], Error **errp); diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h index 4abc180..10390d2 100644 --- a/include/qapi/visitor.h +++ b/include/qapi/visitor.h @@ -32,10 +32,11 @@ void visit_start_struct(Visitor *v, const char *name, void **obj, void visit_end_struct(Visitor *v, Error **errp); void visit_start_implicit_struct(Visitor *v, void **obj, size_t size, Error **errp); -void visit_end_implicit_struct(Visitor *v, Error **errp); +void visit_end_implicit_struct(Visitor *v); + void visit_start_list(Visitor *v, const char *name, Error **errp); GenericList *visit_next_list(Visitor *v, GenericList **list, Error **errp); -void visit_end_list(Visitor *v, Error **errp); +void visit_end_list(Visitor *v); /** * Check if an optional member @name of an object needs visiting. diff --git a/qapi/opts-visitor.c b/qapi/opts-visitor.c index 6d4a91e..62ffdd4 100644 --- a/qapi/opts-visitor.c +++ b/qapi/opts-visitor.c @@ -269,7 +269,7 @@ opts_next_list(Visitor *v, GenericList **list, Error **errp) static void -opts_end_list(Visitor *v, Error **errp) +opts_end_list(Visitor *v) { OptsVisitor *ov = to_ov(v); diff --git a/qapi/qapi-dealloc-visitor.c b/qapi/qapi-dealloc-visitor.c index 49e7cf0..560feb3 100644 --- a/qapi/qapi-dealloc-visitor.c +++ b/qapi/qapi-dealloc-visitor.c @@ -83,7 +83,7 @@ static void qapi_dealloc_start_implicit_struct(Visitor *v, qapi_dealloc_push(qov, obj); } -static void qapi_dealloc_end_implicit_struct(Visitor *v, Error **errp) +static void qapi_dealloc_end_implicit_struct(Visitor *v) { QapiDeallocVisitor *qov = to_qov(v); void **obj = qapi_dealloc_pop(qov); @@ -119,7 +119,7 @@ static GenericList *qapi_dealloc_next_list(Visitor *v, GenericList **listp, return NULL; } -static void qapi_dealloc_end_list(Visitor *v, Error **errp) +static void qapi_dealloc_end_list(Visitor *v) { QapiDeallocVisitor *qov = to_qov(v); void *obj = qapi_dealloc_pop(qov); diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c index b0452cf..2d3743b 100644 --- a/qapi/qapi-visit-core.c +++ b/qapi/qapi-visit-core.c @@ -37,10 +37,10 @@ void visit_start_implicit_struct(Visitor *v, void **obj, size_t size, } } -void visit_end_implicit_struct(Visitor *v, Error **errp) +void visit_end_implicit_struct(Visitor *v) { if (v->end_implicit_struct) { - v->end_implicit_struct(v, errp); + v->end_implicit_struct(v); } } @@ -54,9 +54,9 @@ GenericList *visit_next_list(Visitor *v, GenericList **list, Error **errp) return v->next_list(v, list, errp); } -void visit_end_list(Visitor *v, Error **errp) +void visit_end_list(Visitor *v) { - v->end_list(v, errp); + v->end_list(v); } bool visit_start_union(Visitor *v, bool data_present, Error **errp) diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c index bf25249..597652c 100644 --- a/qapi/qmp-input-visitor.c +++ b/qapi/qmp-input-visitor.c @@ -153,10 +153,6 @@ static void qmp_input_start_implicit_struct(Visitor *v, void **obj, } } -static void qmp_input_end_implicit_struct(Visitor *v, Error **errp) -{ -} - static void qmp_input_start_list(Visitor *v, const char *name, Error **errp) { QmpInputVisitor *qiv = to_qiv(v); @@ -201,11 +197,11 @@ static GenericList *qmp_input_next_list(Visitor *v, GenericList **list, return entry; } -static void qmp_input_end_list(Visitor *v, Error **errp) +static void qmp_input_end_list(Visitor *v) { QmpInputVisitor *qiv = to_qiv(v); - qmp_input_pop(qiv, errp); + qmp_input_pop(qiv, &error_abort); } static void qmp_input_get_next_type(Visitor *v, const char *name, QType *type, @@ -352,7 +348,6 @@ QmpInputVisitor *qmp_input_visitor_new(QObject *obj) v->visitor.start_struct = qmp_input_start_struct; v->visitor.end_struct = qmp_input_end_struct; v->visitor.start_implicit_struct = qmp_input_start_implicit_struct; - v->visitor.end_implicit_struct = qmp_input_end_implicit_struct; v->visitor.start_list = qmp_input_start_list; v->visitor.next_list = qmp_input_next_list; v->visitor.end_list = qmp_input_end_list; diff --git a/qapi/qmp-output-visitor.c b/qapi/qmp-output-visitor.c index db5e618..d367148 100644 --- a/qapi/qmp-output-visitor.c +++ b/qapi/qmp-output-visitor.c @@ -151,7 +151,7 @@ static GenericList *qmp_output_next_list(Visitor *v, GenericList **listp, return list ? list->next : NULL; } -static void qmp_output_end_list(Visitor *v, Error **errp) +static void qmp_output_end_list(Visitor *v) { QmpOutputVisitor *qov = to_qov(v); qmp_output_pop(qov); diff --git a/qapi/string-input-visitor.c b/qapi/string-input-visitor.c index 5347b61..610c233 100644 --- a/qapi/string-input-visitor.c +++ b/qapi/string-input-visitor.c @@ -178,7 +178,7 @@ next_list(Visitor *v, GenericList **list, Error **errp) } static void -end_list(Visitor *v, Error **errp) +end_list(Visitor *v) { StringInputVisitor *siv = to_siv(v); siv->head = true; diff --git a/qapi/string-output-visitor.c b/qapi/string-output-visitor.c index 74de6b6..fd917a4 100644 --- a/qapi/string-output-visitor.c +++ b/qapi/string-output-visitor.c @@ -303,7 +303,7 @@ next_list(Visitor *v, GenericList **list, Error **errp) } static void -end_list(Visitor *v, Error **errp) +end_list(Visitor *v) { StringOutputVisitor *sov = to_sov(v); diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py index 8a741b6..573bb81 100644 --- a/scripts/qapi-visit.py +++ b/scripts/qapi-visit.py @@ -62,7 +62,7 @@ static void visit_type_implicit_%(c_type)s(Visitor *v, %(c_type)s **obj, Error * visit_start_implicit_struct(v, (void **)obj, sizeof(%(c_type)s), &err); if (!err) { visit_type_%(c_type)s_fields(v, obj, errp); - visit_end_implicit_struct(v, &err); + visit_end_implicit_struct(v); } error_propagate(errp, err); } @@ -167,9 +167,7 @@ void visit_type_%(c_name)s(Visitor *v, const char *name, %(c_name)s **obj, Error visit_type_%(c_elt_type)s(v, NULL, &native_i->value, &err); } - error_propagate(errp, err); - err = NULL; - visit_end_list(v, &err); + visit_end_list(v); out: error_propagate(errp, err); } @@ -230,9 +228,7 @@ void visit_type_%(c_name)s(Visitor *v, const char *name, %(c_name)s **obj, Error "%(name)s"); } out_obj: - error_propagate(errp, err); - err = NULL; - visit_end_implicit_struct(v, &err); + visit_end_implicit_struct(v); out: error_propagate(errp, err); }