[Qemu-devel] [PATCH v2] spapr: quantify error messages regarding capability settings

Daniel Black posted 1 patch 4 years, 7 months ago
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git fetch https://github.com/patchew-project/qemu tags/patchew/20190801033819.29664-1-daniel@linux.ibm.com
Maintainers: David Gibson <david@gibson.dropbear.id.au>
There is a newer version of this series
hw/ppc/spapr_caps.c | 47 ++++++++++++++++++++++++++++++---------------
1 file changed, 32 insertions(+), 15 deletions(-)
[Qemu-devel] [PATCH v2] spapr: quantify error messages regarding capability settings
Posted by Daniel Black 4 years, 7 months ago
Its not immediately obvious how cap-X=Y setting need to be applied
to the command line so, for spapr capability error messages, this
has been clarified to:

  ..[try] appending -machine cap-X=Y

The wrong value messages have been left as is, as the user has found
the right location.

Signed-off-by: Daniel Black <daniel@linux.ibm.com>
---
v2 Improved error message thanks David Gibson

Left the "appending" as its not obvious more that one -machine
arguement is allowed.
---
 hw/ppc/spapr_caps.c | 47 ++++++++++++++++++++++++++++++---------------
 1 file changed, 32 insertions(+), 15 deletions(-)

diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
index bbb001f84a..1c0222a081 100644
--- a/hw/ppc/spapr_caps.c
+++ b/hw/ppc/spapr_caps.c
@@ -37,6 +37,8 @@
 
 #include "hw/ppc/spapr.h"
 
+#define CAPABILITY_ERROR(X) "appending -machine " X
+
 typedef struct SpaprCapPossible {
     int num;            /* size of vals array below */
     const char *help;   /* help text for vals */
@@ -194,10 +196,12 @@ static void cap_htm_apply(SpaprMachineState *spapr, uint8_t val, Error **errp)
     }
     if (tcg_enabled()) {
         error_setg(errp,
-                   "No Transactional Memory support in TCG, try cap-htm=off");
+                   "No Transactional Memory support in TCG, try "
+                   CAPABILITY_ERROR("cap-htm=off"));
     } else if (kvm_enabled() && !kvmppc_has_cap_htm()) {
         error_setg(errp,
-"KVM implementation does not support Transactional Memory, try cap-htm=off"
+"KVM implementation does not support Transactional Memory, try "
+                   CAPABILITY_ERROR("cap-htm=off")
             );
     }
 }
@@ -215,7 +219,8 @@ static void cap_vsx_apply(SpaprMachineState *spapr, uint8_t val, Error **errp)
      * rid of anything that doesn't do VMX */
     g_assert(env->insns_flags & PPC_ALTIVEC);
     if (!(env->insns_flags2 & PPC2_VSX)) {
-        error_setg(errp, "VSX support not available, try cap-vsx=off");
+        error_setg(errp, "VSX support not available, try "
+                   CAPABILITY_ERROR("cap-vsx=off"));
     }
 }
 
@@ -229,7 +234,8 @@ static void cap_dfp_apply(SpaprMachineState *spapr, uint8_t val, Error **errp)
         return;
     }
     if (!(env->insns_flags2 & PPC2_DFP)) {
-        error_setg(errp, "DFP support not available, try cap-dfp=off");
+        error_setg(errp, "DFP support not available, try "
+                   CAPABILITY_ERROR("cap-dfp=off"));
     }
 }
 
@@ -249,11 +255,13 @@ static void cap_safe_cache_apply(SpaprMachineState *spapr, uint8_t val,
     if (tcg_enabled() && val) {
         /* TCG only supports broken, allow other values and print a warning */
         error_setg(&local_err,
-                   "TCG doesn't support requested feature, cap-cfpc=%s",
+                   "TCG doesn't support requested feature, "
+                   CAPABILITY_ERROR("cap-cfpc=%s"),
                    cap_cfpc_possible.vals[val]);
     } else if (kvm_enabled() && (val > kvm_val)) {
         error_setg(errp,
-"Requested safe cache capability level not supported by kvm, try cap-cfpc=%s",
+"Requested safe cache capability level not supported by kvm, try "
+                   CAPABILITY_ERROR("cap-cfpc=%s"),
                    cap_cfpc_possible.vals[kvm_val]);
     }
 
@@ -281,7 +289,8 @@ static void cap_safe_bounds_check_apply(SpaprMachineState *spapr, uint8_t val,
                    cap_sbbc_possible.vals[val]);
     } else if (kvm_enabled() && (val > kvm_val)) {
         error_setg(errp,
-"Requested safe bounds check capability level not supported by kvm, try cap-sbbc=%s",
+"Requested safe bounds check capability level not supported by kvm, try "
+                   CAPABILITY_ERROR("cap-sbbc=%s"),
                    cap_sbbc_possible.vals[kvm_val]);
     }
 
@@ -312,7 +321,8 @@ static void cap_safe_indirect_branch_apply(SpaprMachineState *spapr,
                    cap_ibs_possible.vals[val]);
     } else if (kvm_enabled() && (val > kvm_val)) {
         error_setg(errp,
-"Requested safe indirect branch capability level not supported by kvm, try cap-ibs=%s",
+"Requested safe indirect branch capability level not supported by kvm, try "
+                   CAPABILITY_ERROR("cap-ibs=%s"),
                    cap_ibs_possible.vals[kvm_val]);
     }
 
@@ -401,11 +411,13 @@ static void cap_nested_kvm_hv_apply(SpaprMachineState *spapr,
 
     if (tcg_enabled()) {
         error_setg(errp,
-                   "No Nested KVM-HV support in tcg, try cap-nested-hv=off");
+                   "No Nested KVM-HV support in tcg, try "
+                   CAPABILITY_ERROR("cap-nested-hv=off"));
     } else if (kvm_enabled()) {
         if (!kvmppc_has_cap_nested_kvm_hv()) {
             error_setg(errp,
-"KVM implementation does not support Nested KVM-HV, try cap-nested-hv=off");
+"KVM implementation does not support Nested KVM-HV, try "
+                       CAPABILITY_ERROR("cap-nested-hv=off"));
         } else if (kvmppc_set_cap_nested_kvm_hv(val) < 0) {
                 error_setg(errp,
 "Error enabling cap-nested-hv with KVM, try cap-nested-hv=off");
@@ -435,10 +447,12 @@ static void cap_large_decr_apply(SpaprMachineState *spapr,
 
         if (!kvm_nr_bits) {
             error_setg(errp,
-                       "No large decrementer support, try cap-large-decr=off");
+                       "No large decrementer support, try "
+                        CAPABILITY_ERROR("cap-large-decr=off"));
         } else if (pcc->lrg_decr_bits != kvm_nr_bits) {
             error_setg(errp,
-"KVM large decrementer size (%d) differs to model (%d), try -cap-large-decr=off",
+"KVM large decrementer size (%d) differs to model (%d), try "
+                CAPABILITY_ERROR("cap-large-decr=off"),
                 kvm_nr_bits, pcc->lrg_decr_bits);
         }
     }
@@ -454,7 +468,8 @@ static void cap_large_decr_cpu_apply(SpaprMachineState *spapr,
     if (kvm_enabled()) {
         if (kvmppc_enable_cap_large_decr(cpu, val)) {
             error_setg(errp,
-                       "No large decrementer support, try cap-large-decr=off");
+                       "No large decrementer support, try "
+                       CAPABILITY_ERROR("cap-large-decr=off"));
         }
     }
 
@@ -474,10 +489,12 @@ static void cap_ccf_assist_apply(SpaprMachineState *spapr, uint8_t val,
     if (tcg_enabled() && val) {
         /* TODO - for now only allow broken for TCG */
         error_setg(errp,
-"Requested count cache flush assist capability level not supported by tcg, try cap-ccf-assist=off");
+"Requested count cache flush assist capability level not supported by tcg, try "
+                   CAPABILITY_ERROR("cap-ccf-assist=off"));
     } else if (kvm_enabled() && (val > kvm_val)) {
         error_setg(errp,
-"Requested count cache flush assist capability level not supported by kvm, try cap-ccf-assist=off");
+"Requested count cache flush assist capability level not supported by kvm, try "
+                   CAPABILITY_ERROR("cap-ccf-assist=off"));
     }
 }
 
-- 
2.21.0


Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] spapr: quantify error messages regarding capability settings
Posted by Greg Kurz 4 years, 7 months ago
On Thu,  1 Aug 2019 13:38:19 +1000
Daniel Black <daniel@linux.ibm.com> wrote:

> Its not immediately obvious how cap-X=Y setting need to be applied
> to the command line so, for spapr capability error messages, this
> has been clarified to:
> 
>   ..[try] appending -machine cap-X=Y
> 
> The wrong value messages have been left as is, as the user has found
> the right location.
> 
> Signed-off-by: Daniel Black <daniel@linux.ibm.com>
> ---
> v2 Improved error message thanks David Gibson
> 
> Left the "appending" as its not obvious more that one -machine
> arguement is allowed.
> ---
>  hw/ppc/spapr_caps.c | 47 ++++++++++++++++++++++++++++++---------------
>  1 file changed, 32 insertions(+), 15 deletions(-)
> 
> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
> index bbb001f84a..1c0222a081 100644
> --- a/hw/ppc/spapr_caps.c
> +++ b/hw/ppc/spapr_caps.c
> @@ -37,6 +37,8 @@
>  
>  #include "hw/ppc/spapr.h"
>  
> +#define CAPABILITY_ERROR(X) "appending -machine " X

I would make that:

#define CAPABILITY_HINT() "try appending -machine " X

because it is really an hint for the user, not an
error, and all original strings have "try", except...

> +
>  typedef struct SpaprCapPossible {
>      int num;            /* size of vals array below */
>      const char *help;   /* help text for vals */
> @@ -194,10 +196,12 @@ static void cap_htm_apply(SpaprMachineState *spapr, uint8_t val, Error **errp)
>      }
>      if (tcg_enabled()) {
>          error_setg(errp,
> -                   "No Transactional Memory support in TCG, try cap-htm=off");
> +                   "No Transactional Memory support in TCG, try "
> +                   CAPABILITY_ERROR("cap-htm=off"));
>      } else if (kvm_enabled() && !kvmppc_has_cap_htm()) {
>          error_setg(errp,
> -"KVM implementation does not support Transactional Memory, try cap-htm=off"
> +"KVM implementation does not support Transactional Memory, try "
> +                   CAPABILITY_ERROR("cap-htm=off")
>              );
>      }
>  }
> @@ -215,7 +219,8 @@ static void cap_vsx_apply(SpaprMachineState *spapr, uint8_t val, Error **errp)
>       * rid of anything that doesn't do VMX */
>      g_assert(env->insns_flags & PPC_ALTIVEC);
>      if (!(env->insns_flags2 & PPC2_VSX)) {
> -        error_setg(errp, "VSX support not available, try cap-vsx=off");
> +        error_setg(errp, "VSX support not available, try "
> +                   CAPABILITY_ERROR("cap-vsx=off"));
>      }
>  }
>  
> @@ -229,7 +234,8 @@ static void cap_dfp_apply(SpaprMachineState *spapr, uint8_t val, Error **errp)
>          return;
>      }
>      if (!(env->insns_flags2 & PPC2_DFP)) {
> -        error_setg(errp, "DFP support not available, try cap-dfp=off");
> +        error_setg(errp, "DFP support not available, try "
> +                   CAPABILITY_ERROR("cap-dfp=off"));
>      }
>  }
>  
> @@ -249,11 +255,13 @@ static void cap_safe_cache_apply(SpaprMachineState *spapr, uint8_t val,
>      if (tcg_enabled() && val) {
>          /* TCG only supports broken, allow other values and print a warning */
>          error_setg(&local_err,
> -                   "TCG doesn't support requested feature, cap-cfpc=%s",
> +                   "TCG doesn't support requested feature, "
> +                   CAPABILITY_ERROR("cap-cfpc=%s"),

... this one, but it doesn't look like a hint to me. It just tells which
is the unsupported cap.

>                     cap_cfpc_possible.vals[val]);
>      } else if (kvm_enabled() && (val > kvm_val)) {
>          error_setg(errp,
> -"Requested safe cache capability level not supported by kvm, try cap-cfpc=%s",
> +"Requested safe cache capability level not supported by kvm, try "
> +                   CAPABILITY_ERROR("cap-cfpc=%s"),
>                     cap_cfpc_possible.vals[kvm_val]);

Also, we have a dedicated API for hints, which are only printed under
the monitor but ignored under QMP.

