Re: [Qemu-devel] [RFC PATCH 1/3] vmstate: error hint for failed equal checks

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Halil Pasic (pasic@linux.vnet.ibm.com) wrote:
> In some cases a failing VMSTATE_*_EQUAL does not mean we detected a bug
> (it's actually the best we can do). Especially in these cases a verbose
> error message is required.
> 
> Let's introduce infrastructure for specifying a error hint to be used if
> equal check fails.
> 
> Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
> ---
> Macros come in part 2. Once we are happy with the macros
> this two patches should be squashed into one. 
> ---
>  include/migration/vmstate.h |  1 +
>  migration/vmstate-types.c   | 36 +++++++++++++++++++++++++++++++-----
>  2 files changed, 32 insertions(+), 5 deletions(-)
> 
> diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> index 66895623da..d90d9b12ca 100644
> --- a/include/migration/vmstate.h
> +++ b/include/migration/vmstate.h
> @@ -200,6 +200,7 @@ typedef enum {
>  
>  struct VMStateField {
>      const char *name;
> +    const char *err_hint;
>      size_t offset;
>      size_t size;
>      size_t start;
> diff --git a/migration/vmstate-types.c b/migration/vmstate-types.c
> index 7287c6baa6..84d0545a38 100644
> --- a/migration/vmstate-types.c
> +++ b/migration/vmstate-types.c
> @@ -19,6 +19,7 @@
>  #include "qemu/error-report.h"
>  #include "qemu/queue.h"
>  #include "trace.h"
> +#include "qapi/error.h"
>  
>  /* bool */
>  
> @@ -118,6 +119,7 @@ const VMStateInfo vmstate_info_int32 = {
>  static int get_int32_equal(QEMUFile *f, void *pv, size_t size,
>                             VMStateField *field)
>  {
> +    Error *err = NULL;
>      int32_t *v = pv;
>      int32_t v2;
>      qemu_get_sbe32s(f, &v2);
> @@ -125,7 +127,11 @@ static int get_int32_equal(QEMUFile *f, void *pv, size_t size,
>      if (*v == v2) {
>          return 0;
>      }
> -    error_report("%" PRIx32 " != %" PRIx32, *v, v2);
> +    error_setg(&err, "%" PRIx32 " != %" PRIx32, *v, v2);
> +    if (field->err_hint) {
> +        error_append_hint(&err, "%s\n", field->err_hint);
> +    }
> +    error_report_err(err);

I'm a bit worried as to whether the error_append_hint data gets
printed out by error_report_err if we're being driven by a QMP
monitor.
error_report_err uses error_printf_unless_qmp

Since this code doesn't really handle Error *'s back up,
and always prints it's errors into stderr, I'd prefer if you just
used error_report again for the hint, something like:

if (field->err_hint) {
  error_report("%" PRIx32 " != %" PRIx32 "(%s)",
               *v, v2, field->err_hint);
} else {
  error_report("%" PRIx32 " != %" PRIx32, *v, v2);
}

Dave

>      return -EINVAL;
>  }
>  
> @@ -259,6 +265,7 @@ const VMStateInfo vmstate_info_uint32 = {
>  static int get_uint32_equal(QEMUFile *f, void *pv, size_t size,
>                              VMStateField *field)
>  {
> +    Error *err = NULL;
>      uint32_t *v = pv;
>      uint32_t v2;
>      qemu_get_be32s(f, &v2);
> @@ -266,7 +273,11 @@ static int get_uint32_equal(QEMUFile *f, void *pv, size_t size,
>      if (*v == v2) {
>          return 0;
>      }
> -    error_report("%" PRIx32 " != %" PRIx32, *v, v2);
> +    error_setg(&err, "%" PRIx32 " != %" PRIx32, *v, v2);
> +    if (field->err_hint) {
> +        error_append_hint(&err, "%s\n", field->err_hint);
> +    }
> +    error_report_err(err);
>      return -EINVAL;
>  }
>  
> @@ -333,6 +344,7 @@ const VMStateInfo vmstate_info_nullptr = {
>  static int get_uint64_equal(QEMUFile *f, void *pv, size_t size,
>                              VMStateField *field)
>  {
> +    Error *err = NULL;
>      uint64_t *v = pv;
>      uint64_t v2;
>      qemu_get_be64s(f, &v2);
> @@ -340,7 +352,11 @@ static int get_uint64_equal(QEMUFile *f, void *pv, size_t size,
>      if (*v == v2) {
>          return 0;
>      }
> -    error_report("%" PRIx64 " != %" PRIx64, *v, v2);
> +    error_setg(&err, "%" PRIx64 " != %" PRIx64, *v, v2);
> +    if (field->err_hint) {
> +        error_append_hint(&err, "%s\n", field->err_hint);
> +    }
> +    error_report_err(err);
>      return -EINVAL;
>  }
>  
> @@ -356,6 +372,7 @@ const VMStateInfo vmstate_info_uint64_equal = {
>  static int get_uint8_equal(QEMUFile *f, void *pv, size_t size,
>                             VMStateField *field)
>  {
> +    Error *err = NULL;
>      uint8_t *v = pv;
>      uint8_t v2;
>      qemu_get_8s(f, &v2);
> @@ -363,7 +380,11 @@ static int get_uint8_equal(QEMUFile *f, void *pv, size_t size,
>      if (*v == v2) {
>          return 0;
>      }
> -    error_report("%x != %x", *v, v2);
> +    error_setg(&err, "%x != %x", *v, v2);
> +    if (field->err_hint) {
> +        error_append_hint(&err, "%s\n", field->err_hint);
> +    }
> +    error_report_err(err);
>      return -EINVAL;
>  }
>  
> @@ -379,6 +400,7 @@ const VMStateInfo vmstate_info_uint8_equal = {
>  static int get_uint16_equal(QEMUFile *f, void *pv, size_t size,
>                              VMStateField *field)
>  {
> +    Error *err = NULL;
>      uint16_t *v = pv;
>      uint16_t v2;
>      qemu_get_be16s(f, &v2);
> @@ -386,7 +408,11 @@ static int get_uint16_equal(QEMUFile *f, void *pv, size_t size,
>      if (*v == v2) {
>          return 0;
>      }
> -    error_report("%x != %x", *v, v2);
> +    error_setg(&err, "%x != %x", *v, v2);
> +    if (field->err_hint) {
> +        error_append_hint(&err, "%s\n", field->err_hint);
> +    }
> +    error_report_err(err);
>      return -EINVAL;
>  }
>  
> -- 
> 2.11.2
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK