Re: [PATCH v2 2/3] spapr: Use error_append_hint() in spapr_caps.c

[Vladimir Sementsov-Ogievskiy]

11.06.2020 13:44, Vladimir Sementsov-Ogievskiy wrote:
> 11.06.2020 13:39, Greg Kurz wrote:
> > On Thu, 11 Jun 2020 13:21:51 +0300
> > Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> wrote:
> >
> > > 11.06.2020 13:13, Greg Kurz wrote:
> > > > On Thu, 11 Jun 2020 11:50:57 +0200
> > > > Laurent Vivier <lvivier@redhat.com> wrote:
> > > >
> > > > > On 11/06/2020 11:10, Greg Kurz wrote:
> > > > > > We have a dedicated error API for hints. Use it instead of embedding
> > > > > > the hint in the error message, as recommanded in the "qapi/error.h"
> > > > > > header file.
> > > > > >
> > > > > > Since spapr_caps_apply() passes &error_fatal, all functions must
> > > > > > also call the ERRP_AUTO_PROPAGATE() macro for error_append_hint()
> > > > > > to be functional.
> > > > > >
> > > > > > While here, add some missing braces around one line statements that
> > > > > > are part of the patch context. Also have cap_fwnmi_apply(), which
> > > > > > already uses error_append_hint() to call ERRP_AUTO_PROPAGATE() as
> > > > > > well.
> > > > > >
> > > > > > Signed-off-by: Greg Kurz <groug@kaod.org>
> > > > > > ---
> > > > > >    hw/ppc/spapr_caps.c |   95 
> > > > > > +++++++++++++++++++++++++++++----------------------
> > > > > >    1 file changed, 54 insertions(+), 41 deletions(-)
> > > > > >
> > > > > > diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
> > > > > > index efdc0dbbcfc0..2cb7ba8f005a 100644
> > > > > > --- a/hw/ppc/spapr_caps.c
> > > > > > +++ b/hw/ppc/spapr_caps.c
> > > > > ...
> > > > > > @@ -248,6 +249,7 @@ SpaprCapPossible cap_cfpc_possible = {
> > > > > >    static void cap_safe_cache_apply(SpaprMachineState *spapr, uint8_t val,
> > > > > >                                     Error **errp)
> > > > > >    {
> > > > > > +    ERRP_AUTO_PROPAGATE();
> > > > > >        Error *local_err = NULL;
> > > > >
> > > > > I think you should rename it, something like "local_warn" to not be
> > > > > confused with the _auto_errp_prop.local_err...
> > > > >
> > > > > or don't use ERRP_AUTO_PROPAGE(), use the local_err instead and move the
> > > > > warning inside the braces of the if.
> > > > >
> > > > > Same comment for cap_safe_bounds_check_apply() and
> > > > > cap_safe_indirect_branch_apply()
> > > >
> > > > Hmm... local_err isn't useful actually. It looks like we just want
> > > > to call warn_report() directly instead of error_setg(&local_err)
> > > > and warn_report_err(local_err). I'll post a v3.
> > >
> > > something like this I think:
> >
> > Not even that... we have one path (KVM) that directly
> > uses errp and the other path (TCG) that does:
> >
> > Error *local_err = NULL;
> >
> > error_setg(&local_err, ...);
> >
> > if (local_err) {
> >      warn_report_err(local_err);
> > }
> >
> > It really looks like we just want to call warn_report().
>
> yes, I also came this)
>
> > > --- a/hw/ppc/spapr_caps.c
> > > +++ b/hw/ppc/spapr_caps.c
> > > @@ -250,24 +250,23 @@ static void cap_safe_cache_apply(SpaprMachineState 
> > > *spapr, uint8_t val,
> > >                                     Error **errp)
> > >    {
> > >        ERRP_AUTO_PROPAGATE();
> > > -    Error *local_err = NULL;
> > >        uint8_t kvm_val =  kvmppc_get_cap_safe_cache();
> > >        if (tcg_enabled() && val) {
> > >            /* TCG only supports broken, allow other values and print a warning 
> > > */
> > > -        error_setg(&local_err,
> > > +        error_setg(errp,
> > >                       "TCG doesn't support requested feature, cap-cfpc=%s",
> > >                       cap_cfpc_possible.vals[val]);
> > > +        if (*errp) {
> > > +            warn_report_err(*errp);
> > > +            *errp = NULL;
> > > +        }
> > >        } else if (kvm_enabled() && (val > kvm_val)) {
> > >            error_setg(errp,
> > >                       "Requested safe cache capability level not supported by 
> > > KVM");
> > >            error_append_hint(errp, "Try appending -machine cap-cfpc=%s\n",
> > >                              cap_cfpc_possible.vals[kvm_val]);
> > >        }
> > > -
> > > -    if (local_err != NULL) {
> > > -        warn_report_err(local_err);
> > > -    }
> > >    }
> > >
> > >
> > > Or, we need to implement warn_report_errp() function, as I proposed in earlier 
> > > version of auto-propagation series.
> > >
> > > =====
> > >
> > > side idea: what if we make Error to be some kind of enum of pointer-to-pointer 
> > > and pointer-to-function?
> > >
> > > Than, instead of passing pointers to error_abort and error_fatal as special 
> > > casing, we'll pass pointers to functions,
> > > which do appropriate handling of error. And we'll be able to pass warn_report 
> > > function. Not about this patch set,
> > > but seems interesting, isn't it?

Just for record: probably, we'll want at lest something like this (not needed 
in this series):

diff --git a/include/qapi/error.h b/include/qapi/error.h
index 30140d9bfe..25b5da0733 100644
--- a/include/qapi/error.h
+++ b/include/qapi/error.h
@@ -475,4 +475,10 @@ extern Error *error_abort;
  */
 extern Error *error_fatal;
 
+/*
+ * Special error destination to call warn_report_err.
+ * See error_setg() and error_propagate() for details.
+ */
+extern Error *error_warn_report;
+
 #endif
diff --git a/util/error.c b/util/error.c
index b6c89d1412..928eb4cc7a 100644
--- a/util/error.c
+++ b/util/error.c
@@ -27,8 +27,9 @@ struct Error
 
 Error *error_abort;
 Error *error_fatal;
+Error *error_warn_report;
 
-static void error_handle_fatal(Error **errp, Error *err)
+static bool error_handle_special(Error **errp, Error *err)
 {
     if (errp == &error_abort) {
         fprintf(stderr, "Unexpected error in %s() at %s:%d:\n",
@@ -43,6 +44,12 @@ static void error_handle_fatal(Error **errp, Error *err)
         error_report_err(err);
         exit(1);
     }
+    if (errp == &error_warn_report) {
+        warn_report_err(err);
+        return true;
+    }
+
+    return false;
 }
 
 static void error_setv(Error **errp,
@@ -70,8 +77,9 @@ static void error_setv(Error **errp,
     err->line = line;
     err->func = func;
 
-    error_handle_fatal(errp, err);
-    *errp = err;
+    if (!error_handle_special(errp, err)) {
+        *errp = err;
+    }
 
     errno = saved_errno;
 }
@@ -283,7 +291,9 @@ void error_propagate(Error **dst_errp, Error *local_err)
     if (!local_err) {
         return;
     }
-    error_handle_fatal(dst_errp, local_err);
+    if (error_handle_special(dst_errp, local_err)) {
+        return;
+    }
     if (dst_errp && !*dst_errp) {
         *dst_errp = local_err;
     } else {



--
Best regards,
Vladimir