Not sure why it isn't used here but it should be something like:

        error_setg(errp, 
                   "Requested safe cache capability level not supported by kvm");
        error_append_hint(errp, CAPABILITY_HINT("cap-cfpc=%s") "\n",
                          cap_cfpc_possible.vals[kvm_val]);

>      }
>  
> @@ -281,7 +289,8 @@ static void cap_safe_bounds_check_apply(SpaprMachineState *spapr, uint8_t val,
>                     cap_sbbc_possible.vals[val]);
>      } else if (kvm_enabled() && (val > kvm_val)) {
>          error_setg(errp,
> -"Requested safe bounds check capability level not supported by kvm, try cap-sbbc=%s",
> +"Requested safe bounds check capability level not supported by kvm, try "
> +                   CAPABILITY_ERROR("cap-sbbc=%s"),
>                     cap_sbbc_possible.vals[kvm_val]);
>      }
>  
> @@ -312,7 +321,8 @@ static void cap_safe_indirect_branch_apply(SpaprMachineState *spapr,
>                     cap_ibs_possible.vals[val]);
>      } else if (kvm_enabled() && (val > kvm_val)) {
>          error_setg(errp,
> -"Requested safe indirect branch capability level not supported by kvm, try cap-ibs=%s",
> +"Requested safe indirect branch capability level not supported by kvm, try "
> +                   CAPABILITY_ERROR("cap-ibs=%s"),
>                     cap_ibs_possible.vals[kvm_val]);
>      }
>  
> @@ -401,11 +411,13 @@ static void cap_nested_kvm_hv_apply(SpaprMachineState *spapr,
>  
>      if (tcg_enabled()) {
>          error_setg(errp,
> -                   "No Nested KVM-HV support in tcg, try cap-nested-hv=off");
> +                   "No Nested KVM-HV support in tcg, try "
> +                   CAPABILITY_ERROR("cap-nested-hv=off"));
>      } else if (kvm_enabled()) {
>          if (!kvmppc_has_cap_nested_kvm_hv()) {
>              error_setg(errp,
> -"KVM implementation does not support Nested KVM-HV, try cap-nested-hv=off");
> +"KVM implementation does not support Nested KVM-HV, try "
> +                       CAPABILITY_ERROR("cap-nested-hv=off"));
>          } else if (kvmppc_set_cap_nested_kvm_hv(val) < 0) {
>                  error_setg(errp,
>  "Error enabling cap-nested-hv with KVM, try cap-nested-hv=off");
> @@ -435,10 +447,12 @@ static void cap_large_decr_apply(SpaprMachineState *spapr,
>  
>          if (!kvm_nr_bits) {
>              error_setg(errp,
> -                       "No large decrementer support, try cap-large-decr=off");
> +                       "No large decrementer support, try "
> +                        CAPABILITY_ERROR("cap-large-decr=off"));
>          } else if (pcc->lrg_decr_bits != kvm_nr_bits) {
>              error_setg(errp,
> -"KVM large decrementer size (%d) differs to model (%d), try -cap-large-decr=off",
> +"KVM large decrementer size (%d) differs to model (%d), try "
> +                CAPABILITY_ERROR("cap-large-decr=off"),
>                  kvm_nr_bits, pcc->lrg_decr_bits);
>          }
>      }
> @@ -454,7 +468,8 @@ static void cap_large_decr_cpu_apply(SpaprMachineState *spapr,
>      if (kvm_enabled()) {
>          if (kvmppc_enable_cap_large_decr(cpu, val)) {
>              error_setg(errp,
> -                       "No large decrementer support, try cap-large-decr=off");
> +                       "No large decrementer support, try "
> +                       CAPABILITY_ERROR("cap-large-decr=off"));
>          }
>      }
>  
> @@ -474,10 +489,12 @@ static void cap_ccf_assist_apply(SpaprMachineState *spapr, uint8_t val,
>      if (tcg_enabled() && val) {
>          /* TODO - for now only allow broken for TCG */
>          error_setg(errp,
> -"Requested count cache flush assist capability level not supported by tcg, try cap-ccf-assist=off");
> +"Requested count cache flush assist capability level not supported by tcg, try "
> +                   CAPABILITY_ERROR("cap-ccf-assist=off"));
>      } else if (kvm_enabled() && (val > kvm_val)) {
>          error_setg(errp,
> -"Requested count cache flush assist capability level not supported by kvm, try cap-ccf-assist=off");
> +"Requested count cache flush assist capability level not supported by kvm, try "
> +                   CAPABILITY_ERROR("cap-ccf-assist=off"));
>      }
>  }
>  


Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] spapr: quantify error messages regarding capability settings
Posted by Daniel Black 4 years, 7 months ago
On Thu, 1 Aug 2019 12:41:59 +0200
Greg Kurz <groug@kaod.org> wrote:

> On Thu,  1 Aug 2019 13:38:19 +1000
> Daniel Black <daniel@linux.ibm.com> wrote:
> 
> > Its not immediately obvious how cap-X=Y setting need to be applied
> > to the command line so, for spapr capability error messages, this
> > has been clarified to:
> > 
...
> > index bbb001f84a..1c0222a081 100644
> > --- a/hw/ppc/spapr_caps.c
> > +++ b/hw/ppc/spapr_caps.c
> > @@ -37,6 +37,8 @@
> >  
> >  #include "hw/ppc/spapr.h"
> >  
> > +#define CAPABILITY_ERROR(X) "appending -machine " X  
> 
> I would make that:
> 
> #define CAPABILITY_HINT() "try appending -machine " X
> 
> because it is really an hint for the user, not an
> error,

Works for me. At the lowest layer it is a hint.

> and all original strings have "try",

True.

> except...


> > @@ -249,11 +255,13 @@ static void
> > cap_safe_cache_apply(SpaprMachineState *spapr, uint8_t val, if
> > (tcg_enabled() && val) { /* TCG only supports broken, allow other
> > values and print a warning */ error_setg(&local_err,
> > -                   "TCG doesn't support requested feature,
> > cap-cfpc=%s",
> > +                   "TCG doesn't support requested feature, "
> > +                   CAPABILITY_ERROR("cap-cfpc=%s"),  
> 
> ... this one, but it doesn't look like a hint to me. It just tells
> which is the unsupported cap.

This is one of 3 that local_error (commit
006e9d3618698eeef2f3e07628d22cb6f5c2a039) - intentionally just a
warning and to TLDR the commit/Suraj conversation; defaults apply
to all machine types; hardware security measures don't make sense in
TCG; hence warning.

For every function with CAPABILITY_[ERROR|HINT] its called by
spapr_caps_apply, has its errp as &error_fatal (intentionally - spoke
to Suraj - migrations to machines without capabilities need to fail and
defaults (kvm) should be secure unless explicitly disabled).

> >                     cap_cfpc_possible.vals[val]);
> >      } else if (kvm_enabled() && (val > kvm_val)) {
> >          error_setg(errp,
> > -"Requested safe cache capability level not supported by kvm, try
> > cap-cfpc=%s", +"Requested safe cache capability level not supported
> > by kvm, try "
> > +                   CAPABILITY_ERROR("cap-cfpc=%s"),
> >                     cap_cfpc_possible.vals[kvm_val]);  
> 
> Also, we have a dedicated API for hints, which are only printed under
> the monitor but ignored under QMP.

Ok.
 
> Not sure why it isn't used here but it should be something like:

If error_append_hint should be used for fatal errors (all that use
errp), then this patten should be applied further to
CAPABILITY_[HINT|ERROR] functions.

If error_append_hint needs to apply to warnings
cap_[cfpc/sbbc/ibs]_apply functions need to use it.

Would I be right in I'm assuming that the below pattern needs to apply
to both of these cases?

>         error_setg(errp, 
>                    "Requested safe cache capability level not
> supported by kvm");
>         error_append_hint(errp,
> CAPABILITY_HINT("cap-cfpc=%s") "\n", cap_cfpc_possible.vals[kvm_val]);

This is going a little beyond the scope of fixing a message, ok, but
lets not extend the scope too much more.


Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] spapr: quantify error messages regarding capability settings
Posted by Greg Kurz 4 years, 7 months ago
On Fri, 2 Aug 2019 11:03:48 +1000
Daniel Black <daniel@linux.ibm.com> wrote:

> On Thu, 1 Aug 2019 12:41:59 +0200
> Greg Kurz <groug@kaod.org> wrote:
> 
> > On Thu,  1 Aug 2019 13:38:19 +1000
> > Daniel Black <daniel@linux.ibm.com> wrote:
> > 
> > > Its not immediately obvious how cap-X=Y setting need to be applied
> > > to the command line so, for spapr capability error messages, this
> > > has been clarified to:
> > > 
> ...
> > > index bbb001f84a..1c0222a081 100644
> > > --- a/hw/ppc/spapr_caps.c
> > > +++ b/hw/ppc/spapr_caps.c
> > > @@ -37,6 +37,8 @@
> > >  
> > >  #include "hw/ppc/spapr.h"
> > >  
> > > +#define CAPABILITY_ERROR(X) "appending -machine " X  
> > 
> > I would make that:
> > 
> > #define CAPABILITY_HINT() "try appending -machine " X
> > 
> > because it is really an hint for the user, not an
> > error,
> 
> Works for me. At the lowest layer it is a hint.
> 
> > and all original strings have "try",
> 
> True.
> 
> > except...
> 
> 
> > > @@ -249,11 +255,13 @@ static void
> > > cap_safe_cache_apply(SpaprMachineState *spapr, uint8_t val, if
> > > (tcg_enabled() && val) { /* TCG only supports broken, allow other
> > > values and print a warning */ error_setg(&local_err,
> > > -                   "TCG doesn't support requested feature,
> > > cap-cfpc=%s",
> > > +                   "TCG doesn't support requested feature, "
> > > +                   CAPABILITY_ERROR("cap-cfpc=%s"),  
> > 
> > ... this one, but it doesn't look like a hint to me. It just tells
> > which is the unsupported cap.
> 
> This is one of 3 that local_error (commit
> 006e9d3618698eeef2f3e07628d22cb6f5c2a039) - intentionally just a
> warning and to TLDR the commit/Suraj conversation; defaults apply
> to all machine types; hardware security measures don't make sense in
> TCG; hence warning.
> 

Sure. What I meant is that the warning for "cap-cfpc" should be left alone,
otherwise we get:

$ ppc64-softmmu/qemu-system-ppc64 -nodefaults -nographic -machine pseries,accel=tcg
qemu-system-ppc64: warning: TCG doesn't support requested feature, appending -machine cap-cfpc=workaround
qemu-system-ppc64: warning: TCG doesn't support requested feature, cap-sbbc=workaround
qemu-system-ppc64: warning: TCG doesn't support requested feature, cap-ibs=workaround

and even weirder:

$ ppc64-softmmu/qemu-system-ppc64 -nodefaults -nographic -machine pseries,accel=tcg -machine cap-cfpc=workaround
qemu-system-ppc64: warning: TCG doesn't support requested feature, appending -machine cap-cfpc=workaround
qemu-system-ppc64: warning: TCG doesn't support requested feature, cap-sbbc=workaround
qemu-system-ppc64: warning: TCG doesn't support requested feature, cap-ibs=workaround

> For every function with CAPABILITY_[ERROR|HINT] its called by
> spapr_caps_apply, has its errp as &error_fatal (intentionally - spoke
> to Suraj - migrations to machines without capabilities need to fail and
> defaults (kvm) should be secure unless explicitly disabled).
> 
> > >                     cap_cfpc_possible.vals[val]);
> > >      } else if (kvm_enabled() && (val > kvm_val)) {
> > >          error_setg(errp,
> > > -"Requested safe cache capability level not supported by kvm, try
> > > cap-cfpc=%s", +"Requested safe cache capability level not supported
> > > by kvm, try "
> > > +                   CAPABILITY_ERROR("cap-cfpc=%s"),
> > >                     cap_cfpc_possible.vals[kvm_val]);  
> > 
> > Also, we have a dedicated API for hints, which are only printed under
> > the monitor but ignored under QMP.
> 
> Ok.
>  
> > Not sure why it isn't used here but it should be something like:
> 
> If error_append_hint should be used for fatal errors (all that use
> errp), then this patten should be applied further to
> CAPABILITY_[HINT|ERROR] functions.
> 

Hmm... looking again at error_append_hint(), it shouldn't be passed
&error_fatal or &error_abort. This calls for an extra local_err and
error_propagate() dance... Definitely not in the scope of this patch.

> If error_append_hint needs to apply to warnings
> cap_[cfpc/sbbc/ibs]_apply functions need to use it.
> 

The current warnings from commit 006e9d3618698eeef2f3e07628d22cb6f5c2a039
don't contain hints. We could potentially add one that says "try appending
-machine cap-blah=broken" but it doesn't bring much...

> Would I be right in I'm assuming that the below pattern needs to apply
> to both of these cases?
> 
> >         error_setg(errp, 
> >                    "Requested safe cache capability level not
> > supported by kvm");
> >         error_append_hint(errp,
> > CAPABILITY_HINT("cap-cfpc=%s") "\n", cap_cfpc_possible.vals[kvm_val]);
> 
> This is going a little beyond the scope of fixing a message, ok, but
> lets not extend the scope too much more.
> 

Yes, I agree. Your patch should only be about fixing the message.
I'll have a look at the error_append_hint() story when I'm back
from holidays :)

So, to sum up:
- s/CAPABILITY_ERROR/CAPABILITY_HINT and move "try" there
- drop the unwanted change in the "cap-cfpc" warning

With these fixed:

Reviewed-by: Greg Kurz <groug@kaod.org>

Cheers,

--
Greg

Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] spapr: quantify error messages regarding capability settings
Posted by David Gibson 4 years, 7 months ago
On Fri, Aug 02, 2019 at 11:03:48AM +1000, Daniel Black wrote:
> On Thu, 1 Aug 2019 12:41:59 +0200
> Greg Kurz <groug@kaod.org> wrote:
> 
> > On Thu,  1 Aug 2019 13:38:19 +1000
> > Daniel Black <daniel@linux.ibm.com> wrote:
> > 
> > > Its not immediately obvious how cap-X=Y setting need to be applied
> > > to the command line so, for spapr capability error messages, this
> > > has been clarified to:
> > > 
> ...
> > > index bbb001f84a..1c0222a081 100644
> > > --- a/hw/ppc/spapr_caps.c
> > > +++ b/hw/ppc/spapr_caps.c
> > > @@ -37,6 +37,8 @@
> > >  
> > >  #include "hw/ppc/spapr.h"
> > >  
> > > +#define CAPABILITY_ERROR(X) "appending -machine " X  
> > 
> > I would make that:
> > 
> > #define CAPABILITY_HINT() "try appending -machine " X
> > 
> > because it is really an hint for the user, not an
> > error,
> 
> Works for me. At the lowest layer it is a hint.

Oh.. of course it is.  Which means we should be using the
error_append_hint() system that's for exactly this sort of
information.

Sorry I didn't think of that earlier.

> 
> > and all original strings have "try",
> 
> True.
> 
> > except...
> 
> 
> > > @@ -249,11 +255,13 @@ static void
> > > cap_safe_cache_apply(SpaprMachineState *spapr, uint8_t val, if
> > > (tcg_enabled() && val) { /* TCG only supports broken, allow other
> > > values and print a warning */ error_setg(&local_err,
> > > -                   "TCG doesn't support requested feature,
> > > cap-cfpc=%s",
> > > +                   "TCG doesn't support requested feature, "
> > > +                   CAPABILITY_ERROR("cap-cfpc=%s"),  
> > 
> > ... this one, but it doesn't look like a hint to me. It just tells
> > which is the unsupported cap.
> 
> This is one of 3 that local_error (commit
> 006e9d3618698eeef2f3e07628d22cb6f5c2a039) - intentionally just a
> warning and to TLDR the commit/Suraj conversation; defaults apply
> to all machine types; hardware security measures don't make sense in
> TCG; hence warning.
> 
> For every function with CAPABILITY_[ERROR|HINT] its called by
> spapr_caps_apply, has its errp as &error_fatal (intentionally - spoke
> to Suraj - migrations to machines without capabilities need to fail and
> defaults (kvm) should be secure unless explicitly disabled).
> 
> > >                     cap_cfpc_possible.vals[val]);
> > >      } else if (kvm_enabled() && (val > kvm_val)) {
> > >          error_setg(errp,
> > > -"Requested safe cache capability level not supported by kvm, try
> > > cap-cfpc=%s", +"Requested safe cache capability level not supported
> > > by kvm, try "
> > > +                   CAPABILITY_ERROR("cap-cfpc=%s"),
> > >                     cap_cfpc_possible.vals[kvm_val]);  
> > 
> > Also, we have a dedicated API for hints, which are only printed under
> > the monitor but ignored under QMP.
> 
> Ok.
>  
> > Not sure why it isn't used here but it should be something like:
> 
> If error_append_hint should be used for fatal errors (all that use
> errp), then this patten should be applied further to
> CAPABILITY_[HINT|ERROR] functions.
> 
> If error_append_hint needs to apply to warnings
> cap_[cfpc/sbbc/ibs]_apply functions need to use it.
> 
> Would I be right in I'm assuming that the below pattern needs to apply
> to both of these cases?
> 
> >         error_setg(errp, 
> >                    "Requested safe cache capability level not
> > supported by kvm");
> >         error_append_hint(errp,
> > CAPABILITY_HINT("cap-cfpc=%s") "\n", cap_cfpc_possible.vals[kvm_val]);
> 
> This is going a little beyond the scope of fixing a message, ok, but
> lets not extend the scope too much more.
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson